Process Design Manual 

Land Treatment of Municipal 

Wastewater Effluents 
EPA/625/R-06/016 

September 2006 

Process Design Manual 

Land Treatment of Municipal Wastewater Effluents 

Land Remediation and Pollution Control Division 
 

National Risk Management Research Laboratory 
 

Office of Research and Development 
 

U.S. Environmental Protection Agency 
 

Cincinnati, Ohio 
 
Notice

This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and

approved for publication. Mention of trade names or commercial products does not constitute 

endorsement or recommendation for use.

ii
Foreword

The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting the Nation’s land, 

air, and water resources. Under a mandate of national environmental laws, the Agency strives to formulate

and implement actions leading to a compatible balance between human activities and the ability of natural 

systems to support and nurture life. To meet this mandate, EPA’s research program is providing data and 

technical support for solving environmental problems today and building a science knowledge base

necessary to manage our ecological resources wisely, understand how pollutants affect our health, and 

prevent or reduce environmental risks in the future. 

The National Risk Management Research Laboratory (NRMRL) is the Agency’s center for investigation of

technological and management approaches for preventing and reducing risks from pollution that threaten

human health and the environment. The focus of the Laboratory’s research program is on methods and

their cost-effectiveness for prevention and control of pollution to air, land, water, and subsurface resources; 

protection of water quality in public water systems; remediation of contaminated sites, sediments and

ground water; prevention and control of indoor air pollution; and restoration of ecosystems. NRMRL 

collaborates with both public and private sector partners to foster technologies that reduce the cost of 

compliance and to anticipate emerging problems. NRMRL’s research provides solutions to environmental

problems by: developing and promoting technologies that protect and improve the environment; advancing

scientific and engineering information to support regulatory and policy decisions; and providing the technical

support and information transfer to ensure implementation of environmental regulations and strategies at

the national, state, and community levels. 

This publication has been produced as part of the Laboratory’s strategic long-term research plan. It is 

published and made available by EPA’s Office of Research and Development to assist the user community 

and to link researchers with their clients. 

Sally Gutierrez, Director

National Risk Management Research Laboratory 

iii
Abstract 

The U.S. Environmental Protection Agency guidance on land treatment of municipal and industrial

wastewater was updated for the first time since 1984. Significant new technological changes include

phytoremediation, vadose zone monitoring, new design approaches to surface irrigation, center-pivot

irrigation, drip and micro-sprinkler irrigation, and capital and operating costs. Also included in the new 

manual are new performance data on soil-aquifer treatment, a rational model for balancing oxygen uptake

with BOD loadings, and industrial wastewater land application guidance, emphasizing treatment of food

processing wastewater. Costs and energy use of land treatment technologies are updated. 

Slow-rate land treatment remains the most popular type of land treatment system. Many slow-rate

systems are now designed as water reuse systems. Trends in distribution have been toward sprinkler and 

drip irrigation systems. 

A CD which accompanies the document contains copies of earlier editions of the land treatment manual 

and the latest manual for water reuse. 

KEYWORDS: land treatment, soil aquifer treatment, spray irrigation, groundwater monitoring, 

vadose zone sampling, costs 

iv
Contents 

Notice .............................................................................................................................................................. ii 

Foreword ......................................................................................................................................................... iii 

Abstract ........................................................................................................................................................... iv 

Contents.......................................................................................................................................................... v 

Figures ............................................................................................................................................................ viii 

Tables.............................................................................................................................................................. x 

Acknowledgments ........................................................................................................................................... xiii 

Chapter 1 Introduction and Process Capabilities........................................................................................ 1-1 

1.1 Purpose.............................................................................................................................................. 1-1 

1.2 Scope ................................................................................................................................................. 1-1 

1.3 Treatment Processes......................................................................................................................... 1-1 

1.4 Slow Rate Land Treatment ................................................................................................................ 1-2 

1.5 Overland Flow Treatment................................................................................................................... 1-4 

1.6 Soil Aquifer Treatment ....................................................................................................................... 1-4 

1.7 Limiting Design Parameter Concept .................................................................................................. 1-7 

1.8 Guide to Intended Use of Manual ...................................................................................................... 1-7 

1.9 References......................................................................................................................................... 1-7 

Chapter 2 Wastewater Constituents and Removal Mechanisms ............................................................. 2-1 

2.1 Biochemical Oxygen Demand............................................................................................................ 2-1 

2.2 Total Suspended Solids ..................................................................................................................... 2-2 

2.3 Oil and Grease................................................................................................................................... 2-2 

2.4 pH....................................................................................................................................................... 2-3 

2.5 Pathogenic Organisms....................................................................................................................... 2-3 

2.6 Metals................................................................................................................................................. 2-6 

2.7 Nitrogen.............................................................................................................................................. 2-8 

2.8 Phosphorus ........................................................................................................................................ 2-11 

2.9 Potassium .......................................................................................................................................... 2-14 

2.10 Sodium ............................................................................................................................................... 2-14 

2.11 Macronutrients and Micronutrients..................................................................................................... 2-14 

2.12 Trace Organics................................................................................................................................... 2-16 

2.13 Phytoremediation ............................................................................................................................... 2-18 

2.14 References......................................................................................................................................... 2-19 

Chapter 3 Water Movement in Soil and Groundwater................................................................................ 3-1 

3.1 Soil Properties.................................................................................................................................... 3-2 

3.2 Water Movement through Soil ........................................................................................................... 3-4 

3.3 Saturated Hydraulic Conductivity....................................................................................................... 3-7 

3.4 Unsaturated Hydraulic Conductivity................................................................................................... 3-8 

3.5 Percolation Capacity .......................................................................................................................... 3-8 

3.6 Mounding of Groundwater ................................................................................................................. 3-9 

3.7 Drainage Requirements ..................................................................................................................... 3-11 

3.8 Field Testing Procedures ................................................................................................................... 3-12 

3.9 References......................................................................................................................................... 3-18 

v
Chapter 4 Role of Plants in Land Treatment............................................................................................... 4-1 

4.1 Vegetation in Land Treatment............................................................................................................ 4-1 

4.2 Evapotranspiration ............................................................................................................................. 4-1 

4.3 Plant Selection ................................................................................................................................... 4-4 

4.4 Crop Management, Water Quality, and Nutrient Cycle...................................................................... 4-14 

4.5 References......................................................................................................................................... 4-16 

Chapter 5 Site Planning and Selection ....................................................................................................... 5-1 

5.1 Preliminary Land Requirements......................................................................................................... 5-1 

5.2 Site Identification................................................................................................................................ 5-4 

5.3 Site Selection ..................................................................................................................................... 5-8 

5.4 Phase 2 Planning............................................................................................................................... 5-8 

5.5 Cost and Energy Considerations ....................................................................................................... 5-17 

5.6 References......................................................................................................................................... 5-23 

Chapter 6 Preapplication Treatment and Storage ...................................................................................... 6-1 

6.1 EPA Guidance.................................................................................................................................... 6-1 

6.2 Types of Preapplication Treatment.................................................................................................... 6-2 

6.3 Design of Storage Ponds ................................................................................................................... 6-7 

6.4 Operation of Storage Ponds .............................................................................................................. 6-12 

6.5 References......................................................................................................................................... 6-12 

Chapter 7 Distribution Systems .................................................................................................................. 7-1 

7.1 Types of Distribution Systems ........................................................................................................... 7-1 

7.2 General Design Considerations for All Types of Distribution Systems.............................................. 7-3 

7.3 Surface Distribution............................................................................................................................ 7-4 

7.4 Sprinkler Distribution.......................................................................................................................... 7-11 

7.5 Micro Irrigation Distribution System Planning and Design................................................................. 7-22 

7.6 Pumping Stations and Mainlines........................................................................................................ 7-26 

7.7 Distribution Pumping.......................................................................................................................... 7-26 

7.8 Tailwater Pumping ............................................................................................................................. 7-26 

7.9 Mainlines ............................................................................................................................................ 7-27 

7.10 References......................................................................................................................................... 7-27 

Chapter 8 Process Design – Slow Rate Systems....................................................................................... 8-1 

8.1 System Types .................................................................................................................................... 8-1 

8.2 Land Area Determination ................................................................................................................... 8-1 

8.3 Total Acidity Loading.......................................................................................................................... 8-4 

8.4 Salinity................................................................................................................................................ 8-4 

8.5 Design Considerations....................................................................................................................... 8-7 

8.6 Crop, Soil, and Site Management Requirements .............................................................................. 8-9 

8.7 References......................................................................................................................................... 8-15 

Chapter 9 Process Design – Overland Flow Systems................................................................................ 9-1 

9.1 System Concept................................................................................................................................. 9-1 

9.2 Design Procedures............................................................................................................................. 9-2 

9.3 Land Area Requirements ................................................................................................................... 9-5 

9.4 Design Considerations....................................................................................................................... 9-6 

9.5 System Monitoring and Management ................................................................................................ 9-8 

9.6 References......................................................................................................................................... 9-9 

Chapter 10 Process Design – Soil Aquifer Treatment ................................................................................. 10-1 

10.1 Treatment Requirements ................................................................................................................... 10-1 

10.2 Aquifer Characteristics....................................................................................................................... 10-4 

10.3 Hydraulic Loading Rates.................................................................................................................... 10-5 

vi
10.4 Land Area Requirements ................................................................................................................... 10-7 

10.5 Hydraulic Loading Cycle .................................................................................................................... 10-7 

10.6 Design Considerations....................................................................................................................... 10-8 

10.7 Cold Weather Operation .................................................................................................................... 10-9 

10.8 Drainage............................................................................................................................................. 10-10 

10.9 References......................................................................................................................................... 10-12 

Chapter 11 Industrial Wastewater Land Application...................................................................................... 11-1 

11.1 Types of Industrial Wastewaters Applied........................................................................................... 11-1 

11.2 Water Quality and Pretreatment Requirements................................................................................. 11-1 

11.3 Design Considerations....................................................................................................................... 11-4 

11.4 Slow-Rate Land Treatment ................................................................................................................ 11-6 

11.5 Overland Flow Treatment................................................................................................................... 11-7 

11.6 Soil Aquifer Treatment ....................................................................................................................... 11-8 

11.7 References......................................................................................................................................... 11-9 

vii
Figures 

Number Page 

1-1 Slow Rate Hydraulic Pathways .......................................................................................................... 1-3 

1-2 Overland Flow..................................................................................................................................... 1-5 

1-3 SAT Hydraulic Pathways .................................................................................................................... 1-6 

2-1 Nitrogen Cycle in Soil......................................................................................................................... 2-9 

3-1 Natural Resources Conservation Service (NRCS) Soil Textural Classes ......................................... 3-2 

3-2 Porosity, Specific Yield, Specific Retention vs. Soil Grain Size for In situ Consolidated Soils, 

 Coastal Basin, CA.............................................................................................................................. 3-6 

3-3 Specific Yield vs. Hydraulic Conductivity ........................................................................................... 3-6 

3-4 Soil Moisture Characteristics ............................................................................................................. 3-6 

3-5 Approximate Preliminary Percolation Rate vs. NRCS Soil Permeability for SR and SAT. ............... 3-9 

3-6 Schematic of Groundwater Mound .................................................................................................... 3-9 

3-7 Mounding Curve for Center of a Square Recharge Area................................................................... 3-10 

3-8 Mounding Curve for Center of a Rectangular recharge Area, with Different Ratios of 

Length L to Width W........................................................................................................................... 3-10 

3-9 Rise and Horizontal Spread of a Mound Below a Square Recharge Area........................................ 3-11 

3-10 Rise and Horizontal Spread of Mounds Below a Rectangular Recharge Area when 

L = 2W................................................................................................................................................ 3-11 

3-11 Parameters Used in Drain Design ..................................................................................................... 3-12 

3-12 Small-scale Pilot Test Basin .............................................................................................................. 3-13 

3-13 U.S. Army Corps of Engineers (USACE) Basin Test......................................................................... 3-13 

3-14 Grove Preparation for USACE Test................................................................................................... 3-14 

3-15 Grove Preparation for USACE Test................................................................................................... 3-14 

3-16 Typical Test Results, USACE Infiltration Test.................................................................................... 3-14 

3-17 Test Installation for Cylinder Infiltrometer .......................................................................................... 3-15 

3-18 Definition Sketch for Air Entry Permeameter..................................................................................... 3-15 

3-19 Air Entry Permeameter in Use ........................................................................................................... 3-15 

3-20 Definition Sketch for Auger Hole Technique...................................................................................... 3-17 

3-21 Equipment Setup for Auger Hole Test ............................................................................................... 3-17 

4-1 Evaporation from Bare Soil which was Initially Wet .......................................................................... 4-1 

4-2 Nitrogen Uptake for Annual and Perennial Crops.............................................................................. 4-9

4-3 Effect of Salinity on Growth of Field Crops ........................................................................................ 4-11 

4-4 Suitable pH of Mineral Soils for Various Crops.................................................................................. 4-12 

5-1 Two-Phase Planning Process............................................................................................................ 5-1 

5-2 Estimated Storage Days Based on Climatic Factors Alone............................................................... 5-2 

5-3 Landscape Positions.......................................................................................................................... 5-6 

5-4 Sample Log for Test Pit Data............................................................................................................. 5-15 

5-5 Well and Piezometer Installations...................................................................................................... 5-16 

5-6 Vertical Flow Direction Indicated by Piezometers.............................................................................. 5-16 

5-7 Typical Shallow Monitoring Well ........................................................................................................ 5-17 

5-8 Solid Set Sprinkling (buried) Costs, ENR CCI = 6076. (a) Capital Cost; (b) Operation and 

 Maintenance Cost .............................................................................................................................. 5-19 

5-9 Center Pivot Sprinkling Costs, ENR CCI = 6076. (a) Capital Cost; (b) Operation and 

 Maintenance Cost .............................................................................................................................. 5-20 

5-10 Gated Pipe — Overland Flow or Ridge-and-Furrow Slow Rate Costs, ENR CCI = 6076. 

(a) Capital Cost; (b) Operation and Maintenance Cost...................................................................... 5-20

5-11 Rapid Infilitration Basin Costs, ENR CCI + 6076. (a) Capital Cost; (b) Operation and 

 Maintenance Cost .............................................................................................................................. 5-21 

viii
Number Page 

6-1 Virus Removal in Ponds..................................................................................................................... 6-6 

6-2 Fecal Coliform Removal in Ponds – Detention Time vs. Liquid Temperature................................... 6-6 

7-1 Typical Surface Distribution Methods – Ridge and Furrow................................................................ 7-4 

7-2 Typical Gated Pipe Distribution Unit .................................................................................................. 7-6 

7-3 Equal Opportunity Time Along Entire Strip ........................................................................................ 7-8 

7-4 Greater Opportunity Time at Head of Strip: Flow Rate Too Small .................................................... 7-9 

7-5 Greater Opportunity Time at Tail End of Strip: Flow Rate Too Large................................................ 7-10 

7-6. Typical Discharge Valve for Border Strip Application ........................................................................ 7-10 

7-7 Forest Solid Set Sprinkler Irrigation at Clayton County ..................................................................... 7-14 

7-8 Move-Stop Sprinkler Systems............................................................................................................ 7-15 

7-9 Side-Wheel Roll Sprinkler System..................................................................................................... 7-16 

7-10 Continuous Move Sprinkler Systems ................................................................................................. 7-17 

7-11 Reel-Type Traveling Gun Sprinkler.................................................................................................... 7-18 

7-12 Center Pivot Sprinkler Unit................................................................................................................. 7-19 

7-13 Center Pivot Irrigation System ........................................................................................................... 7-19 

7-14 Intersection Between an Elliptical Moving Application Rate Profile Under a Center-pivot 

Lateral and a Typical Infiltration Curve .............................................................................................. 7-20 

7-15 Schematic of the Revolving –Sprinkler Infiltrometer.......................................................................... 7-20 

7-16 Comparison of Relative Application Rates Under Various Center Pivot Sprinkler Packages ........... 7-20 

7-17 Anticipated Center Pivot Performance versus Soil Texture............................................................... 7-21 

7-18 Comparison of Wetting Profiles in Sandy Soil ................................................................................... 7-23 

7-19 Typical Micro Irrigation System Layout.............................................................................................. 7-23 

7-20 Distribution Pumps in the Side of a Storage Pond Dike .................................................................... 7-26 

7-21 Typical Tailwater Pumping Station..................................................................................................... 7-27 

8-1 Leaching Requirement as a Function of Applied Salinity and ECe of Crop Salinity 

 Threshold ........................................................................................................................................... 8-5 

8-2 Example Spreadsheet Used to Calculate the Irrigation Requirements Including Irrigation 

 Efficiency and Leaching Requirements............................................................................................. 8-7 

8-3 Slow Rate Design Procedure............................................................................................................. 8-8 

9-1 Distribution Alternatives for Overland Flow........................................................................................ 9-1 

9-2 Overland-Flow Application Rates and Slope Length ......................................................................... 9-3 

9-3 Bale Wrappers Tightly Seal Each Bale of Hay in Plastic for Storage ................................................ 9-9 

9-4 Plastic Silage Bags for Storing Cut Hay............................................................................................. 9-9 

10-1 Definition Sketch for Lateral Drainage from SAT Systems Underdrains ........................................... 10-10 

10-2 Centrally Located Underdrain ............................................................................................................ 10-11 

10-3 Underdrain System Using Alternating Infiltration and Drying Strips .................................................. 10-11 

11-1 Side Roll Sprinklers Apply Potato-Processing Wastewater Throughout the Winter at 

 Aberdeen, Idaho................................................................................................................................. 11-6 

11-2 Solid Set Sprinklers Apply Tomato-Processing Wastewater to Overland Flow Slopes..................... 11-8 

ix
Tables 

 Number Page 

1-1 Comparison of Land Treatment Process Design Features.................................................................. 1-1 

1-2 Site Characteristics for Land Treatment Processes............................................................................. 1-2 

1-3 Expected Effluent Water Quality from Land Treatment Processes ..................................................... 1-2 

2-1 Typical Organic Loading Rates for Land Treatment Systems ............................................................ 2-1

2-2 BOD5 Removal at Typical Land Treatment Systems ......................................................................... 2-2 

2-3 Suspended Solids Removal at Land Treatment Systems.................................................................... 2-3 

2-4 Virus Transmission through Soil at SAT Land Application Sites ......................................................... 2-5 

2-5 Aerosol Bacteria at Various Sources ................................................................................................... 2-6 

2-6 Recommended Limits for Constituents in Reclaimed Water for Irrigation ........................................... 2-7 

2-7 WHO Recommended Annual and Cumulative Limits for Metals Applied to Agricultural Crop Land .. 2-7 

2-8 Trace Metals in Groundwater Under Hollister, CA Soil Aquifer Treatment Site, mg/L ........................ 2-8 

2-9 Total Nitrogen Removal in Typical Land Treatment Systems.............................................................. 2-10 

2-10 Annual Mineralization Rates for Organic Matter in Biosolids............................................................... 2-11 

2-11 Typical Percolate Phosphorus Concentrations .................................................................................... 2-12 

2-12 Sulfur Uptake by Selected Crops......................................................................................................... 2-15 

2-13 Boron Tolerance of Crops .................................................................................................................... 2-16 

2-14 Values of ECD for Crops with No Yield Reduction .............................................................................. 2-16 

2-15 Volatile Organic Removal by Wastewater Sprinkling........................................................................... 2-17 

2-16 Physical Characteristics for Selected Organic Chemicals ................................................................... 2-18 

2-17 Percent Removal of Organic Chemicals in Land Treatment Systems................................................. 2-19 

3-1 Soil Textural Classes and General Terminology Used in Soil Descriptions ........................................ 3-2 

3-2 Range of Available Soil Moisture for Different Soil Types ................................................................... 3-6 

3-3 Field Estimating of Soil Moisture Content ............................................................................................ 3-7 

3-4 Measured Ratios of Horizontal to Vertical Conductivity....................................................................... 3-8 

3-5 Comparison of Infiltration Measurement Techniques .......................................................................... 3-13 

4-1 Range of Seasonal Crop Evapotranspiration....................................................................................... 4-2 

4-2 Selected Examples of Monthly Normal ETo......................................................................................... 4-2 

4-3 Example Evapotranspiration Values for Southern San Joaquin Valley of California........................... 4-3 

4-4 Pan Coefficient for Class A Evaporation Pans Placed in a Reference Crop Area .............................. 4-3 

4-5 Length of Four Crop Growth Stages for Typical Annual Crops ........................................................... 4-4 

4-6 Crop Coefficient, Kc, for Midseason and Late Season Conditions ...................................................... 4-4

4-7 Crop Coefficient, Kc, for Perennial Forage Crops................................................................................ 4-5 

4-8 Yield Based N, P, and K Uptake of Various Crops .............................................................................. 4-5 

4-9 Typical Effective Rooting Depth of Plants............................................................................................ 4-8 

4-10 Grasses Used at Overland Flow Sites ................................................................................................. 4-9 

4-11 General Effects of Trace Element Toxicity on Common Crops ........................................................... 4-10

4-12 Forested Land Treatment Systems in the United States ..................................................................... 4-11 

4-13 Nitrogen Uptake for Selected Forest Ecosystems with Whole Tree Harvesting.................................. 4-13 

4.14 Biomass and Nitrogen Distributions by Tree Component for Stands in Temperate

 Regions ................................................................................................................................................ 4-14 

4-15 Golf Course Grass Salt Tolerances ..................................................................................................... 4-14 

4-16 Pasture Rotation Cycles for Different Numbers of Pasture Areas ....................................................... 4-17 

5-1 Typical Composition of Raw Municipal Wastewater ............................................................................ 5-1 

5-2 Characteristics of Food Processing Wastewaters Applied to the Land ............................................... 5-2 

5-3 Preliminary Loading Rates for Initial Estimate of Land Requirements................................................. 5-2

5-4 Summary of Climatic Analyses ............................................................................................................ 5-3 

xi
5-5 Site Identification Land Requirements, ha/m3·d (acres/mgd).............................................................. 5-4 

5-6 Types and Sources of Data Required for Land Treatment Site Evaluation......................................... 5-4 

5-7 Land Use Suitability Factors for Identifying Land Treatment Sites ...................................................... 5-5 

5-8 Grade Suitability Factors for Identifying Land Treatment Sites ........................................................... 5-5 

5-9 Soil Textural Classes and General Terminology Used in Soil Descriptions ........................................ 5-6 

5-10 Typical Soil Permeabilities and Textural Classes for Land Treatment................................................. 5-7 

5-11 Rating Factors for Site Selection .......................................................................................................... 5-9 

5-12 Economic Rating Factors for Site Selection ......................................................................................... 5-9 

5-13 Subsurface Factors for Forested SR .................................................................................................... 5-10 

5-14 Soil Factors for Forested SR ................................................................................................................ 5-10 

5-15 Surface Factors for Forested SR.......................................................................................................... 5-10 

5-16 Composite Evaluation of SR Forested Sites ........................................................................................ 5-11 

5-17 Sequence of Field Testing - Typical Order of Testing .......................................................................... 5-11 

5-18 Summary of Field Tests for Land Treatment Processes ...................................................................... 5-11 

5-19 Interpretation of Soil Physical and Hydraulic Properties....................................................................... 5-12 

5-20. Interpretation of Soil Chemical Tests.................................................................................................... 5-13 

5-21 Textural Properties of Mineral Soils...................................................................................................... 5-14 

5-22 Soil Structure Grades............................................................................................................................ 5-14 

5-23 Description of Soil Mottles .................................................................................................................... 5-15 

5-24 Costs of Field Preparation .................................................................................................................... 5-18 

5-25 Comparison of Sprinkler Distribution Capital Costs.............................................................................. 5-19 

5-26 Costs of Underdrains............................................................................................................................ 5-21 

5-27 Costs of Tailwater Return Systems...................................................................................................... 5-21 

5-28 Costs of Runoff Collection for Overland Flow ...................................................................................... 5-21 

5-29 Costs of Recovery Wells ...................................................................................................................... 5-21 

5-30 Options for Land Acquisition and Management at Selected SR Systems ........................................... 5-22 

5-31 Benefits of Land Treatment Systems................................................................................................... 5-22 

5-32 Energy Requirements for Land and Aquatic Treatment Systems........................................................ 5-23 

5-33 Energy Value of Nutrients in Wastewater ............................................................................................ 5-23 

6-1 Guidelines for Assessing the Level of Preapplication Treatment ........................................................ 6-2 

6-2 Reaction Rates for Aerated Ponds, BOD............................................................................................. 6-3 

6-3 Variation of Plug Flow Apparent Rate Constant with Organic Loading Rate for Facultative Ponds.... 6-3 

6-4 Typical pH and Alkalinity Values in Facultative Ponds ........................................................................ 6-5 

6-5 Changes of Microorganisms Concentration During Storage ............................................................... 6-6 

6-6 Application of Membranes for the Removal of Constituents Found in Wastewater............................. 6-7 

6-7 Estimation of Storage Volume Requirements Using Water Balance Calculations .............................. 6-9 

6.8 Final Storage Volume Requirement Calculations ................................................................................ 6-10 

7-1 Description, Advantages, and Disadvantages, of Distribution Systems .............................................. 7-1 

7-2 Sprinkler System Characteristics ......................................................................................................... 7-3 

7-3 Optimum Furrow Spacing .................................................................................................................... 7-5 

7-4 Suggested Maximum Lengths of Furrows, ft ....................................................................................... 7-5 

7-5 Design Guidelines for Graded Borders for Deep-Rooted Crops.......................................................... 7-6 

7-6 Design Guidelines for Graded Borders for Shallow-Rooted Crops...................................................... 7-7 

7-7 Recommended Reductions in Application Rates Due to Grade .......................................................... 7-12 

7-8 Recommended Spacing of Sprinklers.................................................................................................. 7-13 

7-9 Pipe Friction Loss Factors to Obtain Actual Loss in Line with Multiple Outlets ................................... 7-13 

7-10 Recommended Maximum Lane Spacing for Traveling Gun Sprinklers ............................................... 7-18 

7-11 Typical Values for Surface Storage...................................................................................................... 7-21 

7-12 Recommended Soil Contact Pressure for Center Pivots..................................................................... 7-22 

7-13 Relative Resistance to Plugging for Various Emission Devices .......................................................... 7-24 

7-14 Recommended Design Factors for Tailwater Return Systems............................................................ 7-27 

8-1 Nitrogen Loss Factor for Varying C:N Ratios....................................................................................... 8-4 

8-2 Suggested Minimum Process Control Monitoring................................................................................ 8-10 

xii
8-3 Suggested Minimum Effluent Monitoring ............................................................................................. 8-11 

8-4 Flow Measurement Alternatives........................................................................................................... 8-11 

8-5 Soil Monitoring Parameters.................................................................................................................. 8-13 

8-6 Vadose Zone Sampling/Monitoring Alternatives .................................................................................. 8-14 

8-7 Example Crop Monitoring Parameters................................................................................................. 8-15 

8-8 Routine Maintenance Inspection Checklist for Land Application Sites ................................................ 8-15 

9-1 Comparison of Actual and Predicted OF Effluent BOD Concentrations Using Primary and Raw 

Municipal Wastewater.......................................................................................................................... 9-4 

9-2 BOD Removal for Overland Flow Systems.......................................................................................... 9-4 

9-3 Application Rates Suggested for BOD Removal in Overland Flow Design, m3/h ּm (gal/min ּft).... 9-4 

9-4 Ammonia Concentrations (in g/m3) in OF Systems in Garland, TX .................................................... 9-5 

10-1 BOD Removal for Soil Aquifer Treatment Systems.............................................................................. 10-1 

10-2 Nitrogen Removal for Soil Aquifer Treatment Systems ........................................................................ 10-3 

10-3 Phosphorus Removal for Soil Aquifer Treatment Systems .................................................................. 10-3 

10-4 Fractional Attenuation of Estrogenic Activity (Relative to Primary Effluent) During Secondary 

Treatment and Soil Aquifer Treatment................................................................................................. 10-4 

10-5 Typical Wet/Dry Ratios for SAT Systems ............................................................................................. 10-6 

10-6 Typical Hydraulic Loading Rates for SAT Systems .............................................................................. 10-6 

10-7 Suggested Hydraulic Loading Rates Based on Different Field Measurements.................................... 10-7 

10-8 Suggested SAT Loading Cycles ........................................................................................................... 10-8 

10-9 Minimum Number of Basins Required for Continuous Wastewater Application................................... 10-8 

11-1 Characteristics of Various Industrial Wastewaters Applied to Land..................................................... 11-2 

11-2. Comparison of Inorganic and Total Dissolved Solids Measurements in Milk Processing 

 Wastewater and Shallow Groundwater................................................................................................. 11-2 

11-3 Water Quality Parameters in the Settling Basin and First Cell of a Wetland Receiving Dairy 

 Wastewater, Mercer Co., KY ................................................................................................................ 11-4 

11-4 BOD Loading Rates at Existing Industrial Slow Rate Systems ............................................................ 11-5 

11-5 Nitrogen Mineralization of Industrial Wastewaters ............................................................................... 11-5 

11-6 Performance of Paris, TX., Overland Flow System .............................................................................. 11-7 

11-7 Performance of Overland Flow System at Davis, CA........................................................................... 11-8 

11-8 Treatment Performance for Hilmar Cheese Soil Aquifer Treatment System........................................ 11-9 

xiii
Acknowledgments 

This document was developed with the assistance of many individuals. It is an update of the land treatment

manuals that were written in the 1970s and 1980s, and all the contributors have attempted to present up-todate and useful information. They include the authors and technical expert reviewers listed here: 

Project Officer and Author: 

Dr. James E. Smith, Jr. 

US EPA National Risk Management Research Laboratory, (G-75), Cincinnati, OH 45268 

Coordinating Author: 

Robert B. Brobst, P.E 

Biosolids Program Manager, US EPA Region 8, 999 18th St., Suite 500, Denver, CO 80202-2466 

Contractor: 

Brown and Caldwell, 2701 Prospect Park Dr., Rancho Cordova, CA 95670 

Ronald W. Crites – Lead 

Robert A. Beggs 

Lance Hershman 

Diane Nascimento

Jordan W. Smith 

Special Contributions, Technical Assistance and Review: 

Robert K. Bastian 

US EPA Office of Wastewater Management, Washington, DC 

Robert B. Brobst, P.E.

US EPA Region 8, Denver, CO 

Dr. Micheal Overcash

North Carolina State University, Raleigh, NC 

Antonio Palazzo 

US Army Cold Regions Research and Engineering Laboratory, Hanover, NH 

Dr. Robert Rubin

North Carolina State University, Raleigh, NC 

Preparation of Manual for Publication: 

US EPA National Risk Management Research Laboratory, Cincinnati, OH 

Jean Dye 

Ann White 

Steve Wilson

The authors wish to dedicate this manual to the memory of Sherwood C. “Woody” Reed whose advocacy of the 

use of natural systems for wastewater treatment, including land treatment, ponds, and constructed wetlands 

generated much of the scientific data that went into the development of the 1977 and 1981 editions of this 

manual. He conducted or managed numerous field investigations and developed guidance materials, project 

case studies, cost curves, and other materials that have been used extensively in EPA, Water Environment

Federation, and Corps of Engineers publications. He has also written numerous journal articles, conference

papers, and textbooks and taught courses on natural systems and wastewater treatment throughout the U.S. 

and around the world. 

xiv
 

Chapter 1 

Introduction and Process Capabilities

1.1. Purpose 

The purpose of this manual is to provide design criteria

and supporting information for the planning, design,

construction, and operation of land treatment systems. 

Recommended procedures for the planning, design, and

evaluation of land treatment systems for wastewater 

management are presented along with information on

the expected performance and removal mechanisms. 

This document is a revision and supplement to the 

Process Design Manual for Land Treatment of Municipal

Wastewater published in 1981 (US EPA, 1981) and the

Supplement on Rapid Infiltration and Overland Flow that 

was published in 1984 (US EPA, 1984). EPA has 

chosen to provide copies of these manuals, as well as a

copy of the original manual (US EPA, 1977) on a CD, 

which is included with this manual. 

1.2. Scope 

Land treatment is defined as the application of 

appropriately pre-treated municipal and industrial

wastewater to the land at a controlled rate in a designed

and engineered setting. The purpose of the activity is to 

obtain beneficial use of these materials, to improve 

environmental quality, and to achieve treatment goals in

a cost-effective and environmentally sound manner. In 

many cases the production and sale of crops can

partially offset the cost of treatment. In arid climates the 

practice allows the use of wastewaters for irrigation and

preserves higher quality water sources for other 

purposes. 

The scope of this manual is limited to the three 

principal land treatment processes, which are: 

• Slow Rate (SR) 

• Overland Flow (OF)

• Soil Aquifer Treatment (SAT), also known as Rapid 

Infiltration (RI)

Subjects that are new to this revision of the design

manual include phytoremediation or phytoextraction and

land application of food processing wastewater. 

1.3. Treatment Processes 

Typical design features for the three land treatment 

processes are compared in Table 1-1. The typical site 

characteristics are compared in Table 1-2. The expected

quality of the treated water from each process is 

presented in Table 1-3. In most cases the compliance

standards are imposed at the treatment boundary. The

average and expected upper range values are valid for 

the travel distances and applied wastewater as 

indicated. The lower values of expected concentrations 

may reflect background shallow groundwater, especially 

for slow rate. The fate of these materials (plus metals, 

pathogens, salts, and trace organics) is discussed in

Chapter 2. 

Table 1-1. Comparison of Land Treatment Process Design Features 

Feature Slow rate (SR) Overland flow (OF) 

Soil aquifer treatment 

(SAT) 

Minimum pretreatment Primary sedimentation Screening Primary sedimentation

Annual loading rate, m/yr 0.5 - 6 3 – 20 6 – 125 

Typical annual loading rate, m/yr 1.5 10 30 

Field area required, haa 23 - 280 6.5 – 44 3 – 23 

Typical weekly loading rate, cm/wk 1.9 – 6.5 6 – 40b 10 – 240 

Disposition of applied wastewater Evapotranspiration and percolation Evapotranspiration and surface runoff, 

limited percolation

Mainly percolation 

Application techniques Sprinkler, surface or drip Sprinkler or surface Usually surface 

Need for vegetation Required Required Optional 

a

Field area in hectares not including buffer area, roads, or ditches for 3,785 m3/d (1 mgd) flow. b

Range includes screened wastewater to secondary effluent, higher rates for higher levels of pre-application treatment.

1-1 
 

Table 1-2. Site Characteristics for Land Treatment Processes 

Parameter 

Slow Rate 

(SR) 

Overland Flow

(OF) 

Soil aquifer treatment 

(SAT) 

Slope 0 to 20%, Cultivated site 

35%, Uncultivated 

2 to 8 % for final slopesa Not critical 

Soil permeability Moderate to slow Slow to none Rapid 

Groundwater depth 0.6 to 3 mb (2 to 10 ft) Not criticalb 1 m (3 ft) during applicationc

1.5 to 3 m (5-10 ft) during drying 

Climate Winter storage in cold climatesd Same as SR Not critical a

Steeper slopes may be feasible at reduced application rates. b

Impact on groundwater should be considered for more permeable soils. c

Underdrains can be used to maintain this level at locations with shallow groundwater. d

May not be required for forested systems. 

Table 1-3. Expected Effluent Water Quality from Land Treatment Processesa (mg/L unless otherwise noted) 

Parameter 

Slow rateb

(SR) 

Overland flowc

(OF) 

Soil aquifer treatmentd 

(SAT) 

BOD5 < 2 10 5 

TSS < 1 10 2 

NH3/NH4 (as N) < 0.5 < 4 0.5 

Total N 3e 5f 10 

Total P < 0.1 4 1 

Fecal coli (#/100 mL) <1 200 + 10 

a

Quality expected with loading rates at the mid to lower end of the range shown in Table 1-1. b

Percolation of primary or secondary effluent through 1.5 m (5 ft) of unsaturated soil. c

Treating comminuted, screened wastewater using a slope length of 30-36 m (100-120 ft). d

Percolation of primary or secondary effluent through 4.5 m (15 ft) of unsaturated soils; phosphorus and fecal coliform removals increase with flow

 path distance. 

e

Concentration depends on loading rate, C:N ratio, and crop uptake and removal. f

Higher values expected when operating through a moderately cold winter or when using secondary effluent at high rates. 

All three processes require intermittent loading. The

application period may range from a few hours for

overland flow systems to a few days for soil aquifer 

treatment systems. The resting or drying period is critical

to renew aerobic conditions in the soil, renew infiltration

rates in SR and SAT systems, and allow oxidation of

BOD and ammonia. 

1.4. Slow Rate Land Treatment 

Slow rate land treatment is the application of 

wastewater to a vegetated soil surface. The applied 

wastewater receives significant treatment as it flows 

through the plant root/soil matrix. The potential hydraulic 

pathways for the treated water are shown in Figure 1-1. 

The design flow path depends on infiltration, percolation,

lateral flow, and evapotranspiration within the

boundaries of the treatment site. Solids removal 

generally occurs at the soil surface and biological,

chemical and additional physical treatment occurs as the

wastewater percolates through the plant root/soil matrix. 

Off-site runoff of any of the applied wastewater is 

specifically avoided by the system design. The hydraulic 

pathways of the applied water can include: 

• Vegetation irrigation with incremental percolation 

(e.g., precipitation or non-contaminated water for 

salt management). 

• Vegetative uptake with evapotranspiration. 

• Percolation to underdrains or wells for water 

recovery and reuse. 

• Percolation to groundwater and/or lateral subsurface 

flow to adjacent surface waters.

Slow rate land treatment can be operated to achieve a 

number of objectives including: 

• Further treatment of the applied wastewater. 

• Economic return from the use of water and nutrients 

to produce marketable crops. 

• Exchange of wastewater for potable water for 

irrigation purposes in arid climates to achieve overall 

water conservation.

• Development and preservation of open space and 

greenbelts. 

1-2 
 

Figure 1-1. Slow Rate Hydraulic Pathways. 

These goals are not mutually exclusive but it is unlikely 

that all can be brought to an optimum level within the 

same system. In general, maximum cost effectiveness 

for both municipal and industrial systems will be

achieved by applying the maximum possible amount of 

wastewater to the smallest possible land area. That will 

in turn restrict the choice of suitable vegetation and 

possibly the market value of the harvested crop. In the

more humid parts of the United States, optimization of

treatment is usually the major objective for land 

treatment systems. Optimization of agricultural potential

or water conservation goals are generally more

1-3 
 

important in the more arid western portions of the United 

States. 

Optimization of a system for wastewater treatment 

usually results in the selection of perennial grasses 

because a longer application season, higher hydraulic 

loadings, and greater nitrogen loadings compared to 

other annual agricultural crops. Site selection is 

important with municipal wastewater which requires

greater hydraulic capacity. Annual planting and 

cultivation can also be avoided with perennial grasses. 

However, corn and other crops with higher market

values are also grown on systems where treatment is a

major objective. Muskegon, MI (US EPA, 1980) was a 

noted example with over 2020 ha (5,000 acres) of corn, 

alfalfa and soybeans under cultivation. 

Forested systems also offer the advantage of a longer 

application season and higher hydraulic loadings than

typical agricultural crops, but may be less efficient than

perennial grasses for nitrogen removal depending on the 

type of tree, stage of growth and general site conditions.

Early research at the Pennsylvania State University (US 

EPA, 1974) established the basic criteria for full-scale 

forested systems. Subsequent work in Georgia, 

Michigan, and Washington State further refined the

criteria for regional and species differences (McKim, 

1982). A large-scale slow rate forested system in 

Clayton County, GA, designed for 75,700 m3

/d (20 mgd) 

uses 1460 ha (3650 acres) and has been in continuous 

operation since 1981 (Reed and Bastian, 1991; Nutter et 

al., 1996). The largest operational land treatment system 

in the United States is the 3232-ha (8,000-acre) forested 

system in Dalton, GA. 

1.5. Overland Flow Treatment 

Overland flow (OF) is the controlled application of 

wastewater to relatively impermeable soils on gentle

grass covered slopes. The hydraulic loading is typically 

several inches of liquid per week and is usually higher 

than for most SR systems. Vegetation (e.g., perennial 

grasses) in the OF system contributes to slope stability, 

erosion protection, and treatment. 

The design flow path is essentially sheet flow down the 

carefully prepared vegetated surface with runoff 

collected in ditches or drains at the toe of each slope

(Figure 1-2). Treatment occurs as the applied 

wastewater interacts with the soil, the vegetation, and 

the biological surface growths. Many of the treatment 

responses are similar to those occurring in trickling filters 

and other attached growth processes. Wastewater is 

typically applied from gated pipe or nozzles at the top of

the slope or from sprinklers located on the slope surface. 

Industrial wastewaters and those with higher solids 

content typically use the latter approach. A small portion 

of the applied water may be lost to deep percolation and

evapotranspiration, but the major portion is collected in 

the toe ditches and discharged, typically to an adjacent

surface water. Because these systems discharge to 

surface waters, a National Pollutant Discharge

Elimination System (NPDES) permit is required. 

The SR and SAT concepts may include percolate 

recovery and discharge, but the OF process almost 

always includes a surface discharge and the necessary 

permits are required. The purpose of overland flow is 

cost-effective wastewater treatment. The harvest and

sale of the cover crop may provide some secondary

benefit and help offset operational costs, but the primary 

objective is treatment of the wastewater. Crop removal 

should be encouraged since removing the crop also

removes N and P. Design procedures are presented in

Chapter 9. One of the largest municipal overland flow 

systems in the U.S. is in Davis, CA (Crites et al., 2001) 

designed for 18,925 m3

/d (5 mgd) flow and covering 80

ha (200 acres). 

1.6. Soil Aquifer Treatment 

SAT land treatment is the controlled application of 

wastewater to earthen basins in permeable soils at a

rate typically measured in terms of meters of liquid per 

week. As shown in Table 1-2, the hydraulic loading rates 

for SAT are usually higher than SR systems. Any 

surface vegetation that is present has a marginal role for 

treatment due to the high hydraulic loadings. In these

cases, water-tolerant grasses are typically used.

Treatment in the SAT process is accomplished by

biological, chemical and physical interactions in the soil

matrix with the near surface layers being the most active 

zone.

1-4 
 

Figure 1-2. Overland Flow. 

The design flow path involves surface infiltration, 

subsurface percolation and lateral flow away from the

application site (Figure 1-3). A cyclic application, as 

described in Chapter 10, is typical when the operational 

mode includes a flooding period followed by days or 

weeks of drying. Continuous application of well treated

wastewater can be accomplished with low application 

rates. This allows aerobic restoration of the infiltration 

surface and drainage of the applied percolate. The

geohydrological aspects of the SAT site are more critical

than for the other processes and a proper definition of 

subsurface conditions and the local groundwater system 

is essential for design. 

1-5 
 

Figure 1-3. SAT Hydraulic Pathways. 

The purpose of a soil aquifer treatment system is to 

provide a receiver aquifer capable of accepting liquid 

intended to recharge shallow groundwater. System

design and operating criteria are developed to achieve 

that goal. However, there are several alternatives with

respect to the utilization or final fate of the treated water: 

• Groundwater recharge. 

• Recovery of treated water for subsequent reuse or 

discharge. 

• Recharge of adjacent surface streams.

• Seasonal storage of treated water beneath the site 

with seasonal recovery for agriculture. 

The recovery and reuse of the treated SAT effluent is 

particularly attractive in dry areas in arid regions and

studies in Arizona, California, and Israel (Idelovich, 

1981) have demonstrated that the recovery of the 

treated water may be suitable for unrestricted irrigation

on any type of crop. Groundwater recharge may also be

attractive, but special attention is required for nitrogen if 

drinking water aquifers are involved. Unless special

measures (described in Chapter 10) are employed, it is 

unlikely that drinking water levels for nitrate nitrogen (10

mg/L as N) can be routinely attained immediately

beneath the application zone with typical municipal

wastewaters. If special measures are not employed,

there must then be sufficient mixing and dispersion with 

the native groundwater prior to the downgradient 

extraction points. In the more humid regions neither 

recovery nor reuse are typically considered. Examples 

of SAT include the Lake George, NY, system operating 

since 1939, the Calumet, MI, site operating since 1888, 

1-6 
 

and the Hollister, CA, system operating since 1946 (US 

EPA., 1978). 

1.7. Limiting Design Parameter Concept 

The design of all land treatment systems, wetlands, 

and similar processes is based on the Limiting Design 

Parameter (LDP) concept (Crites et al., 2000). The LDP

is the factor or the parameter, which controls the design

and establishes the required size and loadings for a 

particular system. If a system is designed for the LDP it 

will then function successfully for all other less-limiting 

parameters of concern. Detailed discussions on the

interactions in land treatment systems with the major 

wastewater constituents can be found in Chapter 2. 

Experience has shown that the LDP for systems that 

depend on significant infiltration, such as SR and SAT, is 

either the hydraulic capacity of the soil or the ability to 

remove nitrogen to the specified level, when typical

municipal wastewaters are applied. Whichever of these

two parameters requires the largest treatment area

controls design as the LDP, and the system should then

satisfy all other performance requirements. Overland

flow, as a discharging system, will have an LDP which 

depends on the site-specific discharge limits, and the 

parameter which requires the largest treatment area

controls the design. 

1.8. Guide to Intended Use of Manual 

The first chapter introduces the processes and the

concept of limiting design parameter. In Chapter 2 all of 

the wastewater constituents of concern are discussed

along with their fate in land treatment systems and the

removal mechanisms. In Chapter 3 the movement of 

water through soil and groundwater is discussed 

including equations and physical test methods and

procedures. In Chapter 4 the vegetation used in land 

treatment, the nutrient uptake and sensitivity to 

wastewater constituents, and management are

described. 

Planning guidance is provided in Chapter 5 including 

site selection procedures. Preapplication treatment and

storage guidance is presented in Chapter 6 and

wastewater distribution systems are introduced in

Chapter 7. The process design chapters are 8, 9, and 10 

covering slow rate, overland flow, and soil aquifer 

treatment, respectively. Equations and procedures are

presented along with a brief case study of each process. 

Much design and research activity in recent years has

focused on industrial wastewater. In Chapter 11, the 

unique aspects of treating high-strength wastewater from

food processors and other sources are discussed. 

Guidance on land application of biosolids can be found 

in Crites and Tchobanoglous (1998) and US EPA 

(1995). 

1.9. References 

Crites, R.W. and G. Tchobanoglous (1998) Small and 

Decentralized Wastewater Management Systems. 

McGraw-Hill Book Co. New York. 

Crites, R.W., S.C. Reed, and R.K. Bastian (2000) Land

Treatment Systems for Municipal and Industrial

Wastes. McGraw-Hill Book Co. New York. 

Crites, R.W., S.C. Reed, and R.K. Bastian (2001) 

Applying Treated Wastewater to Land. BioCycle, 

42(2) 32-36. 

Idelovitch, E. (1981) Unrestricted Irrigation with

Municipal Wastewater, in: Proceedings, National

Conference on Environmental Engineering, ASCE, 

Atlanta GA, July 8-10. 

McKim, H.L. (1982) Wastewater Application in Forest

Ecosystems, Report 82-19, USA CRREL, Hanover, 

NH. 

Nutter, W.L., L. Philpott, and L.A. Morris (1996) LongTerm Environmental Impacts of Municipal

Wastewater Irrigation to Forests at Clayton County,

Georgia, Proceedings, Land Application of Wastes

in Australia and New Zealand: Research and

Practice, Australian Conference. 

Olson, J.V., R.W. Crites, and P.E. Levine (1980) 

Groundwater Quality at a Rapid Infiltration Site, 

Journal Envir. Engr. Div, Vol 106(5):885-889,

American Society of Civil Engineers. 

Reed, S.C. and R.K. Bastian (1991) Potable Water Via

Land Treatment and AWT, Water Envir. Technology,

3(8)40-47, WEF, Alexandria, VA. 

US EPA (1974) Renovation of Secondary Effluent for 

Reuse as a Water Resource, EPA 660/2-74-016, US

EPA CERI, Cincinnati, OH.

US EPA (1977) Process Design Manual for Land 

Treatment of Municipal Wastewater, EPA 625/1-77-

008, US EPA CERI, Cincinnati, OH. 

US EPA (1978) Long-Term Effects of Land Application 

of Domestic Wastewater. US EPA. EPA-600/2-78-

084. Ada, OK. 

US EPA (1980) Muskegon County Wastewater 

Management System, EPA 905/2-80-004, US EPA

Great Lakes Programs Office, Chicago, IL. 

US EPA (1981) Process Design Manual for Land 

Application of Municipal Wastewater, EPA 625/1-81-

013, US EPA CERI, Cincinnati, OH. 

1-7 
 

US EPA (1984) Process Design Manual, Land 

Treatment of Municipal Wastewater: Supplement on 

Rapid Infiltration and Overland Flow, EPA 625/1-81-

013A, US EPA CERI, Cincinnati, OH. 

US EPA (1995) Process Design Manual, Land 

Application of Sewage Sludge and Domestic

Septage, EPA/625/R-95/001, US EPA NRMRL,

Cincinnati, OH 

1-8 
Chapter 2 

Wastewater Constituents and Removal Mechanisms

An understanding of the basic interactions between 

the wastewater constituents of concern and the soil

treatment system is essential for the determination of the 

limiting design parameter (LDP) for a particular system. 

These interactions are generally the same for all of the

land treatment processes and are therefore discussed

together in this chapter. 

2.1 Biochemical Oxygen Demand 

All land treatment processes are very efficient at 

removal of biodegradable organics, typically 

characterized as biochemical oxygen demand (BOD5). 

Removal mechanisms include filtration, absorption, 

adsorption, and biological reduction and oxidation. Most 

of the responses in slow rate (SR) and soil aquifer 

treatment (SAT) occur at the soil surface or in the nearsurface soils where microbial activity is most intense.

Treatment oxidation-reduction reactions generally occur 

in the upper 1/3 of the slope on the OF sites. Intermittent 

or cyclic wastewater application on these systems is 

necessary to allow the restoration of aerobic conditions 

in the soil profile and maintenance of the infiltration 

capacity at the soil surface.

2.1.1 BOD Loading Rates 

To establish a basis for the amount of degradable

organic matter that can be land applied, the BOD loading 

rate is calculated. The BOD loading rate is defined as

follows: 

LBOD = (kg of BOD applied/day) / (area loaded per day) (cycle time)

(2-1)

Where 

LBOD = kg/ha-d 

Kg of BOD = concentration, mg/L x flow, m3/d x 1000 L/1 

 applied per day m3

x 0.001 kg/g x 1 g/1000 mg

Area loaded = total wetted area receiving wastewater per 

day, ha 

Cycle time = time between subsequent applications to a 

given subplot (days of application plus days of 

drying), days

Example 2.1 BOD Loading Rates 

Conditions: Wastewater with a BOD of 250 mg/L. Slow rate 

land treatment field area of application of 2 ha/day.

Flow of 1000 m3

/d. Cycle time of 7 days between 

wastewater applications. 

Find: Cycle-average BOD loading rate 

Solution: 1. Calculate the kg of BOD applied per day

Kg of BOD applied = 250 mg/L x 1,000 m3

/d x 

0.001 kg/g = 250’’ kg/d 

2. Calculate the BOD loading rate using Eq. 2-1 

L = 250 kg/d / (2 ha/d)(7 d) = 17.9 kg/ha-d 

The BOD is a 5-day test of the oxygen demand

required by microorganisms to biodegradable organics. 

Other quicker tests, often more reliable, include the 

chemical oxygen demand (COD) which is always larger 

than the BOD and the total organic carbon (TOC) test, 

which ranges from greater than the BOD for untreated 

wastewater to less than the BOD for treated effluent 

(Tchobanoglous et al., 2002). The treatment of BOD 

occurs throughout the loading (application period), 

drainage, and the reaeration (drying or resting) period or 

cycle. To maintain aerobic conditions in the soil, the rate

of reaeration in a given cycle should match or exceed 

the rate of BOD exertion. A “rational” model that predicts 

the rate of reaeration depending on soil conditions, the 

depth of application and the reaeration period has been

developed (Smith and Crites, 2001) and is presented in

Chapter 8. Typical BOD loading rates for the three

processes are presented in Table 2-1. 

Table 2-1. Typical Organic Loading Rates for Land Treatment 

Systems (adapted from Reed et al., 1995) 

Process BOD loading (kg BOD5/ha•d)a,b

Slow Rate (SR) 50 – 500 

Soil Aquifer Treatment (SAT) 145 – 1000 

Overland Flow (OF) 40 – 110 a

kg/ha•d x 0.89 = lb BOD5/ac•d b

Lower end of range is typical of municipal systems and upper end is 

typical of industrial strength wastewater.
Essentially all of the treatment in overland flow 

systems (OF) occurs at or near the soil surface or in the 

mat of plant litter and microbial material. Settling of most

particulate matter occurs rapidly in OF systems as the 

applied wastewater flows in a thin film down the slope. 

Algae removal is an exception since the detention time 

on the slope may not be sufficient to permit complete

removal by physical settling (Witherow and Bledsoe, 

1983). The biological material and slimes which develop

on the OF slope are primarily responsible for ultimate 

pollutant removal. These materials are similar to those

found in other fixed film processes, such as trickling

filters, and the presence of aerobic zones and anaerobic 

microsites within the slime layer is to be expected. In a 

properly managed system, with acceptable loadings, the 

aerobic zones dominate. However, there are still 

numerous anaerobic sites that contribute to the 

breakdown of the more refractory organics (Crites et al., 

2000). 

2.1.2 BOD Removal 

A few examples of removal of BOD by land treatment

processes receiving municipal wastewater are 

summarized in Table 2-2. Long-term effects studies (US 

EPA, 1979; Hossner et al., 1978; Koerner and Haws,

1979; Leach et al., 1980; and US EPA, 1978) generated 

much of the available data. Because the basic treatment 

mechanism is biological, all three processes have a

continually renewable capacity for BOD5 removal as 

long as the loading rate and cycle allows for preservation 

and/or restoration of aerobic conditions in the system. 

Laboratory studies in 1998 with soil columns indicated

that BOD5 removal to low “background” levels was 

independent of the level of pretreatment, independent of 

soil type, and essentially independent of infiltration rate

(ASU et al., 1998). These responses confirm the results 

presented in Table 2-2 and also confirm the fact that

high levels of preapplication treatment are not necessary 

for effective BOD5 removal in municipal land treatment 

systems.

2.2 Total Suspended Solids 

Total suspended solids (TSS) are generally not an 

LDP in the design of municipal land treatment systems. 

SR and SAT systems are very effective for removal of 

suspended solids. Filtration through the soil profile is the 

principal removal mechanism. OF systems depend on

sedimentation and entrapment in the vegetative litter or 

on the biological slimes and are typically less efficient 

than SR or SAT. However, OF systems can produce

better than secondary effluent quality for total suspended

solids when either screened wastewater or primary

effluent is applied. 

TSS removal at a number of land treatment systems 

receiving municipal wastewaters is summarized in

Table 2-3. Suspended solids removal in OF systems

receiving facultative lagoon effluents is not always 

effective due to the variability of algal species present

and the short detention time on the slope. The seasonal 

variation in performance of the Davis, CA system, shown

in Table 2-3, clearly illustrates this problem. See Chapter 

9 for additional information on this issue.

2.3 Oil and Grease 

Oil and grease, also known as fats, oil, and grease

(FOG), should not be a factor for land treatment of 

typical municipal wastewaters unless there is a spill 

somewhere in the municipal collection system. There is 

Table 2-2. BOD5 Removal at Typical Land Treatment Systems (adapted from Crites et al., 2000) 

BOD5

Process/Location Hydraulic Loading (m/yr

a

) Applied (mg/L) Soil Water Drainage (mg/L) Sample Depth (mb) 

SR 

Hanover, NH 1.2 –7.6 40-92 0.9-1.7 1.5 

San Angelo, TX 3 89 1.0 7.6 

Yarmouth, MAc 1 85 <2.0 1.0 

SAT

Lake George, NY 43 38 1.2 3.2 

Phoenix, AZ 110 15 1.0 9 

Hollister, CA 15 220 8.0 7.6 

OF 

Hanover, NH 7.6 72 9 -- 

Easley, SC 8.2 200 23 -- Davis, CA 12.5 112 10 -- a

m/yr x 3.28 = ft/yr. b

m x 3.28 = ft. cGiggey et al., 1989.
Table 2-3. Suspended Solids Removal at Land Treatment Systems (adapted from Leach et al., 1980 and Crites et al., 2000)

Soil Water Drainage - Total suspended solids, mg/L 

Process/location Applied Effluenta

Slow Rate (SR) 

Hanover, NH 60 <1 

Typical value 120 <1 

Soil Aquifer Treatment (SAT)

Phoenix, AZ 20 – 100 <1 

Hollister, CA 274 10 

Typical Value 120 2 

Overland Flow (OF)

Ada, OK (raw wastewater) 160 8 

Hanover, NH (primary) 59 7 

Easley, SC (screened wastewater) 186 8 

Utica, MS (fac. lagoon) 30 8 

Davis, CA (fac. lagoon) 

 Summer 121 80 

 Fall 86 24 

 Winter 65 13 a

Example depths and loading rates for SR and SAT systems are shown in Table 2-2.

still no need to design the land treatment component for 

such an emergency because standard containment and

clean-up procedures can be used when needed. Oil and 

grease are more likely to be a routine component in 

industrial wastewaters. The most likely sources are

petroleum, and animal and vegetable oils. Loading rates 

and removals are discussed in Chapter 11 (US EPA, 

1972). 

2.4 pH 

The pH range suitable for biological treatment is 

typically between 5 and 9 (Crites and Tchobanoglous,

1998). Soil generally has a large buffer capacity such

that wastewater pH can be attenuated and biological 

treatment efficiency is not impaired. Organic acids in

food processing wastewater are easily degradable, as 

described in Chapter 11, and do not impose a limitation 

on wastewater treatment. 

Crops can also tolerate a relatively large range in pH. 

Optimum pH for crop growth has been reported to be

between 6.4 and 8.4. Low soil pH can result in metals 

becoming more soluble and potentially leaching to 

groundwater. A pH of 6 or above is currently considered

adequate to protect against crop uptake of most metals 

(Page et al., 1987). Metal concentrations in municipal 

effluent are typically well below the values of concern in

Section 2.6. If the practitioner is concerned about excess 

metal uptake into the crop, monitoring of the crop would

be prudent. 

2.5 Pathogenic Organisms 

The known pathogens of concern in land treatment 

systems are parasites, bacteria, and viruses. The

potential pathways of concern are to groundwater, 

contamination of crops, translocation or ingestion by

grazing animals, and human contact through off site

transmission via aerosols or runoff. The removal of 

pathogens in land treatment systems is accomplished by 

adsorption, desiccation, radiation, filtration, predation, 

and decay due to exposure to sunlight (UV) and other 

adverse conditions. Fecal coliforms are used as an

indicator of fecal contamination. Fecal contamination

occurs from livestock as well as other warm blood

animals. It is not uncommon to find “background” fecal

coliform concentrations of 102

 or greater concentration. 

The SR process is the most effective, removing about

five logs (105

) of fecal coliforms within a depth of a 0.6 m

(2 ft). The SAT process typically can remove two to 

three logs of fecal coliforms within several meters of 

travel, and the OF process can remove about 90 percent

of the applied fecal coliforms (Reed et al., 1995). 

2.5.1 Parasites 

Parasites may be present in all municipal wastewaters. 

Parasites, such as Ascaris, E.histolytica and 

Cryptosporidium have been recovered from

wastewaters. Under optimum conditions the eggs of

these parasites, particularly Ascaris can survive for 

many years in the soil (US EPA. 1985). Because of their 

weight and size, parasite cysts and eggs will settle out in

preliminary treatment or in storage ponds, so, if present

most will be found in the raw sludge and possibly in the 

biosolids. 

There is no evidence available indicating transmission

of parasitic disease from application of wastewater in

properly operated land treatment systems.

Transmission of parasites via sprinkler aerosols should

not be a problem due to the weight of the cysts and

eggs. The World Health Organization (WHO) considers 

parasite exposure by field workers to be the most

significant risk for irrigation with wastewater. They

recommend ponds for the short-term retention of

untreated wastewater as a simple solution for the 

problem (Chang et al, 1995). 
2.5.2 Crop Contamination 

The major concerns for crop contamination are

directed toward retention and persistence of the 

pathogens on the surfaces of the plant until consumed

by humans or animals, or the internal infection of the 

plant via the roots. The persistence of polio virus on the 

surfaces of lettuce and radishes, for up to 36 days, has 

been demonstrated. About 99 percent of the detectable 

viruses were gone in the first five to six days. The 

general policy in the U.S. is not to grow vegetables to be

consumed raw on land treatment systems without high 

levels of treatment, including filtration and disinfection. 

Internal contamination of plants with viruses has been 

demonstrated with transport from the roots to the leaves. 

However, these results were obtained with soils 

inoculated with high concentrations of viruses and then

the roots were damaged or cut. No contamination was 

found when roots were undamaged or when soils were

not inoculated with the high virus concentrations (Crites 

et al., 2000; US EPA 1985). 

Criteria for irrigation of pasture with primary effluent in

Germany require a period of 14 days before animals are 

allowed to graze. Bell and Bole demonstrated that fecal

coliforms from sprinkling of wastewater on the surfaces

of alfalfa hay were killed by ten hours of bright sunlight 

(Bell and Bole 1978). Similar experiments with Reed

canarygrass found 50 hours of sunlight were required. 

It was recommended that a one-week rest period prior to

grazing be provided to ensure sufficient sunlight, for 

Reed canary, orchard, and brome grasses used for

forage or hay (Bell and Bole, 1978). Because fecal

coliforms have survival characteristics similar to

salmonella, these results should be applicable to both 

organisms. However, the current management practice

for restricting grazing at biosolids application sites is a

minimum of 30 days in the U.S.A. 

2.5.3 Runoff Contamination 

Wastewater constituents that are applied to the land 

enter the plant root/soil matrix. Suspended solids 

become part of the soil after these are filtered out of the

wastewater. The rainfall runoff from fields irrigated with

wastewater may contain dissolved wastewater 

constituents. 

Runoff from a land treatment site might be a potential 

pathway for pathogen transport. Proper system design

and operation should eliminate runoff from adjacent 

lands entering the site and runoff of applied wastewater

from the site. Overland flow is an exception in the latter 

case because treated effluent and stormwater runoff are

discharged from the site. The quality of rainfall runoff 

from an overland flow system is equal or better in quality 

than the normal (non-rainfall induced) renovated

wastewater runoff. 

The NPDES permitting authority should be consulted 

with respect to the current storm water regulations (40

CFR 122.26). Storage of runoff for up to one “time-ofconcentration” or 24 hours may be necessary to capture 

the first flush of stormwater. 

2.5.4 Groundwater Contamination 

The risk of groundwater contamination by pathogens 

involves the movement of bacteria or virus to aquifers 

that are then used for drinking purposes without further 

treatment. The risk is minimal for OF systems but 

highest for SAT systems due to the high hydraulic 

loading and the coarse texture and relatively high

permeability of the receiving soils. 

The removal rate of bacteria can be quite high in the

finer-textured agricultural soils commonly used for SR 

systems. Results from a five-year study in Hanover, NH

(Jenkins and Palazzo, 1981) applying both primary and 

secondary effluent to two different soils indicated

essentially complete removal of fecal coliforms within a 

1.5 m (5 ft) soil profile. The soils involved were a fine

textured silt loam and a coarser textured loamy sand and

the concentrations of fecal coliform in the applied

wastewaters ranged from 105

 for primary effluent to 103

for secondary effluent. In similar research in Canada 

(Bell and Bole, 1978), undisinfected effluent was applied 

to grass-covered loamy sand. Most of the coliform were

retained in the top 75 mm (3 in) of soil and none

penetrated below 0.68 m (27 in). Die-off occurred in two

phases: an initial rapid phase within 48 hours of 

application when 90 percent of the bacteria died,

followed by a slower decline during a two-week period

when the remaining 10 percent were eliminated (Jenkins

and Palazzo, 1981). 

Removal of virus, which is at least partially dependent 

on cation exchange and adsorption reactions, is also

quite effective in these finer textured agricultural soils. 

Most of the concern and the research work on virus 

transmission in soils have focused on SAT systems. A 

summary of results from several studies is presented in 

Table 2-4. The SAT basins in the Phoenix system

consisted of about 0.77 m (30 in) of loamy sand

underlain by coarse sand and gravel layers. During the

study period indigenous virus were always found in the 

applied wastewater, but none were recovered in the

sampling wells. 

At Santee, CA, secondary effluent was applied to

percolation beds in a shallow stratum of sand and

gravel. The percolate moved laterally to an interceptor 

trench approximately 458 m (1,500 ft) from the beds.

Enteric virus was isolated from the applied effluent but 
none were ever found at the 61 m (200 ft) and 122 m 

(400 ft) percolate sampling points. 

Lance and others have examined the problem of virus 

desorption in the laboratory (Lance and Gerba, 1980).

Using soil columns it was shown that applications of

distilled water or rainwater could cause adsorbed viruses 

to move deeper into the soil profile under certain 

conditions. However, viruses were not desorbed if the

free water in the column drained prior to application of 

the distilled water. This suggests that the critical period

would be the first day or two after wastewater

application. Rainfall after that period should not cause

additional movement of viruses in the soil profile. A 

desorbed virus should have further opportunities for 

readsorption in the natural case, assuming there are no 

macropores Lance’s work with polio virus in soil

columns, containing calcareous sand, indicated that 

most viral particles are retained near the soil surface. 

Increasing the hydraulic loading from 0.6 m/d per day to 

1.2 m/d (2 to 4 ft/d) caused a virus breakthrough (about

one percent of the applied load) at the bottom of the 2.4 

m (8 ft) column (Lance and Gerba, 1980). However, 99 

percent of the viral particles were still removed at

hydraulic loadings as high as 12 m/d (39 ft/d). Lance 

suggested that the velocity of water movement through 

the soil may be the single most important factor affecting

the depth of virus penetration in soils. Column studies 

(Arizona State University et al, 1998) have confirmed the 

earlier work by Lance. In this recent study, high virus 

removal efficiencies (>99%) were observed in one meter 

of soil at low infiltration rates. Assuming a first order 

decay relationship, if 99 percent removal of virus 

occurred in one meter of soil then 99.999 percent would 

be removed in three meters of soil. This same study 

routinely observed a four log (99.99%) removal of 

Cryptosporidium after passing through one meter of soil

even at the highest infiltration rates. 

2.5.5 Aerosols 

Pathogen concentrations in aerosols caused by

sprinkling wastewater is a function of their concentration 

in the applied wastewater and the aerosolization 

efficiency. Aerosolization efficiency, which is the

percentage of the wastewater that is converted to 

aerosols during sprinkling, can vary from 0.1 percent to

nearly 2 percent, with 0.3 to 1 percent being typical

(Crook, 1998). 

The potential for aerosol transport of pathogens from

land treatment sites is a controversial health issue. The

lay public, and many professionals, tend to

misunderstand what aerosols are and confuse them with 

the water droplets, which emerge from sprinkler nozzles.

Aerosols are almost colloidal in size ranging from 20

microns in diameter and smaller. UV light, heat and

desiccation significantly reduce small aerosol particles. It 

is prudent to design any land treatment systems so that

the larger water droplets emerging from the sprinklers 

are contained within the site. The public acceptance of a 

project will certainly be enhanced if it is understood that 

neither their persons nor their property will become “wet” 

from the sprinkler droplets (Reed et al., 1995). 

Bacterial aerosols are present in all public situations 

and will tend to increase with the number of people and

their proximity. Sporting events, theaters, public 

transportation, public toilets, etc., are all potential 

locations for airborne infection. Bacterial concentrations 

in aerosols at various locations, all of which involve the

use or treatment of wastewaters, are summarized in

Table 2-5. The cooling water for the power plant that is

cited uses some disinfected effluent as make-up water. 

The aerosol concentration at this cooling tower is 

roughly the same as measured just outside the sprinkler 

impact zone at the California (Pleasanton) operation 

where undisinfected effluent is used. It does not appear 

that bacterial aerosols at or near land treatment sites are

any worse than other sources. In fact, the opposite

seems true, the aerated pond in Israel and the activated 

sludge systems have higher aerosol concentrations than

the land treatment systems listed in the table. Aerosol

studies in metropolitan areas for example have indicated 

a bacterial concentration of 0.11 particles/m3

 (4

particles/ft3

) per cubic foot or air in downtown Louisville, 

Table 2-4. Virus Transmission through Soil at SAT Land Application Sites (Reed et al., 1995)

Virus concentration (pfu/L) 

Location Sampling depth or distance (m) Applied 

Soil water drainage at 

sample point 

Phoenix, AZ (Jan to Dec 1974) 3-9 8 

27 

24 

2 

75 

11 

0 

0 

0 

0 

0 

0 

Gainesville, FL (Apr to Sept 1974) 7 0.14 

0.14 

0.14 

0.14 

0.14 

0.14 

0.14 

0.005 

0 

0 

0 

0 

0 

0 

0 

Santee, CA (1966) 61 Concentrated type 3 polio virus 0 

0.14 
Table 2-5. Aerosol Bacteria at Various Sources (Reed et al., 1995)

Location Downwind distance, m (ft) 

Total aerobic bacteria, #/m3

(#/ft3

)

a

Total coliform bacteria, #/m3

(#/ft3

)

a

Activated sludge tank, Chicago, IL 9-30 (30-100) 11.2 (396) 0.006 (0.2) 

Activated sludge tank, Sweden 0 (0) 80 (2,832) -- 

Power plant cooling tower, California 0 (0) 2.4 (83) -- 

Aerated pond, Israel 30 (100) -- 0.23 (8) 

Sprinklersb

, Ohio 30 (100) 0.4 (14) 0.003 (0.1) 

Sprinklersc, Israel 30 (100) -- 0.094 (3.3) 

Sprinklersc

, Arizona 45 (150) 0.6 (23) 0.006 (0.2) 

Sprinklersc

, Pleasanton, CA 9-30 (30-100) 2.1 (73) 0.006 (0.2) a

Aerosol counts are per cubic meter of air sampled (#/ft3). b. Disinfected effluent applied. c. Undisinfected effluent applied. 

KY, during daylight hours, and an annual average of 1.6

bacterial particles/m3

 in Odessa, Russia. The aerosols 

from the land treatment systems listed in Table 2-5 fall 

within this range. 

An epidemiological study at an activated sludge plant 

in the Chicago area (Camann, 1978) documented

bacteria and virus in aerosols on the plant site. 

However, the bacterial and viral content of the air, the 

soil, and the surface waters in the surrounding area were 

not different than background levels and no significant 

illness rates were revealed within a 4.8 km (3 mile) 

radius of the activated sludge plant. A similar effort was 

undertaken at an activated sludge plant in Oregon with a

school playground approximately 10 m (30 ft) from the

aeration tanks. It can be inferred from these studies, 

since the concentrations of bacteria and viruses in land

treatment aerosols are similar to those from activated

sludge treatment systems. The risks of adverse health 

effects should be similar to those presented by properly

operated land treatment systems. 

The aerosol measurements at the Pleasanton, CA 

land treatment system demonstrated that salmonella and

viruses survived longer than the traditional coliform

indicators (Camann, 1978). However, the downwind 

concentration of viruses was very low at 1.1 x 10-5

plaque-forming units (pfu/m3

) ( 0.0004 pfu/ft3). 

The source for these measurements was undisinfected 

effluent from high-pressure impact sprinklers, and the

sampling point was 49 m (160 ft) from the sprinkler 

nozzle. The concentration cited is equal to one virus 

particle in every 7 m3

 (250 ft3) of air. Assuming a normal

breathing intake of about 0.002 m3

/min (0.07 ft3/min) it 

would take 59 hours of continuous exposure by a system 

operator to inhale that much air. In normal practice an 

operator at Pleasanton might spend up to one hour per 

day within 49 m (160 ft) of the sprinklers. This is 

equivalent to the time an activated sludge operator

spends servicing the aeration tanks. At this rate the 

operator at Pleasanton would be exposed to less than 

four virus particles per year and the risk to the adjacent 

population would appear to be non-existent. 

US EPA guidelines have recommended a fecal

coliform count of 1,000/100 mL for recreational 

applications, based on standards for general irrigation

water and for bathing waters and body contact sports. 

With respect to the aerosol risk of spraying such waters,

Shuval has reported that when the coliform

concentration at the nozzle was below 1,000/100 mL, no 

viruses were detected at downwind sampling stations, 

the nearest of which was 10 m (33 ft) away. (Shuval and

Teltch, 1979). Procedures have been developed for 

estimating the downwind concentrations of aerosol 

microorganisms from sprinkler application of wastewater

(US EPA, 1982). 

2.6 Metals 

The removal of metals in the soil is a complex process 

involving the mechanisms of adsorption, precipitation, 

ion exchange, biogeochemical reactions, uptake (by

plants and microorganisms) and complexation.

Adsorption of most trace elements occurs on the 

surfaces of clay minerals, metal oxides, and organic 

matter; as a result, fine textured and organic soils have a

greater length of time that water is in contact with the 

soil. The SR land treatment process is the most effective 

for metals removal because of the finer textured soils 

and the greater opportunity for contact and adsorption.

SAT can also be quite effective but a longer travel 

distance in the soil will be necessary due to the higher 

hydraulic loadings and coarser textured soils. Overland

flow (OF) systems allow minimal contact with the soil

and typically remove between 60 and 90 percent 

depending on the hydraulic loading and the particular 

metal. 

2.6.1 Micronutrients 

Several metals are micronutrients that are considered

essential for plant nutrition, for example:
• Copper 

• Iron 

• Manganese 

• Molybdenum

• Nickel 

• Zinc 

2.6.2 Metals 

The major concern with respect to metals is the 

potential for accumulation in the soil profile and then

subsequent translocation, via crops or animals, through 

the food chain to man. The metals of greatest concern

are cadmium (Cd), lead (Pb), mercury (Hg), and arsenic 

(As). The concentrations of metals that can be safely 

applied to crops are presented in Table 2-6. Most crops 

do not accumulate lead but there is some concern with 

respect to ingestion by animals grazing on forages or 

soil to which biosolids have been applied. In general,

zinc, copper, and nickel will be toxic to the crop before

their concentration in plant tissues reaches a level that 

poses a significant risk to human or animal health. 

Cadmium is the greatest concern because the 

concentration of concern for human health is far below

the level that could produce toxic effects in the plants. 

WHO has published guidelines for annual and

cumulative metal additions (based on US EPA’s Part 

503 rule) to agricultural crop land (Chang et al., 1995). 

Adverse effects should not be expected at these loading

rates. These loading rates are presented in Table 2-7. 

Although they were developed for biosolids applications,

it is prudent to apply the same criteria for wastewater 

applications. 

2.6.3 Metals Removal in Crops and Soils 

It is not possible to predict the total renovative capacity 

of a land treatment site with simple ion exchange or soil

adsorption theories. Although the metals are

accumulated in the soil profile, the accumulation 

resulting from repeated applications of wastewater does 

not seem to be continuously available for crop uptake. 

Work by several investigators with biosolids 

demonstrates that the metals uptake in a given year is 

more dependent on the concentration of metals in the 

biosolids most recently applied and not on the total 

accumulation of metals in the soil. 

The capability of metal uptake varies with the type of 

crop grown. Swiss chard, and other leafy vegetables 

take up more metals than other types of vegetation. 

Metals tend to accumulate in the liver and kidney tissue

of animals grazing on a land treatment site or if fed 

harvested products. Tests done on a mixed group of 60

Hereford and Angus steers that graze directly on the 

pasture grasses at the Melbourne, Australia land treatTable 2-6. Recommended Limits for Constituents in Reclaimed 

Water for Irrigation (Rowe, D.R. and I. M. Abel-Magid, 1995) 

Element 

For waters used 

continuously

on all soil, mg/L 

For use up to 

20 years on 

fine-textured soils of 

pH 6.0 to 8.5, mg/L 

Aluminum 5.0 20.0 

Arsenic 0.10 2.0 

Beryllium 0.10 0.50 

Boron 0.75 2.0-10.0 

Cadmium 0.010 0.050 

Chromium 0.10 1.0 

Cobalt 0.050 5.0 

Copper 0.20 5.0 

Fluoride 1.0 15.0 

Iron 5.0 20.0 

Lead 5.0 10.0 

Lithium 2.5a 2.5a

Manganese 0.20 10.0 

Molybdenum 0.010 0.050b

Nickel 0.20 2.0 

Selenium 0.020 0.020 

Zinc 2.0 10.0 a

Recommended maximum concentration for irrigating citrus is 

0.075 mg/L. 

b

For only acid fine-textured soils or acid soils with relatively high 

iron oxide contents. 

Table 2-7. WHO Recommended Annual and Cumulative Limits for 

Metals Applied to Agricultural Crop Land (Chang et al., 1995)

Metal 

Annual loading ratea

(kg/hac

) 

Cumulative loading ratea

(kg/hac

) 

Arsenic 2.0 41 

Cadmium 1.9 39 

Chromium 150 3,000 

Copper 75 1,500 

Lead 15 300 

Mercury 0.85 17 

Molybdenum 0.90 18 

Nickel 21.0 420 

Selenium 5.0 100 

Zinc 140 2,800 a

Loading kg/ha per 365 day period. b

Cumulative loading over lifetime of site. 

c

kg/ha x 0.89 = lb/ac. 

ment site (untreated raw sewage applied) showed that 

“the concentrations of cadmium, zinc and nickel found in

the liver and kidney tissues of this group are within the 

expected normal range of mammalian tissue.” 

(Anderson, 1976). Anthony (1978) has reported on

metals in bone, kidney and liver tissue in mice and

rabbits which were indigenous to the Pennsylvania State 

University land treatment site and no adverse impacts 

were noted. 

The average metal concentrations in the shallow 

groundwater beneath the Hollister, CA, rapid infiltration

site are shown in Table 2-8. After 33 years of operation 
Table 2-8. Trace Metals in Groundwater Under Hollister, CA Soil 

Aquifer Treatment Site, mg/L (Pound, Crites and Olson, 1978)

Metal Groundwater concentration 

Cadmium 0.028 

Cobalt 0.010 

Chromium <0.014 

Copper 0.038 

Iron 0.36 

Lead 0.09 

Manganese 0.96 

Nickel 0.13 

Zinc 0.081 

the concentration of cadmium, chromium, and cobalt

were not significantly different from normal off-site 

groundwater quality. The concentration of the other 

metals listed was somewhat higher than the off-site

background levels. 

The metal concentrations in the upper foot of soils in 

the SAT basins at the Hollister, CA system are still below 

or near the low end of the range for typical agricultural

soils, after 33 years of operation. 

In OF systems, the major mechanisms responsible for 

trace element removal include sorption on clay colloids 

and organic matter at the soil surface and in the litter 

layer, precipitation as insoluble hydroxy compounds, and 

formation of organometallic complexes. The largest 

proportion of metals accumulates in the biomass on the

soil surface and close to the initial point of application.

2.7 Nitrogen 

The removal of nitrogen in land treatment systems is

complex and dynamic due to the many forms of nitrogen 

(N2, organic N, NH3, NH4, NO2, NO3) and the relative

ease of changing from one oxidation state to the next. 

The nitrogen present in typical municipal wastewater is 

usually present as organic nitrogen (about 40 percent) 

and ammonia/ammonium ions (about 60 percent). 

Activated sludge and other high-rate biological 

processes can be designed to convert all of the 

ammonia ion to nitrate (nitrification). Typically only a

portion of the ammonia nitrogen is nitrified and the major 

fraction in most system effluents is still in the ammonium

form (ammonia and ammonium are used

interchangeably in this text). 

Because excessive nitrogen is a health risk, it is 

important in the design of all three land treatment 

concepts to identify the total concentration of nitrogen in

the wastewater to be treated as well as the specific 

forms (i.e., organic, ammonia, nitrate, etc.) expected. 

Experience with all three land treatment processes 

demonstrates that the less oxidized the nitrogen is when

entering the land treatment system the more effective

will be the retention and overall nitrogen removal. 

2.7.1 Soil Responses 

The soil plant system provides a number of 

interrelated responses to wastewater nitrogen. The

organic N fraction, usually associated with particulate 

matter is entrapped or filtered out of the applied liquid

stream. The ammonia fraction can be lost by 

volatilization, taken up by the crop or adsorbed by the 

clay minerals in the soil. Nitrate can be taken up by the 

vegetation, or converted to nitrogen gas via 

denitrification in macro or micro anaerobic zones and 

lost to the atmosphere or leached through the soil

profile. The decomposition (mineralization) of organic 

nitrogen contained in the particulate matter proceeds 

slowly. This aspect is more critical for sludge and

biosolids application systems where the solids fraction is 

a very significant part of the total application. As the

organic solids decompose, the contained organic 

nitrogen is mineralized and released as ammonia. This 

is not a major concern for most municipal wastewater 

land treatment systems, with the exception of those 

systems receiving facultative lagoon effluent containing

significant concentrations of algae. The organic content 

of the algae must be considered in project design

because it can represent a significant ammonia load on

the system. 

Nitrification is effective in all three of the basic land

treatment concepts as long as the necessary aerobic 

status of the site is maintained or periodically restored. 

However, having the system produce nitrate from

ammonium reduces the efficiency to remove nitrogen

since it increases leaching to groundwater. Under 

favorable conditions (i.e., sufficient alkalinity, suitable 

temperatures, etc.) nitrification ranging from 5 to 50 mg/L 

per day is possible. Assuming that these reactions are

occurring with the adsorbed ammonia ions in the top four 

inches of a fine-textured soil means that up to 67 kg/ha

(60 lb/acre) can be converted to nitrate per year. 

The maintenance and/or restoration of aerobic 

conditions in the soil are the reason for the short

application periods and cyclic operations that are

required in land treatment systems. In SAT systems, for 

example, the ammonia adsorption sites are saturated

with ammonium during the early part of the application 

cycle. The aerobic conditions are restored as the system 

drains during the rest period and the soil microbes

convert the adsorbed ammonium to nitrate. At the next 

application cycle ammonium adsorption sites are again

available and much of the nitrate is denitrified as 

anaerobic conditions develop. Denitrifying bacteria are

common soil organisms and the occurrence of anaerobic 

conditions, at least at microsites, can be expected at 

both SR and OF systems as well as SAT. 
2.7.2 Nitrogen Cycle 

The nitrogen cycle in soil is presented in Figure 2-1. 

Nitrification is a conversion process, not a removal 

process for nitrogen. Denitrification, volatilization, soil

storage and crop uptake are the only true removal 

pathways available. Crop uptake is the major pathway 

considered in the design of most slow-rate systems, but

the contribution from denitrification and volatilization can

be significant depending on site conditions and

wastewater type. Immobilization and soil storage can be

significant with wastewaters having a carbon-to-nitrogen 

(C:N) ratio of 12:1 or more. In SAT, ammonia adsorption 

on the soil particles followed by nitrification typically 

occurs, but denitrification is the only important actual

removal mechanism. For OF, crop uptake, volatilization, 

and denitrification can all contribute to nitrogen removal. 

Crop uptake of nitrogen is discussed in detail in Chapter 

4 and in the process design chapters. Nitrogen removal

data for typical SR, SAT, and OF systems are shown in

Table 2-9. 

Figure 2-1. Nitrogen Cycle in Soil. 
Table 2-9. Total Nitrogen Removal in Typical Land Treatment Systems (US EPA, 1981 and Crites et al., 2000) 

Process/Location Process Applied Wastewater (mg/L) Soil Water Drainage (mg/L)

SR 

Dickinson, ND 12 3.9 

Hanover, NH 28 7.3 

Roswell, NM 66 10.7 

San Angelo, TX 35 6.1 

SAT

Calumet, MI 24 7 

Ft. Devens, MA 50 20 

Hollister, CA 40 3 

Phoenix, AZ 27 10 

OF 

Ada, OK (raw wastewater) 34 7 

(primary effluent) 19 5 

(secondary effluent) 16 8 

Easley, SC (pond effluent) 7 2 

Utica, MS (pond effluent) 20 7 

2.7.3 Nitrates 

The U.S. primary drinking water standard for nitrate 

(as N) is set at 10 mg/L. The pathway of concern in SR 

and SAT systems is conversion of wastewater nitrogen

to nitrate and then percolation to drinking water aquifers.

When potable aquifers, sole source aquifers, or wellhead

protection areas are involved, the current guidance

requires that all drinking water standards be met at the

land treatment project boundary. As a result, nitrogen 

often becomes the LDP for SR systems because of its

relatively high concentration as compared to other 

drinking water parameters. Chapter 8 presents complete

design details for nitrogen removal in these systems. 

There are a number of safety factors inherent in the 

approach that insures a conservative design. The 

procedure assumes that all of the applied nitrogen will

appear as nitrate (i.e., complete nitrification) and within

the same time period assumed for the application (no

time lag or mineralization of ammonia) and there is no

credit for mixing or dispersion with the in-situ

groundwater. 

2.7.4 Design Factors 

The nitrogen mass balance for SAT systems would not 

usually include a component for crop uptake. The

percolate nitrogen concentration is not a concern for OF 

systems since the percolate volume is generally

considered to be negligible. As indicated previously, 

application of biosolids does include a mineralization 

factor to account for the previous organic nitrogen

deposits. There are four potential situations where a 

mineralization factor might be included in the nitrogen

balance for SR and OF systems: 

• Industrial wastewaters with high solids 

concentrations having significant organic nitrogen 

content. 

• Grass covered systems where the grass is cut but

not removed. 

• Pasture systems with intense animal grazing and 

animal manure left on the site. 

• Biosolids or manure added to the site as 

supplemental fertilizers. 

2.7.4.1 Organic Nitrogen 

 Mineralization rates, developed for wastewater 

biosolids are given in . The values are the 

percent of the organic nitrogen present that is 

mineralized (i.e., converted to inorganic forms such as

ammonia, nitrate, etc.) in a given year. The fraction of 

the biosolids organic N initially applied, or remaining in

the soil, that will be mineralized during the time intervals 

shown are provided as examples only and may be quite

different for different biosolids, soils and climates.

Therefore, site-specific data, or the best judgment of 

individuals familiar with N dynamics in the soil-plant 

system involved, should always be used in preference to

these suggested values. For example, 40 percent of the 

organic nitrogen in raw sludge would be mineralized 

during the first year, 20 percent the second year, and so 

forth. With consistent annual applications to a site, the 

cumulative mineralization approaches 60 percent

Table 2-10

.

The mineralization rate is related to the initial organic 

nitrogen content, which in turn is related to treatment 

level for the biosolids in question. Easily degraded
Table 2-10. Annual Mineralization Rates for Organic Matter in Biosolids (US EPA 1995)

Mineralization rate (%) 

Time after biosolids 

application (years) Unstabilized primary Aerobically digested Anaerobically digested Composted 

 0-1 40 30 30 10 

 1-2 20 15 10 5 

 2-3 10 8 5 a

 3-4+ 5 4 a -- a

Annual rate drops to 3%. Once the mineralization rate becomes less than 3%, no net gain of plant available nitrogen above that normally obtained 

from the mineralization of soil organic matter is expected. Therefore, additional credits for residual biosolids N do not need to be calculated. 

industrial biosolids would be comparable to raw 

municipal biosolids. Industrial solids with a high

percentage of refractory or stable humic substances

might be similar to composted biosolids. A specific test 

procedure is available to determine under incubation

what the actual mineralization rate is for a particular 

waste that is high in organic nitrogen (Gilmour and Clark,

1988; Gilmour et al., 1996). 

Animal manures would be similar to digested sludges 

and it would be conservative to assume that grass 

cuttings and other vegetative litter would decay at the

same rates as digested sludges. The examples below 

illustrate the use of the factors in Table 2-10 for two 

possible situations. 

Example 2.2 Nitrogen Cycling in Greenbelts

Conditions: Slow-rate land treatment site used as a greenbelt 

parkway. The grasses are cut but not removed 

from the site. At the annual wastewater loading 

rates used, the grasses will take up about 250 

kg/ha•yr (222 lb/ac•yr).

Find: The nitrogen contribution from the on-site decay

of the cut grass. 

Solution: The most conservative assumption is to use 

aerobically digested sludge rates from Table 2-

10 and to assume that all of the nitrogen is in the 

organic form. 

1. In first year: 250 kg/ha (0.30) = 75 kg/ha 

2. In second year: 

The 2nd year cutting 

250 (0.3) = 75kg/ha 

Residue from 1st year (250-75) (0.15) = 26 

Total, 2nd year = 101 kg/ha 

3. In third year: 

The 3rd year cutting 

(250)(0.30) = 75 kg/ha 

Residue from 2nd year (250-75)(0.15) = 26 

Residue from 1st year (250-101)(0.08) = 12 

Total, 3rd year = 113kg/ha 

4. In fourth year:

The 4th year cutting 

= 75kg/ha 

Residue from 3rd year = 26 

Residue from 2nd year = 12 

Residue from 1st year (250-113)(0.04) = 5 

Total, 4th year = 118 kg/ha 

5. In fifth year: = 75 kg/ha 

The 5th year cutting 

Residue from 4th year = 26 

Residue from 3rd year = 12 

Residue from 2nd year = 5 

Residue from 1st year (250-118)(0.04) = 5 

Total, 5th year = 123 kg/ha 

6. As shown by the sequence above, the amount of nitrogen 

contributed becomes relatively stable after the third or fourth year and 

increases only slightly thereafter. In this example, it can be assumed 

that about 120 kg/ha of nitrogen is returned to the soil each year from

the cut grass. For this case, that would be about 48 percent of the 

nitrogen originally taken up by the grass, so the net removal is still 

very significant (52 percent). The 48 percent returned is also 

significant, and would be included in the nitrogen mass balance in a 

conservative design. 

1. Annual available 

organic nitrogen

(300 kg/ha)(0.50) = 150 kg/ha 

2. Using digested 

mineralization rates 

from Table 2-11:

 First year

contribution 

(150)(0.30) = 45 kg/ha 

 Second year

contribution 

45 + (150-45)(0.15) = 61 kg/ha 

 Third year 

contribution 

45 + 16+ ((150-61)(0.08)) = 68 kg/ha 

And so forth 

These two examples illustrate the critical importance of

knowing the form of nitrogen is in when it is applied to

the land treatment site. This is particularly important if 

elaborate pretreatment is provided because the nitrogen

may not then be in the simple, and easily managed,

combination of organic nitrogen and ammonia that is 

present in untreated municipal wastewater and primary

effluents. Any nitrogen losses which occur during this 

preapplication treatment or storage should be

considered. Facultative lagoons or storage ponds can

remove up to 85 percent of the contained nitrogen under 

ideal conditions (Reed et al., 1995). Such losses are 

especially significant when nitrogen is the LDP for 

design because any reduction in nitrogen prior to land

application will proportionally reduce the size and

therefore the cost of the land treatment site. 

2.8 Phosphorus 

The presence of phosphorus in drinking water supplies 

does not have any known health significance but 
phosphorus is considered to be the limiting factor for 

eutrophication of fresh, non-saline surface waters so its

removal from wastewaters is often necessary.

Phosphorus is present in municipal wastewater as 

orthophosphate, polyphosphate, and organic 

phosphates. The orthophosphates are immediately 

available for biological reactions in soil ecosystems. The

necessary hydrolysis of the polyphosphates proceeds 

very slowly in typical soils so these forms are not as 

readily available. Industrial wastewaters may contain a 

significant fraction of organic phosphorus. 

2.8.1 Removal Mechanisms 

Phosphorus removal in land treatment systems can 

occur through plant uptake, biological, chemical, and/or 

physical processes. The nitrogen removal described in

the previous section is almost entirely dependent on 

biological processes so the removal capacity can be

maintained continuously or restored by proper system 

design and management. In contrast, phosphorus

removal in the soil depends to a significant degree on 

chemical reactions which are slowly renewable. As a 

result, the retention capacity for phosphorus will be 

gradually reduced over time, but not exhausted. At a 

typical SR system for example it has been estimated

thata 0.3 m (1 ft) depth of soil may become saturated 

with phosphorus every ten years (US EPA, 1981). The

removal of phosphorus will be almost complete during

the removal period and percolate phosphorus should not 

be a problem until the entire design soil profile is utilized 

some SR sites phosphorus may limit the design life of 

the site; an example might be a site with coarse textured 

sandy soils with underdrains at a shallow depth which

discharge to a sensitive surface water. In this case

theuseful life of the site might range from 20 to 60 years 

depending on the soil type, underdrain depth, 

wastewater characteristics, and loading rates. 

Crop uptake contributes to phosphorus removal at SR

systems, but the major removal pathway in both SR and 

RI systems is in the soil. Typical plant concentrations for 

nitrogen are 1 percent to 2 percent and for phosphorus

the concentrations are 0.2 percent to 0.4 percent. The

phosphorus is removed by adsorption/precipitation 

reactions when clay, oxides of iron and aluminum, and

calcareous substances are present. The phosphorus 

removal increases with increasing clay content and with

increasing contact time in the soil. The percolate

phosphorus values listed in Table 2-11 for SR systems

are close to the background levels for natural

groundwater at these locations. 

Soil Aquifer Treatment 

There is no crop uptake in SAT systems and the soil

characteristics and high hydraulic loading rates typically 

used require greater travel distances in the soil for 

effective phosphorus removal. Data from several of the

SAT systems in Table 2-11 indicate a percolate 

phosphorus concentration approaching background

levels after travel through the sub soils. Most of these 

systems (Vineland, Lake George, Calumet, Ft Devens) 

had been in operation for several decades prior to 

collection of the percolate samples. 

Table 2-11. Typical Percolate Phosphorus Concentrationsa (Crites et al., 2000)

Location Soil type 

Travel distanceb 

 (m) 

Soil water drainage phosphorus 

(mg/L) 

SR 

Hanover, NH Sandy loam 1.5 0.05 

Muskegon, MI Loamy sand 1.5 0.04 

Tallahassee, FL Fine sand 1.2 0.1 

Penn. State, PAc Silt loam 1.2 0.8 

Helen, GAc Sandy loam 1.2 0.17 

SAT

Hollister, CA Gravely sand 6.7 7.4 

Phoenix, AZ Gravely sand 9.1 4.5 

Ft. Devens, MA Gravely sand 1.5 9.0 

Calumet, MI Gravely sand 9.1 0.1 

Boulder, CO Gravely sand 3.0 2.3 

Lake George, NY Sand 0.9 

183 

1.0 

0.014 

Vineland, NJ Sand 9.1 

122 

1.5 

0.27 a

 Applied wastewater, typical municipal effluent, TP ≈ 8 to 14 mg/L. b

 Total percolate travel distance from soil surface to sampling point SR systems. c

 Forested SR system. 
An equation to predict phosphorus removal at SR and

SAT land treatment sites has been developed from data

collected at a number of operating systems (US EPA 

1980). The equation was developed from performance

data with the coarse textured soils at SAT sites. 

Equation 2-2 is solved in two steps, first for the vertical 

flow component, from the soil surface to the subsurface

flow barrier (if one exists) and then for the lateral flow to 

the outlet point x. The calculations are assuming

saturated flow conditions, so the shortest possible 

detention time will result. The actual vertical flow in most

cases will be unsaturated, so the actual detention time 

will be much longer than is calculated with this 

procedure, and therefore the actual phosphorus removal 

will be greater. If the equation predicts acceptable

phosphorus removal then there is some assurance that 

the site will perform reliably and detailed tests should not

be necessary for preliminary work. Detailed phosphorus

removal tests should be conducted for final design of 

projects where phosphorus removal is critical. 

2.8.3 Overland Flow 

The opportunities for contact between the applied

wastewater and the soil are limited to surface reactions 

in OF systems and as a result phosphorus removals

typically range from 40 to 60 percent. Phosphorus

removal in overland flow can be improved by chemical 

addition and then precipitation on the treatment slope. 

At Ada, OK, the US EPA demonstrated the use of alum 

additions (Al to TP mole ratio 2:1) to produce a total 

phosphorus concentration in the treated runoff of 1 mg/L

(US EPA, 1981). At Utica, MS, mass removals ranged 

between 65 and 90 percent with alum as compared to

less than 50 percent removal without alum (Crites,

1983). 

Px = Po (e - (k)(t)) (2-2)

Where: 

Px = total phosphorus in percolate at distance x on the flow

path (mg/L)

Po = total phosphorus in applied wastewater, mg/L 

k = rate constant, at pH 7, d-1

= 0.048 d-1 (pH 7 gives most conservative value)

t = detention time to point x, d 

= (x)(W)/(Kx)(G) 

x = distance along flow path, m (ft)

W = saturated soil moisture content, assume 0.4 

Kx = hydraulic conductivity of soil in direction x, m/d (ft/d) 

Thus: 

Kv = vertical conductivity, KH = horizontal conductivity

G = hydraulic gradient for flow system, dimensionless 

= 1.0 for vertical flow

 = Δh/L for horizontal flow

Δh = elevation difference of water surface between origin of 

horizontal flow and end point x, m (ft) 

L = length of horizontal flow path, m (ft).

Example 2.4 Phosphorus Removal 

Conditions: Assume a site where wastewater percolate moves 

5 m vertically through the soil to the groundwater 

table and then 45 m horizontally to emergence in 

a small stream. The initial phosphorus 

concentration is 10 mg/L, the vertical hydraulic 

conductivity Kv = 1 m/d, the horizontal hydraulic 

conductivity KH = 10 m/d, and the difference in 

groundwater surface elevations between the site 

and the stream is 1 m. 

Find: The phosphorus concentration in the percolate 

when emerging in the stream and the total 

detention time in the soil. 

Solution: Use Equation 2-2. Phosphorus concentration at 

end of vertical flow : 

 t = 2.0 d

1m/d

(5 m)(0.4) =

 Px = (10 mg/L)(e-(0.048)(2.0)

) 

= 9.1 mg/L 

Percolate phosphorus concentration at the 

stream: 

t = (45 m)(0.4)/(10 m/d)(1 m/45 m) = 81 d 

 Px = (9.1 mg/L)(e- (0.048)(81)

) 

= 0.18 mg/L 

Total detention time in soil = 2 d + 81 d = 83 d 

 Typical municipal wastewaters will have between 5 

and 20 mg/L of total phosphorus. Industrial wastewaters 

can have much higher concentrations, particularly from 

fertilizer and detergent manufacturing. Food processing

operations can also have high phosphate effluents. 

Some typical values are: Dairy products 9 to 210 mg/L 

PO4, Grain Milling 5 to 100 mg/L PO4, Cattle feed lots 60

to 1,500 mg/L PO4. 

Example 2.5 Determine Phosphorus Loading to Match 

Useful Life of Site 

Conditions: Assume a silty loam soil, adsorption tests 

indicate a useful capacity for phosphorus equal 

to 9,000 kg/ha per meter of depth. Site to be 

grass covered, grass uptake of phosphorus is 

35 kg/ha•yr, grass to be harvested and taken 

off site. The projected operational life of the 

factory and the treatment site is equal to 30 

years. The phosphorus concentration in the 

wastewater is 20 mg/L. The treatment site is 

underdrained with drainage water discharged to 

adjacent surface waters with an allowable 

discharge limit of 1.0 mg/L TP. Because of the 

underdrains, the practical soil treatment depth 

is 2 m. 

Find: The acceptable annual wastewater loading 

during the 30 yr useful life. 
Solution: 1. Lifetime crop contribution = (35 kg/ha•yr)(30 

yr) = 1050 kg/ha 

2. Lifetime soil contribution = (9000 kg/ha) (2

m) = 18000 kg/ha 

3. Total 30 yr phosphorus removal capacity = 

19,050 kg/ha (Step 1 + Step 2).

4. Average annual phosphorus loading = 

(19,050 kg/ha)/(30 yr) = 635 kg/ha•yr 

5. Wastewater loading (Q) = (635 

kg/ha•yr)/(20 g/m3

) = 3.175 m/yr

Note: Design credit is not taken in this example for the 1.0 mg/L TP

allowed in the underdrain effluent. This is because the treatment 

system will essentially remove all of the phosphorus during the 

useful life of the system until breakthrough occurs; until that point is 

reached the effluent concentration should be well below the 

allowable 1 mg/L level. 

2.9 Potassium 

As a wastewater constituent, potassium usually has no

health or environmental significance. It is, however, an

essential nutrient at sufficient levels for vegetative 

growth, and is not typically present at sufficient levels in 

wastewaters in the optimum combination with nitrogen

and phosphorus. If a land treatment system depends on 

crop uptake for nitrogen removal, it may be necessary to 

add supplemental potassium to maintain nitrogen

removals at the optimum level. Equation 2-3, developed

by A. Palazzo, can be used to estimate the supplemental

potassium that may be required where the in-situ soils 

have a low level of natural potassium. This most

commonly occurs in the northeastern part of the U.S. 

KS = (0.9)(U) - KWW (2-3) 

Where: 

KS = annual supplemental potassium needed, (kg/ha) 

U = estimated annual nitrogen uptake of crop, (kg/ha)

KWW = potassium applied in wastewater, (kg/ha) 

(kg/ha) x (0.8922) = lb/ac 

2.10 Sodium 

Sodium is typically present in all wastewaters. High

levels of sodium can be directly toxic to plants but most 

often its influence on soil salinity or soil alkalinity is the 

more important problem. Growth of sensitive plants 

becomes impaired where the salt content of the soil

exceeds 0.1 percent. Salinity also has a direct bearing

on the osmotic potential of the soil solution, which

controls the ability of the plant to absorb water. Adverse 

crop effects can also occur from sprinkler operations in

arid climates using water with significant concentrations 

of sodium or chloride (see Chapter 4). The leaves can

absorb both elements rapidly and their accumulation on 

the leaf surfaces in arid climates can result in toxicity

problems (Reed et al., 1995). 

Sodium is not permanently removed in the soil but is 

rather involved in the soil cation exchange process. 

These reactions are similar to those occurring in water 

softening processes and involve sodium, magnesium, 

and calcium. In some cases, where there is an excess 

of sodium with respect to calcium and magnesium in the 

water applied to high clay content soils, there can be an

adverse effect on soil structure. The resulting 

deflocculation and swelling of clay particles can

significantly reduce the hydraulic capacity of the soil.

The relationship between sodium, calcium, and

manganese is expressed as the Sodium Adsorption

Ratio (SAR) as defined by Equation 2-4.

SAR = (Na)/[(Ca + Mg)/2] 0.5 (2-4)

Where: 

SAR = Sodium adsorption ratio 

Na = Sodium concentration, milliequivalents/L 

Ca = Calcium concentration, milliequivalents/L 

Mg = Magnesium concentration, milliequivalents/L 

A SAR of 10 or less should be acceptable on soils with 

significant clay content (15 percent clay or greater).

Soils with little clay, or non-swelling clays can tolerate an 

SAR up to 20. It is unlikely that problems of this type will 

occur with application of municipal effluents in any 

climate since the SAR of typical effluents seldom

exceeds 5 to 8. Industrial wastewaters can be of more

concern. The washwater from ion exchange water 

softening could have an SAR of 50, and some food 

processing effluents range from about 30 to over 90. As 

discussed in Chapter 4, SAR problems are affected by

the TDS of the wastewater, with more adverse effects 

occurring with low TDS water. Many western states have 

recommended irrigation water quality for SAR and EC.

Local state agricultural universities should be consulted. 

The common remedial measure for SAR induced soil

swelling or permeability loss is the surface application of

gypsum or another inexpensive source of calcium. The 

addition of water allows the calcium to leach into the soil

to exchange with the sodium. An additional volume of 

water is then required to leach out the salt solution. 

2.11 Macronutrients and Micronutrients 

Most plants also require magnesium, calcium, and

sulfur, and depending on soil characteristics, there may 

be deficiencies in some locations. Other micronutrients 

important for plant growth include iron, manganese, zinc, 

boron, copper, molybdenum and nickel. Generally, there

is a sufficient amount of these elements in municipal
wastewaters, and in some cases an excess can lead to

phytotoxicity problems. 

2.11.1 Sulfur 

Sulfur is usually present in most wastewaters either in 

the sulfate or sulfite form. The source can be either 

waste constituents or background levels in the 

community water supply.Sulfate is not strongly retained

in the soil but is usually found in the soil solution. 

Sulfates are not typically present in high enough

concentrations in municipal wastewaters to be a concern

for design of land treatment systems. Secondary 

drinking water standards limit sulfate to 250 mg/L, 

irrigation standards recommend 200 to 600 mg/L 

depending on the type of vegetation. Industrial 

wastewaters from sugar refining, petroleum refining, and 

Kraft process paper mills might all have sulfate or sulfite

concentrations requiring special consideration. Crop

uptake accounts for most sulfur removal with the low 

levels in municipal wastewater. 

If sulfur is the LDP, then the design procedure is similar 

to that described previously for nitrogen. It is prudent to 

assume that all of the sulfur compounds applied to the

land will be mineralized to sulfate. The 250 mg/L

standard for drinking water sulfate would then apply at 

the project boundary when drinking water aquifers are

involved. It should be assumed in sizing the system that 

the major permanent removal pathway is to the 

harvested crop and the values in Table 2-12 can be 

used for estimating purposes. If industrial wastes have 

particularly high organic contents there may be 

additional immobilization of sulfur. It is recommended

that specific pilot tests be run for industrial wastewaters 

of concern to determine the potential for removal under 

site specific conditions. 

2.11.2 Boron 

Boron is an essential micronutrient for plants but 

becomes toxic at relatively low concentrations

(<1 mg/L) for sensitive plants. The soil has some 

Example 2.6 Sodium Adsorption Ratio 

Conditions: A municipal effluent with: Na 50 mg/L, Ca 15 

mg/L, Mg 5 mg/L

Find: The SAR of this effluent. 

Solution: Atomic weights: Na = 22.99, Ca = 40.08, 

Mg = 24.32 

Meq Na = (1)(50 mg/L)/(22.99) = 2.17 

Meq Ca = (2)(15 mg/L)/(40.08) = 0.75 

Meq Mg = (2)(5 mg/L)/(24.32) = 0.41 

SAR = (2.17)/ [(0.75 + 0.41)/2]0.5 = 2.85

Table 2-12. Sulfur Uptake by Selected Crops

Crop 

Harvested mass 

Metric As 

tons/ha noted

Sulfur removed 

(kg/ha) lbs/ac 

Corn 12.5 200 bu/ac 49 43.8 

Wheat 5.6 83 bu/ac 25 22.3 

Barley 5.4 100 bu/ac 28 25 

Alfalfa 13.4 6 ton/ac 34 30.4 

Clover 9.0 4 ton/ac 20 17.9 

Coastal Bermuda grass 22.4 10 ton/ac 50 44.6 

Orchard grass 15.7 7 ton/ac 56 50 

Cotton 1.3(USA) 2.5 

 bale/ac 

 26 23.2 

adsorptive capacity for boron if aluminum and iron

oxides are present. The soil reactions are similar to 

those described previously for phosphorus but the 

capacity for boron is low. A conservative design

approach assumes that any boron not taken up by the 

plant is available for percolation to the groundwater. 

Plant uptake of boron in corn silage of about 0.006 

kg/ha•yr (0.005 lb/ac•yr) and in alfalfa of 0.91 to 1.8 

kg/ha•yr (0.81 to 1.6 lb/ac•yr) have been reported 

(Overcash and Pal, 1979). At the SR land treatment site 

in Mesa, AZ the applied municipal effluent had 0.44 

mg/L boron, and the groundwater beneath the site 

contained 0.6 mg/L. At another SR operation at 

Camarillo, CA the wastewater boron was 0.85 mg/L and 

the groundwater beneath the site was 1.14 mg/L. The

increase in boron, in both cases, is probably due to

water losses from evapotranspiration. Table 2-13 lists

the boron tolerance of common vegetation types. 

Table 2-13. Boron Tolerance of Crops (Reed et al., 1995)

I. Tolerant II. Semi-tolerant III. Sensitive 

Alfalfa Barley Fruit crops 

Cotton Corn Nut trees 

Sugar beets Milo 

Sweet clover Oats 

Turnip Tobacco

Wheat 

Industrial wastewaters with 2 to 4 mg/L boron could be

successfully applied to crops in Category I in Table 2-13, 

1 to 2 mg/L boron for Category II and less than 1 mg/L

for Category III (Overcash and Pal, 1979). Boron may

not be the LDP for process design and may be the 

determinant on which crop to select. Both OF and SAT

systems will be less effective for boron removal than SR 

systems because of the same factors discussed 

previously for phosphorus. Injection experiments at the 

Orange County, CA, groundwater recharge project

injected treated municipal effluent with 0.95 mg/L

boron.After 166 m (545 ft) travel in the soil the boron

concentration was still 0.84 mg/L (Reed, 1972). 
2.11.3 Selenium 

Selenium is a micronutrient for animals but is non 

essential for plants. However, in high concentrations it is

toxic to animals and birds and many plants can

accumulate selenium to these toxic levels without any 

apparent effect on the crop. Plants containing 4 to 5 

mg/L selenium are considered toxic to animals (Reed et

al., 1995). Selenium can be adsorbed weakly by the 

hydrous iron oxides in soils and this is of more concern

in the southeastern US where soils tend to have very 

high iron oxide contents. In arid climates with significant 

evaporation, surficial soils can eventually accumulate 

toxic levels of selenium as occurred at the famous

Kesterson Marsh in California. Selenium is not likely to 

be the LDP for land treatment design with municipal

wastewaters. 

2.11.4 Fixed Dissolved Solids 

There are a number of potential measurements of 

salinity including total dissolved solids (TDS), electrical

conductivity (EC), and fixed dissolved solids (FDS). The 

FDS is the more appropriate test for salinity in any 

wastewater with a significant portion of volatile dissolved 

solids (VDS). For industrial wastewaters (see Chapter

11), FDS is the most appropriate test. Alternatively, the 

sum of the inorganic cations and anions can be used as

a measure of salinity. 

Salinity problems are of most concern in arid regions 

because applied water will be increased in salinity due to 

evapotranspiration, and because system design in arid 

regions is typically based on applying the minimal 

amount of water needed for the crop to grow. The

combination of these factors will result in a rapid build-up 

of salts in the soil unless mitigation efforts are applied. A 

standard approach is to determine crop water needs and

then add to that a leaching requirement (LR) to ensure

that an adequate volume of water passes through the 

root zone to remove excess salts. The LR can be

determined if the salinity or electrical conductivity (EC) of 

the irrigation water, and the maximum allowable EC in

the percolate to protect a specific crop are known (Reed

et al., 1995). The salt content of irrigation waters is often 

expressed as mg/L of TDS, and can be converted to 

conductivity terms (mmho/cm) by dividing mg/L by 

0.640. [Note: this relationship is only valid for water with 

essentially no volatile dissolved solids.] Equation 2-5 can

be used to estimate the LR. 

LR = [(EC)I/(EC)D] x 100 (2-5) 

Where: 

LR = leaching requirement as a percent 

ECI = average conductivity of irrigation water (including natural 

precipitation), mmho/cm 

ECD = required conductivity in drainage water to protect the crop, 

mmho/cm 

Typical values of ECD for crops without yield reduction 

are given in Table 2-14. 

Table 2-14. Values of ECD for Crops with No Yield Reduction (Ayers, 

1977)

Crop Electrical Conductivity ECD, 

mmho/cm 

Bermuda grass 13 

Barley 12 

Sugar beets 10 

Cotton 10 

Wheat 7 

Tall fescue 7 

Soybeans 5 

Corn 5 

Alfalfa 4 

Orchard grass 3 

Once the leaching requirement (LR) has been

determined the total water application can then be

calculated with Equation 2-6. 

LW = (CU)/(1 - LR/100) (2-6)

Where:

LW = required total water application, inches 

CU = consumptive water use by the crop between water 

applications, inches 

LR = leaching requirement (as a percent) 

Example 2.7 Leaching Requirement 

Conditions: Given a wastewater effluent with 800 mg/L 

salinity, corn is the growing crop with ECD = 5 

mmho/cm, consumptive use between irrigations 

= 3 inches. 

Find: The total water requirement. 

Solution: Conductivity of the effluent = (800/0.640) = 

1.25 mmho/cm 

LR = (1.25 )/(5) x 100 = 25%

 LW = (3)/(1 - 0.25) = 4 inches

A “rule of thumb” for total water needs to prevent salt 

buildup in arid climates is to apply the crop needs plus 

about 10 to 15 percent. Salinity problems and leaching

requirements are not to be expected for land treatment 

systems in the more humid portions of the US because

natural precipitation is higher and higher hydraulic 

loadings are typically used to minimize the land area

required. 

2.12 Trace Organics 

Volatilization, adsorption, and then biodegradation are

the principal methods for removing trace organic 

compounds in land treatment systems. Volatilization can 
occur at the water surface of treatment and storage

ponds, and SAT basins, in the water droplets used in

sprinklers, in the water films on OF slopes, and on the 

exposed surfaces of biosolids. Adsorption occurs 

primarily on the organic matter, such as plant litter and 

similar residues, present in the system. Microbial activity 

then degrades the biologically degradable adsorbed

materials. 

2.12.1 Volatilization 

The loss of volatile organics from a water surface can 

be described with first order kinetics, since it is assumed 

that the concentration in the atmosphere above the 

water surface is essentially zero. Equation 2-7 is the 

basic kinetic equation and Equation 2-8 can be used to

estimate the “half life” of the contaminant of concern. 

Ct/CO = e - (KVOL)(t)/(y) (2-7)

Where: 

Ct = concentration at time t, mg/L 

CO = concentration at t = 0, mg/L 

KVOL = volatilization mass transfer coefficient, cm/h 

= (K)(y) 

KM = overall volatilization rate coefficient, h-1

y = depth of liquid, cm 

t1/2 = (0.6930(y)/(KVOL) (2-8)

Where: 

t1/2 = time when concentration Ct = 1/2(CO), h 

The volatilization mass transfer coefficient (KM) is a

function of the molecular weight of the contaminant and

the air/water partition coefficient as defined by the 

Henry’s law constant as shown by Equation 2-9. 

KVM = [(B1)/(y)][(H)/(B2 + H)(M1/2)] (2-9)

Where: 

KV

H = Henry’s law constant, 10 M = volatilization mass transfer coefficient, h-1

5

 (atm)(m3)(mol

-1) 

M = molecular weight of contaminant of concern, g/mol 

B1, B2 = coefficients specific to system of concern, dimensionless 

Dilling (Dilling, 1977) determined values for a variety of volatile

chlorinated hydrocarbons at a well mixed water surface: B1 = 2.211 B2 = 0.01042 

Jenkins et al (Jenkins et al., 1985) determined values for a number of 

volatile organics on an overland flow slope: 

 B1 = 0.2563 B2 = 5.86 x 10-4

The coefficients for the overland flow case are much

lower because the movement of water down the slope is 

non turbulent and may be considered almost laminar 

flow (Reynolds number 100 to 400). The average depth 

of flowing water on this slope was about 1.2 cm.

Using a variation of Equation 2-9, Parker and Jenkins 

determined the volatilization losses from the droplets at 

a low-pressure, large droplet wastewater sprinkler 

(Parker and Jenkins, 1986). In this case the y term in the

equation is equal to the average droplet radius; as a 

result, their coefficients are only valid for the particular 

sprinkler used. Equation 2-10 was developed by Parker

and Jenkins for the organic compounds listed in 

Table 2-15. 

ln(Ct/CO) = 4.535[K’M + 11.02 x 10-4] (2-10)

Table 2-15. Volatile Organic Removal by Wastewater Sprinkling 

(Parker and Jenkins, 1986)

Substance Calculated K’M for Eq. 2-12, 

(cm/min) 

Chloroform 0.188 

Benzene 0.236 

Toluene 0.220 

Chlorobenzene 0.190 

Bromoform 0.0987 

n-Dichlorobenzene 0.175 

Pentane 0.260 

Hexane 0.239 

Nitrobenzene 0.0136 

m-nitrotoluene 0.0322 

PCB 1242 0.0734 

Napthalene 0.144 

Phenanthrene 0.0218 

2.12.2 Adsorption 

Sorption of trace organics to the organic matter 

present in the land treatment system is thought to be the 

primary physicochemical mechanism of removal. The

concentration of the trace organic which is sorbed

relative to that in solution is defined by the partition 

coefficient KP which is related to the solubility of the 

chemical. This value can be estimated if the octanolwater partition coefficient KOW and the percentage of 

organic carbon in the system are defined. Jenkins, et al., 

1985 determined that sorption of trace organics on an

overland flow slope could be described with first order 

kinetics with the rate constant defined by Equation 2-11. 

KSORB = (B3/y)[ KOW/(B4 + K)(M)1/2] (2-11)

Where: 

KSORB = sorption coefficient, h-1

B3 = coefficient specific to the treatment system 

= 0.7309 for the OF system studied 

y = depth of water on OF slope, 1.2 cm 

KOW = octanol-water partition coefficient 

B4 = coefficient specific to the system 

= 170.8 for the overland flow system studied 

M = molecular weight of the organic chemical, g/mol 

In many cases the removal of these organics is due to 

a combination of sorption and volatilization. The overall
process rate constant KSV is then the sum of the

coefficients defined with Equations 2-9 and 2-11, with 

the combined removal described by Equation 2-12. 

- (KSV)(t)

Ct/CO = e (2-12)

Where: 

KSV = overall rate constant for combined volatilization and 

sorption 

= KVM + KSORB

Ct = concentration at time t, mg/L (or μg/L) 

CO = initial concentration, mg/L (or μg/L) 

Table 2-16 presents the physical characteristics of a

number of volatile organics for use in the equations 

presented above for volatilization and sorption. 

2.12.3 Removal Performance 

A number of land treatment systems have been studied

extensively to document the removal of priority pollutant 

organic chemicals. This is probably due to the concern

for groundwater contamination. Results from these 

studies have generally been positive. The removal

performance for the three major land treatment concepts 

is presented in Table 2-17. The removals observed in 

the SR systems were after 1.5 m (5 ft) of travel in the

soils specified, and a low pressure, large droplet

sprinkler was used for the applications. The removals 

noted for the OF system were measured after a flow on 

a terrace about 30 m (100 ft) long, with application via

gated pipe at the top of the slope. The SAT data were

obtained from sampling wells about 200 m (600 ft) downgradient of the application basins. 

The removals reported in Table 2-17 for SR systems 

represent concentrations in the applied wastewater 

ranging from 2 to 111 μg/L, and percolate concentrations 

ranging from 0 to 0.4 μg/L. The applied concentrations in

the OF system ranged from 25 to 315 μg/L and from 0.3

to 16 μg/L in the OF runoff. At the SAT system influent 

concentrations ranged from 3 to 89 μg/L and the 

percolate ranged from 0.1 to 0.9 μg/L. 

2.13 Phytoremediation 

Phytoremediation involves the use of plants to treat or

stabilize contaminated soils and groundwater (US EPA, 

2000). The technology is complex and is only introduced 

here. The technology has emerged as a response to the 

clean-up efforts for sites contaminated with toxic and

hazardous wastes. Contaminants which have been

successfully remediated with plants include petroleum 

hydrocarbons, chlorinated solvents, metals,

radionuclides, and nutrients such as nitrogen and

phosphorus. In 1998 it was estimated by Glass that at 

least 200 field remediations or demonstrations have 

been completed or are in progress around the world

(Glass, 1999). However, the “remediation” technology as 

currently used is not “new” but rather draws on the basic 

ecosystem responses and reactions documented in this 

and other chapters in this book. The most common

applications depend on the plants to draw contaminated 

soil water to the root zone where either microbial activity 

or plant uptake of the contaminants provides the desired

removal. Evapotranspiration, during the growing season 

provides for movement and elimination of the 

contaminated groundwater. Once taken up by the plant 

the contaminants are either sequestered in plant 

biomass or possibly degraded and metabolized to a

volatile form and transpired. In some cases the plant

roots can also secrete enzymes which contribute to

degradation of the contaminants in the soil.

Obviously, food crops and similar vegetation, which 

might become part of the human food chain, are not

used on these remediation sites. Grasses and a number 

of tree species are the most common choices. Hybrid 

Table 2-16. Physical Characteristics for Selected Organic Chemicals (Reed et al., 1995) 

Substance KOW

a Hb Vapor pressurec Md

Chloroform 93.3 314 194 119 

Benzene 135 435 95.2 78 

Toluene 490 515 28.4 92 

Chlorobenzene 692 267 12.0 113 

Bromoform 189 63 5368 253 

m-Dichlorobenzene 2.4 x 103 360 2.33 147 

Pentane 1.7 x 103 125,000 520 72 

Hexane 7.1 x 103 170,000 154 86 

Nitrobenzene 70.8 1.9 0.23 122 

m-nitrotoluene 282 5.3 0.23 137 

Diethylphthalate 162 0.056 7 x 10-4 222 

PCB 1242 3.8 x 105 30 4 x 10-4 26 

Napthalene 2.3 x 103 36 8.28 x 10-2 128 

Phenanthrene 2.2 x 104 3.9 2.03 x 10-4 178 

2,4-Dinitrophenol 34.7 0.001 -- 184 

a. Octanol-water partition coefficient. b. Henry’s law constant, 105 atm(m3

/mol) at 20°C and 1 atm. c. Vapor pressure at 25°C.

d. Molecular weight, g/mol. 
Table 2-17. Percent Removal of Organic Chemicals in Land Treatment Systems (Reed et al., 1995)

SR 

Substance Sandy soil Silty soil OF SAT 

Chloroform 98.57 99.23 96.50 >99.99 

Benzene >99.99 >99.99 99.00 99.99 

Toluene >99.99 >99.99 98.09 >99.99 

Chlorobenzene 99.97 99.98 98.99 >99.99 

Bromoform 99.93 99.96 97.43 >99.99 

Dibromochloromethane 99.72 99.72 98.78 >99.99 

m-nitrotoluene >99.99 >99.99 94.03 a 

PCB 1242 >99.99 >99.99 96.46 >99.99 

Napthalene 99.98 99.98 98.49 96.15 

Phenanthrene >99.99 >99.99 99.19 a 

Pentachlorophenol >99.99 >99.99 98.06 a 

2,4-Dinitrophenol a a 93.44 a 

Nitrobenzene >99.99 >99.99 88.73 a 

m-Dichlorobenzene >99.99 >99.99 a 82.27 

Pentane >99.99 >99.99 a a 

Hexane 99.96 99.96 a a 

Diethylphthalate a a a 90.75 

a. Not reported. 

Poplar trees have emerged as the most widely used

species. These trees grow faster than other northern

temperate zone trees, they have high rates of water and

nutrient uptake, they are easy to propagate and

establish from stem cuttings, and the large number of 

species varieties permit successful use at a variety of 

different site conditions. Cottonwood, willow, tulip, 

eucalyptus, and fir trees have also been used. Wang, et 

al., for example, have demonstrated the successful 

removal by hybrid poplar trees (H11-11) of carbon

tetrachloride (15 mg/L in solution) (Wang et al., 1999). 

The plant degrades and dechlorinates the carbon 

tetrachloride and releases the chloride ions to the soil

and carbon dioxide to the atmosphere. 

Indian mustard and maize have been studied for the

removal of metals from contaminated soils (Lombi et al., 

2001). Alfalfa has been used to remediate a fertilizer spill 

( Russelle et al., 2001). 

2.14 References 

Anderson, N. (1976) Notice Paper Number 15, 

Legislative Assembly, Victoria, Australia. 

Anthony, R.G. (1978) Effects of Municipal Wastewater

Irrigation on Selected Species of A Animals, in: 

Proceedings, Land Treatment Symposium, U.S.A. 

CRREL, Hanover, NH. 

Arnold, R.G., D.D. Quanrad, G. Wilson, P. Fox, B. 

Alsmadi, G. Amy, and J. Debroux (1996) The Fate 

of Residual Wastewater Organics During SoilAquifer Treatment, presented at: Joint AWWA/WEF 

Water Reuse Conference, San Diego, CA. 

Arizona State University, University of Arizona, 

University of Colorado (1998) Soil Treatability Pilot 

Studies to Design and Model Soil Aquifer Treatment 

Systems, AWWA Research Foundation, Denver, 

CO. 

Asano T., Editor (1998) Wastewater Reclamation and 

Reuse Vol. 10 Water Quality Management Library, 

Technomic Publishing Co., Lancaster, PA. 

Ayers, R.S. (1977) Quality of Water for Irrigation, Jour. 

Irrigation Division, ASCE, Vol 103(IRZ):135-154, 

ASCE, New York, NY. 

Bastian, R.K. (1993) Summary of 40CFR Part 503, 

Standards for the Use or Disposal of Sewage

Sludge, US EPA, OWM, Washington, DC. 

Bausmith, D.S. and R.D. Neufeld (1999) Soil 

Biodegradation of Propylene Glycol Based Aircraft 

Deicing Fluids, Jour. WEF, 71(4):459-464. 

Bell, R.G. and J.B. Bole (1978) Elimination of Fecal

Coliform Bacteria from Soil Irrigated with Municipal 

Sewage Lagoon Effluent, Jour. Envir. Qual. Vol. 7, 

193-196. 

Burken, J.G., J.L. Schnoor (1996) Phytoremediation:

Plant Uptake of Atrazine and Role of Root Exudates, 

Jour. ASCE EED 122/11 958-963, ASCE, New York, 

NY. 

Camann, D (1978) Evaluating the Microbiological 

Hazard of Wastewater Aerosols, Contract Report 

DAMD 17-75-C-5072, US AMBRDL, Ft. Detrick, MD.

Chang, A.C., A.L. Page, and T. Asano (1995) 

Developing Human Health-related Chemical 

Guidelines for Reclaimed Wastewater and Sewage 

Sludge Applications in Agriculture, WHO/EOS/95.20, 

World Health Organization, Geneva, 114 pp. 
Crites , R.W. (1983) Chapter 9 - Land Treatment, 

WPCF MOP FD-7 Nutrient Control, WPCF, 

Alexandria, VA. 

Crites, R. and G. Tchobanoglous (1998) Small and 

Decentralized Wastewater Management Systems, 

McGraw Hill Co., New York, NY. 

Crites, R.W., S.C. Reed, and R.K. Bastian (2000) Land 

Treatment Systems for Municipal and Industrial 

Wastes. McGraw-Hill Book Co. New York. 

US EPA (1980) Muskegon County Wastewater 

Management System, EPA 905/2-80-004, US EPA 

RS Kerr Laboratory, Ada, OK. 

Dilling, W.L. (1977) Interphase Transfer Processes II, 

Evaporation of Chloromethanes, Ethanes, 

Ethylenes, Propanes, and Propylenes from Dilute 

Aqueous Solutions, Comparisons with Theoretical 

Predictions, Environ. Sci. Technol. 11:405-409. 

Giggey, M.D., R.W. Crites, and K.A. Brantner (1989) 

Spray Irrigation of Treated Septage on Reed 

Canarygrass, JWPCF, 61:333-342. 

Gilmour, J.T. and M.D. Clark (1988) Nitrogen Release 

from Wastewater Sludge: A Site-Specific Approach, 

JWPCF, 60:494-498. 

Gilmour, J.T., M.D. Clark and S.M. Daniel (1996) 

Predicting Long-Term Decomposition of Biosolids 

with the Seven Day Test. Jour. Env. Qual., 25:766-

770. 

Glass, D.G. (1999) International Activities in 

Phytoremediation: Industry and Market Overview, 

Phytoremediation and Innovative Strategies for 

Specialized Remedial Applications, p 95-100, 

Battelle Press, Columbus, OH. 

Harrison, R.B., C. Henry, D. Xue, J. Canary, P. Leonard, 

and R. King (1997) The Fate of Metals in Land 

Application Systems, in: Proceedings “The Forest 

Alternative - Principals and Practice of Residuals 

Use, University of Washington, Seattle, WA. 

Hutchins, S.R., M.B. Thomsom, P.B. Bedient, and C.H. 

Ward (1985) Fate of Trace Organics During Land 

Application of Municipal Wastewater, Critical Review 

Environmental Control, 15(4)355-416. 

Jenkins, T.F. and A.J. Palazzo (1981) Wastewater 

Treatment by a Slow Rate Land Treatment System, 

CRREL Report 81-14, USA CRREL, Hanover, NH. 

Jenkins, T.F., D.C. Leggett, L.V. Parker, and J.L. 

Oliphant (1985) Trace Organics Removal Kinetics 

in Overland Flow Land Treatment, Water Research, 

19(6)707-718. 

Lance, J.C. and C.P. Gerba (1980) Poliovirus 

Movement During High Rate Land Filtration of 

Sewage Water, Jour. Env. Qual., 9(1):31-34. 

Lombi, E., F.J. Zhao, S.J. Dunham, and S.P. McGrath 

(2001) Phytoremediation of Heavy Metal – 

Contaminated Soils: Natural Hyperaccumulation 

versus Chemically Enhanced Phytoextraction. JEQ, 

Vol. 30, pp. 1919-1926. 

Overcash, M.R. and D. Pal (1979) Design of Land 

Treatment Systems for Industrial Wastes, Ann Arbor 

Science, Ann Arbor, MI. 

Page, A.L., T.J. Logan, and J.A. Ryan (1987) Land 

Application of Sludge: Food Chain Implications. 

Lewis Publishers, Chelsea, MI. 

Parker, L.V. and T.F. Jenkins (1986) Removal of TraceLevel Organics by Slow-Rate Land Treatment, 

Water Research, 20(11)1417-1426. 

Reed, S.C. (ed) (1972) Wastewater Management by 

Disposal on the Land, Special Report 171, USA 

CRREL, Hanover, NH. 

Reed, S.C., R.W. Crites and E.J. Middlebrooks (1995) 

Natural Systems for Waste Management and 

Treatment - Second Edition, McGraw Hill, New York, 

NY. 

Rowe, D. R. and I. M. Abdel-Magid (1995), Handbook of 

Wastewater Reclamation and Reuse, CRC Press, 

Inc., 550 pp. 

Russelle, M.P., J.F.S Lamb, B.R. Montgomery, D.W. 

Elsenheimer, B.S. Miller, and C.P. Vance (2001) 

Alfalfa Rapidly Remediates Excess Inorganic 

Nitrogen at a Fertilizer Spill Site. JEQ, Vol. 30, pp. 

30-36. 

Sheikh, B., P. Cort, W. Kirkpatrick, R. Jaques and T. 

Asano (1990) Monterey Wastewater Reclamation 

Study for Agriculture. Research JWPCF, 62:216-

226, WEF, Alexandria, VA.

Shuval, H.I. and B. Teltch (1979) Hygienic Aspects of 

the Dispersion of the Enteric Bacteria and Virus by

Sprinkled Irrigation of Wastewater, in Proceedings of 

AWWA Water Reuse Symposium.

Smith, J.W. and R.W. Crites (2001) Rational Method for 

the Design of Organic Loading Rates in a Land 

Application System. Proceedings of WEFTEC 2001, 

Atlanta, GA.

Tchobanoglous, G., F.L. Burton and H.D. Stensel (2002) 

Wastewater Engineering, Treatment and Reuse, 

Fourth Edition, McGraw-Hill, New York.

US EPA (1972) Oily Waste Disposal by Soil Cultivation, 

EPA-R2-72-110, US EPA, Washington, DC. 
US EPA (1973) National Academy of Science – National 

Academy of Engineering Water Quality Criteria

1972: A Report of the Committee on Water Quality 

Criteria. EPA-R3-73-033. Washington, DC. 

US EPA (1978) Long Term Effects of Land Application 

of Domestic Wastewater - Hollister, CA Rapid 

Infiltration Site, EPA/600/2-78-084, US EPA, 

Cincinnati, OH. 

US EPA (1978) Sewage Disposal on Agricultural Soils: 

Chemical and Microbiological Implications. EPA600/2-78-131a. 

US EPA, (1979) Long Term Effects of Land Application 

of Domestic Wastewater, Dickinson, ND Slow Rate, 

EPA-600/2-79-144, US EPA ORD, Washington, DC. 

US EPA (1979) Long Term Effects of Land Application 

of Domestic Wastewater - Roswell, NM, EPA 600/2-

79-047, ORD, US EPA Washington, DC. 

US EPA (1979) Long Term Effects of Land Application 

of Domestic Wastewater - Roswell, NM, EPA 600/2-

79-047, ORD, US EPA Washington, DC. 

US EPA (1980) Summary of Long Term Rapid 

Infiltration Studies, EPA-600/2-80-165, US EPA R.S.

Kerr Laboratory, Ada, OK. 

US EPA (1981) Process Design Manual for Land 

Treatment of Municipal Wastewater, EPA-625/1-81-

013, US EPA CERI, Cincinnati, OH. 

US EPA (1982) Estimating Microorganism Densities in 

Aerosols from Spray Irrigation of Wastewater, US 

EPA/-600/9-82-003, US EPA, Cincinnati, OH. 

US EPA (1984) Process Design Manual Land 

Treatment of Municipal Wastewater - Supplement on 

Rapid Infiltration and Overland Flow, EPA-625/1-81-

013a, US EPA CERI, Cincinnati, OH. 

US EPA (1985) Health Effects of Land Application of 

Municipal Sludge, EPA/600/1-85/015, NTIS #PB86-

19745678, NTIS, Springfield, VA. 

US EPA. (1995) Process Design Manual for Land 

Application of Sewage Sludge and Domestic 

Septage. EPA/625/R-95/001. 

US EPA (2000) Introduction to Phytoremediation, 

EPA/600/R-99/107. Washington, DC.

Wang, X., L.E. Newman and M.P. Gordon (1999) 

Biodegradation of Carbon Tetrachloride by Popular 

Trees: Results from Cell culture and field

Experiments, in: Phytoremediation and Innovative 

Strategies for Specialized Remedial Applications, 

Battelle Press, Columbus, OH.

Witherow, J.L.and B.E. Bledsoe (1983) Algae Removal 

by the Overland Flow Process, JWPCF, Vol. 55, No. 

10, 1256-1262.
Chapter 3 

Water Movement in Soil and Groundwater 

The hydraulic capacity of the soil to accept and 

transmit water is crucial to the design of soil aquifer 

treatment (SAT) systems and important in the design of 

most slow rate (SR) systems. The physical and chemical 

and microbial properties of soil influence the ability of 

water to move through soil. The important hydraulic 

factors for SAT and SR treatment systems that are 

discussed in this section are infiltration, vertical 

permeability (percolation), horizontal permeability, 

groundwater mounding, and the relationship between 

predicted capacity and actual operating rates. 

3.1 Soil Properties 

The hydraulics of soil systems are controlled by the 

physical, biological, and chemical properties of soil. 

Important physical properties include texture, structure, 

and soil depth. Chemical characteristics that can be 

important include soil pH and buffer capacity, the redox 

potential of soil, organic matter, cation exchange 

capacity, exchangeable sodium percentage, and 

background nutrient levels. Preliminary information on 

these soil properties and on soil permeability can be 

obtained from the Natural Resources Conservation 

Service (NRCS) and its soil surveys and maps. 

Soil surveys will normally provide broad scale soil 

maps delineating the apparent boundaries of soil series 

with the surface texture and slope. A written description 

of each soil series provides limited information on 

chemical properties, engineering applications, 

interpretive and management information, slopes, 

drainage, erosion potentials, and general suitability for 

most kinds of crops grown in the particular area. 

Additional information on soil characteristics and 

information regarding the availability of soil surveys can 

be obtained directly from the NRCS. The NRCS serves 

as the coordinating agency for the National Cooperative 

Soil Survey, and as such, cooperates with other 

government agencies, universities, the Agricultural 

Extension Services, and private consultants in obtaining 

and distributing soil survey information. Such information 

is valuable in preliminary evaluations for land treatment 

systems, but verification at any specific site is critical 

and essential in design and permitting. Much of the 

NRCS information is available on the Internet at 

www,nrcs,usda,gov/technical/efotg including soil survey 

information. 

3.1.1 Physical Properties 

Physical properties of soils relate to the solid particles 

of the soil and the manner in which they are aggregated. 

Soil texture describes the size and distribution of the soil 

particles. The manner in which soil particles are 

aggregated is described as the soil structure. Together, 

soil texture and structure help determine the ability of the 

soil to hold and transport water and air. Soil structure 

and texture are important characteristics that relate to 

permeability and suitability for land treatment. 

Texture 

Soil textural classes are defined on the basis of the 

relative percentage of the three classes of particle size--

sand, silt, and clay. Sand particles range in size from 2.0 

mm to 0.05 mm; silt particles range from 0.05 mm to 

0.002 mm; and particles smaller than 0.002 mm are 

clay. From the particle size distribution, the Natural 

Resources Conservation Service’s (NRCS’s) textural 

class can be determined using the textural triangle 

shown in Figure 3-1. Common soil-texture terms and the 

relationship to textural class names are listed in Table 3-

1. The particle size classification used by NRCS is the 

USDA classification system; others include AASHO, 

ASTM, and ISSS. 

Fine-textured soils do not drain rapidly and retain large 

percentages of water for long periods of time. As a 

result, infiltration and percolation are slower and crop 

management is more difficult than with more freely 

drained soils such as loams. Fine-textured soils are 

generally best suited to overland flow systems. Mediumtextured soils exhibit the best balance for wastewater 

renovation and drainage. Loam (medium texture) soils 

are generally best suited for slow rate systems. Coarsetextured soils (sandy soils) can accept large quantities of 

water and do not retain moisture in the root zone very 

long. This feature is important for crops that cannot 

withstand prolonged submergence or saturated root 

zones. A moderately coarse-textured soil is best for SAT 

systems. Coarse-textured soils with a significant silt or 

clay content (>10%) are not desirable for SAT systems 

because these soils have relatively low permeabilities. 

3-1 
Figure 3-1. Natural Resources Conservation Service (NRCS) Soil Textural Classes (Nielson et al., 1973). 

Table 3-1. Soil Textural Classes and General Terminology Used in 

Soil Descriptions 

3.2 General terms 3.2.1 Basic soil textural 

class names 

3.2.2 Com

mon name 

Texture 

Sandy soils Coarse Sand 

Loamy Sand 

Moderately

coarse 

Sandy loam 

Fine sandy loam 

Loamy soils Medium Very fine sandy loam 

Loam 

Silt loam 

Silt 

Moderately fine Clay loam 

Sandy clay loam 

Silty clay loam 

Clayey soils Fine Sandy clay

Silty clay

Clay

Structure 

Structure refers to the shape and degree of soil 

particle aggregation. The pattern of pores and 

aggregates defined by soil structure influences water 

movement, heat transfer, air movement, and porosity in 

soils. If soil aggregates resist disintegration when the 

soil is wetted or tilled, it is well structured. The large 

pores in well-structured soils conduct water and air, 

making well-structured soils desirable for infiltration. A 

well-structured soil is generally more permeable than 

unstructured material of the same type. SAT systems 

are suited for sand or loamy sand. 

Soil Depth to Annual High Water Level 

Adequate soil depth is needed for retention of 

wastewater constituents on soil particles, for plant root 

development, and for microbial action. Adequate depth 

is also required in SR and SAT systems to separate the 

zone of wastewater treatment from the saturated soil 

layers. Retention of wastewater constituents, is a 

function of residence time of wastewater in the soil. 

Residence time depends on the application rate and the 

soil permeability. 

The type of land treatment process being considered 

will determine the minimum acceptable soil depth. For 

SR, the soil depth can be 0.6 to 1.5 m (2 to 5 ft), 

depending on the soil texture and crop type. For 

example, soil depths of 0.3 to 0.6 m (1 to 2 ft) can 

support grass or turf, whereas deep rooted crops do 

better on soil depths of 1.2 to 1.5 m (4 to 5 ft). Because 

soils form in layers, the horizontal layering is important in 

assessing soil depth. Forested SR systems can be 

established with soil depths of 0.3 m (1 ft) or more. 

3-2 
The soil depth for SAT should be at least 1.5 m (5 ft) 

and preferably 1.5 to 3 m (5 to 10 ft). Overland flow 

systems require sufficient soil depth to form slopes that 

are uniform and to maintain a vegetative cover. A 

finished slope should have a minimum of 0.15 to 0.3 m 

(6 to 12 in) of soil depth. 

3.1.2 Chemical Properties 

Soil chemical properties affect plant growth, 

wastewater renovation, and can affect hydraulic 

conductivity. Soil pH affects plant growth, bacterial 

growth, and retention of elements such as phosphorus in 

the soil. Soil pE (redox potential) affects the existence of 

oxidized or reduced species of chemical elements in the 

soil. Organic matter can improve soil structure and 

thereby improve the hydraulic conductivity. Sodium can 

reduce the hydraulic conductivity of soil by dispersing 

clay particles and destroying the structure that allows 

water movement. The chemical properties of soil should 

be determined prior to design to evaluate the capacity of 

the soil to support plant growth and to renovate 

wastewater. 

Soil pH and Buffer Capacity 

Soil pH has been called the master variable because it 

affects chemical, biological, and physical soil properties. 

Likewise, soil pH is influenced by many factors such as 

precipitation, irrigation water, carbonic acid dissociation, 

organic matter, mineral weathering, bio-uptake and 

release, aluminum hydroxy polymers, and nitrogen 

fertilizers (Sposito, 1989). Soil pH has a significant 

influence on the solubility of various compounds, the 

activities of microorganisms, and the bonding of ions to 

exchange sites. Soil pH can limit crop growth by 

influencing the availability of root uptake of elements, 

including nutrients and metals. The activity of soil 

microorganisms is also affected by pH. Soil pH affects 

chemical solubility, biochemical breakdown by 

microorganisms, and adsorption to soil particles, thereby 

influencing the mobility of chemical constituents in the 

soil. Soil physical properties can also be influenced by 

soil pH by influencing the dispersion of clays and the 

formation of soil aggregates. The soil buffering capacity 

is important to prevent drastic fluctuations in soil pH that 

can have a detrimental affect on plants and soil 

microorganisms. Most buffering is provided by cation 

exchange or the gain or loss of H+

 ions of pH-dependent 

exchange sites on clay and humus particles. The wellbuffered soil would have a higher amount of organic 

matter and/or highly charged clay than the moderately 

buffered soil (Brady and Weil, 2002). Soil organic matter 

has many reactive sites in which hydrogen ions can 

associate and dissociate. Exchangeable ions on the 

surface of clay minerals and humus can also associate 

or dissociate with hydrogen ions. Therefore, the cation 

exchange capacity (CEC), the quantity of exchangeable 

cations that a particular soil can adsorb, influences the 

soil’s buffering capacity. 

Soil Redox 

The redox potential (Eh) of soil is a measure of the 

reduction and oxidation states of chemical elements in 

soil and affects soil aeration. The redox potential of a 

soil is dependent on the presence of oxidizing agents 

such as oxygen and pH. Redox potential is measured in 

volts with an electrode. The electron activities of 

chemical species in soil can also be expressed as pE, a 

nondimensional parameter related to Eh by the following 

equation: 

pE F

RT Eh2.3 = (3-1)

Where Eh = redox potential in volts 

R (universal gas constant) = 8.314 Jmol-1K-1

T = temperature in Kelvin 

F (Faraday constant) = 96,500 coulombs mol-1

 2.3 RT/F = 0.059 volts at 25 deg C 

 pE = hypothetical electron activity

The influence of soil redox on both chemical and 

microbial species can greatly affect the mobility of 

chemical constituents in the soil as well as wastewater 

renovation. In addition, soil pE indirectly affects soil 

structure because of the influence on microbial activity. 

If a soil is well aerated, oxidized states such as Fe(III) 

and nitrate (NO3

-

) are dominant. Reduced forms of 

elements, such as Fe(II) and ammonium (NH4

+

), are 

found in poorly aerated soils. Low pE’s correspond to 

highly reducing species and high pE’s to oxidizing 

species. The largest pE value observed in the soil 

environment is just below +13.0 and the smallest is near 

-6.0 (Sposito, 1989). The most important chemical 

elements affected by soil redox reactions are carbon, 

nitrogen, oxygen, sulfur, manganese, and iron. As the 

pE of a soil drops below +11.0, oxygen can be reduced 

to water. Below pE +5.0, oxygen is consumed in the 

respiration processes of aerobic microorganisms. With 

no oxygen present in the soil, nitrate can be reduced at 

pE values below +8.0 and nitrate is utilized by 

microorganisms as an electron acceptor. Generally, 

denitrifying bacteria function in the pE range between 

+10 and 0. As the soil pE drops between +7 and +5, 

iron and manganese are reduced. Iron reduction does 

not occur until oxygen and nitrate are depleted. 

Manganese reduction however can proceed in the 

presence of nitrate. As the pE decreases below +2.0, a 

soil becomes anoxic. Sulfate reduction can occur when 

pE is less than 0 and is catalyzed by anaerobic 

3-3 
microorganisms. Sulfate reducing bacteria do not grow 

at pE values above +2.0. 

Organic Matter 

Soil organic matter (SOM generally only referred to as 

OM) contents range from 0.5 to 5 percent on a weight 

basis in the surface of mineral soils to 100 percent 

organic matter, if fertilizers are added (Sparks, 1995). 

The organic content of soil influences the structure and 

formation of soil aggregates. Water retention of the soil 

is increased by organic matter because the infiltration 

rate and water holding capacity of the soil is increased 

through improved soil structure. Organic matter provides 

the energy substrate for soil microorganisms, which in 

turn aid in the formation of aggregates. Decaying 

organic matter (humic substances) reacts with silicate 

clay particles and iron and aluminum oxides and form 

bridges between soil particles. In addition, the pH and 

buffer capacity of a soil is influenced by organic matter 

content. 

Soil organic matter has a high specific surface area 

and the majority of the surface soil cation exchange 

capacity (CEC) is attributed to SOM. Because of the 

large amount of surface sites, organic matter is an 

important sorbent of plant nutrients, metal cations, and 

organic chemicals. The uptake and availability of plant 

nutrients, particularly micronutrients, is greatly affected 

by soil organic matter. Organic matter also forms stable 

complexes with polyvalent cations such as Fe3+, Cu2+, 

Ca2+, Mn2+, and Zn2+, and decreases the uptake of 

metals by plants and the mobility of metals in the soil. 

Salinity and Exchangeable Sodium Percentage 

Soil salinity and sodicity (high sodium content) can 

have a major effect on the structure of soils. Salinity, the 

concentration of soluble ionic substances, affects plant 

growth primarily in the soil root zone. Electrical 

conductivity (EC) is a measure of soil salinity. Guidelines 

exist for controlling root zone salinity and calculating 

leaching requirements of applied irrigation water for 

varying types of crops according to salt tolerance. High 

levels of salinity in the root zone of crops can reduce the 

ability of plants to move water from the soil through the 

plant. 

Soils containing excessive exchangeable sodium are 

termed "sodic" or "alkali." A soil is considered sodic if the 

percentage of the CEC occupied by sodium, the 

exchangeable sodium percentage (ESP), exceeds 15 

percent. If a soil has high quantities of sodium and the 

EC is low, soil permeability, hydraulic conductivity, and 

the infiltration rate is decreased due to the swelling and 

dispersion of clays and slaking of aggregates (Sparks, 

1995). Fine-textured soils may be affected at an ESP 

above 10 percent, but coarse-textured soil may not be 

damaged until the ESP reaches about 20 percent. 

3.2 Water Movement through Soil 

Estimates of the hydraulic properties of the site are 

crucial to designing land treatment systems. The 

capacity of the soils to accept and transmit water is 

important for the design of SAT systems and may be 

limiting in the design of SR systems. Water movement in 

soil can be characterized as either saturated flow or 

unsaturated flow. 

3.2.1 Infiltration Rate 

The rate at which water enters the soil surface, 

measured in millimeters per hour (mm/hr) or inches per 

hour (in/hr), is the infiltration rate. The infiltration rate is 

usually higher at the beginning of water application than 

it is several hours later. Infiltration rates are related to 

the extent of large, interconnected pore spaces in the 

soil. Coarse textured soils with many large pores have 

higher infiltration rates than fine textured-soils or soils in 

which the pore space is reduced in size by compaction 

or a breakdown of soil aggregates. 

For a given soil, initial infiltration rates may vary 

considerably, depending on the initial soil moisture level. 

Dry soil has a higher initial rate than wet soil because 

there is more empty pore space for water to enter. The 

drier the deeper layer of soil, the larger the potential 

gradient between the wetting front and the soil beneath, 

and hence the more rapid the intake rate (Withers and 

Vipond, 1987). The short-term decrease in infiltration 

rate is primarily due to the change in soil structure and 

the filling of large pores as clay particles absorb water 

and swell. Thus, adequate time must be allowed when 

running field tests to achieve a steady intake rate. 

Infiltration rates are affected by the ionic composition 

of the soil-water, the type of vegetation, the rate and 

duration of water application, and tillage of the soil 

surface. Factors that have a tendency to reduce 

infiltration rates include clogging by suspended solids in 

wastewater, classification of fine soil particles, clogging 

due to biological growths, gases produced by soil 

microbes, swelling of soil colloids, and air entrapped 

during a wetting event (Jarrett and Fritton, 1978) (Parr 

and Bertran, 1960). These influences are all likely to be 

experienced when a site is developed into a land 

treatment system. The net result is to restrict the 

hydraulic loadings of land treatment systems to values 

substantially less than those predicted from the steadystate intake rates, requiring reliance on field-developed 

correlations between clean water infiltration rates and 

satisfactory operating rates for full-scale systems. 

Generally, whenever water is ponded over the soil 

surface, the rate of water application exceeds the soil 

3-4 
infiltration or permeability. It should be recognized that 

good soil management practices can maintain or even 

increase operating rates, whereas poor practices can 

lead to substantial decreases. 

Techniques for measuring soil infiltration rate in the 

field are discussed in Section 3.8.1. Infiltration rates can 

also be estimated with the use of simple mathematical 

models. The US EPA funded research for the 

determination of methods based on soil physics to 

quantify the rate of soil water movement due to 

infiltration. The three types of methods are divided into 

empirical models (examples are Kostiakov and Horton), 

and Mechanistic Approaches such as Green-Ampt 

models, and Richards equation models, and the Philips 

model (an analytical solution to the Richards equation). 

Evaluations of selected models under different site 

conditions were also conducted (US EPA 1998; US 

EPA, 1998). 

3.2.2 Intake 

The rate at which water in a furrow enters the soil is 

referred to as the intake rate (Hansen et al., 1980). 

Irrigation texts have used the term "basic intake rate" as 

synonymous with infiltration rate (Pair et al., 1975). In 

furrow irrigation the intake rate is influenced by the 

furrow size and shape. Therefore, when the 

configuration of the soil surface influences the rate of 

water entry, the term intake rate should be used rather 

than the term infiltration rate (which refers to a relatively 

level surface covered with water). 

3.2.3 Permeability 

The permeability or hydraulic conductivity (used 

interchangeably in this manual) is the velocity of flow 

caused by a unit hydraulic gradient. Permeability is an 

intrinsic soil property, not influenced by the gradient, and 

this is an important difference between infiltration and 

permeability. 

Vertical permeability is also known as percolation. 

Lateral flow is a function of the gradient and the 

horizontal permeability (which is generally different from 

the percolation rate). Permeability is affected mostly by 

the soil physical properties. Changes in water 

temperature can affect permeability slightly (Hansen et 

al., 1980). 

3.2.4 Transmissivity 

Transmissivity of an aquifer is the product of the 

permeability (K) and the aquifer thickness. It is the rate 

at which water is transmitted through a unit width of 

aquifer under a unit hydraulic gradient. 

3.2.5 Specific Yield 

The term specific yield is the volume of water released 

from a known volume of saturated soil under the force of 

gravity and inherent soil tension (U.S. Department of the 

Interior, 1978). The specific yield is also referred to as 

the storage coefficient and the drainable voids. The 

primary use of specific yield is in aquifer calculations 

such as drainage and mound height analyses. 

For relatively coarse-grained soils and deep water 

tables, it is usually satisfactory to consider the specific 

yield a constant value. As computations are not 

extremely sensitive to small changes in the value of 

specific yield, it is usually satisfactory to estimate it from 

knowledge of other soil properties, either physical as in 

Figure 3-2 (Todd, 1964), or hydraulic as in Figure 3-3

(U.S. Department of the Interior, 1978). To clarify 

Figure 3-2, specific retention is equal to the porosity 

minus the specific yield. 

For fine-textured soils, especially as the water table 

moves higher in the profile, the specific yield may not 

have a constant value because of capillarity (Childs, 

1969) (Duke, 1972). The effect of decreasing specific 

yield with increasing water table height can lead to 

serious difficulties with mound height analysis. 

3.2.6 Water-Holding Capacity 

Soil water can be classified as hygroscopic, capillary, 

and gravitational. Hygroscopic water is a very thin film 

on the surface of soil particles and is not removed by 

gravity or by capillary forces. Capillary water is the water 

held by surface tension in soil pores against gravity. 

Gravitational water is the water that occupies the 

larger pores of the soil and will drain by gravity if 

favorable drainage is provided (Hansen et al., 1980). 

The water-holding capacity of a soil refers to the 

condition where the volumetric water content at 

saturation is essentially the same as total porosity. 

3-5 
Figure 3-2. Porosity, Specific Yield, Specific Retention vs. Soil Grain 

Size for In situ Consolidated Soils, Coastal Basin, CA (Todd, 1964). 

Figure 3-3. Specific Yield Vs. Hydraulic Conductivity (Department of 

the Interior, 1978). 

Soil water can also be classified according to its 

availability to plant root systems. As illustrated in Figure 

3-4, the maximum available water occurs at saturation 

(point 1), when all the pore space is filled with water. 

When the soil water drops to point 3, only hygroscopic 

water is left, which is mostly unavailable to plants. 

Figure 3-4. Soil Moisture Characteristics (Crites et al., 2000). 

3.2.7 Field Capacity 

When gravitational water has been removed, the 

moisture content of the soil has been called the field 

capacity. In this condition, water has moved out of the 

macropores and been replaced by air in the surface 

profile. In practice the field capacity is measured two 

days after water application and can range from 3 

percent moisture for fine sand to 40 percent for clay. The 

range of moisture percentages for field capacity for 

various soil types is presented in Table 3-2. 

Relationships of field conditions to soil moisture content 

are presented in Table 3-3. 

At field capacity, a soil is holding the maximum 

amount of water useful to plants. Additional water would 

occupy large pores and reduce the potential for aeration, 

before draining of gravitational water. Sufficient pore 

space is filled with air at field capacity to allow optimum 

aeration for support of aerobic microorganisms. 

It should be noted that field capacity as described can 

not truly exist. Water will continue to drain under gravity 

to an impermeable barrier. However drainage does 

decrease rapidly for coarse grain soils – perhaps in two 

days. However fine grained soils do not show the same 

abrupt decrease and therefore the term field capacity is 

less meaningful. 

Table 3-2. Range of Available Soil Moisture for Different Soil Types 

Soil type 3.3 Moisture 

percentage 

Depth of available water 

per unit depth of soil, 

mm/m (in/ft)

Field 

capacity

Permanent 

wilting point 

Fine sand 3-5 1-3 25-42 (0.3-0.5) 

Sandy loam 5-15 3-8 42-108 (0.5-1.3) 

Silt loam 12-18 6-10 58-133 (0.7-1.6) 

Clay loam 15-30 7-16 100-183 (1.2-2.2) 

Clay 25-40 12-20 167-292 (2.0-3.5) 

3-6 
Table 3-3. Field Estimating of Soil Moisture Content*

Fine texture Medium texture Moderately

coarse 

texture 

Coarse 

texture 

No free water after 

squeezing, wet, 

outline on hand 

Same as fine 

texture 

Same as 

fine texture 

Same as fine 

texture 

0.0 0.0 0.0 0.0 

Easily ribbons out 

between fingers, 

has slick feeling 

Forms a very

pliable ball, 

sticks readily if 

high in clay

Forms

weak ball, 

breaks 

easily, will 

not stick 

Sticks 

together 

slightly, may

form a very

weak ball 

under 

pressure 

0.0-0.6 0.0-0.5 0.0-0.4 0.0-0.2 

Forms a ball, 

ribbons out 

between thumb and 

forefinger 

Forms a ball, 

sometimes 

sticks slightly

with pressure 

Tends to 

ball under 

pressure 

but will not 

hold 

together 

Appears dry, 

will not form 

a ball when 

squeezed 

0.6-1.2 0.5-1.0 0.4-0.8 0.2-0.5 

Somewhat pliable, 

will form a ball 

when squeezed 

Somewhat 

crumbly but hold 

together from 

pressure 

Appears 

dry, will not 

form a ball 

Appears dry, 

will not form 

a ball 

1.2-1.9 1.0-1.5 0.8-1.2 0.5-0.8 

Hard, baked, 

cracked 

Powdery, dry, 

sometimes 

slightly crusted 

but easily

broken down 

into powdery

condition 

Dry, loose, 

flows 

through 

fingers 

Dry, loose, 

single 

grained flows 

through 

fingers 

1.9-2.5 1.5-2.0 1.2-1.5 0.8-1.0 

* The numerical values are the amount of water (in) that would be 

needed to bring the top foot of soil to field capacity. 

3.2.8 Permanent Wilting Point 

The soil moisture content at which plants will wilt from 

lack of water is known as the permanent wilting point. By 

convention, the permanent wilting point for most 

cultivated plants is taken to be that amount of water 

retained by the soil when the water potential is –15 bars. 

The soil will appear to be dusty, but some water remains 

in the micopores and in thin films around soil particles. 

The available moisture content or plant available water 

is generally defined as the difference between the field 

capacity and the permanent wilting point (between –0.1 

to –0.3 and –15 bars). This represents the moisture that 

can be stored in the soil for subsequent use by plants. 

The amount of capillary water remaining in the soil that 

is unavailable to plants can be substantial, especially in 

fine-textured soils and soils high in organic matter. For 

SR systems with poorly drained soils, this stored 

moisture is important to design loadings. 

As an approximation the permanent wilting 

percentage can be obtained by dividing the field capacity 

by 2. For soils with high silt content, divide the field 

capacity by 2.4 to obtain permanent wilting percentage. 

3.3 Saturated Hydraulic Conductivity

Saturated flow through soils takes place when soil 

pores are completely filled with water. At least part of the 

soil profile may be completely saturated under certain 

conditions. Hydraulic conductivity is a measure of the 

ease with which liquids and gases pass through soil. In 

general, water moves through saturated soils or porous 

media in accordance with Darcy's equation: 

dl

dH K

A

Q

q = = (3-2) 

Where

q = flux of water, the flow, Q per unit cross-sectional area, A, m/d (ft/d) 

Q = flow rate, m3

/d (ft3/d) 

A = area of cross-section perpendicular to the flow, m2

 (ft2) 

K = hydraulic conductivity (permeability), m/d (ft/d) 

dH/dl= hydraulic gradient, m/m (ft/ft) 

The total head (H) can be assumed to be the sum of 

the soil-water pressure head (h), and the head due to 

gravity (Z), or H = h + Z. The hydraulic gradient is the 

change in total head (dH) over the path length (dl). 

The hydraulic conductivity is defined as the 

proportionality constant, K. The conductivity (K) is not a 

true constant but a rapidly changing function of water 

content. Even under conditions of constant water 

content, such as saturation, K may vary over time due to 

increased swelling of clay particles, change in pore size 

distribution due to classification of particles, and change 

in the chemical nature of soil-water. However, for most 

purposes, saturated conductivity (K) can be considered 

constant for a given uniform soil. The K value for flow in 

the vertical direction will not necessarily be equal to K in 

the horizontal direction. This condition is known as 

anisotropy. It is especially apparent in layered soils and 

those with large structural units. An illustration of 

anisotropic conditions is shown in Table 3-4. 

The value of K depends on the size and number of 

pores in the soil or aquifer material. Orders of 

magnitudes for vertical conductivity (Kv) values in ft/day 

for typical soils are (Bouwer, 1978): 

Soil or Aquifer Material Kv, ft/d

Clay soils (surface) 0.03 – 0.06 

Deep clay beds 3 x 10-8 – 0.03 

Clay, sand, gravel mixes (till) 0.003 – 0.3 

Loam soils (surface) 0.3 – 3.0 

Fine sand 3 – 16 

Medium sand 16 – 66 

Coarse sand 66 – 300 

Sand and gravel mixes 16 – 330 

Gravel 330 – 3300 

The conductivity of soils at saturation is an important 

parameter because it is used in Darcy’s equation to 

3-7 
estimate groundwater flow patterns and is useful in 

estimating soil infiltration rates. Conductivity is frequently 

estimated from other physical properties, but much 

experience is required and results are not sufficiently 

accurate for design purposes (Bouwer, 1978) (Freeze 

and Cherry, 1979) (Taylor and Ashcroft, 1972) (Richard, 

1965) (O’Neal, 1952). For example, hydraulic 

conductivity is largely controlled by soil texture: coarser 

materials having higher conductivities. However, in 

some cases the soil structure may be equally important: 

well-structured fine soils having higher conductivities 

than coarser unstructured soils. 

In addition, hydraulic conductivity for a specific soil 

may be affected by variables other than those relating to 

grain size, structure, and pore distribution. Temperature, 

ionic composition of the water, and the presence of 

entrapped air can alter conductivity values (Bouwer, 

1978). 

Table 3-4. Measured Ratios of Horizontal to Vertical Conductivity

Site Horizontal conductivity Kh, m/d (ft/day) Kh/Kv Remarks 

 1 42 (138) 2.0 Silty

 2 75 (246) 2.0 

 3 56 (184) 4.4 

 4 100 (328) 7.0 Gravelly

 5 72 (236) 20.0 Near terminal moraine 

 6 72 (236) 10.0 Irregular succession of sand and gravel layers (from K 

measurements in field) 

 6 86 (282) 16.0 (From analysis of recharge flow system) 

3.4 Unsaturated Hydraulic Conductivity

Darcy's law for velocity of flow in saturated soils also 

applies to unsaturated soils. As the moisture content 

decreases, however, the cross-sectional area through 

which the flow occurs also decreases and the 

conductivity is reduced. 

The conductivity of soil varies dramatically as water 

content is reduced below saturation. As an air phase is 

now present, the flow channel is changed radically and 

now consists of an irregular solid boundary and the airwater interface. The flow path becomes more and more 

tortuous with decreasing water content as the larger 

pores empty and flow becomes confined to the smaller 

pores. Compounding the effect of decreasing crosssectional area for flow is the effect of added friction as 

the flow takes place closer and closer to solid particle 

surfaces. The conductivity of sandy soils, although much 

higher at saturation than loam soils, decreases more 

rapidly as the soil becomes less saturated. In most 

cases, the conductivities of sandy soils eventually 

become lower than finer soils. This relationship explains 

why a wetting front moves more slowly in sandy soils 

than in medium or fine textured soils after irrigation has 

stopped, and why there is little horizontal spreading of 

moisture in sandy soils after irrigation. 

3.5 Percolation Capacity

The percolation capacity of SR and SAT systems is a 

critical parameter in planning, design, and operation. 

The capacity will vary within a given site and may 

change with time, season and different management. 

For planning purposes the infiltration capacity can be 

estimated from the vertical permeability rates assigned 

by the NRCS (Figure 3-5). 

3.5.1 Design Percolation Rate 

To account for required intermittent applications 

(reaeration), the variability of the actual soil permeability 

within a site, and the potential reduction with time, a 

small percentage of the vertical permeability is used as 

the design percolation rate. This small percentage 

ranges from 4 to 10 percent of the saturated vertical 

permeability as shown in Figure 3-5. The value used for 

clear water permeability should be for the most 

restrictive layer in the soil profile. Design rates based on 

field measurement (Section 3.8) may be calculated 

using different percentages. If the planned application 

season is less than 365 days, the percolation rate 

should be reduced to coincide with the planned 

application period. 

3.5.2 Calculation of Vertical Permeability 

The rate at which water percolates through soil 

depends on the average saturated permeability (K) of 

the profile. If the soil is uniform, K is assumed to be 

constant with depth. Any differences in measured values 

of K are then due to normal variations in the 

measurement technique. Thus, average K may be 

computed as the arithmetic mean of n samples: 

n

K K K K K n

am

+ + + + = 1 2 3 L (3-3) 

Where Kam = arithmetic mean vertical conductivity

3-8 
Many soil profiles approximate a layered series of 

uniform soils with distinctly different K values, generally 

decreasing with depth. For such cases, it can be shown 

that average K is represented by the harmonic mean of 

the K values from each layer (Bouwer, 1969): 

n

n

hm

K

d

K

d

K

d

D K

+ + +

=

L

2

2

1

1

(3-4) 

Where D = overall soil profile depth 

 dn = depth of nth layer 

 Khm = harmonic mean conductivity

Figure 3-5. Approximate Preliminary Percolation Rate vs. NRCS Soil 

Permeability for SR and SAT. 

The Zones A through G Refer to Clearwater Permeability for the Most 

Restrictive Layer in the Soil Profile (Kv = in/h): A = very slow), <0.06; B 

= slow, 0.06 to 0.20; C = moderately slow, 0.20 to 0.60; D = moderate, 

0.60 to 2.0; E = moderately rapid, 2.0 to 6.0; F = rapid, 6.0 to 20; G = 

very rapid, >20 

If a bias or preference for a certain K value is not 

indicated by statistical analysis of field test results, a 

random distribution of K for a certain layer or soil region 

must be assumed. In such cases, it has been shown 

that the geometric mean provides the best and most 

conservative estimate of the true K (Bouwer, 1969) 

(Rogowski, 1972) (Nielson et al., 1973): 

Kgm = (K1 . K2 . K3 . ...Kn)

1/n (3-5)

Where Kgm = geometric mean conductivity

3.5.3 Profile Drainage 

For SR and SAT systems the soil profile must drain 

between applications to allow the soil to reaerate. The 

time required for profile drainage is important to system 

design and varies with the soil texture and the presence 

of restrictions (such as fragipans, clay pans, and 

hardpans). In sandy soils without vertical restrictions, 

the profile can drain in one to two days. In clayey soils 

drainage may take five days or more. The drying period 

between applications also depends on the evaporation 

rate. 

3.6 Mounding of Groundwater 

If water that infiltrates the soil and percolates vertically 

through the zone of aeration (also known as vadose 

zone or unsaturated zone) encounters a water table or 

an impermeable (or less permeable) layer, a 

groundwater "mound" will begin to grow (Figure 3-6). 

Figure 3-6. Schematic of Groundwater Mound. 

If the mound height continues to grow, it may 

eventually encroach on the zone of aeration to the point 

where renovation capacity is affected. Further growth 

may result in intersection of the mound with the soil 

surface, which will reduce infiltration rates. This problem 

can usually be identified and analyzed before the system 

is designed and built if the prior geologic and hydrologic 

information is available for analysis. 

3.6.1 Prediction of Mounding 

Groundwater mounding can be estimated by applying 

heat-flow theory and the Dupuit-Forchheimer 

assumptions (Rogowski, 1972). These assumptions are 

as follows: 

3-9 
1. Flow within groundwater occurs along horizontal 

flow lines whose velocity is independent of depth. 

2. The velocity along these horizontal streamlines is 

proportional to the slope of the free water surface. 

Using these assumptions, heat-flow theory has been 

successfully compared to actual groundwater depths at 

several existing SAT sites. To compute the height at the 

center of the groundwater mound, one must calculate 

the values of: 

W/[4 α t ]1/2 and Rt (3-6)

Where W = width of the recharge basin, ft 

Figure 3-7. Mounding Curve for Center of a Square Recharge Area 

(Bianchi and Muckel, 1970). 

α = aquifer constant = 

V

KD , ft2

/d (3-7)

Where: 

K = aquifer (horizontal) hydraulic conductivity, ft/d 

D = saturated thickness of the aquifer, ft 

V = specific yield or fillable pore space of the soil, ft3

/ft3

t = length of wastewater application, d 

R = I/V, ft/d, rate of rise if no lateral flow occurred 

where I = application rate, ft/d 

Once the value of W/[4αt]1/2 is obtained, one can use 

dimensionless plots of W/[4αt]1/2 versus ho/Rt, provided 

as Figure 3-7 (for square recharge areas) and Figure 

3-8 (for rectangular recharge areas), to obtain the value 

of ho/Rt, where ho is the rise at the center of the mound. 

Using the calculated value of Rt, one can solve for ho. 

Figure 3-8. Mounding Curve for Center of a Rectangular recharge 

Area, with Different Ratios of Length L to Width W (Bianchi and 

Muckel, 1970). 

Figure 3-9 (for square recharge areas) and 

Figure 3-10 (for recharge areas that are twice as long as 

they are wide) can be used to estimate the depth to the 

mound at various distances from the center of the 

recharge basin. Again, the values of W/[4 α t]1/2 and Rt 

must be determined first. Then, for a given value of x/W, 

where x equals the horizontal distance from the center of 

the recharge basin, one can obtain the value of ho/Rt 

from the correct plot. Multiplying this number by the 

calculated value of Rt results in the rise of the mound, 

Ho, at a distance x from the center of the recharge site. 

The depth to the mound from the soil surface is then the 

difference between the distance to the groundwater 

before recharge and the rise due to the mound. 

To evaluate mounding beneath adjacent basins, 

Figure 3-9 and Figure 3-10 should be used to plot 

groundwater table mounds as functions of distance from 

the center of the plot and time elapsed since initiation of 

wastewater application. Then, critical mounding times 

should be determined, such as when adjacent or 

relatively close basins are being flooded, and the 

mounding curves of each basin at these times should be 

superimposed. Additional discussions on groundwater 

mounding and predicting mounds is included in 

reference (Bouwer, 1999) (Bouwer et al., 1999). At sites 

where drainage is critical because of severe land 

limitations or extremely high groundwater tables, the 

engineer should use the approach described in 

reference (Nielson et al., 1973) to evaluate mounding. 

3-10 
Figure 3-9. Rise and Horizontal Spread of a Mound Below a Square 

Recharge Area (Bianchi and Muckel, 1970). 

Figure 3-10. Rise and Horizontal Spread of Mounds Below a 

Rectangular Recharge Area when L = 2W (Bianchi and Muckel, 1970). 

In areas where both the water table and the 

impermeable layer underneath the aquifer are relatively 

close to the soil surface, it may be possible to avoid the 

complicated mounding analysis by using the following 

procedure: 

1. Assume underdrains are needed and calculate the 

underdrain spacing (Section 3.7). 

2. If the calculated underdrain spacing is `between 15 

and 50 m (50 and 160 ft), underdrains will be 

required and there is no need to verify that the 

mound will reach the soil surface. 

3. If the calculated spacing is less than about 10 m (30 

ft), the loading rate may have to be reduced for the 

project to be economically feasible. 

4. If the calculated spacing is greater than about 50 m 

(160 ft), mounding should be evaluated to determine 

if any underdrains will be necessary. 

This procedure is not appropriate for unconfined or 

relatively deep aquifers. For such aquifers, mounding 

should always be evaluated. 

3.7 Drainage Requirements 

Generally, underdrains are spaced 15 m (50 ft) or 

more apart. Depths of drains vary from 0.9 to 2.4 m (3 

to 8 ft) for SR systems and 2.4 to 4.6 m (8 to 15 ft) for 

SAT systems. In soils with high lateral permeability, the 

underdrains may be as much as 150 m (500 ft) apart. 

The closer the drain spacing is, the more control there 

will be over depth of the groundwater table. The cost of 

drains increases with decreasing drain spacing, so the 

economics of using more drains must be weighed 

against finding a site with deeper groundwater, or less 

vertical restriction to percolation, or using a lower 

application rate. 

One method of determining drain spacing is the 

Hooghhoudt method. The parameters used in the 

method are shown in Figure 3-11. The assumptions 

used in this method are (Luthin, 1978): 

3-11 
Figure 3-11. Parameters Used in Drain Design (Luthin, 1978). 

1. The soil is homogeneous with a lateral permeability, 

K. 

2. The drains are evenly spaced a distance S apart. 

3. The hydraulic gradient at any point is equal to the 

slope of the water table above that point. 

4. Darcy's Law is valid. 

5. An impermeable layer underlies the drain at a depth 

d. 

6. The rate of replenishment (wastewater application 

plus natural precipitation) is Lw + P.

To determine drain placement, the following equation is 

useful (Luthin, 1978): 

( )

0.5

2 4 ⎥

⎦

⎤ ⎢

⎣

⎡ + + = d H

L P

KH S

w

(3-8) 

where S = drain space, m (ft) 

K = horizontal hydraulic conductivity of the soil, m/d (ft/d) 

H = height of the ground water mound above the drains, m 

(ft) 

Lw = annual wastewater loading rate, expressed as a daily

rate, m/d (ft/d) 

P = average annual precipitation rate, expressed as a daily

rate, m/d (ft/d) 

d = distance from drains to underlying impermeable layer, 

m (ft.) 

Once the drain spacing has been calculated, drain 

sizing should be determined. Usually, 150 or 200 mm (6 

or 8 in) drainage laterals are used. The laterals connect 

to a collector main that must be sized to convey the 

expected drainage flow. Drainage laterals should be 

placed so that they will be free flowing; the engineer 

should check drainage hydraulics to determine 

necessary drain slopes. The outlet conditions associated 

with drainage are critical and, once established, must 

not be modified. 

3.8 Field Testing Procedures 

Field testing procedures for measuring and estimating 

the infiltration rate and permeability of a soil are 

summarized in this section.

3.8.1 Infiltration Rate 

The infiltration rate of a soil is defined as the rate at 

which water enters the soil from the surface. When the 

soil profile is saturated with negligible ponding above the 

surface, the infiltration rate is equal to the effective 

saturated conductivity of the soil profile. 

Although the measured infiltration rate on a particular 

site may decrease in time due to surface clogging 

phenomena, the subsurface vertical permeability at 

saturation will generally remain constant. Thus, the 

short-term measurement of infiltration serves reasonably 

well as an estimate of the long-term saturated vertical 

permeability if infiltration is measured over a large area. 

The value that is required in land treatment design is 

the long-term acceptance rate of the entire soil surface 

on the proposed site for the actual wastewater effluent to 

be applied. The value that can be measured is only a 

short-term equilibrium acceptance rate for a number of 

particular areas within the overall site. 

There are many potential techniques for measuring 

infiltration including flooding basin, cylinder 

infiltrometers, sprinkler infiltrometers and air-entry 

permeameters. A comparison of these four techniques 

is presented in Table 3-5. In general, the test area and 

the volume of water used should be as large as 

practical. The two main categories of measurement 

techniques are those involving flooding (ponding over 

the soil surface) and rainfall simulators (sprinkling 

infiltrometer). The flooding type of infiltrometer supplies 

water to the soil without impact, whereas the sprinkler 

infiltrometer provides an impact similar to that of natural 

rain. Flooding infiltrometers are easier to operate than 

sprinkling infiltrometers, but they almost always give 

higher equilibrium infiltration rates. The sprinkler test is 

especially useful for agricultural SR operations. As 

discussed previously, soil sorting and surface sealing 

can occur with some soils and a sprinkler test will 

evaluate the possibility. Sprinkler tests are not really 

needed for grassed or forested sites or where surface 

application of wastewater is anticipated. 

3-12 
Because the basic intent of all these tests is to define 

the saturated vertical hydraulic conductivity of the soil 

(Kv), and since wastewater will typically be "clean" after 

a few inches of travel, it is usually acceptable to use 

clean water for these tests. There are exceptions, and 

the actual wastewater should be used when: 

1. High suspended solids or algae are expected in 

effluents used for SAT. 

2. Industrial effluents with significantly different pH or 

ionic composition than the soil and soil water. 

3. Effluents that will contain toxic or hazardous 

materials with potential for reaction with the soil 

components. 

Basin Tests 

All infiltration tests should always be run at the actual 

locations and depths that will be used for the operational 

system. This is especially important for SAT systems. 

Pilot-scale basin tests are strongly recommended. 

These should be at least 9.3 m2

 (100 ft2) in area, located 

in the same soil zone that will be used in the full-scale 

system. Construction of the test basin should be done 

with the same techniques that will be employed full 

scale. The test basin should then be operated for 

several weeks using the same wet and dry cycles that 

are planned for full scale. A typical small-scale pilot test 

basin is illustrated in Figure 3-12. 

The number of test basins required will depend on the 

system size and the uniformity of the soils and 

topography. One will serve for relatively small systems 

with uniform soils. In larger systems a separate basin 

should be used for every major soil type, which may 

require one basin for every 2-4 ha (5-10 acres) of total 

system area. When extremely variable conditions are 

encountered, the test basin should be full sized (0.4 to 

1.2 ha or 1 to 3 acres) to insure reliability. If successful, 

it can then be incorporated into the operational system. 

A smaller-scale basin type test has been developed by 

the U.S. Army Corps of Engineers (Abele et al., 1980). 

The purpose was to have a reproducible procedure with 

a larger surface area and zone of influence than existing 

infiltrometers and permeameters. The test facility prior 

to flooding (note the cylinder infiltrometer in the right 

foreground) is illustrated in Figure 3-13. The metal ring is 

aluminum flashing and is 3 m (10 ft) in diameter. 

Installation details are provided in Figure 3-14 and 

Figure 3-15. 

Table 3-5. Comparison of Infiltration Measurement Techniques 

Measurement 

technique 

3.8.2 Water use 

per test, L 

Time per 

test, h 

Equipment needed Comments 

3.8.3 Flooding 

basin 

2,000-10,000 4-12 Backhoe or blade Tensiometers may be used 

Cylinder infiltrometer 400-700 1-6 Cylinder or earthen berm Should use large-diameter cylinders (3 ft diameter) 

(1 meter) 

Sprinkler infiltrometer 1,000-1,200 1.5-3 Pump, pressure tank 

sprinkler, cans 

For sprinkler applications, soil should be at field 

capacity before test 

Air entry permeameter 

(AEP) 

10 0.5-1 AEP apparatus, 

standpipe with reservoir 

Measures vertical hydraulic conductivity. If used to 

measure rates of several different soil layers, rate is 

harmonic mean of conductivities from all soil layers 

Figure 3-12. Small-scale Pilot Test Basin (Crites, et. al., 2000). Figure 3-13. U.S. Army Corps of Engineers (USACE) Basin Test. 

3-13 
F

Figure 3-14. Grove Preparation for USACE Test. 

Figure 3-15. Grove Preparation for USACE Test. 

Tensiometers are used in the central part of the test 

area to insure that saturated conditions prevail during 

the test period. One should be placed in each soil 

horizon. In soils lacking well-developed horizons, a 

uniform spacing down to about 0.6 m (2 ft) will be 

suitable. Following installation and calibration of the 

tensiometers, a few preliminary flooding events are 

executed to achieve saturation. Evidence of saturation is 

the reduction of tensiometer readings to near zero 

through the upper soil profile. Then a final flooding event 

is monitored to derive a cumulative intake versus time 

curve.

Typical test results are illustrated in Figure 3-16. The 

"limiting" value of 6.35 mm/h (0.25 in./h) was selected for 

design in this case. 

Figure 3-16. Typical Test Results, USACE Infiltration Test. 

Cylinder Infiltrometers 

The equipment setup for a test is shown in 

Figure 3-17. To run a test, a metal cylinder is carefully 

driven or pushed into the soil to a depth of about 100 to 

150 mm (4 to 6 in). Cylinders from 150 to 350 mm (6 to 

14 in) diameter have generally been used in practice, 

with lengths of about 250 to 300 mm (10 to 12 in). 

Lateral flow is minimized by means of "buffer zone" 

surrounding the central ring. The buffer zone is 

commonly provided by another cylinder 400 to 750 mm 

(16 to 30 in) diameter, driven to a depth of 50 to 100 mm 

(2 to 4 in), and kept partially full of water during the time 

of infiltration. This particular mode of making 

measurements has come to be known as the doublecylinder or double-ring infiltrometer method. Care must 

be taken to maintain the water levels in the inner and 

outer cylinders at the same level during the 

measurements. Alternately, buffer zones are provided by 

diking the area around the intake cylinder with low (75 to 

100 mm or 3 to 4 in) earthen dikes. 

3-14 
Figure 3-17. Test Installation for Cylinder Infiltrometer. 

If the cylinder is installed properly and the test 

carefully performed, the technique should produce data 

that at least approximate the vertical component of flow. 

In most soils, as the wetting front advances downward 

through the profile, the infiltration rate will decrease with 

time and approach a steady-state value asymptotically. 

This may require as little as 20 to 30 minutes in some 

soils and many hours in others. 

Test results can be plotted as shown on Figure 3-16

and design values derived. The procedure is relatively 

simple and quick and uses a small amount of water. The 

test has been commonly used for some time in 

agricultural projects and is familiar to most field 

investigation firms. However, the small size of the test 

limits the zone of influence. A large number of tests 

would be required for most situations. An ASTM 

standard exists for the test. 

Air Entry Permeameters (AEP) 

This device, developed by Dr. Herman Bouwer 

(Bouwer, 1978) has been successfully used for the 

investigation and design of land treatment systems. A 

sketch of the device is shown on Figure 3-18 and 

Figure 3-19 illustrates the device in use. The cylinder is 

steel, about 10 in (250 mm) in diameter and about 5 in 

(125 mm) deep. Operating instructions for the unit are: 

1. The cylinder is driven into the ground to a depth of 3 

to 4 in (75 to 100 mm) (a cylinder driver with sliding 

weight is used for this purpose). 

2. Using a section of 1-in x 2-in (25 to 50 mm) lumber 

and a hammer, the soil along the inner perimeter of 

the cylinder is packed down and against the cylinder 

wall to insure a good bond between the cylinder and 

the soil. In loose or cracked soil, compacting around 

the outside of the cylinder may also be necessary. 

3. In case of a bare soil surface, the soil is covered 

with a 12.5 to 25 mm (1/2- to 1-in) layer of coarse, 

clean sand. A disk or similar object is placed on the 

sand in the center of the cylinder to break the water 

stream from the supply pipe. 

4. The surface of the foam rubber gasket is cleaned 

and a thin coat of grease is applied. 

Figure 3-18. Definition Sketch for Air Entry Permeameter. 

Figure 3-19. Air Entry Permeameter in Use (from H. Bouwer). 

3-15 
5. The lid-assembly with the air valve open and the 

gauge and supply valves closed is placed on the 

cylinder. The gauge should be properly primed and 

air bubbles should not be present in the tubing 

connecting the gauge to the cylinder. A round 

bubble-level is placed on the lid to determine the 

highest point. The lid assembly is then rotated so 

that the air escape valve is at the highest point. 

6. The lid is fastened with four small C-clamps or 

welder's vice-grip pliers until it rests firmly on the rim 

of the metal cylinder. Lead weights are placed on 

the lid to offset the upward hydrostatic force when 

the supply valve is open. 

7. The plastic reservoir at the top of the galvanized 

pipe is filled with water and the air in the pipe is 

allowed to escape. The supply valve at the bottom of 

the galvanized pipe is opened while maintaining the 

water supply to the plastic reservoir. When the 

water has driven out the air from inside the cylinder, 

the air valve is closed. 

8. The vacuum gauge is removed from the holder and 

lifted to about the water level in the plastic reservoir. 

The gauge valve at the plastic lid is opened, which 

causes the needle on the gauge to go to zero. 

Tilting the gauge will then reset the memory pointer 

to zero. The gauge valve is closed and the gauge is 

replaced on the gauge holder. 

9. Time and water level readings are taken so that the 

rate of fall of the water level in the reservoir, dH/dt, 

(just before closing the supply valve) can be 

calculated. 

10. When the depth of the wet front is expected to be at 

about 100 mm (4 in) the supply valve is closed. 

Experience will tell how much or how long water 

needs to be applied to achieve this depth. 

11. The gauge valve is opened. When the gauge 

indicates approximately atmospheric pressure inside 

the cylinder, the weights are removed from the 

plastic lid. 

12. When the memory pointer has lost contact with the 

gauge needle, minimum pressure has occurred. As 

soon as loss of contact is observed, the memory 

pointer is read, the gauge valve is closed, and the 

air escape valve is opened. The lid assembly is 

removed and the depth of the wet front is measured. 

This can be done by pushing a quarter-inch rod into 

the soil and observing the depth where the 

penetration resistance is considerably increased. 

Another way is to quickly remove any remaining 

water in the cylinder, taking the cylinder out of the 

soil, and digging with a spade to visually determine 

the position of the wet front. Dyes and electricconductivity probes may also offer possibilities for 

wet-front detection. To facilitate accurate 

assessment of the depth of the wet front, the soil 

should not be too wet at the time of the test. 

13. Calculate Pa as: 

Pa = Pmin + G + L (3-9)

Where 

Pa = air entry value of soil in inches of water 

Pmin = minimum pressure head in inches water as determined by

maximum reading on the vacuum gage 

G = height of gage above soil surface, in. 

L = depth of wet front, in. 

If, for example, the maximum gage reading corresponds to -33 in. 

water and L + G = 18 in., Pa is calculated as -14 in. water. 

14. Calculate the water entry (air exit) value Pw as 0.5 

Pa.

15. Calculate the saturated hydraulic conductivity Ks as 

( )

t a c

r

s H L P R

dH dt LR K

0.5

2 / 2

+ − = (3-10)

Where 

dH/dt = rate of fall of water level in reservoir just before closing 

supply valve. 

Ht = height above soil surface of water level in reservoir when 

supply valve is closed. 

Rr = radius of plastic reservoir. 

Rc = radius of permeameter cylinder 

16. Calculate K at zero soil water pressure head for 

sorption as 0.5 Ks. 

Note: For most agricultural and coarse-textured soils, 

Pa numerically will be small compared to Ht. Under those 

conditions, Pa is not important and can be taken as zero 

(or as some arbitrary small value, for example - 4 in.) in 

the above equation. This greatly simplifies the 

equipment and the field procedure, since the vacuum 

gage and the measurement of minimum pressure inside 

the cylinder are then not needed. 

The AEP test takes less time and less water than 

cylinder infiltrometers, and the simplicity of the test 

permits a very large number of repetitions with very 

small quantities of water. However, the small size of the 

apparatus limits the zone of influence so the results are 

only valid for the few inches below the test surface. 

Several repetitions with depth will be necessary to 

characterize the soil profile at a particular location. A 

successful approach is to dig a test pit with a backhoe 

with one end of the pit inclined to the surface. Benches 

can then be excavated by hand in the different horizons 

or at depths of choice and an AEP test run on each 

3-16 
"step." The bench should be about 3 ft wide. The other 

walls of the test pit can then be used for the routine soils 

investigations. A combination of test basins on the site, 

supplemented by AEP tests in the remaining areas is 

recommended as the investigation techniques for most 

projects. 

3.8.2 Horizontal Hydraulic Conductivity 

The groundwater flow path will be parallel to the 

hydraulic gradient. In the general situation this is 

essentially horizontal, except immediately beneath an 

application zone when mounding occurs. The flow of 

water will be vertical at the center of the mound and at 

an angle parallel to the gradient at the edge of the 

mound. The capability of the soil at the edge of the 

mound to transmit the applied flow in a lateral direction 

in time. The determination of this horizontal conductivity 

is therefore essential, particularly for SAT systems. 

Most soils are not homogeneous, but rather are at 

least somewhat stratified, reflecting deposition or 

consolidation patterns. There are often thin layers or 

lenses of fine textured material that will impede vertical 

flow between highly permeable layers of soil. As a result 

the potential for flow in the horizontal direction is often 

many times greater than in the vertical direction. In 

situations with shallow groundwater or where mounding 

or lateral flow are a significant factor for design, it is 

necessary to measure the horizontal conductivity (Kh) in 

the field. 

Auger Hole Test 

The auger hole test is the most common and most 

useful of the field tests available for determining 

horizontal hydraulic conductivity. A hole is bored to a 

certain distance below the water table. The water in the 

hole is then pumped out. The rate at which the hole 

refills is a function of the hydraulic conductivity of the 

soil, and the geometry of the hole. It is possible to 

calculate the Kh with the measured rate of rise and the 

other factors defined on Figure 3-20. The general set up 

for the test is shown in Figure 3-21. The equipment 

required includes a suitable pump, an auger, a 

stopwatch, and a device for measuring the depth of 

water in the hole as it rises. In unstable soils a 

perforated casing or well screens will be necessary to 

maintain an open hole. The Bureau of Reclamation uses 

100 mm (4 in) thin wall pipe with 60, 1/8 in by 1-in slots 

per ft of length. 

Figure 3-20. Definition Sketch for Auger Hole Technique. 

Figure 3-21. Equipment Setup for Auger Hole Test. 

The determination of hydraulic conductivity is affected 

by the location of the barrier or lower impermeable layer. 

In the case where the barrier is at the bottom of the hole, 

Kh can be defined as (terms as shown on): 

( )

⎟

⎠

⎞ ⎜

⎝

⎛

Δ

Δ

⎟

⎠

⎞ ⎜

⎝

⎛ + −

= t

y

y H

y H r

r Kh

10 2

15,000 2 (3-11)

Where 

Kh = horizontal hydraulic conductivity, m/d 

r = radius of hole, m 

H = initial depth of water in hole, m 

H = (D-B) 

A = depth (from reference point) to water after pumpout, m 

R = depth (from reference point) to water after refill, m 

3-17 
y = average depth to water in hole during the refill period, m 

y = (R-B) - 1/2Δy 

Δy = raise of water level in the timed interval Δt, m 

Δy = (A-R) 

Δt = time required to give Δy, s

The more usual case is when the impermeable layer is 

some distance below the bottom of the hole; in this case 

Kh is given by: 

( )

⎟

⎠

⎞ ⎜

⎝

⎛

Δ

Δ

⎟

⎠

⎞ ⎜

⎝

⎛ + −

= t

y

y H

y H r

r Kh

20 2

16,667 2 (3-12)

All terms as defined previously. 

This equation is only valid when: 

2 1⁄2 in < 2r < 5 1⁄2 in 

10 in < H < 80 in 

y > 0.2H 

G > H 

y < 1⁄4 H - (D - A) 

Measurement of horizontal hydraulic conductivity may 

still be necessary in the absence of a groundwater table. 

An example might be the presence of fragipan or other 

hard pan layers at shallow depth. These would restrict 

vertical flow and might result in unacceptable mounding 

unless the horizontal conductivity of the overlying 

material is suitable. The shallow well pump-in test 

described in U.S. Department of the Interior (1978) can 

be used in such cases. In effect, it is the reverse of the 

auger hole test described above. 

3.9 References 

Abele, G., H. McKim, B. Brockett, and J. Ingersol (1980) 

Infiltration Characteristics of Soils at Apple Valley, 

MN. Clarence Cannon Dam, MO., and Deer Creek, 

OH., Land Treatment Sites. 

Bianchi, W.C. and C. Muckel (1970) Ground-Water 

Recharge Hydrology. U.S. Department of 

Agriculture, Agricultural Research Service. ARS 

41161. December. 

Bouwer, H. (1999) Artificial Recharge of Groundwater: 

Systems, Design, and Management. 

In: Hydraulic Design Handbook. Mays, L.W. (ed.). 

Mc Graw-Hill, New York, NY. 

Bouwer, H., J.T. Back, and J.M. Oliver (1999) 

Predicting Infiltration and Ground-Water Mounds for 

Artificial Recharge. Journal of Hydrologic 

Engineering. October. 

Bouwer, H. (1978) Groundwater Hydrology, New York: 

McGraw-Hill Book Co. 

Bouwer, H. (1969) Planning and Interpreting Soil 

Permeability Measurement. Journal Irrigation and 

Drainage Div. ASCE 28:391-402. 

Brady, N. C. and R.R. Weil (2002) The Nature and 

Properties of Soils, Thirteenth Edition. Prentice Hall. 

Upper Saddle River, NJ. 

Childs, E.C. (1969) An Introduction to the Physical 

Basis of Soil Water Phemomena. John Wiley & 

Sons, Ltd. London. 

Crites, R. W., R. K. Bastian, and S. C. Reed. 2000. Land 

Treatment System for Municipal and Industrial 

Wastes. McGraw-Hill, New York, NY. 

Duke, H.R. (1972) Capillary Properties of Soils – 

Influence upon Specific Yield. Transcripts of the 

American Society of Agricultural Engineers. 15:688-

691. 

Freeze, R.A., and J.A. Cherry (1979) Groundwater. 

Prentice-Hall. Englewood Cliffs, NJ. 

Hansen, V.E., O.W. Israelson and G.E. Stringham 

(1980) Irrigation Principles and Practices, Fourth 

Edition. John Wiley & Sons, New York. 

Jarrett, A.R. and D.D.Fritton (1978) Effect of Entrapped 

Soil Air on Infiltration. Transactions American 

Society of Agricultural Engineers. 21:901-906. 

Luthin, J. N. (1978) Drainage Engineering, Third 

Edition, Water Science and Civil Engineering 

Department, University of California - Davis, Robert 

E. Krieger Publishing Company, Huntington, NY. 

Nielson, D.R., J.W. Biggar and K.T. Erb (1973) Spatial 

Variability of Field-Measured Soil-Water Properties. 

Hilgardia. 42:215-259. 

O’Neal, A.M. (1952) A Key for Evaluating Soil 

Permeability by Means of Certain Field Clues. In: 

Proceedings Soil Science Society of America. 

16:312-315. 

3-18 
Pair, C.H. et al. (1975) Sprinkler Irrigation, Fourth 

Edition. Sprinkler Irrigation Association, Silver 

Spring, MD. 

Parr, J.F. and A.R. Bertran (1960) Water Infiltration into 

Soils. In: Advances in Agronomy, Norman, A.G. 

(Ed.) Academic Press, New York; pp. 311-363. 

Richards, L.A (1965) Physical Condition of Water in 

Soil. In: Methods of Soil Analysis. Part 1, 

Agronomy 9. Black, C.A. (ed.). American Society of 

Agronomy, Inc., Madison, WI. pp. 131-136. 

Rogowski, A.S. (1972) Watershed Physics: Soil 

Variability Criteria. Water Resources Research 

8:1015-1023. 

Sparks, D. L (1995) Environmental Soil Chemistry. 

Academic Press. San Diego. 

Sposito, G. (1989) The Chemistry of Soils. Oxford 

University Press, Inc., New York. 

Taylor, S.A. and Q.L. Ashcroft (1972) Physical 

Edaphology. W.H. Freeman & Co., San Francisco. 

Todd, D.K. (1964) Groundwater. In: Handbook of 

Applied Hydrology. Chow, V.T. (Ed.) McGraw-Hill 

Book Co., New York. 

U.S. Department of the Interior, Bureau of Reclamation 

(1978) Drainage Manual, 1st edition. 

US EPA (1998) Estimation of Infiltration Rate in the 

Vadose Zone: Compilation of Simple Mathematical 

Models. Volume I. U.S. Environmental Protection 

Agency, Subsurface Protection and Remediation 

Division, National Risk Management Research 

Laboratory, Ada, OK 74820. EPA/600/R-97/128a. 

US EPA. (1998) Estimation of Infiltration Rate in the 

Vadose Zone: Application of Selected Mathematical 

Models, Volume II. National Risk Management 

Research Laboratory, US EPA, Ada. OK. 

EPA/600/R-97/128b. 

Withers, B. and S. Vipond (1987) Irrigation Design and 

Practice, Second Edition. Cornell University Press, 

Ithaca, NY. 

3-19 
Chapter 4 

Role of Plants in Land Treatment 

In this chapter the characteristics of crops that affect 

their use in land treatment -- water use and tolerance,

nutrient uptake, and toxicity concerns -- are described.

Guidance on crop selection for each land treatment 

process is provided. Crop management aspects of

agricultural, silivicultural, and horticultural crops are also 

discussed. 

4.1 Vegetation in Land Treatment 

The primary role of vegetation in a land treatment 

system is to recycle nutrients in the waste into a 

harvestable crop, but vegetation plays a distinct role in 

each land treatment process. SR also offers an

opportunity for economic return by sale of harvested

crops. In OF vegetation is the support media for 

biological activity and is needed for erosion protection. 

The grass in OF systems also removes significant

nutrients and slows the flow of wastewater so that

suspended solids can be filtered and settled out of the 

flow stream. Vegetation is not typically part of SAT 

systems. It can play a role in stabilization of the soil

matrix and can maintain long-term infiltration rates, but 

does not appear to have a major impact on treatment

performance for SAT systems.

Plant uptake is not the only form of nutrient 

transformation or removal from the soil-plant systems 

utilized in land treatment, but plant growth does impact

all mechanisms either directly or indirectly. Municipal 

effluent often has an insufficient carbon to nitrogen ratio 

to support high rates of denitrification. Plant roots can

supply a source of degradable carbon that can assist

denitrification (Meyer, 2002). 

4.2 Evapotranspiration 

Evapotranspiration (ET) is the sum of plant

transpiration and evaporation from plant and soil

surfaces. As commonly defined, ET does not include

other components of evaporation or losses such as: 

• Deep percolation 

• Wind drift 

• Droplet evaporation in the air 

• Run-off 

Sophisticated computer models separate transpiration 

and evaporation components of ET. However, more sitespecific data for reference ET are available. Crop ET

based on reference ET adjusted for a specific crop is 

sufficiently accurate for water balances and irrigation 

scheduling. 

4.2.1 Transpiration 

Transpiration is the water that passes from the soil into 

the plant roots. Less than 1 percent of the water taken

up by plants is actually consumed in the metabolic 

activity of the plant (Rosenberg, 1974) the remainder 

passes through the plant and leaves by evaporation 

through the stomata. 

The drier and hotter the air, the higher the transpiration

rate. The drier the soil, the slower the transpiration, 

because the water is held tighter to the soil and plants 

adjust the stomata to conserve liquid, reducing growth. 

A specific plant variety will have a genetic potential to 

transpire a certain quantity during the growing season. 

The transpiration on a given day depends on the plant 

growth stage, weather conditions, the availability of 

water, and general plant health. Non-plant based models 

used to calculate ET assume transpiration is not 

impacted by plant health or water stress. 

4.2.2 Evaporation 

Evaporation s water converted from liquid to vapor that

does not pass through the plant. Evaporation may occur 

from wet soil or plant surfaces. When plants are young,

a large portion of ET is evaporation from the soil surface. 

When plants achieve 70 to 80 percent canopy cover, soil

evaporation will increase ET by only 10 to 25 percent. 

The increase of ET due to soil evaporation only occurs 

immediately after irrigation when the soil surface is wet

(stage 1) as illustrated in Figure 4-1. Actual evaporation

(E) drops off with time, relative to potential evaporation

(Ep) stage 2 in Figure 4-1.

Figure 4-1. Evaporation from Bare Soil which was Initially Wet 

(Hanks , 1992).

Soil evaporation is increased by maintaining moist 

surface conditions. Surface or sprinkler irrigation losses

are similar to drip irrigation on a wetted surface area

4-1 
basis. However, with drip irrigation a small percentage 

of the surface is wet all the time compared to surface

and sprinkler irrigation that has a large percentage of the

area wet for only a small amount of time. The exceptions 

are sub-surface drip, which has very little evaporation, 

and surface sprinklers with small frequent sprinkler 

applications, which can evaporate up to 100 percent of 

the applied water. When applications are so small that 

only the plant canopy and soil surface is wetted nearly 

all the water is lost to evaporation without any infiltration

into the soil. Research is inconclusive whether water 

evaporated from the plant surface reduces plant 

transpiration requirements. 

4.2.3 Calculating ET 

Crop evapotranspiration (ETc) is commonly estimated 

based on a rigorously defined reference crop

evapotranspiration (ETo) and a crop coefficient (Kc) 

representing the specific crop and growth stage. 

ETc = ETo·Kc (4-1) 

Crop ETc allows for the calculation of required

irrigation water. The difference between applied water 

and ETc is equal to the amount of deep percolation. 

Table 4-1 contains a range of expected ETc of a variety 

of crops throughout the United States. Further 

discussion of ETo and Kc is included in the subsequent 

subsections.

Table 4-1. Range of Seasonal Crop Evapotranspiration 

Crop ETc, in Crop ETc, in 

Alfalfa 24-74 Grass 18-45 

Avocado 26-40 Oats 16-25 

Barley 15-25 Potatoes 18-24 

Beans 10-20 Rice 20-45 

Clover 34-44 Sorghum 12-26 

Corn 15-25 Soybeans 16-32 

Cotton 22-37 Sugar beets 18-33 

Deciduous trees 21-41 Sugarcane 39-59 

Grains (small) 12-18 Vegetables 10-20 

Grapes 16-35 Wheat 16-28 

In humid regions, ETo is sufficiently accurate to predict 

ET for perennial full cover crops. Table 4-2 contains 

monthly estimated reference ET values for various 

humid and subhumid climates. In areas such as the San

Joaquin Valley of California monthly ET rarely varies

more than 10 percent. 

Table 4-3 shows an example of alfalfa and grass ETo

with the corresponding evapotranspiration rates of

various crops. 

4.2.4 Reference ET 

Reference ET (ETo) is a term used to describe the 

evapotranspiration rate from a known surface, such as 

grass or alfalfa (alfalfa ETo normal exceeds grass ETo

by 0 to 30 percent). ETo is expressed in either

centimeters or inches. The ETo for an average year is 

referred to as normal year ETo. 

Rather than measuring the water consumption in the

reference crop, ETo is often calculated from weather 

data or pan evaporation. Pan evaporation, as defined by

the U.S. Weather Bureau’s Class A pan, is commonly 

used for sizing pond systems and therefore, is often

available to engineers designing land application

systems. Pans store more heat than crops and 

consequently result in more evaporation. The pan 

evaporation is normally higher than ET (10 percent for 

humid conditions and 15 percent for dry conditions).

The coefficients in Table 4-4 can be used to convert pan 

evaporation to ETo using Equation 4-2.

ETo = Kpan · Epan (4-2) 

Where, ETo = reference evapotranspiration 

 Kpan = pan coefficient (Table 4-4) 

 Epan = pan evaporation 

Evaporation pans are difficult to maintain and 

numerous weather networks now gather ET data with

models that have been developed over the last 50 years. 

The evapotranspiration models are based on different 

Table 4-2. Selected Examples of Monthly Normal ETo (US EPA, 1981)

Centimeters/Month (Inches/Month) Month Paris, TX Central, MO Jonesboro, GA Seabrook, NJ Hanover, NH Brevard, NC 

Jan 0.6 0.3 0.5 0.1 0.0 0.1 

Feb 0.6 0.5 0.5 0.1 0.0 0.1 

Mar 1.4 1.2 1.2 0.8 0.0 0.8 

Apr 2.7 2.6 2.3 1.6 1.2 1.8 

May 4.0 4.3 4.4 3.0 3.3 3.0 

June 5.9 5.8 5.9 4.6 5.2 4.1 

July 6.4 6.8 6.3 5.6 5.5 4.6 

Aug 6.5 6.1 6.0 5.4 4.8 4.2 

Sept 3.9 4.1 4.4 4.0 3.0 3.0 

Oct 2.6 2.5 2.3 2.0 1.6 1.8 

Nov 1.1 1.0 1.0 0.8 0.1 0.6 

Dec 0.6 0.4 0.5 0.1 0.0 0.1 

Annual 36.3 35.6 35.3 28.1 24.7 24.2 

4-2 
Table 4-3. Example Evapotranspiration Values for Southern San Joaquin Valley of California (Burt, 1995) 

Evapotranspiration Rate, Millimeters/Month (Inches/Month) 

Month 

ETo, 

alfalfa 

ETo, 

grass 

Alfalfa 

Hay Cotton Citrus 

Deciduous 

orchard w/o 

cover drop 

Deciduous 

orchard w/ 

cover drop 

Grape 

Vines Small Grains 

January 0.88 0.69 0.73 0.85 0.68 0.41 

February 2.41 1.97 1.99 1.52 1.98 1.99 

March 3.75 3.13 3.11 2.32 1.49 3.33 0.05 3.92 

April 6.19 5.24 5.11 0.48 3.75 3.63 5.89 1.16 6.37 

May 7.98 6.78 6.71 2.06 4.85 5.58 8.10 4.13 6.24 

June 9.03 7.65 7.32 6.68 5.06 6.83 9.08 6.00 0.63 

July 9.32 7.92 7.80 10.03 5.27 7.59 9.58 6.72 

August 8.44 7.14 6.92 8.76 4.73 6.85 8.41 5.96 

September 6.03 5.08 5.16 4.47 3.57 4.87 5.89 3.30 

October 4.55 3.75 3.63 0.77 2.69 3.02 3.90 1.22 

November 1.92 1.52 1.61 1.18 0.07 1.58 0.14 

December 0.71 0.55 0.60 0.38 0.50 0.09 

TOTAL 61.2 51.4 50.7 33.3 35.9 40.8 58.9 28.7 19.8 

Table 4-4. Pan Coefficient for Class A Evaporation Pans Placed in a 

Reference Crop Area (Doorenbos and Pruitt, 1977)

Wind, km/h (mi/h) Relative Humidity, % 

Low, <40 Medium, 40-70 High, >70 

Light, <4.5 0.75 0.85 0.85 

Moderate, 4.5 0.70 0.80 0.80 

Strong, 11-18 0.65 0.70 0.75 

Very Strong, >18 0.55 0.60 0.65 

climatic variables. Relationships were often subject to

rigorous local calibrations, but proved to have limited

global validity. Testing the accuracy of the methods 

under a new set of conditions is laborious, timeconsuming and costly, and yet evapotranspiration data 

are frequently needed at short notice for project planning

or irrigation scheduling design. 

In an effort to meet the need for reliable

evapotranspiration data, the Food and Agriculture 

Organization of the United Nations (FAO) published

Irrigation and Drainage Paper No. 24 (Doorenbos and

Pruitt, 1977). The paper presented four methods with 

different data needs to calculate the reference crop

evapotranspiration (ETo): the Blaney-Criddle, radiation, 

modified Penman, Penman-Monteith and pan

evaporation methods. The modified Penman method 

was considered to offer the best results with minimum 

possible error in relation to a living grass reference crop.

The Blaney-Criddle method was recommended when 

only mean air temperature was available (Jensen et al., 

1973). 

The methods reviewed by FAO were calibrated for tenday or monthly calculations. The Blaney-Criddle method 

was recommended for periods of one month or longer.

Proliferation of remote sensing of climatic data and the 

more accurate assessment of crop water use has 

revealed weaknesses in the methodologies (Allen et al., 

1998). Deviations from computed to observed values 

were often found to exceed ranges indicated by FAO 

Paper 24. The modified Penman was frequently found to 

overestimate ETo, even by up to 20 percent for low 

evaporative conditions. The FAO published Irrigation

and Drainage Paper No. 56 (Allen et al., 1998) and

recommend the FAO Penman-Monteith method as the

sole ETo method for determining reference

evapotranspiration. The FAO Penman-Monteith equation

with 24-hour data produces accurate results (Allen et al., 

1998). The method, the derivation, the required

meteorological data and the corresponding definition of 

the reference surface are described in FAO paper 56.

While the Blaney-Criddle is not recommended for 

irrigation scheduling it has sufficient accuracy for initial 

planning. The Arizona Department of Environmental 

Quality uses a water reuse model based on BlaneyCriddle. 

Unless the site is remote, seasonal ETo data are

normally available from the local agricultural extension

offices, Land Grant Universities, or agricultural research

stations. The California Irrigation Management 

Information System (CIMIS) operates over 100 weather 

stations. CIMIS uses the Modified Penman to define

normal monthly ETo and daily ETo. Daily ETo is 

available for download via the internet the following 

morning. The state climatalogist often will be aware of 

such networks. A list of state climatology offices is 

included in Appendix A. 

4.2.5 Crop Coefficients 

Crop coefficients (Kc) are determined by the ratio of 

the measured ETc and ETo. The derived Kc is a 

dimensionless number (usually between 0.1 and 1.2) 

that is multiplied by the ETo value to arrive at a crop ET

(ETc) estimate. Because of the method of calculation,

4-3 
Kc is dependent on the reference ETo used in the 

calculation. Crop coefficients vary by crop, stage of

growth, and by climate. Care should be used to match

the Kc to the proper ETo. Local agricultural extension 

offices have Kc values for crops commonly grown in

their area. 

Crop coefficients change based on the growth stage of

the plant and are commonly divided into four growth 

stages. Table 4-5 shows the estimated length of growth

stages for various crops.

1 Initial growth stage (10 percent ground cover) 

2 Crop-development (up to 80 percent groundcover) 

3 Midseason stage (effective full groundcover) 

4 Late-season stage (full maturity until harvest) 

If local crop coefficients are not available, estimates 

from Table 4-6 and Table 4-7 can be used. The

reference ETo in Tables 4-6 and 4-7 is calculated from 

FAO modified Penman-Montieth. Coefficients for annual

crops (row crops) will vary widely through the season, 

with a small coefficient in the early stages of the crop 

(when the crop is just a seedling) to a large coefficient 

when the crop is at full cover (the soil completely 

shaded). Orchards with cover crops between tree rows 

will have larger coefficients than orchards without cover

crops.

4.3 Plant Selection 

Varieties (cultivars) of major grain, food, and fiber 

crops are bred specifically for different regions of the 

United States because of differences in growing 

seasons, moisture availability, soil type, winter

temperatures, and incidence of plant diseases. 

Otherregional issues include infrastructure for postharvest processing and demand for harvested products.

A regional approach, therefore, is recommended for 

selection and management of vegetation at land

treatment sites (Jensen et al., 1973). One of the easiest

methods for determining regional compatibility is to 

investigate the surrounding plant systems. Once regional

issues are considered, the final criteria should be based 

Table 4-6. Crop Coefficient, Kc, for Midseason and Late Season 

Conditions (Doorenbos and Pruitt, 1977) 

Crop Crop stage Kc Humida Kc Dryb

Alfalfac 1-4 0.85 0.95 

Barley 3 1.05 1.15 

4 0.25 0.20 

Clover 1-4 1.00 1.05 

Corn 3 1.05 1.15 

4 0.55 0.60 

Cotton 3 1.05 1.20 

4 0.65 0.65 

Grain 3 1.05 1.15 

4 0.30 0.25 

Grapes 3 0.80 0.90 

4 0.65 0.70 

Oats 3 1.05 1.15 

4 0.25 0.20 

Pasture grass 1-4 0.95 1.00 

Rice 3 1.1 1.25 

Sorghum 3 1.00 1.10 

4 0.50 0.55 

Soybeans 3 1.00 1.10 

4 0.45 0.45 

Sugar beets 3 1.05 1.15 

4 0.90 1.00 

Wheat 3 1.05 1.15 

4 0.25 0.20 a Humidity 70 percent, light wind 0-16 mi/h. b Humidity 20 percent, light wind 0-16 mi/h. c Peak factors are 1.05 for humid conditions and 1.15 for dry conditions. 

on nutrient uptake, compatibility with hydraulic loading 

(quantity and timing), and salt tolerance.

4.3.1 Nutrients 

Historically, EPA Design Manuals have presented 

nutrient management as a simple load per acre

determination. The recommended loading did not

consider the site specific nutrient requirements of a crop.

The description that follows is intended to add a

component of comprehensive nutrient management to 

the EPA guidelines on wastewater irrigation and reuse.

Crop nutrient additions should be based on the

development of a nutrient management plan (NMP). A 

NMP is a pollution prevention plan applied to agricultural 

Table 4-5. Length of Four Crop Growth Stages for Typical Annual Crops (Doorenbos and Pruitt, 1977)

Growth Stage (Days) 

Crop 1 2 3 4 

Barley 15 20-30 50-65 30-40 

Corn 20-30 35-50 40-60 30-40 

Cotton 30 50 55-60 45-55 

Grain, small 20-25 30-35 60-65 40 

Sorghum 20 30-35 40-45 30 

Soybeans 20 30-35 60 25 

Sugar beets 25-45 35-60 50-80 30-50 

4-4 
Table 4-5. Crop Coefficient, Kc, for Perennial Forage Crops 

(Doorenbos and Pruitt, 1977)

Condition 

Crop 

Kc 

Humid, light 

to moderate

wind 

Kc 

Dry, light to 

moderate wind 

Alfalfa 

 Minimum 0.50 0.40 

 Mean 0.85 0.95 

 Peak 1.05 1.15 

Grass for hay

 Minimum 0.60 0.55 

 Mean 0.80 0.90 

 Peak 1.05 1.10 

Clover, grass legumes 

 Minimum 0.55 0.55 

 Mean 1.00 1.05 

 Peak 1.05 1.15 

Pasture 

 Minimum 0.55 0.50 

 Mean 0.95 1.00 

 Peak 1.05 1.10 

Kc (minimum) represents conditions just after cutting. 

Kc (mean) represents value between cuttings. 

Kc (peak) represents conditions before harvesting under 

dry soil conditions. Under wet conditions increase values 

by 30 percent. 

and silvicultural operations. The elements of a NMP 

include: 

1. Site maps, including a soil map 

2. Location and description of sensitive resource areas 

3. Soil, plant, water, and organic material sample

analysis results 

4. Current and planned crop production sequence or

crop rotation 

5. Expected yield 

6. Quantification of all nutrient sources available 

7. A nutrient budget for the crop rotation being planned

8. Recommended rates, timing, and method of nutrient 

application 

9. Operation and maintenance of the nutrient

management plan 

Crop yields are measured in units of production.

Typically yields for crops such as soybeans, corn and

other grain crops are expressed in bushels per acre

while forage crop yields are expressed as pounds per 

acre. Bushel is a volumetric unit (30.3 L/bu) and the 

mass per bushel varies with the crop. Yield-based

uptake of N, P, and K for various crops is presented in 

Table 4-8. 

The specific yield expected for a site can be estimated 

from soil information available from the NRCS or from 

local offices of the Cooperative Extension Service.

Responsible farm operators, as a part of normal

production records, will develop accurate measures of 

crop yield. Crop nutrient requirements are based on an 

assessment of realistic yield estimates of the receiver 

site. 

A key component of a comprehensive nutrient 

management plan is to balance the required level of 

those nutrients necessary for plant growth with the 

nutrient loading from the wastewater and subsequent

nutrient losses. Insufficient levels of plant nutrient will

result in deficiencies in crop quality and reduced crop

yield while the over-application of nutrients may result in 

adverse environmental impact. The relationship of 

nutrient availability to yield is non-linear. If the nitrogen 

loading is reduced to half of the expected uptake, it can

not be assumed that half the uptake will result. The 

actual yield and nutrient uptake will be a function of the 

initial soil reserve and resulting nutrient stress. Soil and

tissue analysis are used determine proper nutrient

deficiency and proper nutrient loading. 

Plants require 16 essential nutrients to produce

biomass. Wastewater from municipal, industrial and 

agricultural sources generally contain many of these

essential nutrients. These nutrients should be applied to 

sites at rates to optimize plant production while creating 

no adverse environmental conditions. Nutrient

management efforts must consider all nutrients 

managed on a site including: soil reserves, nutrient

applications from commercial sources and waste 

addition, crop residues, and legume credits. 

Nitrogen, phosphorus, and potassium are considered 

the essential macronutrients and are required at 

moderately high levels to support a healthy crop.

Nitrogen is particularly sensitive because of the potential

for this nutrient to migrate through the root zone of plants 

and to groundwater. Recently regulatory agencies are

beginning to consider phosphorus as a limiting nutrient

because of the potential to exit a site with runoff. Any

wastewater treatment operation should include a nutrient 

management plan that incorporates plans for 

management of nitrogen, phosphorus, and potassium.

Table 4-6. Yield Based N, P, and K Uptake of Various Crops

Percent of Dry Harvested Material Crop Dry Weight lb/bu Typical Yield/acre-yr 

Plant Part N P K 

Grain Crops 

Barley 48 50 bu 

1 Ton straw 

1.82 

0.75 

0.34 

0.11 

0.43 

1.25 

Buckwheat 48 30 bu 

0.5 Tons straw

1.65 

0.78 

0.31 

0.05 

0.45 

2.26 

4-5 
Percent of Dry Harvested Material Crop Dry Weight lb/bu Typical Yield/acre-yr 

Plant Part N P K 

Corn 56 120 bu 

4.5 Tons straw

1.61 

1.11 

0.28 

0.20 

0.40 

1.34 

Oats 32 80 bu 

2 Tons straw

1.95 

0.63 

0.34 

0.16 

20.49 

1.66 

Rice 45 5,500 lb 

2.5 Tons straw

1.39 

0.60 

0.24 

0.09 

0.23 

1.16 

Rye 56 30 bu 

1.5 Tons straw

2.08 

0.50 

0.26 

0.12 

0.49 

0.69 

Sorghum 56 60 bu 

3 Tons straw

1.67 

1.08 

0.36 

0.15 

0.42 

1.31 

Wheat 60 40 bu 

1.5 Tons straw

2.08 

0.67 

0.62 

0.07 

0.52 

0.97 

Oil Crops 

Flax 56 15 bu 

1.75 Tons straw 

4.09 

1.24 

0.55 

0.11 

0.84 

1.75 

Oil palm -- 22,000 lb 

5 Tons fronds & stems 

1.13 

1.07 

0.26 

0.49 

0.16 

1.69 

Peanuts 22-30 2,800 lb 

2.2 Tons vines 

3.60 

2.33 

0.17 

0.24 

0.50 

1.75 

Rapeseed 50 35 bu 

3 Tons straw

3.60 

4.48 

0.79 

0.43 

0.76 

3.37 

Soybeans 60 35 bu 

2 Tons stover 

6.25 

2.25 

0.64 

0.22 

1.90 

1.04 

Sunflower 25 1,100 lb 

4 Tons stover 

3.57 

1.50 

1.71 

0.18 

1.11 

2.92 

Fiber Crops 

Cotton 600 lb. Lint and 

1,000 lb seeds 

burs & stalks 

2.67 

1.75 

0.85 

0.22 

0.83 

1.45 

Pulpwood 98 cords 

bark, branches 

0.12 

0.12 

0.02 

0.02 

0.06 

0.06 

Forage Crops 

Alfalfa 4 tons 2.25 0.22 1.87 

Bahiagrass 3 tons 1.27 0.13 1.73 

Big bluestem 3 tons 0.99 0.85 1.75 

Birdsfoot trefoil 3 tons 2.49 0.22 1.82 

Bluegrass-pasted 2 tons 2.91 0.43 1.95 

Bromegrass 5 tons 1.87 0.21 2.55 

Clover-grass 6 tons 1.52 0.27 1.69 

Dallisgrass 3 tons 1.92 0.20 1.72 

Guineagrass 10 tons 1.25 0.44 1.89 

Bermudagrass 8 tons 1.88 0.19 1.40 

Indiangrass 3 tons 1.00 0.85 1.20 

Lespedeza 3 tons 2.33 0.21 1.06 

Little bluestem 3 tons 1.10 0.85 1.45 

Orchardgrass 6 tons 1.47 0.20 2.16 

Pangolagrass 10 tons 1.30 0.47 1.87 

Paragrass 10.5 tons 0.82 0.39 1.59 

Red clover 2.5 tons 2.00 0.22 1.66 

Reed 

canarygrass 

6.5 tons 1.35 0.18 

Ryegrass 5 tons 1.67 0.27 1.42 

Switchgrass 3 tons 1.15 0.10 1.90 

Tall fescue 3.5 tons 1.97 0.20 2.00 

Timothy 2.5 tons 1.20 0.22 1.58 

Wheatgrass 1 ton 1.42 0.27 2.68 

Forest 

Leaves 0.75 0.06 0.46 

Northern hardwoods 50 tons/harvest 0.20 0.02 0.10 

Douglas fir 76 tons/harvest 0.16 

Fruit Crops 

Apples 12 tons 0.13 0.02 0.16 

Bananas 9,900 lb. 0.19 0.02 0.54 

Cantaloupe 17,500 lb. 0.22 0.09 0.46 

Grapes 12 tons 0.28 0.10 0.50 

Oranges 54,000 lb. 0.20 0.02 0.21 

Peaches 15 tons 0.12 0.03 0.19 

Pineapple 17 tons 0.43 0.35 1.68 

Tomatoes 22 tons 0.30 0.04 0.33 

Silage Crops 

4-6 
Percent of Dry Harvested Material Crop Dry Weight lb/bu Typical Yield/acre-yr 

Plant Part N P K 

Alfalfa haylage (50%dm) 10 wet/5 dry 2.79 0.33 2.32 

Corn silage (35% dm) 20 wet/7 dry 1.10 0.25 1.09 

Forage sorghum (30% dm) 20 wet/6 dry 1.44 0.19 1.02 

Oat haylage (40% dm) 10 wet/4 dry 1.60 0.28 0.94 

Sorghum-sudan (50% dm) 10 wet/5 dry 1.36 0.16 1.45 

Sugar Crops 

Sugarcane 37 tons 0.16 0.04 0.37 

Sugar beets 

Tops 

20 tons 0.20 

0.43 

0.03 

0.04 

0.14 

1.03 

Tobacco 

All types 2,100 lb. 3.75 0.33 4.98 

Turf Grass 

Bluegrass 2 tons 2.91 0.43 1.95 

Bentgrass 2.5 tons 3.10 0.41 2.21 

Bermudagrass 4 tons 1.88 0.19 1.40 

Vegetable Crops 

Bell peppers 9 tons 0.40 0.12 0.49 

Beans, dry 0.5 ton 3.13 0.45 0.86 

Cabbage 20 tons 0.33 0.04 0.27 

Carrots 13 tons 0.19 0.04 0.25 

Cassava 7 tons 0.40 0.13 0.63 

Celery 27 tons 0.17 0.09 0.45 

Cucumbers 10 tons 0.20 0.07 0.33 

Lettuce (heads) 14 tons 0.23 0.08 0.46 

Onions 18 tons 0.30 0.06 0.22 

Peas 1.5 tons 3.68 0.40 0.90 

Potatoes 14.5 tons 0.33 0.06 0.52 

Snap beans 3 tons 0.88 0.26 0.96 

Sweet corn 5.5 tons 0.89 0.24 0.58 

Sweet potatoes 7 tons 0.30 0.04 0.42 

Table beets 15 tons 0.26 0.04 0.28 

Wetland Plants

Cattails 8 tons 1.02 0.18 

Rushes 1 ton 1.67 

Saltgrass 1 ton 1.44 0.27 0.62 

Sedges 0.8 ton 1.79 0.26 

Water hyacinth 3.65 0.87 

Duckweed 3.36 1.00 2.13 

Arrowweed 2.74 

Phragmites 1.83 0.10 0.52 

Treated wastewater contains many essential nutrients, 

but in ratios often inadequate for many plants. The

nutrients often present in treated wastewater include

nitrate nitrogen, ammonium nitrogen, and organic 

nitrogen, organic and inorganic phosphorus, potassium,

and others. Prior to developing a nutrient management

plan, the form of nutrient present in a wastestream must

be determined and specific plans must be developed to 

assure proper utilization. All crops require a balanced

nutrient input: optimum N:P:K ratios are generally 4:1:2. 

If these ratios are not available in wastewater, 

adjustments should be made to correct the imbalances. 

4.3.2 Agricultural Crops 

Common agricultural forage and field crops are

integral to SR process for nitrogen removal. OF systems 

require a perennial close-growing grass crop to support 

microbial populations. Both systems require crops with

low sensitivity to wastewater constituents and minimum 

management requirements.

The highest uptake of nitrogen, phosphorus, and 

potassium can generally be achieved by perennial 

grasses and legumes. It should be recognized that 

whereas legumes normally fix nitrogen from the air, they 

will preferentially take up nitrogen from the soil-water 

solution if it is present. The potential for harvesting 

nutrients with annual crops is generally less than with 

perennials because annuals use only part of the 

available growing season for growth and active uptake. 

Alfalfa removes nitrogen and potassium in larger

quantities and at a deeper rooting depth than most

agricultural crops as shown in Table 4-7. Corn is an 

attractive crop because of the potentially high rate of 

economic return as grain or silage. Intercropping is a

method of expanding the nutrient and hydraulic capacity

of a field corn crop system. A dual system of rye

intercropped with corn to maximize the period of nutrient

uptake was studied in Michigan and Minnesota

(Brockway et al., 1982). For such dual corn-ryegrass 

cropping systems, rye can be seeded in the standing 

corn in August, or after the harvest in September. The

4-7 
growth of rye in the spring, before the corn is planted,

allows the early application of high nitrogen wastewater. 

While planting the corn, a herbicide can be applied in

strips to kill some rye so that the corn can be seeded in 

the killed rows. With the remaining rye absorbing 

nitrogen, less is leached during the early growth of the

corn. Alternatively, forage grasses can be intercropped

with corn. This "no-till" corn management consists of

planting grass in the fall and then applying a herbicide in 

the spring before planting the corn. When the corn 

completes its growth cycle, grass is reseeded. Thus,

cultivation is reduced; water use is maximized; nutrient

uptake is enhanced; and revenue potential is increased. 

Table 4-7. Typical Effective Rooting Depth of Plants (Burt, 1995)

Plant Effective rooting depth, m (ft)

Alfalfa 1.2-2.0 (4-6) 

Avocado 0.6-1.0 (2-3) 

Banana 0.6-1.0 (2-3) 

Barley 1.0-1.5 (3.5) 

Beans 0.3-1.0 (1-3) 

Citrus 0.6-1.5 (2-5) 

Corn 1.0-1.5 (3-5) 

Cotton 1.2-2.0 (4-6) 

Deciduous Orchard 1.2-2.0 (4-6) 

Grains, small 1.0-1.2 (3-4) 

Grapes 1.0-2.0 (3-6) 

Grass 1.0-1.2 (3-4) 

Lettuce 0.3-0.6 (1-2) 

Melons 0.6-1.0 (2-3) 

Potatoes 0.6-1.0 (2-3) 

Safflower 1.5-2.0 (5-6) 

Sorghum 1.0-1.5 (3-5) 

Strawberries 0.3-0.6 (1-2) 

Sugarbeet 1.0-1.5 (3-5) 

Sugarcane 1.2-2.0 (4-6) 

Tomatoes 1.0-1.5 (3-5) 

Turf grass 0.2-0.5 (0.5-1.5)

In areas with a long growing season, such as 

California, selection of a double crop is an excellent 

means of increasing the revenue potential as well as the 

annual consumptive water use and nitrogen uptake of

the crop system. Double crop combinations that are

commonly used include summer crops of short season

varieties of soybeans, silage corn, or sorghum and 

winter crops of barley, oats, wheat, vetch, or annual 

forage grass as a winter crop. 

The most common agricultural crops grown for 

revenue using wastewater are corn (silage), alfalfa 

(silage, hay, or pasture), forage grass (silage, hay or 

pasture), grain sorghum, cotton, and grains. However, 

any crop, including food crops, may be grown with 

reclaimed wastewater after suitable preapplication 

treatment. In Monterey, CA, disinfected tertiary effluent

is used to grow lettuce, broccoli, celery, cauliflower, and 

artichokes. At the level of treatment achieved at 

Monterey, the use of the reclaimed water is more of a 

recycled water project than a land treatment. Fewer 

metals were found in the reclaimed wastewater than 

conventional fertilizers. Because recycled water quality 

is similar to that of other water sources, Monterey is not

labeling the produce to indicate that it is grown with 

recycled water (Jaques et al.,1999). 

The grass crop for OF must have high moisture 

tolerance, long growing season, and be suited to the 

local climate. A mixture of grasses is generally preferred

over a single species as shown in Table 4-8. The 

mixture should contain grasses whose growth

characteristics complement each other, such as sod

formers and bunch grasses and species that are

dormant at different times of the year. 

Another advantage of using a mixture of grasses is 

that, due to natural selection, one or two grasses will 

often predominate. A successful combination of grasses 

has been Reed canarygrass, tall fescue, and ryegrass 

(see Table 4-8). In the south and southwest, dallisgrass,

bermudagrass and redtop have also been successful. In 

northern climates, substitution of orchardgrass for the 

dallisgrass and redtop is recommended.

At Hanover, NH, barnyardgrass invaded the OF slopes 

and began to dominate the perennial grasses. Being an 

annual grass, when the barnyardgrass died, it left bare

areas that were subject to erosion (Palazzo et al., 1982). 

Grasses to be avoided include those sensitive to salt 

(like clover) and those that have long slender seed stalks 

(Johnson grass and yellow foxtail). In the early stages of

development Johnson grass will provide an effective

cover; however, with maturity the bottom leaves die off 

and the habitat for microorganisms becomes reduced. 

Nitrogen 

The rate of nitrogen uptake by crops changes during 

the growing season and is a function of the rate of dry

matter accumulation and the nitrogen content of the 

plant. For planning and nutrient balances, the rate of 

nitrogen uptake can be correlated to the rate of plant 

transpiration. Consequently, the pattern of nitrogen 

uptake is subject to many environmental and

management variables and is crop specific. Examples of

measured nitrogen uptake rates versus time are shown 

in Figure 4-2 for annual crops and perennial forage 

grasses receiving wastewater. The plant uptake curves 

assume that the applied nitrogen exceeds the rate of 

uptake (is not limiting growth) and that the applied 

nitrogen is plant-available (in the inorganic form). 

Some forage crops can have even higher nitrogen

uptakes than those in. Californiagrass, a wetland 

4-8 
Table 4-8. Grasses Used at Overland Flow Sites (US EPA, 1973)

Site Type of Grass 

Ada, OK. Annual ryegrass, bermudagrass, and Kentucky 31 fescue 

Carbondale, IL Tall fescue 

Davis, CA Fescue and perennial ryegrass 

Easley, SC. Kentucky 31 fass fescue 

Hanover, NH Orchardgrass, quackgrass, Reed canarygrass, 

perennial ryegrass 

Hunt-Wesson (Davis, CA.) Fescue, trefoil, Reed canarygrass

Campbell Soup Co. (Paris, TX.) Reed canarygrass, redtop, tall fescue 

Utica, MS Reed canarygrass, Kentucky 31 fescue, perennial ryegrass, common bermudagrass 

Figure 4-2. Nitrogen Uptake for Annual and Perennial Crops.

species, widely distributed in the subtropics, was grown

with effluent in Hawaii (Handley, 1981). Mean crop yield

was 96 mt/ha-yr (43 tons/acre-yr and nitrogen uptake

was 2.1 mt/ha-yr (1,870 lb/acre-yr. The nitrogen crop

uptake for turfgrasses in Tucson (common

bermudagrass overseeded with winter ryegrass) is 0.59 

mt/ha-yr (525 lb/acre-yr) (Pepper, 1981). 

Essentially all nitrogen absorbed from the soil by plant 

roots is in the inorganic form of either nitrate (NO3) or

ammonium (NH4) Generally young plants absorb

ammonium more readily than nitrate; however, as the

plant ages the reverse is true. Soil conditions that 

promote plant growth (warm and well aerated) also 

promote the microbial conversion of ammonium to 

nitrate. As a result, nitrates are generally more abundant 

when growing conditions are most favorable. Once 

inside the plant, the majority of the nitrogen is 

incorporated into amino acids, the building blocks of

protein. Protein is approximately 16 percent nitrogen by

weight. Nitrogen makes up from 1 to 4 percent of the 

plants harvested dry weight. 

Phosphorus 

Phosphorus is part of the plant genetic material

ribonucleic (RNA) and energy transfer with adenosine 

triphosphate (ATP). Phosphorus is available for 

absorption by plants from the soil as the orthophosphate

ions (H2PO4

-2 and HPO4-3). Aluminum, iron, calcium, 

and organic matter quickly bind phosphorus into highly 

insoluble compounds. The concentration of 

orthophosphate ion in soil solution is commonly less 

than 0.05 mg/L, so an equilibrium is established between

the soluble ion and the adsorbed form in soil. 

The amount of phosphorus in municipal effluent is 

usually higher than plant requirements. Fortunately, the

relative immobility of phosphorus in soil profile allows for 

application of phosphorus in excess of crop 

requirements.

4-9 
Table 4-9. General Effects of Trace Element Toxicity on Common Crops (Kabata-Pendias and Pendias 2000)

Element Symptoms Sensitive Crop 

Al Overall stunting, dark green leaves, purpling of stems, death of leaf tips, and 

coralloid and damaged root system. 

Cereals 

As Red-brown necrotic spots on old leaves, yellowing and browning of roots, 

depressed tillering. 

No specific crop 

B Margin or leaf tip chlorosis, browning of leaf points, decaying growing points, and 

wilting and dying-off of older leaves. 

Cereals, potatoes, tomatoes, cucumbers, 

sunflowers, mustard 

Cd Brown margin of leaves, chlorosis, reddish veins and petioles, curled leaves, and 

brown stunted roots. 

Legumes (bean, soybean), spinach radish, 

carrots, and oats. 

Co Interveinal chloriosis in new leaves followed by induced Fe chlorosis and white leaf 

margins and tips, and damaged root tips. 

No specific crop 

Cr Chlorosis of new leaves, injured root growth. No specific crop 

Cu Dark green leaves followed by induced Fe Chlorosis, thick, short, or barbed-wire 

roots, depressed tillering. 

Cereals and legumes, spinach, citrus, seedlings, 

and gladiolus. 

F Margin and leaf tip necrosis; chlorotic and red-brown points of leaves. Gladiolus, grapes, fruit trees, and pine trees 

Fe Dark green foliage, stunted growth of tops and roots, dark brown to purple leaves 

of some plants (“bronzing” disease of rice). 

Rice and tobacco 

Hg Severe stunting of seedlings and roots, leaf chlorosis and browning of leaf points. Sugarbeets, corn and roses. 

Mn Chlorosis and necrotic lesions on old leaves, blackish-brown or red necrotic spots, 

accumulation of MnO2 particles in epidermal cells, drying tips of leaves, and 

stunted roots. 

Cereals, legumes, potatoes, and cabbage. 

Mo Yellowing or browning of leaves, depressed root growth, depressed tillering. Cereals 

Ni Interveinal chlorosis in new leaves, gray-green leaves, and brown and stunted 

roots. 

Cereals 

Pb Dark green leaves, wilting of older leaves, stunted foliage, and brown short roots. No specific crop 

Rb Dark Leaves, stunted foliage, and increasing amount of shoots. No specific crop 

Se Interveinal chlorosis or black spots at Se content at about 4 mg/L and complete 

bleaching or yellowing of younger leaves at higher Se content; pinkish spots on 

roots. 

No specific crop 

Zn Chlorotic and necrotic leaf tips, interveinal chlorosis in new leaves, retarded growth 

of entire plant, injured roots resemble barbed wire. 

Cereals and spinach. 

Potassium

Potassium is used in large amounts by many crops, 

but typical wastewater is relatively deficient in this 

element. For example, at 15 mg/L, a typical wastewater 

contains 40 lb/acre-ft. In many cases, fertilizer potassium

(or biosolids potassium) may be needed for optimal plant 

growth depending on the soil and crop. For soils having

low levels of natural potassium, a relationship has been

developed to estimate potassium loading requirements, 

see Equation 2-3 in Chapter 2 (US EPA, 1981). 

Micronutrients 

In addition to the three major macronutrients, calcium 

and sulfur are also macronutrients, and there are many

micronutrients. The micronutrients important to plant 

growth (in descending order) are: iron, manganese, zinc, 

boron, copper, molybdenum, nickel and occasionally, 

sodium, silicon, chloride, and cobalt. Most wastewaters 

contain an ample supply of these elements. Symptoms 

of trace element toxicity are presented in Table 4-9. The 

descriptions should be used to indicate sensitive crops 

and diagnoses of toxicity should be confirmed with 

tissue analysis. The concentration of these elements in 

most municipal wastewaters is well below the toxic level 

of all crops; however, phytotoxicity may occur as a result

of long-term accumulation of these elements in the soil. 

Salinity 

Salts can accumulate in the soil causing osmotic

stress on plants. Osmotic stress caused by salt is similar

to the impact of moisture stress and is amplified as soil 

dries. All water has salts. Municipal effluent has an

approximate increase of 150 to 380 mg/L total dissolved 

solids (not all inorganic salts) over the source water 

depending on what industries also discharge (Metcalf

and Eddy, 1991). Under dry conditions, salts are not 

adequately leached out of the root zone and can build up

to cause osmotic stress. Plants that are salt sensitive or 

only moderately tolerant show progressive decline in

growth and yields as levels of salinity increase. Figure

4-3 contains salt tolerance of common crops. Some 

species are tolerant to salinity, yet sensitive during

germination. It is general practice to use supplemental

water for germination when available. 

4-10 
pH 

Natural biochemical reactions drive the soil pH to a

stable condition. A range of pH between 3 and 11 has 

been applied successfully to land treatment systems.

Extended duration of low pH can change the soil fertility 

and lead to leaching of metals. When the acidity is 

comprised of mostly organic acids, then the water will be 

neutralized as the organics are oxidized. 

Most field crops grow well in soils with a pH range of 

5.5 to 8.0. Some crops, like asparagus or cantaloupes 

with a high calcium requirement, prefer a soil pH greater 

than 7.0. If the pH of the soil begins to drop, liming is 

recommended to return the pH to the desirable range for 

crop production. Figure 4-4 shows a range optimal pH

of various crops on a mineral soil. The pH range shown 

in Figure 4-4 is that of the soil extract, not the effluent,

which will neutralized in the soil. 

Because soil can treat large amounts of organics 

acids, it is recommended the pH of wastewater be pH 

5.0 and 9.0). Chemical acids and bases used during pH 

adjustment will add to the dissolved solids and should be 

avoided if salinity is a problem. Organic acids, such as 

acetic acid, can be used to reduce pH with out adding to 

the fixed dissolved solids, but the organic component will

increase BOD.

4.3.3 Silviculture 

Existing forested land or newly planted stands provide

an excellent area for land treatment systems. The most 

common forest crops used in SR systems have been

mixed hardwoods and pines. A summary of 

representative operational systems and types of forest

crops used is presented in Table 4-10. The growth

response of trees will vary in accordance with a number 

of factors; one of the most important is the adaptability of 

the selected species to the local climate. Local foresters 

should be consulted for specific recommendations on

the likely response of selected species. 

Vegetative uptake and storage of nutrients depend on

the species and forest stand density, structure, age, 

length of season, and temperature. In addition to the 

trees, there is also nutrient uptake and storage by the

understory tree and herbaceous vegetation. 

The role of the understory vegetation is particularly 

important in the early stages of tree establishment. 

Forests take up and store nutrients and return a portion 

of those nutrients back to the soil in the form of leaf fall 

and other debris such as dead trees. Upon 

decomposition, the nutrients are released and taken up

by the trees. During the initial stages of growth (1 to 2 

yr), tree seedlings are establishing a root system; 

Figure 4-3. Effect of Salinity on Growth of Field Crops (USDA, 1992).

Table 4-10. Forested Land Treatment Systems in the United 

States (Crites et al., 2000)

Location Design Flow, mgd Tree Types 

Dalton, GA 30.0 Pines 

Clayton, Co., GA 19.5 Loblolly pines, 

hardwood 

Helen, GA 0.02 Mixed pine and 

hardwood 

St. Marys, GA 0.3 Slash pine 

Mackinaw City, MI 0.2 Aspen, birch, 

white pine 

State College, PA 3.0 Mixed hardwood,

pine 

West Dover, VT 0.55 Hardwood 

balsam, hemlock, 

spruce 

4-11 
biomass production and nutrient uptake are relatively 

slow. To prevent leaching of nitrogen to groundwater 

during this period, nitrogen loading must be limited or 

understory vegetation must be established that will take

up and store applied nitrogen that is in excess of the tree

crop needs. 

Nitrogen Uptake 

The estimated annual nitrogen uptake of forest

ecosystems in selected regions of the United States is 

presented in Table 4-11. These rates are considered

Figure 4-4. Suitable pH of Mineral Soils for Various Crops. 

4-12 
Table 4-11. Nitrogen Uptake for Selected Forest Ecosystems 

With Whole Tree Harvesting

Tree Age,

Years

Average Annual 

Nitrogen Uptake 

lb/(acre-year) 

Eastern forests: 

 Mixed hardwoods 40-60 200 

 Red pine 25 100 

 Old field with white 

 spruce plantation 15 200 

 Pioneer succession 5-15 200 

 Aspen sprouts - 100 

Southern forests: 

 Mixed hardwoods 40-60 250 

 Loblolly pine with

 no understory 20 200 

 Loblolly pine with

 understory 20 250 

Lake states forests: 

 Mixed hardwoods 50 100 

 Hybrid poplara 5 140 

Western forests: 

 Hybrid poplara 4-5 270 

 Douglas fir plantation 15-25 200 a

Short-term rotation with harvesting at 4 to 5 years; represents 

first-growth cycle from planted seedlings. 

*lb/acre-yr = 1.12 lg/ha-yr1.

maximum estimates of net nitrogen uptake including

both the understory and overstory vegetation during the

period of active tree growth. 

Because nitrogen stored within the biomass of trees is 

not uniformly distributed among the tree components, 

the amount of nitrogen that can actually be removed with 

a forest crop system will be substantially less than the

storage estimates given in Table 4-11 unless 100

percent of the aboveground biomass is harvested 

(whole-tree harvesting). If only the merchantable stems 

are removed from the system, the net amount of 

nitrogen removed by the system will be less than 30 

percent of the amount stored in the biomass (Keeney, 

1980). 

The distributions of biomass and nitrogen for naturally 

growing hardwood and conifer (pines, Douglas fir, fir, 

larch, etc.) stands in temperate regions are shown in 

Table 4-12. For deciduous species, whole-tree

harvesting must take place in the summer when the 

leaves are on the trees if maximum nitrogen removal is 

to be achieved. 

Leaves make only 2 percent of the biomass on a dry 

weight for northern hardwoods. Harvesting hardwoods 

with leaves will increase nutrient removal by the 

following percentages: 

12% Calcium 

15% Potassium 

 4% Phosphorus

19% Nitrogen (Hornbeck and Kropelin, 1982).

Following the initial growth stage, the rates of growth 

and nutrient uptake increase and remain relatively 

constant until maturity is approached and the rates 

decrease. When growth rates and nutrient uptake rates 

begin to decrease, the stand should be harvested or the

nutrient loading decreased. Maturity may be reached at

20 to 25 yr for southern pines, 50 to 60 yr for hardwoods,

and 60 to 68 yr for some of the western conifers such as 

Douglas fir. Of course, harvesting may be practiced well 

in advance of maturity as with short-term rotation 

management. 

Eastern Forests. During the past 35 years 

wastewater has been applied to several forest

ecosystems at the Pennsylvania State University 

(Sopper and Kerr, 1979). Satisfactory renovation was 

obtained in all systems (eastern mixed hardwoods and

red pine) when wastewater was applied during the

growing season at 2.54 cm/wk (1 in/wk) with annual

nitrogen loadings of 150 kg/ha (134 lb/acre). The white

spruce/old field forest ecosystem produced a percolate

nitrogen concentration of 7.4 mg/L (nitrate-N) when the

hydraulic loading was 5 cm/wk (2 in/wk) and the annual

nitrogen loading was 308 kg/ha (275 lb/acre). 

Southern Forests. In a study of a southern mixed 

hardwood (80% hardwood, 20% pine) forest near Helen, 

Georgia on a 30% slope with a loading rate of 7.5 cm/wk 

(3 in/wk), about 60% of the applied nitrogen was 

accounted for in uptake and denitrification. The nitrogen

loading was 680 kg/ha (608 lb/acre) and the percolate

nitrate-N concentration was 3.7 mg/L (Nutter and

Schultz, 1978). 

Lake States Forests. Studies at Michigan State 

University have shown rather poor nitrogen removal by 

mature northern hardwoods. Younger forest systems

and poplar plantations have shown greater nitrogen

uptake, especially during the years when herbaceous 

cover is present (McKim et al., 1982). 

Western Forests. The wastewater renovation

capacity of a newly established plantation of Douglas fir

and a mature 50-yr old Douglas fir forest was studied

with wastewater nitrogen loadings of 350 to 400 kg/ha-yr 

(310 to 360 lb/acre-yr) (Cole and Schiess, 1978). The

uptake rates, presented in Table 4-11, reflect a 

substantial uptake by the understory grasses. 

4-13 
Table 4-12. Biomass and Nitrogen Distributions by Tree Component for Stands in Temperate Regions (US EPA, 1981)

Conifers,% Hardwoods, % 

Tree component Biomass Nitrogen Biomass Nitrogen 

Roots 10 17 12 18 

Stems 80 50 65 32 

Branches 8 12 22 42 

Leaves 2 20 1 8 

Phosphorus and Trace Metals 

The assimilative capacity for both phosphorus and 

trace metals is controlled more by soil properties than 

plant uptake. The relatively low pH (4.2 to 5.5) of most

forest soils is favorable to the retention of phosphorus

but not trace metals. However, the high level of organic 

matter in forest soil improves the metal removal 

capacity. The amount of phosphorus in trees is small, 

usually less than 30 kg/ha (27 lb/acre); therefore, the

amount of annual phosphorus accumulation in the 

biomass is quite small. 

4.3.4 Horticultural 

Horticultural plants offer a benefit over agricultural 

production crops because the harvest is not ingested. 

Although it has been clearly demonstrated that reuse

irrigation with highly treated effluent meets the water 

quality criteria for turf grass use (USGA, 1994), many 

golf course managers are reluctant to use effluent at the

risk of loss from visual appearance in both irrigation 

ponds and turf quality. Devitt and Morris (2000) 

monitored golf course quality at both courses with 

effluent and with municipal water. Because of the

nutrient content of the effluent irrigation ponds with 

effluent had increased algal growth and loss of clarity. 

However, effluent ponds with aquatic vegetation

phosphate levels were lower and clarity higher, 

suggesting that the plant played a significant role in

maintaining healthier ponds. Turf quality without 

sufficient leaching showed impaired quality independent

of water type. Various golf course grasses can be 

chosen as a salt management strategy. Table 4-13

shows salt tolerances of various grasses. Salt issues for

turf quality can be managed with sufficient leaching, but 

a greater concern is associated with mixed landscape

plant receiving overhead spray irrigation (Devitt and

Morris, 2000). 

4.4 Crop Management, Water Quality,

and Nutrient Cycle 

Crop planting, harvesting and pest control are 

management areas requiring proper techniques to

ensure a healthy crop. 

4.4.1 Crop Planting, Harvesting 

Cultivating 

Local extension services or other experts should be 

consulted regarding planting techniques and schedules.

Most crops require a period of dry weather before 

harvest to mature and reach a moisture content

compatible with harvesting equipment. Soil moisture at 

harvest time should be low enough to minimize

compaction by harvesting equipment. For these reasons,

Table 4-13. Golf Course Grass Salt Tolerances

ECe (dS/m) Grass 

Very Sensitive (<1.5) Annual bluegrass 

Colonial bentgrass 

Rough bluegrass 

Centipedegrass 

Moderately Sensitive (1.6 - 3.0) Kentucky bluegrass Most zoysia spp.

Moderately Tolerant (3.1 - 6.0) Creeping bentgrass 

Fine-leaf fescues 

Bahiagrass 

Buffalograss 

Blue grama 

Annual ryegrass 

Tolerant (6.1 – 10.0) Seaside bentgrass 

Common bermudagrass 

Tall Fescue 

Perennial ryegrass 

Zoysia japonica (some) 

Zoysia matrella (some)

Kikuyu

Wheatgrasses 

Very Tolerant (10.1 to 20.0) Hybrid bermudagrasses (some) 

St. Augustinesgrass 

Salt grass 

Alkaligrass (Fults, Salty)

Superior Tolerance (>20.0) Seashore paspalum (some) a The plant classification values and rankings are based on those traditionally used for all plants (Carrow and Duncan, 1998). The exception is the 

"Superior Tolerance" class, which is added to classify grasses that are true halophytes with salinity tolerances well above most plants. 

4-14 
application should be discontinued well in advance of 

harvest. The time required for drying will depend on the 

soil drainage and the weather. A drying time of 1 to 2 

weeks is usually sufficient if there is no precipitation. 

However, advice on this should be obtained from local

experts and sufficient land area should be available to 

account for the time required for drying. 

Harvesting of grass crops and alfalfa involves regular

cuttings, and a decision regarding the trade-off between

yield and quality must be made. Advice can be obtained 

from local agricultural experts. In the northeast and north

central states, three cuttings per season have been

successful with grass crops. When supplemental

fertilizer is required, records should be kept documenting 

the type of fertilizer used, area of application, amount

applied. 

4.4.2 Grazing 

Grazing of pasture by beef cattle or sheep can provide

an economic return for SR systems. No health hazard

has been associated with the sale of the animals for 

human consumption. Grazing animals return nutrients to

the ground in their waste products. The chemical state 

(organic and ammonia nitrogen) and rate of release of 

the nitrogen reduces the threat of nitrate pollution of the

groundwater. Much of the ammonia-nitrogen volatilizes

and the organic nitrogen is held in the soil where it is 

slowly mineralized to ammonium and nitrate forms. See 

Chapter 2 for nitrogen cycling from livestock. 

In terms of pasture management, cattle or sheep must 

not be allowed on wet fields to avoid severe soil

compaction and reduced soil infiltration rates. Wet

grazing conditions can also lead to animal hoof 

diseases. Pasture rotation should be practiced so that 

wastewater can be applied immediately after the 

livestock are removed. In general, a pasture area should

not be grazed longer than 7 days. Typical regrowth 

periods between grazings range from 14 to 36 days. 

Depending on the period of regrowth provided, one to 

three water applications can be made during the

regrowth period. Rotation grazing cycles for 2 to 8

pasture areas are given in Table 4-16. At least 3 to 4 

days of drying time following an application should be 

allowed before livestock are returned to the pasture. 

4.4.3 Agricultural Pest Control 

Problems with weeds, insects, and plant diseases are 

aggravated under conditions of frequent water 

application, particularly when a single crop is grown year 

after year or when no-till practices are used. Most pests 

can be controlled by selecting resistant or tolerant crop

varieties and by using pesticides in combination with 

appropriate cultural practices. State and local experts 

should be consulted in developing an overall pest control

program for a given situation. 

4.4.4 Overland Flow Crop Management 

After the cover crop has been established, the OF 

slopes will need little, if any, maintenance work. It will, 

however, be necessary to mow the grass periodically. A

few systems have been operated without cutting, but the

tall grass tends to interfere with maintenance operations.

Normal practice has been to cut the grass two or three

times a year. The first cutting may be left on the slopes. 

After that, however, it is desirable to remove the cut 

grass. The advantages of doing so are that additional 

nutrient removal is achieved, channeling problems may 

be more readily observed, and revenue can sometimes 

be produced by the sale of hay. Depending on the local

market conditions, the cost of harvesting can at least be 

offset by the sale of hay (US EPA, 1981). 

Slopes must be allowed to dry sufficiently such that 

mowing equipment can be operated without leaving ruts 

or tracks that will later result in channeling of the flow. 

The drying time required before mowing varies with the 

soil and climatic conditions and can range from a few 

days to a few weeks. The downtime required for 

harvesting can be reduced by a week or more, if greenchop harvesting is practiced instead of mowing, raking,

and baling. Care must be taken to minimize pathogen

effects. However, local markets for green-chop must 

exist for this method to be feasible. 

It is common for certain native grasses and weeds to 

begin growing on the slopes, but usually they have little 

impact on treatment efficiency and it is generally not 

necessary to eliminate them. However, there are

exceptions, and the local extension services should be

consulted for advice. 

Proper management of the slopes and the application

schedule will prevent conditions conducive to mosquito 

breeding. Other insects are usually no cause for 

concern, although an invasion of certain pests such as

army worms may be harmful to the vegetation and may 

require periodic insecticide application.

4.4.5 Forest Crop Management 

The type of forest crop management practice selected 

is determined by the species mix grown, the age and

structure of the stand, the method of reproduction best

suited and/or desired for the favored species, terrain, 

and type of equipment and technique used by local 

harvesters. The most typical forest management 

situations encountered in land treatment are

management of existing forest stands reforestation, and

short-term rotation. 

4-16 
Table 4-14. Pasture Rotation Cycles for Different Numbers of Pasture Areas

Number of Pastures Rotation Cycle 

Days

Regrowth Period

Days

Grazing Period 

Days

2 28 14 14 

3 30 20 10 

4 28 21 7 

5 35 28 7 

6 36 30 6 

7 42 36 6 

8 40 35 5 

Established Forests. The general objective of the

forest management program is to maximize biomass 

production. The compromise between fully attaining a 

forest's growth potential and the need to operate

equipment efficiently (distribution and harvesting

equipment) requires fewer trees per unit area. These 

operations will assure maintenance of a high nutrient

uptake by the forest. 

In even-aged forests, trees will all reach harvest age at 

the same time. The usual practice is to clear-cut these

forests at harvest age and regenerate a stand by either 

planting seedlings, sprouting from stumps (called 

coppice), or a combination of several of the methods. 

Even-aged stands may require a thinning at an

intermediate age to maintain maximum biomass 

production. Coniferous forests, in general, must be

replanted, whereas hardwood forests can be reproduced 

by coppice or natural seeding. For uneven-aged forests,

the desired forest composition, structure, and vigor can

be best achieved through thinning and selective harvest. 

However, excessive thinning can make trees susceptible 

to wind throw and caution is advised in windy areas.

The objectives of these operations would be to maintain

an age class distribution in accordance with the concept

of optimum nutrient storage. The maintenance of fewer 

trees than normal would permit adequate sunlight to 

reach the understory to promote reproduction and

growth of the understory. Thinning should be done 

initially prior to construction of the distribution system 

and only once every 10 years or so to minimize soil and

site damage.

The concept of "whole-tree harvesting" should be 

considered for all harvesting operations, whether it be 

thinning, selection harvest, or clear-cut harvest. Wholetree harvesting removes the entire standing tree: stem, 

branches, and leaves. Thus, 100 percent of nitrogen

accumulated in the aboveground biomass would be

removed. 

Prescribed fire is a common management practice in

many forests to reduce the debris or slash left on the site 

during conventional harvesting methods. During the 

operation, a portion of the forest floor is burned and

nitrogen is volatilized. Although this represents an

immediate benefit in terms of nitrogen removal from the

site, the buffering capacity that the forest floor offers is 

reduced and the likelihood of a nitrate leaching to the 

groundwater is increased when application of 

wastewater is resumed. 

Reforestation. Wastewater nutrients often stimulate 

the growth of the herbaceous vegetation to such an

extent that it competes with and shades out the

desirable forest species. Herbaceous vegetation is 

necessary to act as a nitrogen sink while the trees are

becoming established, and therefore, cultural practices 

must be designed to control but not eliminate the 

herbaceous vegetation. As the tree crowns begin to

close, the herbaceous vegetation will be shaded and its 

role in the renovation cycle reduced. Another alternative 

to control of the herbaceous vegetation is to eliminate it 

completely and reduce the hydraulic and nutrient loading

during the establishment period. 

Short-Term Rotation. Short-term rotation forests are 

plantations of closely spaced hardwood trees that are

harvested repeatedly on cycles of less than 10 yr. The 

key to rapid growth rates and biomass development is

the rootstock that remains in the soil after harvest and

then resprouts. Short-term rotation harvesting systems 

are readily mechanized because the crop is uniform and 

relatively small. 

Using conventional tree spacings of 8 to 12 ft (2.4 to

3.6 m), research on systems where wastewater has 

been applied to short-term rotation plantations has 

shown that high growth rates and high nitrogen removal

are possible (US EPA, 1981). Planted stock will produce 

only 50 percent to 70 percent of the biomass produced

following cutting and resprouting (US EPA, 1981). If

nitrogen and other nutrient uptake is proportional to

biomass, the first rotation from planted stock will not

remove as much as subsequent rotations from coppice. 

Therefore, the initial rotation must receive a reduced

nutrient load or other herbaceous vegetation must be

employed for nutrient storage. Alternatively, closer tree

spacings may be used to achieve desired nutrient 

uptake rates during initial rotation. 

4.5 References 

Allen, R. G., L. S. Pereira, D. Raes, and M. Smith

(1998) Crop evapotranspiration - Guidelines for 

computing crop water requirements - FAO Irrigation

4-17 
and drainage paper 56. FAO - Food and Agriculture

Organization of the United Nations. Rome. 

Brockway, D.G. et al. (1982) The Current Status on the 

Selection and Management of Vegetation for Slow

Rate and Overland Flow Application Systems to

Treat Municipal Wastewater in the North Central

Region of the United States. In: Land Treatment of

Municipal Wastewater, D'Itri, F.M. (Ed.) Ann Arbor,

MI: Ann Arbor Science, pp.5-18. 

Burt, C. M. (1995) The Surface Irrigation Manual. 

Waterman Industries, Inc.

Carrow, R. N. and R. R. Duncan (1998) Salt-Affected

Turfgrass Sites: Assessment and Treatment. Ann 

Arbor Press, Chelsea, MI. 

Crites, R.W., S.C. Reed, and R.K. Bastian (2000) Land

Treatment Systems for Municipal and Industrial

Wastes. McGraw-Hill Book Co. New York. 

Cole, D.W. and P. Schiess (1978) Renovation of 

Wastewater and Response of Forest Ecosystems: 

the Pack Forest Study. Proceedings of the

International Symposium on Land Treatment of 

Wastewater. Vol. 1, Hanover, NH. pp. 323-331. 

Devitt, D. A. and R. L. Morris (2002) Monitoring Golf 

Course Transition to Reuse Water in Southern

Nevada. American Water Works: Water Sources 

Conference-Reuse, Resources, Conservation. 

January 27-30, 2002, Las Vegas, NV. 

D'Itri, F.M. (1982) Land Treatment of Municipal

Wastewater: Vegetation Selection and Management,

Ann Arbor, MI: Ann Arbor Science. 

Doorenbos, J. and W. O. Pruitt (1977) Crop

Requirements, FAO Irrigation and Drainage Paper 

24. Food and Agricultural Organization of the United

Nations, Rome. 

Handley, L.L. (1981) Effluent Irrigation of 

Californiagrass. Proceedings Water Reuse

Symposium II, Vol. 2, AWWA Research Foundation, 

Washington, DC. 

Hanks, R.J. (1992) Applied Soil Physics. Second

edition. Springer-Verlang. New York. 

Hornbeck, J. W. and W. Kropeline (1982) Nutrient 

removal and leaching from a whole-tree harvest of 

northern hardwoods. Journal of Environmental

Quality. 11:309-316. 

Jaques, R., G. Antosz, R. Cooper, and B. Sheikh (1999) 

Pathogen Removal Effectiveness of a Full-Scale

Recycling Plant. WEFTEC ’99, New Orleans, LA. 

Jensen, M.E. et al. (1973) Consumptive Use of Water 

and Irrigation Water Requirements. ASCE

Committee on Irrigation Water Requirements. 

Kabata-Pendias, A and H. Pendias. (2000). Trace

Elements in Soil and Plants, 3rd ed. CRC, Boca 

Raton, FL. 

Keeney, D.R. (1980) Prediction of soil nitrogen

availability in forest ecosystems: a literature review. 

Forest Science. 26:159-171. 

Metcalf and Eddy (1991) Wastewater Engineering: 

Treatment, Disposal, Reuse. 3rd Edition. Rev. G. 

Tchobanoglous and F. Burton. McGraw-Hill, Inc. 

Nutter, W.L., R.C. Schultz, and G.H. Brister (1978) 

Land Treatment of Municipal Wastewater on Steep

Forest Slopes in the Humid Southeastern United

States. Proceedings of the International Symposium 

on Land Treatment of Wastewater, Vol. 1. Hanover, 

NH. pp. 265-274. 

Palazzo, A.J., T.F. Jenkins, and C.J Martel (1982) 

Vegetation Selection and Management for Overland

Flow Systems. In: Land Treatment of Municipal

Wastewater, D'Itri, F.M. (Ed.) Ann Arbor, MI: Ann 

Arbor Science, pp. 135-154. 

Pepper, I.L. (1981) Land Application of Municipal

Effluent on Turf. In: Proceedings of the 1981

Technical Conference Silver Spring, MD: The

Irrigation Association. 

Rosenberg, N. J. (1974) Microclimate: The Biological

Environment. John Wiley & Sons. New York. 

Sopper, W.E. and S.N. Kerr (1979) Renovation of

Municipal Wastewater in Eastern Forest 

Ecosystems, In: Utilization of Municipal Sewage 

Effluent and Sludge on Forest and Disturbed Land. 

University Park, PA: The Pennsylvania State 

University Press. pp. 61-76. 

USDA. (1992) Part 651 – Agricultural Waste

Management Field Handbook. 

US EPA (1973) Wastewater Treatment and Reuse by

Land Application. Vol. II. EPA-660/02-73-006B, Aug.

1973. 

US EPA (1981) Process Design Manual: Land

Treatment of Municipal Wastewater. EPA 625/1-81-

013. 

USGA (1994) Wastewater Reuse for Golf Course

Irrigation. Lewis Publishers. 

4-18 
Chapter 5 

Site Planning and Selection

Site selection and process considerations in land 

treatment are interrelated. The ability of the land

treatment processes to remove wastewater constituents 

described in Chapter 2, the discharge quality criteria,

and the soil and other site characteristics affect the 

choice of the appropriate land treatment process. The 

presence of a suitable site within an economical

transmission distance from the wastewater source will 

determine if a land treatment system can be 

implemented. Because the selection of a process and

site for land treatment are related, a 2-phased planning

procedure is often used. The two phases are presented 

in Figure 5-1 (US EPA, 1981b). Phase 1 involves 

identification of potential sites via screening of available 

information and experience. If potential sites for any land

treatment processes are identified, the study moves into 

Phase 2. Phase 2 includes an in-depth consideration of 

the processes including field investigations, preliminary 

design and cost estimates, evaluation of the alternatives,

and selection of the most economical and appropriate 

alternative. 

5.1 Preliminary Land Requirements 

The first phase involves estimating preliminary land 

area requirements based on wastewater and climate 

characteristics, identifying potential sites and, evaluating

the sites based on technical and economic factors, and

selecting potential sites.

Preliminary land requirements can be estimated for 

each land treatment process, based on wastewater 

characteristics, required loading rates, storage needs 

and climatic conditions. 

5.1.1 Wastewater Characteristics 

Wastewater characteristics include average annual 

flows and concentrations of constituents such as BOD5, 

suspended solids, nitrogen, phosphorus and trace

elements. 

Municipal wastewater flows range typically from 246 – 

379 liters per capita per day [65 to 100 gallons per capita 

per day (gpcd) (Crites and Tchobanoglous, 1998).

Industrial wastewater flows are too variable to generalize

and must be estimated from information specific to the 

product and wastewater generating operations. Existing

wastewater flow records or water use records should be

used whenever available. 

Figure 5-1. Two-Phase Planning Process.

Constituent concentrations that are seen typically in

municipal wastewater are presented in Table 5-1. These 

characteristics represent typical medium strength 

wastewater. For municipal land treatment systems,

BOD5 and suspended solids loadings seldom limit 

system capacity. If nitrogen removal is required, nitrogen

loading may limit the system capacity. Nitrogen removal 

capacity depends on the crop grown, if any, and on

system management practices. In some cases, other 

wastewater constituents such as phosphorus or trace

elements may control design. This is rare, however, and

most municipal systems will be limited either by 

hydraulic capacity or nitrogen loading. 

Table 5-1. Typical Composition of Raw Municipal Wastewater

(Crites and Tchobanoglous, 1998)

Constituent Concentration, g/m3 (mg/L)

BOD5 210 

Suspended Solids 210 

Nitrogen, total 35 

 Organic nitrogen 13 

 Ammonia nitrogen 22 

Phosphorus, total 7 

Potassium 15 

5-1 
Industrial wastewaters vary widely in their 

characteristics, especially for organics, metals, and

nitrogen. Characteristics of food processing wastewaters 

that have been applied directly to the land are presented

in Table 5-2 (Crites, 1982a). Wastewater

characterization is necessary in planning for industrial

land application systems (see Chapter 11). It is 

important to consider whether there are sufficient

nutrients in industrial wastewaters to support plant 

growth in SR systems. Applications may need to

supplement nutrients with other sources for proper plant

fertility (e.g., commercial fertilizers. 

Table 5-2. Characteristics of Food Processing Wastewaters 

Applied to the Land

Constituent Concentration, g/m3

 (mg/L)* 

BOD5 200 - 33,000 

Suspended Solids 200 - 3,000 

Total fixed dissolved solids <1,800 

Total nitrogen 10 – 1,900 

pH, units 3.5 – 12.0 

Temperature, °C < 65 

*Except as noted. 

5.1.2 Preliminary Loading Rates 

In the absence of site information, typical loading rates 

can be assumed to initiate the planning process. For SR

systems the degree of preapplication treatment (either 

primary or secondary) has little affect on the loading 

rate. For OF and SAT systems, higher loading rates can

usually be used with higher quality effluent. Typical 

loading rates for preliminary estimates of land

requirements are presented in Table 5-3 (Crites, et al., 

2000). The rates in Table 5-3 are necessarily 

conservative. Once a potential site has been analyzed

and the ability to meet discharge requirements is 

assessed, the loading rates can be modified. In

calculating the annual loading rates in SR systems it 

should be noted that annual crops (e.g., corn) differ from

perennial (e.g., grass). Loading rates will vary annually

with annual crops and may be more consistent with

perennial crops. 

Table 5-3. Preliminary Loading Rates for Initial Estimate of 

Land Requirements

Process 

Loading Rate, 

mm/week (in/week) 

Slow rate 

 Agricultural 38 (1.5) 

 Forest 25 (1.0) 

Soil Aquifer Treatment 

 Primary effluent 305 (12)

 Secondary effluent 508 (20)

Overland flow

 Screened wastewater and 

 primary effluent 

102 (4) 

 Secondary effluent 203 (8) 

5.1.3 Storage Needs 

Storage for wastewater may be necessary due to cold

weather, excessive precipitation, or crop management. 

Land treatment systems also may need storage for flow 

equalization, system backup and reliability, and system 

management, including crop harvesting (SR and OF) 

and spreading basin maintenance (SAT). Reserve 

application areas can be used instead of storage for 

these system management requirements. 

For preliminary estimates it is usually sufficient to base 

storage needs on climatic factors. A map showing

storage days based on cold weather and excessive

precipitation is presented in Figure Figure 5-2 (Whiting, 

1976. This figure should be used for a preliminary

estimate of storage needed for OF systems. For SR 

systems using agricultural crops, the crop management 

time for harvesting and planting should be added to the

storage days taken from Figure 5-2. The values in 

Figure 5-2 may not be valid for SAT and forested SR 

systems, since both are sometimes operated during

subfreezing weather. For SAT and forested SR system, 

a minimum storage of 7 to 14 days can be assumed for

preliminary estimates of land area. If application rates 

are reduced during cold weather, additional storage will 

be required. 

Figure 5-2. Estimated Storage Days Based on Climatic Factors Alone.

5.1.4 Climatic Factors and Data Sources 

Local climate may affect (1) the water balance (and

thus the acceptable wastewater hydraulic loading rate),

(2) the length of the growing season, (3) the number of 

days per year that a land treatment system cannot be

operated, (4) the storage capacity requirement, (5) the 

loading cycle of SAT systems, (6) crop selection, and (7) 

the amount of stormwater runoff. For this reason, local 

precipitation, evapotranspiration, temperature, and wind 

values must be determined before design criteria can be 

5-2 
established. Whenever possible, at least 10 years of

data should be used to obtain these values. 

Three publications of the National Oceanic and

Atmospheric Administration (NOAA) provide sufficient

data for most communities. The “Monthly Summary of 

Climatic Data” provides basic information, including total

precipitation, temperature maxima and minima, and

relative humidity, for each day of the month and every 

weather station in a given area. Whenever available,

evaporation data are included. An annual summary of 

climatic data, entitled “Local Climatological Data”, is 

published for a small number of major weather stations. 

Included in this publication are the means, and extremes 

of all the data on record to date for each station. The 

“Climate Summary of the United States” provides 10-

year summaries of the monthly climatic data. Other data 

included are:

• Total precipitation for each month of the 10-year 

period 

• Mean number of days that precipitation exceeded 

0.25 and 1.27 cm (0.10 and 0.50 inch) during each

month (see www for further information). 

• Total snowfall for each month of the period 

• Mean temperature for each month of the period 

• Mean daily temperature maxima and minima for 

each month 

• Mean number of days per month that the 

temperature was less than or equal to 0oC or greater

than or equal to 32.5oC 

A fourth reference that can be helpful is EPA's “Annual

and Seasonal Precipitation Probabilities” (Thomas and

Whiting, 1977a). This publication includes precipitation

probabilities for 93 stations throughout the United States. 

Data requirements for planning purposes are

summarized in Table 5-4 (Crites et al., 2000). 

5.1.5 Site Area Estimate 

The amount of land required for a land treatment 

system includes the area needed for buffer zones,

preapplication treatment, storage, access roads, 

pumping stations, and maintenance and administration 

buildings, environmental sensitivity, in addition to the

land actually required for treatment. Depending on

growth patterns in the study area, and on the 

accessibility of the land treatment site, additional land

may be required for future expansion or for 

emergencies.

Preliminary site area requirements can be estimated 

from wastewater flows, storage needs, and preliminary 

loading rates. The relationship between field area, 

loading rates, and operating period is shown in Equation

5-1, presented in both metric and English standard units. 

LP

Q F = 3.65 (metric)

or 

LP

Q F = 13,443 (U.S. customary) (5-1)

Where: 

F = field area, ha (acres) 

Q = average flow, m3

/d (mgd) 

L = loading rate, cm/wk (in/wk) 

(Preliminary values from Table 5-3) 

P = period of application, wk/yr 

3.65 = metric conversion factor = 

year

cm days

m d

ha m 100 365

/

0.0001 3

× × ⋅ x 1/m

13,443 = conversion factor = 

year

inch days

mgd

acre ft 12 365

3.069 × × ⋅ x 1/ft

The period of application (P) from Equation 5-1 can be

approximated by dividing the estimated storage period

from Figure 5-2 by 52 wks./yr. Typical site areas

requirements for a 3,785 m3

/day (some editors like

0.044m3

sec

-1) (1 mgd) flow for all three systems are 

presented in Table 5-5 (Crites et al., 2000). For SR and

SAT systems the numbers in Table 5-5 include 20 

percent extra area over the calculated field area to

account for unusable land. For OF systems, in Table 5-

5, the extra land area is 40 percent to account for the 

additional inefficiency in constructing OF slopes. 

Table 5-4. Summary of Climatic Analyses

Factor Data Required Analysis Use 

Precipitation Annual average, maximum, 

minimum 

Frequency Water balance 

Rainfall storm Intensity, duration Frequency Runoff estimate 

Temperature Days with average below freezing Frost-free period Storage, treatment efficiency, crop 

growing season 

Wind Velocity, direction — Cessation of sprinkling 

Evapotranspiration Annual, monthly average Annual distribution Water balance 

5-3 
5.2 Site Identification 

To identify potential land treatment sites it is necessary 

to obtain data on land use, soil types, topography, 

geology, groundwater, surface water hydrology, and 

applicable water rights issues. The types and sources of

data needed to identify and evaluate potential sites are

presented in Table 5-6 (Crites et al., 2000). 

5.2.1 Use of Overlay Maps

The complexity of site identification depends on the 

size of the study area and the nature of the land use. 

One approach is to start with land use plans and identify 

undeveloped land. Map overlays can then help the

planner or engineer to organize and study the combined

effects of land use, slope, relief, and soil permeability. 

Use of Geographic Information Systems (GIS) will ease

this process. Criteria can be set on these four factors,

and areas that satisfy the criteria can then be located. If 

this procedure is used as a preliminary step in site 

identification, the criteria should be reassessed during 

each iteration. Otherwise, strict adherence to such

criteria may result in overlooking either sites or land

treatment opportunities. 

5.2.2 Site Suitability Factors 

Potential land treatment sites are identified using a 

deductive approach (Sills et al., 1978). First, any

constraints that might limit site suitability are identified. 

In most study areas, all land within the area should be

evaluated for each land treatment process. The next 

step is to classify broad areas of land near the area

where wastewater is generated according to their land

treatment suitability. Factors that should be considered 

include current and planned land use, topography, soils,

geology, groundwater and surface water hydrology. 

Table 5-5. Site Identification Land Requirements, ha/m3·d (acres/mgd)

System Land Requirements, ha/m3

·d (acres/mgd) 

Slow rate, agricultural: 

 No storage 0.021 (200) 

 1 month’s storage 0.024 (225) 

 2 month’s storage 0.027 (250) 

 3 month’s storage 0.029 (275) 

 4 month’s storage 0.034 (315) 

 5 month’s storage 0.037 (350) 

 6 month’s storage 0.044 (415) 

Slow rate, forest: 

 No storage 0.033 (310) 

 1 month’s storage 0.036 (335) 

Soil aquifer treatment: 

 Primary effluent 0.0032 (30) 

 Secondary effluent 0.0016 (15) 

Overland flow: 

Storage (months) Applying screened wastewater Applying secondary effluent 

0 0.0096 (90) 0.019 (180) 

1 0.0107 (100) 0.021 (200) 

2 0.0117 (110) 0.023 (220) 

3 0.0128 (120) 0.026 (240) 

4 0.0149 (140) 0.030 (280) 

Table 5-6. Types and Sources of Data Required for Land Treatment Site Evaluation

Type of Data Principal Source 

Topography USGS topographic quads 

Soil type and permeability NRCS soil survey

Temperature 

(mean monthly and growing season) 

NRCS soil survey, NOAA, local airports, newspapers 

Precipitation 

(mean monthly, maximum monthly) 

NRCS soil survey, NOAA, local airports, newspapers 

Evapotranspiration and evaporation 

(mean monthly)

NRCS soil survey, NOAA, local airports, newspapers, agricultural extension service 

Land Use NRCS soil survey, aerial photographs from the Agricultural Stabilization and Conservation 

Service, and county assessor’s plats 

Zoning Community planning agency, city or county zoning maps 

Agricultural practices NRCS soil survey, agricultural extension service, country agents, crop consultants 

Surface and groundwater discharge requirements State or EPA 

Groundwater (depth and quality) State water agency, USGS, driller’s logs of nearby wells 

5-4 
Land Use 

Land use in most communities is regulated by local, 

county and regional zoning laws. Land treatment

systems must comply with the appropriate zoning

regulations. For this reason, the planner should be fully 

aware of the actual land uses and proposed land uses in

the study area. The planner should attempt to develop

land treatment alternatives that conform to local land use

goals and objectives. Land treatment systems may 

conform with the following land use objectives: 

• Protection of open space that is used for land

treatment 

• Production of agricultural or forest products using

wastewater on the land treatment site 

• Reclamation of land by using wastewater to

establish vegetation on scarred land

• Augmentation of parklands by irrigating such lands 

with wastewater

• Management of flood plains by using flood plain

areas for land treatment, thus precluding land 

development on such sites 

• Formation of buffer areas around major public

facilities, such as airports 

To evaluate present and planned land uses, city, 

county and regional land use plans should be consulted. 

Because such plans often do not reflect current land 

use, site visits are recommended to determine existing 

land use. Aerial photographic maps may be obtained

from the Natural Resources Conservation Service

(NRCS) or the local assessor's office. USGS is an 

additional source for aerial photo or satellite images. 

Many of the information sources are available on

Internet. Other useful information may be available from

the USGS, including true color, false color, infrared, and 

color infrared aerial photos of the study area. 

Once the current and planned land uses have been 

determined, these should be plotted on a study area

map. Then, land use suitability may be plotted using the 

factors shown in Table 5-7 (Moser, 1978). 

Both land acquisition procedures and treatment 

system operation are simplified when few land parcels 

(few land owners) are involved and contiguous parcels 

are used. Therefore, parcel size is an important 

parameter. Usually, information on parcel size can be 

obtained from county assessor or county recorder maps.

Again, the information should be plotted on a map of the 

study area. 

Topography 

Steep grades limit a site's potential because the 

amount of runoff and erosion that may occur is 

increased, crop cultivation is made more difficult, and

saturation of steep slopes may lead to unstable soil

conditions. The maximum acceptable grade depends on

soil characteristics and the land treatment process used 

(Table 1-2). 

Grade and elevation information can be obtained from 

USGS topographic maps, which usually have scales of 

1:24,000 (7.5 minute series) or 1:62,500 (15 minute 

series). Grade suitability may be plotted using the

criteria listed in Table 5-8 (Moser, 1978). 

Relief is another important topographical consideration 

and is the difference in elevation between one part of a

land treatment system and another. The primary impact

of relief is the effect on the cost of conveying wastewater 

to the land application site. Often, the economics of 

pumping wastewater to a nearby site must be compared 

with the cost of constructing gravity conveyance to more

distant sites.

Table 5-7. Land Use Suitability Factors for Identifying Land Treatment Sites (Moser, 1978)

Type of System 

Land Use Factor Agricultural Slow Rate Forest Slow Rate Overland Flow Soil Aquifer Treatment 

Open or cropland High Moderately high High High 

Partially forested Moderate High Moderate Moderate 

Heavily forested Low High Low Low

Built upon (residential, 

commercial, or industrial) 

Low Very low Very low Very low 

Table 5-8. Grade Suitability Factors for Identifying Land Treatment Sites (Moser, 1978)

Slow Rate Systems 

Grade Factor, % Agricultural Forest Overland Flow Soil Aquifer Treatment 

0 – 12 High High High High 

12 – 20 Low High Moderate Low

20+ Very low Moderate Eliminate Eliminate 

5-5 
A site's susceptibility to flooding also can affect its 

desirability. The flooding hazard of each potential site 

should be evaluated in terms of both the possible

severity and frequency of flooding as well as the extent 

of flooding. In some areas, it may be preferable to allow 

flooding of the application site provided offsite storage is 

available. Further, crops can be grown in flood plains if 

flooding is infrequent enough to make farming

economical. 

The landscape position and landform for each suitable 

area should be noted. Figure 5-3 can be used as a guide 

for identifying landscape positions. This information is

useful in estimating surface and subsurface drainage

patterns. For example, hilltops and sideslopes can be

expected to have good surface and subsurface

drainage, while depressions and footslopes are more

likely to be poorly drained (US EPA, 1980). 

Figure 5-3. Landscape Positions.

Overland flow sites can be located in flood plains 

provided they are protected from direct flooding which

could erode the slopes. Flood plain sites for SAT basins 

should be protected from flooding by the use of levees. 

Summaries of notable floods and descriptions of 

severe floods are published each year as the USGS 

Water Supply Papers. Maps of certain areas inundated

in past floods are published as Hydrologic Investigation

Atlases by the USGS. The USGS also has produced

more recent maps of flood prone areas for many regions

of the country as part of the Uniform National Program

for Managing Flood Losses. These maps are based on 

7.5 minute (1:24,000) topographic sheets and identify 

areas that lie within the 100 year flood plain. Additional

information on flooding susceptibility is available from

local offices of the U.S. Army Corps of Engineers and 

local flood control districts. Many county/city zoning 

offices have flood plain information 

Soils 

Common soil-texture terms and the relationship to the

NRCS textural class names are listed in Table 5-9

(Crites et al., 2000). 

In general, Fine-textured soils do not drain well and 

retain water for long periods of time. Thus, infiltration is

slower and crop management is more difficult than for 

freely drained soils such as loamy soils. Fine-textured

sloping soils are best suited for the OF process. Loamy

or medium-textured soils are desirable for the SR 

process, although sandy soils may be used with certain 

crops that grow well in rapidly draining soils. Soil 

structure and soil texture are important characteristics 

that relate to permeability and acceptability for land

treatment. Structure refers to the degree of soil particle

aggregation. A well structured soil is generally more

permeable than unstructured material of the same type. 

The SAT process is suited for sandy or loamy soils.

Soils surveys are usually available from the NRCS. 

Soil surveys normally contain maps showing soil series 

boundaries and textures to a depth of about 1.5 m (5 ft). 

In a survey, limited information on chemical properties,

grades, drainage, erosion potential, general suitability for 

locally grown crops, and interpretive and management 

information is provided. Where published surveys are

not available, information on soil characteristics can be 

obtained from the NRCS, through the local county agent. 

Much of this information is now available on the web at 

NRCS’s Electronic Field Office Guide 

(http://www.nrcs.usda.gov/technical/efotg/, (verified

August 22, 2005). 

Although soil depth, permeability, and chemical

characteristics significantly affect site suitability, data on 

these parameters are often not available before the site

investigation phase. If these data are available, they 

should be plotted on a study area map along with soil

Table 5-9. Soil Textural Classes and General Terminology Used in Soil Descriptions

General Terms

Common Name Texture Basic Soil Textural Class Names 

Sandy soils Coarse Sand, loamy sand

Moderately coarse Sandy loam, fine sandy loam 

Loamy soils Medium Very fine sandy loam, loam, silt loam, silt 

Moderately fine Clay loam, sandy clay loam, silty clay loam 

Clayey soils Fine Sandy clay, silty clay, clay

5-6 
texture. In identifying potential sites, the planner should

keep in mind that adequate soil depth is needed for root

development and for thorough wastewater treatment. 

Further, permeability requirements vary among the land

treatment processes. Desirable permeability ranges are

shown by process in Table 5-10 together with desired

soil texture (Crites et al., 2000). The NRCS permeability 

class definitions are also shown in Figure 3-5. 

Geology 

Certain geological formations are of interest during

phase 1 investigations. Discontinuities and fractures in 

bedrock may cause short-circuiting or other unexpected 

groundwater flow patterns. Impermeable or semipermeable layers of rock, clay, or hardpan can result in

perched groundwater tables. The USGS and many state 

geological surveys have maps indicating the presence

and effects of geological formations. These maps and

other USGS studies may be used to plot locations within

the study area where geological formations may limit the 

suitability for land treatment. 

Groundwater 

A knowledge of the regional groundwater conditions is 

particularly important for SAT and SR sites. Overland

flow will not usually require an extensive hydrogeologic 

investigation. There is sufficient removal of pollutants in 

the applied wastewater before reaching a permanent

groundwater resource is the primary concern. The depth

to groundwater and seasonal fluctuation are measures 

of the aeration zone. When several layers of stratified

groundwater underlie a particular site, the occurrence of 

the vertical leakage between layers should be evaluated. 

Direction and rate of groundwater flow and aquifer 

permeability together with groundwater depth are useful 

in predicting the effect of applied wastewater on the 

groundwater regime. The extent of recharge mounding, 

interconnection of aquifers, perched water tables, the 

potential for surfacing groundwater, and design of 

monitoring and withdrawal wells are dependent on 

groundwater flow data. 

Much of the data required for groundwater evaluation 

may be determined through use of existing wells. Wells 

that could be used for monitoring should be listed and

the relative location described. Historical data on quality, 

water levels, and quantities pumped from the operation 

of existing wells may be of value. Such data include 

seasonal groundwater-level variations, as well as 

variations over a period of years. The USGS maintains a

network of about 15,800 observation wells to monitor 

water levels nationwide. Records of about 3,500 of these

wells are published in Water-Supply Paper Series,

"Groundwater-Levels in the United States." Many local, 

regional, and state agencies compile drillers' boring logs 

that are also valuable for defining groundwater 

hydrology. Even though USGS has the monitoring well

network the local, state people have better data. 

Land treatment of wastewater can provide an

alternative to surface discharge of conventionally treated 

wastewater. However, the adverse impact of percolated 

wastewater on the quality of the groundwater must be

considered. Existing groundwater quality should be 

determined and compared to quality standards for its 

current or intended use. The expected quality of the

renovated wastewater can then be compared to 

determine which constituents in the renovated water 

might be limiting. The USGS "Groundwater Data

Network" monitors water quality in observation wells 

across the country. In addition, the USGS undertakes 

project investigations or groundwater studies in

cooperation with local, state, or other federal agencies to 

appraise groundwater quality. Such reports may provide 

a large part of the needed groundwater data. 

Surface Water Hydrology 

Surface water hydrology is of interest in land treatment

processes because of stormwater run-on and runoff. 

Considerations relating to surface runoff control apply to 

both SR and OF. SAT processes are designed for no

runoff. 

The control of stormwater runoff both onto and off a 

land treatment site must be considered. First, the 

facilities constructed as part of the treatment system

must be protected against erosion and washout from

extreme storm events. For example, where earthen

ditches and/or terraces are used, erosion control from

stormwater runoff must be provided. The degree of 

control of runoff to prevent the destruction of the physical 

system should be based on the economics of replacing

equipment and structures. There is no standard extreme 

storm event in the design of drainage and runoff

Table 5-10. Typical Soil Permeabilities and Textural Classes for Land Treatment

Land Treatment Processes 

Slow Rate Soil Aquifer Treatment Overland Flow

Soil permeability range, mm/h 

(in/h) 

1.5 – 50 

(0.06 – 2.0)

> 50 

(> 2.0) 

< 5 

(< 0.2) 

Permeability class range Moderately slow to moderately

rapid 

Rapid Slow

Textural class Clay loams to sandy Loams Sandy and sandy loams Clays and clay loams 

Unified soil classification GM-d, SM-d, ML, OL, MH, PT GW, GP, SW, SP GM-u, GC, SM-u, SC, CL, OL, CH, 

OH 

5-7 
collection systems, although a 10-year return, 24-hr 

storm is suggested as a minimum. See Chapter 9 for 

further discussion of storm water runoff of overland flow 

sites.

5.2.3 Water Rights 

Land application of wastewaters may cause several 

changes in drainage and flow patterns (Dewsnup and

Jensen, 1973): 

1. Site drainage may be affected by land preparation, 

soil characteristics, slope, method of wastewater

application, cover crops, climate, buffer zones, and 

spacing of irrigation equipment. 

2. Land application may alter the pattern of flow in the

body of water that would have received the

wastewater discharge. Although this may diminish

the flow in the body of water, it also may increase 

the quality. The change may be continuous or

seasonal. 

3. Land application may cause surface water diversion, 

because wastewaters that previously would have

been carried away by surface waters are now

applied to land and often diverted to a different 

watershed. 

Two basic types of water rights laws exist in the United

States: riparian laws, which emphasize the right of 

riparian landowners along a watercourse to use of the

water, and appropriative laws, which emphasize the right

of prior users of the water (Dewsnup and Jensen, 1973). 

Most riparian or land ownership rights are in effect east

of the Mississippi, whereas most appropriative rights are 

in effect west of the Mississippi River. 

Most states divide their water laws into three

categories: (1) waters in well-defined channels or basins

(natural watercourses), (2) superficial waters not in

channels or basins (surface waters), and (3) 

underground waters not in well-defined channels or 

basins (percolating waters or groundwater). 

The state or local water master or water rights 

engineer should be consulted to avoid potential 

problems. Other references to consider are the 

publications, “A Summary-Digest of State Water Laws,” 

available from the National Water Commission (US EPA,

1977b), and “Land Application of Wastewater and State

Water Law,” Volumes I and II (US EPA, 1977b and 

1978). If problems develop or are likely with any of the

feasible alternatives, a water rights attorney should also

be consulted.

5.3 Site Selection 

Once the data on site characteristics are collected and 

mapped, the site evaluation and selection process can

proceed. If the number of sites are few and their relative 

suitability clearly apparent, a simple economic 

comparison will lead to selection of the best site. If a

number of sites are to be compared, a site screening 

procedure can be used. 

5.3.1 Site Screening Procedure 

The general procedure for site suitability rating can be 

used to compare different sites or it can be used to 

screen a large site that may have portions suitable to

different land treatment processes. A procedure

incorporating economic factors is presented for SAT and

OF systems. A procedure specific to SR forest systems

is also included. 

The general procedure is to assign numerical values to 

various site characteristics, with larger numbers

indicating highest suitability. The individual numbers for 

each site or sub-area are then added together to obtain

the overall suitability rating. The rating factors in Table

5-11 are applicable to all processes. Site rating factors 

and weightings should vary to suit the needs of the local

area and type of sites available. 

5.3.2 Screening Procedure with Economic 

Factors 

In addition to the rating factors listed in Table 5-11

(Taylor, 1981) the economics of site development are 

often critical. These include distance from the 

wastewater source, elevation differences and the costs 

for land acquisition and management. Table 5-12

presents rating factors for these concerns (Crites et al., 

2000). 

5.3.3 Procedure for Forested SR Systems 

A procedure has been developed for forested SR 

systems that incorporates climatic, soil, geologic,

hydrologic and vegetation factors (Taylor, 1981). The

procedure involves the use of rating values for 

subsurface factors (Table 5-13), soils (Table 5-14), and

surface factors (

Table 5-15) together with the composite rating in Table

5-16. 

Based on the ratings in these tables, an estimate of 

the preliminary hydraulic loading can be made using 

Table 5-16. This procedure was developed for sprinkler 

irrigation of forested sites in the southeastern United 

States. 

5.4 Phase 2 Planning 

Phase 2, the site investigation phase, occurs only if 

sites with potential have been identified in Phase 1. 

5-8 
During Phase 2, field investigations are conducted at the 

selected sites to determine whether land treatment is 

Table 5-11. Rating Factors for Site Selection (Taylor, 1981)

Slow Rate Systems 

Characteristic Agricultural Forest Overland Flow Rapid Infiltration 

Soil depth, ft*(a)

1 – 2 E† E 0 E 

2 – 5 3 3 4 E 

5 – 10 8 8 7 4 

> 10 9 9 7 8 

Minimum depth to groundwater, ft

<4 0 0 2 E 

4 – 10 4 4 4 2 

> 10 6 6 6 6 

Permeability, in/h‡(b)

< 0.06 1 1 10 E 

0.06 – 0.2 3 3 8 E 

0.2 – 0.6 5 5 6 1 

0.6 – 2.0 8 8 1 6 

> 2.0 8 8 E 9 

Grade, % 

0 – 5 8 8 8 8 

5 – 10 6 8 5 4 

10 – 15 4 6 2 1 

15 – 20 0 5 E E 

20 – 30 0 4 E E 

30 – 35 E 2 E E 

> 35 E 0 E E 

Existing or planned land use 

Industrial 0 0 0 0 

High-density residential/urban 0 0 0 0 

Low-density residential/urban 1 1 1 1 

Forested 1 4 1 1 

Agricultural or open space 4 3 4 4 

Overall suitability rating§

Low < 15 < 15 < 16 < 16 

Moderate 15 – 25 15 – 25 16 – 25 16 – 25 

High 25 - 35 25 – 35 25 - 35 25 – 35 

Note: The higher the maximum number in each characteristic, the more important the characteristic; the higher the ranking, the greater the suitability.

* Depth of the profile to bedrock. † Excluded; rated as poor. ‡ Permeability of most restrictive layer in soil profile. 

§ Sum of values. 

a

ft x 0.3048 = m b

in/h x 2.54 = cm/h 

Table 5-12. Economic Rating Factors for Site Selection 

(Taylor, 1981)

Characteristic Rating Value 

Distance from wastewater source, milesa

0 – 2 8 

2 – 5 6 

5 – 10 3 

> 10 1 

Elevation difference, ftb

< 0 6 

0 – 50 5 

50 – 200 3 

> 200 1 

Land cost and management 

No land purchase, farmer-operated 5 

Land purchased, farmer-operated 3 

Land purchased, city- or industry-operated 1 a

mile x 1.609 = km b

ft x 0.3048 = m 

technically feasible. When sufficient data have been

collected, preliminary design criteria are calculated for 

each potential site. Using these criteria, capital and

operation and maintenance costs are estimated. These

cost estimates and other nonmonetary factors are used 

to evaluate the sites selected during Phase 1 for cost 

effectiveness. On the basis of this evaluation, a land

treatment alternative is selected for design. 

5.4.1 Field Investigations 

The factors regarding groundwater conditions, soil 

properties, and other site attributes not only influence the 

initial site selection and concept feasibility decisions but 

are critical for the final system design. As with all other 

engineering projects, the type of test required and the 

specific procedure are relatively easy to describe. The

more difficult decision is how many tests, and in what 

5-9 
locations, for a particular project. Too little field data may 

lead to erroneous conclusions while too much will result

in unnecessarily high costs with little refinement in the

design concept. Experience indicates that where 

uncertainty exists, it is prudent to adopt a conservative 

posture relative to data-gathering requirements. 

Table 5-13. Subsurface Factors for Forested SR 

(Taylor, 1981)

Characteristics Rating Value* 

Depth to groundwater on barrier, fta

< 4 0 

4 – 10 4 

> 10 6 

Depth to bedrock, fta

< 5 0 

5 – 10 4 

> 10 6 

Type of bedrock 

Shale 2 

Sandstone 4 

Granite-gneiss 6 

Exposed bedrock, % of total area

< 33 0 

10 – 33 2 

1 – 10 4 

None 6 

*0 – 9, site not feasible; 10 – 13, poor; 14 – 19, good; 

 and 20 – 24, excellent. a

ft x 0.3048 = m .

Table 5-14. Soil Factors for Forested SR (Taylor, 1981)

Characteristics Rating Value* 

Infiltration rate, in/ha

< 2 2 

2 – 6 4 

> 6 6 

Hydraulic conductivity, in/ha

> 6 2 

< 2 4 

2 – 6 6 

CEC, meq/100 g

< 10 1 

10 – 15 2 

> 15 3 

Shrink-swell potential (NRCS) 

High 1 

Low 2 

Moderate 3 

Erosion classification (NRCS) 

Severely eroded 1 

Eroded 2 

Not eroded 3 

*5 – 11, poor; 12 – 16, good; and 17 – 21, excellent. a

in/h x 2.54 = cm/h. 

Table 5-15. Surface Factors for Forested SR (Taylor, 1981)

Characteristics Rating Value* 

Dominant vegetation 

Pine 2 

Hardwood or mixed 3 

Vegetation age, years 

Pine 

> 30 3 

20 – 30 3 

< 20 4 

Hardwood 

> 50 1 

30 – 50 2 

< 50 3 

Mixed pine/hardwood 

> 40 1 

25 – 40 2 

< 25 3 

Slope, % 

> 35 0 

0 – 1 2 

2 – 6 4 

7 – 35 6 

Distance to flowing stream, fta

50 – 100 1 

100 – 200 2 

> 200 3 

Adjacent land use 

High-density residential/urban 1 

Low-density residential/urban 2 

Industrial 2 

Undeveloped 3 

*3 – 4, not feasible; 5 – 9, poor; 9 – 14 good; and 

15 – 19, excellent. a

ft x 0.3048 = m.

Table 5-17 presents field tests for a land treatment

project. When possible, available data are first used for 

calculations or decisions that may then necessitate 

additional field tests. Guidance for wastewater

constituents and soil properties is provided for each land

treatment process in Table 5-18 (Crites et al., 2000).

Generally relatively modest programs of field testing and

data analysis will be satisfactory, especially for small

systems.

5.4.2 Soil Properties 

A critical element in site selection and process design

is the capability of the site soils to move the design 

quantities of water in the expected direction at the

expected rates. These are important requirements for 

slow rate (SR) systems and are absolutely critical for soil

aquifer treatment (SAT) because of the much higher 

hydraulic loadings. 

5-10 
Table 5-16. Composite Evaluation of SR Forested Sites (Taylor, 1981)

Evaluation ratings from Tables 5-13 to 5-15 

Poor Good Excellent Hydraulic Loading, in/weeka

3 0 0 Not feasible 

2 1 0 < 1.0 

2 0 1 < 1.0 

1 2 0 1.0 – 1.5 

1 1 1 1.0 – 1.5 

1 0 2 1.5 – 2.0 

0 3 0 2.0 – 2.5 

0 2 1 2.0 – 2.5 

0 1 2 2.5 – 3.0 

0 0 3 2.5 – 3.0 a

 in/week x 2.54 = cm/week

Table 5-17. Sequence of Field Testing - Typical Order of Testing (US EPA, 1981b)

Field Tests 

Test Pits Bore Holes Infiltration Rate Soil Chemistry

Remarks Usually with a backhoe, 

includes inspection of existing 

NRCS reports, road cuts, etc. 

Drilled or augered includes 

inspection of driller’s logs for 

local wells, water table levels 

Match the expected method of 

application, if possible 

Includes review of NRCS 

survey

Information to 

obtain 

Depth of profile, texture, 

structure, soil layers

restricting percolation 

Depth to groundwater, depth 

to impermeable layer(s) 

Expected minimum infiltration 

rate 

Specific data relating to crop 

and soil management, 

phosphorus and heavy metal 

retention 

Estimates now

possible 

Need for vertical conductivity

testing 

Groundwater flow direction Hydraulic capacity based on 

soil permeability (subject to 

drainage restrictions) 

Crop limitations. Soil 

amendments. Possible 

preapplication requirements 

Additional field 

tests 

Vertical conductivity

(optional) 

Horizontal conductivity

Additional 

estimates 

Refinement of loading rates Mounding analysis, 

dispersion, need for drainage 

— Quality of percolate 

Number of tests Depends on size, soil 

uniformity, needed soil tests, 

type of system. Typical 

minimum of 3-5 per site 

Depends on system type 

(more for RI than SR), soil 

uniformity, site size. Typical 

minimum of 3 per site 

Depends on size of site, 

uniformity of soil. Typical 

minimum of 2 per site. 

Depends on uniformity of soil 

types, type of test, size of site 

Table 5-18. Summary of Field Tests for Land Treatment Processes

Processes 

Properties 

Slow Rate 

(SR) 

Soil Aquifer Treatment (SAT) Overland Flow

(OF) 

Wastewater constituents Nitrogen, phosphorus, SAR*, EC*,

boron 

BOD, SS, nitrogen, phosphorus BOD, SS, nitrogen, phosphorus 

Soil physical properties Depth of profile, texture and 

structure 

Depth of profile, texture and structure Depth of profile, texture and 

structure 

Soil hydraulic properties Infiltration rate 

Subsurface permeability

Infiltration rate 

Subsurface permeability

Infiltration rate (optional) 

Soil chemical properties pH, CEC, exchangeable cations (% 

of CEC), EC*, metals†

, phosphorus 

adsorption (optional) 

pH, CEC, phosphorus adsorption

(optional) 

pH, CEC, exchangeable cations 

(% of CEC)

*May be more significant for arid and semiarid areas. †

Background levels of metals in the soil should be determined if food chain crops are planned.

Physical Characteristics 

Site identification and selection will ordinarily be based

on existing field data available from a NRCS county soil

survey and other sources. The next step involves some

physical exploration on the site. This preliminary

exploration is of critical importance to subsequent 

phases of the project. The field exploration is important 

and has two purposes: (1) verification of existing data 

and (2) identification of probable, or possible, site 

limitations. For example, the presence of wet areas, 

water-loving plant species, or surficial salt crusts should 

alert the designer to the need for detailed field studies 

directed toward the problem of drainage. The presence

5-11 
of rock outcroppings would signify the need for more

detailed subsurface investigations than might normally 

be required. If a stream were located near the site, there

would need to be additional study of the surface and

near-surface hydrology; nearby wells require details of 

the groundwater flow, and so on. These points may 

seem obvious. There are many systems that have failed 

because of just such obvious conditions: limitations that 

were not recognized until after design and construction

were complete. 

The methods of construction and system operation

that will be used can also be critically important

depending on the soil properties encountered and must 

be considered in the site and concept selection process.

The characteristics of the soil profile in the undisturbed

state may be completely altered when the design

surface is exposed or by inadvertent compaction during

construction. Fine textured soils are particularly 

susceptible to compaction. For example, if the design 

surface layer contains a significant clay fraction and if

that surface is exposed for growth of row crops in a SR 

system the impact of rainfall and sprinkler droplets may 

result in sorting of the clay fines and a partial sealing of

the surface. Such problems can be managed, but the

field investigation must provide sufficient data so that 

such conditions can be anticipated in the design. 

SAT Systems 

Soil properties, topography, and construction methods 

are particularly critical for SAT systems. A site with a

heterogeneous mixture of soil types containing scattered

lenses of fine textured soil may be impossible to

adequately define with a typical investigation program. If 

such a site cannot be avoided for SAT, a large-scale 

pilot test basin is suggested for definition of site 

hydraulic characteristics. If the pilot test is successful, 

the test basin, if properly located, can then be included

in the full scale system.

An SAT site with undulating topography may require a

scattered array of basins to remain in desirable soils or 

may necessitate major cut and fill operations for a

compact site. SAT basins should always be constructed 

in cut section if at all possible. Experience has shown 

that construction with soils that have a fine fraction

(passing No. 200 sieve [< 0.075mm]) of more than 5 

percent can result in problems (Reed, 1982). Clayey 

sands with fines exceeding 10 percent by weight should

be avoided altogether as fill material for basin infiltration 

surfaces. Pilot scale test basins are recommended

whenever SAT systems are to be designed on backfilled 

soils.

Construction 

Construction activity, either cut or fill, for SAT or SR 

systems can have a drastic effect on soil permeability if 

clayey sands are present. Such activity should only be 

permitted when the soil moisture is on the dry side of

"optimum." Optimum Moisture refers to a moisture soil 

density relationship: used in the construction industry to

obtain optimum soil compaction. Inadvertent compaction

with the soil on the wet side of optimum moisture content 

could result in the same bulk density for the soil but an

order of magnitude reduction in permeability. If such 

compaction is limited to the top foot of the surface layer, 

a final ripping and disking may correct the problem. 

Compaction of this type on sequential layers of fill may

not be correctable. 

The importance of soil texture for concept and site 

selection was described in Chapter 3 of this manual, 

and is based on the USDA soil classes (Figure 3-1).

Table 5-19 summarizes the interpretation of these 

physical and hydraulic properties. 

Table 5-19. Interpretation of Soil Physical and Hydraulic Properties 

(Crites, et al., 2000)

Property Interpretation 

Depth of soil profile, fta

< 1 – 2 Suitable for OF* 

> 2 – 5 Suitable for SR and OF 

5 – 10 Suitable for all processes 

Texture and structure 

Fine texture, poor structure Suitable for OF 

Fine texture, well-structured Suitable for SR and possibly OF 

Coarse texture, well-structured Suitable for SR and SAT 

Infiltration rate, in/hb

0.2 – 6 Suitable for SR 

> 2.0 Suitable for SAT

< 0.2 Suitable for OF 

Subsurface permeability

Exceeds or equals infiltration rate Infiltration rate limiting 

Less than infiltration May limit application rate 

*Suitable soil depth must be available for shaping of overland flow

slopes. 

Slow rate process using a grass crop may also be suitable. a

ft x 0.3048 = m b

in/h x 2.54 = cm/h. 

Chemical Properties 

The influence of soil chemical properties on 

permeability and infiltration was discussed in detail in 

Chapter 3. Adverse chemical reactions between the

wastewater and the soil are not expected for municipal 

and most industrial effluents. The main concern is 

usually retention or removal of a particular chemical by

the soil system and Chapter 2 provides more details. 

Differences in the chemical characteristics between

the applied wastewater and the soil may induce

chemical changes in the soil. At Muskegon, MI, for 

5-12 
example, the initial wastewater applications flushed

dissolved iron out of the soil profile, showing up as a

reddish turbidity in the drain water. Fresno, CA, also had 

turbidity problems when high-quality river water 

(snowmelt) was applied to relatively saline soils 

(Nightingale, 1983). This low salinity water dispersed the

submicron soil colloids in the upper 3.66 m (12 ft) of the

soil profile. The colloids are then flocculated as mixing

occurs with the more saline groundwater. This turbidity 

problem has persisted for 10 years but does not affect 

water quality in down gradient wells. 

Soil chemistry data is usually obtained via routine

laboratory tests on representative samples obtained

from test pits or borings. Table 5-20 summarizes the 

interpretation of typical soil chemical tests. 

Test Pits and Borings

Following an initial field reconnaissance, some 

subsurface exploration will be needed. In the preliminary 

stages, this consists of digging pits, usually with a

backhoe, at several carefully selected locations.

Besides exposing the soil profile for inspection and

sampling, the purpose is to identify subsurface features 

that could develop into site limitations, or that point to 

potential adverse features. Conditions such as fractured, 

near-surface rock, hardpan layers, evidence of mottling

in the profile, lenses of gravel and other anomalies 

should be carefully noted. For OF site evaluations, the 

depth of soil profile evaluation can be the top 0.9 m (3 ft) 

or so. The evaluation should extend to 1.5 m (5 ft) for SR 

and 3 m (10 ft) or more for SAT systems. 

Representative samples are obtained from the test pits 

and analyzed to determine the physical and chemical

properties discussed above. It is possible with

experience to estimate soil texture in the field with small 

samples taken directly from the walls of the test pit. To 

determine the soil texture, moisten a sample of soil 

about 12.7 to 25.4 mm (0.5 to 1 in) in diameter. There

should be just enough moisture so that the consistency

is like putty. Too much moisture results in a sticky

material, which is hard to work. Press and squeeze the 

sample between the thumb and forefinger. Gradually 

press the thumb forward to try to form a ribbon from the 

soil. By using this procedure, the texture of the soil can

be easily described with the criteria given in Table 5-21

(US EPA, 1980). 

If the soil sample ribbons (loam, clay loam, or clay), it 

may be desirable to determine if sand or silt

predominate. If there is a gritty feel and a lack of smooth 

talc-like feel, then sand very likely predominates. If there

is a lack of a gritty feel but a smooth talc-like feel, then

silt predominates. If there is not a predominance of 

either the smooth or gritty feel, then the sample should 

not be called anything other than a clay, clay loam, or

loam. If a sample feels quite smooth with little or no grit 

in it, and will not form a ribbon, the sample would be

called silt loam. 

Table 5-20. Interpretation of Soil Chemical Tests (US EPA, 1981)

Test Results Interpretation 

pH of saturated soil paste 

< 4.2 Too acid for most crops to do well 

4.2 – 5.5 Suitable for acid-tolerant crops and forest systems

5.5 – 8.4 Suitable for most crops 

> 8.4 Too alkaline for most crops; indicates a possible sodium problem 

CEC, meq/100 g

1 – 10 Sandy soils (limited adsorption) 

12 – 20 Silty loam (moderate adsorption)

> 20 Clay and organic soils (high adsorption) 

Exchangeable cations, % of CEC (desirable range)

Sodium 5 

Calcium 60 – 70 

Potassium 5 – 10 

Magnesium 10 – 20 

ESP, % of CEC 

< 5 Satisfactory

> 10 Reduced permeability in fine-textured soils 

> 20 Reduced permeability in coarse-textured soils 

ECe, mmhos/cm at 25% of saturation extract 

< 2 No salinity problems 

2 – 4 Restricts growth of very salt-sensitive crops 

4 – 8 Restricts growth of many crops 

8 – 16 Restricts growth of all but salt-tolerant crops 

> 16 Only a few very salt-tolerant crops make satisfactory yields 

5-13 
Table 5-21. Textural Properties of Mineral Soils

Feeling and Appearance 

Soil Class Dry Soil Moist Soil 

Sand Loose, single grains which feel gritty. Squeezed in 

the hand, the soil mass falls apart when the 

pressure is released 

Squeezed in the hand, it forms a cast which crumbles when touched. 

Does not form a ribbon between thumb and forefinger 

Sandy Loam Aggregates easily crushed; very faint velvety

feeling initially, but with continued rubbing the 

gritty feeling of sand soon dominates 

Forms a cast which bears careful handling without breaking. Does not 

form a ribbon between thumb and forefinger 

Loam Aggregates are crushed under moderate 

pressure; clods can be quite firm. When 

pulverized, loam has velvety feel that becomes 

gritty with continued rubbing. Cast bear careful 

handling 

Cast can be handled quite freely without breaking. Very slight tendency

to ribbon between thumb and forefinger. Rubbed surface is rough 

Silt loam Aggregates are firm but may be crushed under 

moderate pressure. Clods are firm to hard. 

Smooth, flourlike feel dominates when soil is 

pulverized. 

Cast can be freely handled without breaking. Slight tendency to ribbon 

between thumb and forefinger. Rubbed surface has a broken or rippled 

appearance 

Clay loam Very firm aggregates and hard clods that strongly

resist crushing by hand. When pulverized, the soil 

takes on a somewhat gritty feeling due to the 

harshness of the very small aggregates which 

persist 

Cast can bear much handling without breaking. Pinched between the 

thumb and forefinger, it forms a ribbon whose surface tends to feel 

slightly gritty when dampened and rubbed. Soil is plastic, sticky, and 

puddles easily. 

Clay Aggregates are hard; clods are extremely hard 

and strongly resist crushing by hand. When 

pulverized, it has a gritlike texture due to the 

harshness of numerous very small aggregates 

which persist 

Cast can bear considerable handling without breaking. Forms a flexible 

ribbon between thumb and forefinger and retains its plasticity when 

elongated. Rubbed surface has a very smooth, satin feeling. Sticky

when wet and easily puddled 

Beginning at the top or bottom of the pit sidewall, 

obvious changes in texture with depth are noted. 

Boundaries that can be seen are marked. When the 

textures have been determined for each horizon (layer), 

its depth, thickness, and texture layer are recorded. 

Soil structure (Table 5-22) has a significant influence

on soil acceptance and transmission of water. Soil 

structure refers to the aggregation of soil particles into 

clusters of particles, called peds, that are separated by

surfaces of weakness. These surface of weakness are

often seen as cracks in the soil. These planar pores can 

greatly modify the influence of soil texture on water 

movement. Well-structured soils with large voids 

between peds will transmit water more rapidly than 

structureless soils of the same texture, particularly if the 

soil has become dry before the water is added. Finetextured, massive soils (soils with little structure) have 

very slow percolation rates. 

Table 5-22. Soil Structure Grades (US EPA, 1980)

Grade Characteristics 

Structureless No observable aggregation 

Weak Poorly formed and difficult to see. Will not 

retain shape on handling 

Moderate Evident but not distinct in undisturbed soil. 

Moderately durable on handling 

Strong Visually distinct in undisturbed soil. Durable on 

handling 

Soil structure can be examined in the pit with a pick or

similar device to expose the natural cleavages and 

planes of weakness. The color and color patterns in soil 

are also good indicators of the drainage characteristics

of the soil. It is often advantageous to prepare the soil pit

so the sun will be shining on the face during the 

observation period. Natural light will give true color 

interpretations. Artificial lighting should not be used. 

Color may be described by estimating the true color 

for each horizon or by comparing the soil with the colors 

in a soil color book. In either case, it is particularly 

important to note the colors or color patterns. Soil color 

is generally measured by a Munsell Soil Color Chart

(see www. munsell.com) verified August 25, 2005. 

Seasonally high groundwater tables are preferably 

detected by borings made during the wet season of the

year for the site. An indication of seasonally high 

groundwater can be observed by the presence of redox 

features (mottles or discolored soils) in the wall of the 

test pit. Mottling in soils is described by the color of the

soil matrix and the color or colors, size, and number of 

the mottles. Each color may be given a Munsell

designation and name. However, it is often sufficient to

say the soil is mottled. A classification of mottles used by 

the USDA is shown in Table 5-23. Color photographs of

typical soil mottles can be used to assist in identification 

(US EPA, 1980). 

5-14 
Table 5-23. Description of Soil Mottles (US EPA, 1980)

Character Class Limit 

Few 2% of exposed face 

Common 2 – 20% of exposed face 

Abundance 

Many 20% of exposed face 

Fine 0.25 ina

 longest dimension 

Medium 0.25 – 0.75 ina longest dimension 

Size 

Coarse 7 – 75 ina longest dimension 

Faint Recognized only by close observation 

Distinct Readily seen but not striking 

Contrast 

Prominent Obvious and striking 

All of the data collected in the test pit on texture, 

thickness of each horizon, structure, color, and presence

of water should be recorded in the field. A sample log is 

shown in Figure 5-4 (Crites et al., 2000). 

in x 2.54 = cm 

Figure 5-4. Sample Log for Test Pit Data.

In some site evaluations, the backhoe pits will not yield

sufficient information on the profile. Auger holes or bore

holes are frequently used to explore soil deposits below 

the limits of pit excavation. Augers are useful to relatively 

shallow depths compared to other boring techniques.

Depth limitation for augering varies with soil type and

conditions, as well as hole diameter. In unconsolidated 

materials above water tables, 12.7-cm (5-in) diameter 

holes have been augered beyond 3.51 m (11.5 ft). 

Cuttings that are continuously brought to the surface

during augering are not suitable for logging the soil 

materials. Withdrawal of the auger flights for removal of

the cuttings near the tip represents an improvement as a 

logging technique. The best method is to withdraw the

flights and obtain a sample with a Shelby tube or splitspoon sampler. 

Boring methods, which can be used to probe deeper 

than auguring, include churn drillings, jetting, and rotary

drilling. When using any of these methods it is preferable 

to clean out the hole and secure a sample from the 

bottom of the hole with a Shelby tube or split-spoon

sampler.

5.4.3 Groundwater Conditions 

The position, the rate of flow, and the direction of flow

of the natural groundwater beneath the site are critical

elements in the field investigation. Some key questions 

to be answered by the investigation are:

1. How deep beneath the surface is the (undisturbed) 

water table? 

2. How does the natural water table depth fluctuate

seasonally? 

3. How will the groundwater table respond to the

proposed wastewater loadings? 

4. In what direction and how fast will the mixture of 

percolate and groundwater move from beneath the

area of application? Is there any possibility of 

transport of contaminants to deeper potable 

aquifers? 

5. What will be the quality of this mixture as it flows 

away from the site boundaries? 

6. Do any restrictions exist along the site boundary that

may limit the groundwater flow? 

7. If any of the conditions measured or predicted above

are found to be unacceptable, what steps can be

taken to correct the situation? 

Groundwater Depth and Hydrostatic Head 

A groundwater table is defined as the contact zone 

between the free groundwater and the capillary zone. It 

is the level assumed by the water in a hole extended a

short distance below the capillary zone. Groundwater 

conditions are regular when there is only one

groundwater surface and when the hydrostatic pressure 

increases linearly with depth. Under this condition, the

piezometric pressure level is the same as the free

groundwater level regardless of the depth below the 

groundwater table at which it is measured. Referring to

Figure 5-5 (US EPA, 1981b), the water level in the

"piezometer" would stand at the same level as the "well"

in this condition. 

5-15 
Figure 5-5. Well and Piezometer Installations.

In contrast to a well, a piezometer is a small diameter 

open pipe driven into the soil such that (theoretically) 

there can be no leakage around the pipe. As the

piezometer is not slotted or perforated, it can respond

only to the hydrostatic head at the point where its lower 

open end is located. The basic difference between water 

level measurement with a well and hydrostatic head

measurement with a piezometer is shown in Figure 5-5. 

Occasionally there may be one or more isolated

bodies of water "perched" above the main water table 

because of lenses of impervious strata that inhibit or 

even prevent seepage past them to the main body of 

groundwater below. 

Reliable determination of either groundwater levels or 

pressures requires that the hydrostatic pressures in the 

bore hole and the surrounding soil be equalized. 

Attainment of stable levels may require considerable

time in impermeable materials. Called hydrostatic time

lag, this may be from hours to days in materials of 

practical interest. 

Two or more piezometers located together, but 

terminating at different depth, can indicate the presence, 

direction and magnitude (gradient) of components of 

vertical flow if such exists. Their use is indicated 

whenever there is concern about movement of 

contaminants downward to lower living aquifers. Figure

5-6 shows several observable patterns with 

explanations. Details on the proper installation of wells 

and piezometers are described in the US DOI “Drainage

Manual” (1978). 

Groundwater Flow 

Exact mathematical description of flow in the saturated 

zones beneath and adjacent to (usually downgradient) 

land treatment systems is a practical impossibility. 

However, for the majority of cases the possession of 

sufficient field data will allow an application of Darcy's 

equation (see Equation 3-1, and related discussion in 

Chapter 3) to determine the volume of flow and the

mean travel time, as well as estimating the mounding 

that will be created by the wastewater applications. The 

calculation procedures are presented in detail. The

necessary field data include: 

1. Depth to groundwater. 

2. Depth to any impermeable barrier. 

3. Hydraulic gradient determined from water levels in

several observation wells at known distances apart.

Establishing the gradient also determines the

direction of flow. 

4. Specific yield (see Chapter 3). 

5. Hydraulic conductivity in the horizontal direction (see

Chapter 3). 

Figure 5-6. Vertical Flow Direction Indicated by Piezometers (US 

EPA, 1981).

Data for items 1 and 3 can be obtained from periodic 

water-level observations, over a period of months, from

simple wells installed on the site. Figure 5-7 illustrates a 

typical shallow well. 

The number and locations required will depend on the

size of the project and the complexity of the groundwater 

system. Typical locations are up gradient of the site,

several on the site, and on the down-gradient boundary. 

In general, groundwater levels will tend to reflect the 

surface contours and flow toward adjacent surface

waters. In a complex situation it may be necessary to 

install a few exploratory wells and then complete the

array based on the preliminary data. If properly located, 

many of these wells can also serve for performance

monitoring during system operation. It is necessary to 

determine the elevation at the top of each well. The

depth to water can then be determined with a weighted, 

chalked tape or other sensing devices. Contours 

showing equal groundwater elevation can then be 

interpolated from the well data and plotted on a site map. 

This in turn allows determination of the hydraulic 

gradient and the flow direction. 

Subsurface Permeability and Infiltration Rate 

Methods for investigating subsurface permeability and 

infiltration rate are discussed in Sections 3.8.1 and 3.8.2,

respectively. 

5-16 
Mixing of Wastewater Percolate with 

Groundwater 

An analysis of the mixing of percolate with native 

groundwater is needed for SR and SAT systems that 

discharge to groundwater if the quality of this mixture as 

it flows away from the site boundaries is a concern. The 

concentration of any constituent in this mixture can be 

calculated as follows: 

P gw

P P gw gw

mix Q Q

C Q C Q C ++ = (5-2)

Where 

Cmix = concentration of constituent in mixture 

Cp = concentration of constituent in percolate 

Qp = flow of percolate

Cgw = concentration of constituent in groundwater

Qgw = flow of groundwater 

Figure 5-7. Typical Shallow Monitoring Well (Crites et al., 2000).

The flow of groundwater can be calculated from

Darcy's Law (Equation 3-1) if the gradient and horizontal 

hydraulic conductivity are known. This is not the entire 

groundwater flow, but only the flow within the mixing 

depth. Equation 5-2 is only valid if there is complete

mixing between the percolate and the native 

groundwater. This is usually not the case. Mixing in the 

vertical direction may be substantially less than mixing in 

the horizontal direction, and density, salinity, and

temperature differences between the percolate and

groundwater may inhibit mixing and the percolate may in 

some cases "float" as a plume on top of the groundwater

for some distance. The percolation of natural rainfall 

down gradient of the application site can also serve to 

dilute the plume. 

An alternative approach to estimating the initial dilution

is to relate the diameter of the mound developed by the 

percolate to the diameter of the application area. This 

ratio has been estimated to be 2.5 to 3.0. This ratio 

indicates the relative spread of the percolate and can be

used to relate the mixing of percolate with groundwater. 

Thus, an upper limit of 3 for the dilution ratio can be 

used when groundwater flow is substantially (5 to 10

times) more than the percolate flow. If the groundwater 

flow is less than 3 times the percolate flow, the actual 

groundwater flow should be used in Equation 5-2. 

5.4.4 Selection of Preliminary Design

Criteria 

From information collected during the field

investigations, the engineer can confirm the suitability of 

the sites for the identified land treatment process(es). 

Using the loading rates described previously (Section

5.6.2), the engineer should then select the appropriate 

hydraulic loading rate for each land treatment process 

that is suitable for each site under consideration. Based

on the hydraulic loading rates, estimates for land area,

preapplication treatment, storage, and other system 

requirements can be determined. Reuse and recovery

options should also be outlined. 

5.5 Cost and Energy Considerations 

Once the preliminary design criteria have been

identified, the land treatment alternatives should be

evaluated on the basis of capital costs, revenueproducing benefits, and energy requirements. Based on

these final evaluations, an appropriate plan can then be

selected and the land treatment system design initiated. 

There are eight major categories of capital costs for 

land treatment systems: 

1. Transmission

2. Pumping 

3. Preapplication treatment 

4. Storage 

5. Field preparation/Crop establishment 

6. Distribution 

7. Recovery 

8. Land acquisition 

In addition, there are costs associated with monitoring,

administration buildings, roads, and service and interest

factors. There also may be costs for fencing, relocation 

5-17 
of residents and purchase of water rights. Depending on 

the site management, SR and OF systems may have 

costs associated with crop planting, cultivating and

harvesting. 

Operation and maintenance (O&M) costs associated 

with all of the eight categories of capital costs except for 

land purchase and field preparation. These O&M costs 

can be divided into categories of labor, power and

materials. Labor and materials for distribution and 

recovery are presented in this chapter. Power costs for 

pumping can be estimated from the energy 

requirements. All costs in this chapter are for July 1999

using an Engineering News-Record Construction Cost 

Index (ENRCCI) of 6076. These costs are only planning 

level values and should not be used for designed system 

cost estimating. 

5.5.1 Transmission 

Transmission of wastewater to application sites can 

involve gravity pipe, open channels or pressure force

mains. Pumping can also be involved with gravity flow 

transmission, but is required for force main transmission. 

Costs of transmission depend on the pipe or the channel

size and can be estimated using US EPA (1981c). 

5.5.2 Pumping 

Pumping facilities for land treatment, as described in

Chapter 7, range from full pumping stations to tailwater 

pumping facilities (see Section 5.5.7). Capital costs for 

transmission pumping depend on the type of structure

that is designed. For example, a fully enclosed wet

well/dry well structure, pumps, piping and valves, 

controls and electrical can cost $500,000 for a 3,785 

m3

/d (1 mgd) peak flow and a 45-m (150-ft) of total 

pumping head. For structures that are built into the dike 

of a pond, the capital cost of the pumping station for the

same flow and head can be $300,000. 

5.5.3 Preapplication Treatment 

Preapplication treatment for land treatment (Chapter 6)

ranges from preliminary screening to advanced 

secondary treatment where reuse systems are

developed. Where a completely new land treatment

system is to be constructed, it is usually cost-effective to 

minimize preapplication treatment and use screening or 

short detention-time ponds for OF and treatment ponds 

for SR and SAT. Costs of preapplication can be

estimated from data in Reed, et al. (1979), US EPA 

(1981c), Tchobanoglous, et al. (1979), and Asano and

Tchobanoglous (1992). Many processes can be used

for preapplication treatment, including wetlands or 

overland flow for treatment prior to SAT or SR systems. 

Overland flow slope construction costs include the 

same items as for land leveling. A cut of 265 m3

/ha (500

yd3

/acre) would correspond to nominal construction on

pre-existing slopes. A cut of 529 m3

/ha (1,000 yd3/acre) 

corresponds to constructing 45-m (150-ft) wide slopes at

2 percent slope from initially level ground. A cut of 741

m3

/ha (1,400 yd3/acre) corresponds to 75-m (250-ft) 

slope widths on 2.5 percent slopes from initially level 

ground. 

5.5.4 Storage 

Storage ponds vary in cost depending on initial site 

conditions, need for liners, and the depth and volume of 

wastewater to be stored. Cost data are available from

Reed et al. (1979), US EPA (1981c), Tchobanoglous et

al. (1979), and Crites (1998). 

5.5.5 Field Preparation 

Costs for field preparation can include site clearing

and rough grading, land leveling and overland flow slope

construction. Costs of each of these types of field 

preparation are presented in Table 5-24 for various 

conditions. Site clearing costs include bulldozing of

existing vegetation, rough grading, and disposal of 

debris onsite. Offsite disposal of debris will cost 1.8 to

2.2 times the values in Table 5-24 (US EPA., 1979b).

Land leveling costs include surveying, earthmoving, 

finish grading ripping in two directions, disking, 

equipment mobilization, and landplaning. In many cases, 

106 m3

/ha (200 yd3/acre) will be sufficient, while 397 

m3

/ha (750 yd3/acre) represents considerable 

earthmoving. 

 Table 5-24. Costs of Field Preparation 

ENR CCI = 6076

Type of Cost Capital Cost, $/acreb

Site Clearing 

Grass only 30 

Open field, some brush 220 

Brush and trees 1,450 

Heavily wooded 2,890 

Land Leveling 

200 yd3/acrea 360 

500 yd3/acre 720 

750 yd3

/acre 1,010 

Overland flow slope construction 

500 yd3/acre 1,300 

1,000 yd3

/acre 2,170 

1,500 yd3

/acre 2,890 a

yd3/acre x 1.9 = m3/ha b

acre x 0.4047 = ha 

5.5.6 Distribution 

Slow rate systems are capable of using a wide variety 

of sprinkler and surface distribution systems. In

contrast, OF systems usually employ fixed sprinkler of 

gated pipe surface distribution and RI systems generally 

employ surface spreading basins. 

5-18 
Solid set sprinkling, described in Chapter 7, is the 

most expensive type of sprinkler system. As shown in

Table 5-25 (Crites, 1998), portable and continuous-move 

systems are considerably less expensive on an initial 

capital cost basis. Capital and O&M costs are presented 

in detail for solid set and center pivot sprinkling. 

Table 5-25. Comparison of Sprinkler Distribution Capital Costs

Sprinkler Type Comparative Cost 

Portable hand move 0.13 

Traveling gun 0.22 

Side roll 0.22 

Center pivot 0.50 

Linear move 0.65 

Solid set 1.00 

Solid Set Sprinkling 

The capital and O&M costs for buried solid set 

systems are presented in Figure 5-8. For the SR system 

in Figure 5-8, the laterals are spaced 30 m (100 ft) apart 

and the sprinklers are 24 m (80 ft) apart on the lateral. 

Laterals are buried 0.45 m (18 in) and mainlines are 

buried 0.9 m (36 in). The pipe material is PVC while the 

risers are galvanized steel. Flow to the laterals is 

controlled by hydraulically operated automatic valves.

There are 5.4 sprinklers per acre at the specified 

spacing. If more sprinklers are included (smaller 

spacing), increase the capital and labor costs by using

Equation 5-3:

Cost Factor = 0.68 + 0.06(S) (5-3) 

Where: 

Cost factor = multiplier times from Figure 5-8 

S = sprinklers/acre 

Conversion factor: acre = 0.4047 ha 

For overland flow, the slopes are 75 m (250 ft) wide at

a 2.5 percent grade. The laterals are 21 m (70 ft) from 

the top of the slope and sprinklers are 30 m (100 ft) 

apart. Other factors are the same as for the SR system. 

For O&M, the labor rate is $15.00/h including fringes. 

Materials cost includes replacement of sprinklers and 

valve controllers every 10 year. 

Center Pivot Sprinkling 

Capital and O&M costs for center pivot sprinkling in 

Figure 5-9. The center pivot machines are electricallydriven and heavy-duty units. Multiple units are included

for areas over 16 ha (40 acres) with a maximum area

per unit of 53 ha (132 acres). Distribution piping is buried

0.9 m (3 ft). Labor costs are based on $15.00/h and 

power costs are based on 3.5 days/week operation for 

each unit and $0.02/MJ ($0.08/kWh). Materials cost

includes minor repair parts and overhaul of units every 

10 years. 

Surface Distribution for OF or SR

Costs for gated pipe distribution for OF and SR systems 

are presented in Figure 5-10. The OF slope is 60 m (200

ft) wide with the gated aluminum pipe distribution at the 

top of the slope. For SR systems, the furrows or borders 

are 360 m (1,200 ft) long on rectangular-shaped fields.

Graded border systems, under similar conditions of 

border length, can use buried pipelines with alfalfa 

valves at similar capital costs. Labor costs are based on 

a $15.00/h wage including fringes. Materials cost 

includes replacement of gated pipe after 10 years. 

Soil Aquifer Treatment Basins 

Costs for SAT basins are presented in Figure 5-11. 

There are a minimum of 2 basins and a maximum basin

size of 8 ha (20 acres). Costs include inlet and outlet 

control structures and control valves. Dikes are 1.2 m (4 

ft) high with an inside slope of 3:1, an outside slope of2:1 

and a 1.8-m (6-ft) wide dike crest. Dikes or berms are

formed from excavated native material. Labor costs 

Figure 5-8. Solid Set Sprinkling (buried) Costs, ENR CCI = 6076. 

(a) Capital Cost; (b) Operation and Maintenance Cost.

5-19 
Figure 5-9. Center Pivot Sprinkling Costs, ENR CCI = 6076. 

(a) Capital Cost; (b) Operation and Maintenance Cost. 

are based on a $15.00/h wage including fringe benefits. 

Materials cost includes rototilling or disking the basin

surface every 6 months and major repair of the dikes 

every 10 years. 

5.5.7 Recovery 

Recovery systems can include underdrains (for SR or

SAT), tailwater return for SR surface application, runoff 

collection for OF, and recovery wells for SAT. 

Underdrains 

Costs for underdrain systems are presented in Table

5-26 for spacings between drains of 30 and 120 m (100

and 400 ft). Drains are buried 1.8 to 2.4 m (6 to 8 ft) 

deep and discharge into an interception ditch along the 

length of the field. 

Labor costs are based on a $15.00/h wage rate 

including fringes, and labor involves inspection and

unclogging of drains at the outlets. Materials cost 

includes high-pressure jet cleaning of drains every 5

years, annual cleaning of interception ditches, and major 

repair of the interception ditch after 10 years. 

Figure 5-10. Gated Pipe — Overland Flow or Ridge-andFurrow Slow Rate Costs, ENR CCI = 6076. 

(a) Capital Cost; (b) Operation and Maintenance Cost. 

Tailwater Return 

Tailwater from ridge-and-furrow or graded border 

systems must be recycled either to the storage ponds or

to the distribution system. Typically 25 to 30 percent of 

the applied flow should be expected as tailwater. Capital 

costs, presented in Table 5-27, include drainagecollection ditches, storage sump or pond, pumping

facilities, and a 60-m (200-ft) return force main. Labor, at 

$15.00/h including fringe benefits, includes operation of

the pumping system and maintenance of the ditches,

sump, pump, and return system. Materials cost includes

major repair of the pumping station after 10 years.

Power cost is based on $0.02/MJ ($0.08/kWh). 

Runoff Collection for OF 

Runoff collection can consist of an open ditch or a 

buried pipeline with inlets. Costs for open ditches,

presented in Table 5-28, include a network of ditches 

sized for a 5.1-cm/h (2-in/h) storm, culverts under 

service roads, and concrete drop structures every 300 m 

(1,000 ft) (for larger systems). For gravity pipe systems, 

5-20 
Figure 5-11. Rapid Infiltration Basin Costs, ENR CCI = 6076. 

(a) Capital Cost; (b) Operation and Maintenance Cost.

Table 5-26. Costs of Underdrains (US EPA., 1979b)

ENR CCI = 6076

Type of Cost $/acreb

Capital costs 

 100-fta spacing 2,890 

 400-ft spacing 1090 

O&M costs 

Labor 

 100-ft spacing 52 

400-ft spacing 22 

Materials 

 100-ft spacing 140 

 400-ft spacing 90 a

ft x 0.3048 = m. b

acre x 0.4047 = ha. 

Table 5-27. Costs of Tailwater Return Systems (Reed et al., 1979) 

ENR CCI = 6076

Type of Cost Cost 

0.1 mgda

 of Recovered Water 

 Capital, $ 60,000 

 O&M: 

 Power, $/year 375 

 Labor, $/year 375 

 Materials, $/year 180 

1.0 mgd of Recovered Water 

 Capital, $ 145,000 

 O&M: 

 Power, $/year 4,000 

 Labor, $/year 900 

 Materials, $/year 700 a

 mgd x 3.7854x103 = m3/day. 

the costs include a network of interceptor pipes with 

inlets every 75 m (250 ft) and accessholes every 150 m 

(500 ft). 

Labor costs are based on $15.00/h including fringe 

benefits. Materials cost includes biannual cleaning of 

ditches and major repair every 10 years. 

Table 5-28. Costs of Runoff Collection for Overland Flow (Reed et al., 

1979)

ENR CCI = 6076

Type of Cost $/acrea

Capital costs: 

Gravity pipe system 2,300 

Open ditch system 360 

O&M costs: $/acre·year

Labor 

 Gravity pipe 8 

Open ditch 30 

Materials 

 Gravity pipe 7 

 Open ditch 40 a

 acre x 0.4047 = ha. 

Recovery Wells 

Costs for recovery wells for SAT systems are

presented in Table 5-29 for well depths of 15 and 30 m

(50 and 100 ft). Capital costs include gravel-packed

wells, vertical turbine pumps, simple shelters over each

well, controls, and electrical work. Labor, at $15.00/h, 

includes operation and preventative maintenance.

Materials cost includes repair work performed by 

contract, and replacement of parts. Power cost is based

on $0.02/MJ ($0.08/kWh). Monitoring wells are generally 

a minimum of 100 mm (4 in) in diameter and typically 

cost $130 to $200/m ($40 to $60/ft) (US EPA, 1979). 

Table 5-29. Costs of Recovery Wells (Reed et al., 1979)

ENR CCI = 6076

Type of Cost Cost 

1.0 mgda of recovered water: 

Capital, $: 

 50 ftb

 depth 29,000 

 100 ft depth 50,000 

O&M, $/yr: 

 Power, 50-ft depth 9,500 

 Power, 100-ft depth 18,900 

 Labor 6,000 

 Materials 800 q

mgd x 3.7854x103 = m3/day. b

ft x 0.3048 = m.

5.5.8 Land 

Land can be controlled by direct purchase, lease, or 

contract. The land for preapplication treatment and

storage is usually purchased, however, field area for SR 

5-21 
systems is sometimes leased or a contract is formed

with the landowner. Options used by selected

communities for land acquisition and management for 

selected SR systems are presented in Table 5-31

(Crites, 1981 and Christensen, 1982). As shown in Table

5-31, contracts for effluent use are utilized in several SR 

systems. Fee simple purchase is generally used for OF 

and SATsites. 

5.5.9 Benefits 

Revenue producing benefits from land treatment 

systems can include sale of crops, lease of land, sale of

wastewater or recycled water, and contracts that may 

involve all of these benefits. Examples of revenueproducing benefits are presented in Table 5-30 (Crites,

1981, 1982, and 1998, Christensen, 1982, US EPA, 

1995, and US EPA, 1979a). The examples are for SR 

systems, which generally have the greatest potential for

revenue production. Crop sale from OF systems can

offset a small portion of O&M costs, but generally cannot 

be expected to more than offset the cost of harvesting 

and removal of the grass or hay. For SAT systems in 

water-short areas, the potential for recovery and reuse of 

the percolate should be investigated. 

Sale of crops can be a significant source of revenue if 

the community is willing to invest in the necessary 

equipment for crop harvest and storage. For ezample, 

Muskegon County realized gross revenues of 

$1,000,000 from the sale of corn (US EPA 1979a). 

Cash rent for SR cropland is very popular in the west 

with 5-year agreements being common. Rents range

from $2 to $32/ha ($5 to $80/acre). Contracts for 

wastewater irrigation, rental of irrigation equipment, or 

for the use pastureland for cattle grazing have also been

utilized. Examples include El Reno, OK; Dickinson, ND; 

Mitchell, SD; Tuolumne County, CA; Santa Rosa, CA; 

and Petaluma, CA.(Crites, 1982 and NACD, 1981). 

5.5.10 Energy Requirements 

The energy requirements for land treatment systems 

include power for pumping, preapplication treatment,

wastewater distribution, and fuel for crop planting and

harvesting and for biosolids transport and spreading. In 

addition, energy is needed for heating and cooling of 

buildings, lighting and vehicle operation. 

Pumping. Pumping for transmission, distribution, 

tailwater return, and recovery is a major energy use in 

most land treatment systems. The energy required can

be calculated using Equation 5-4: 

( )( )

( )( )( )

F E

Q TH t Energy Use = (5-4)

Where 

Energy Use = annual usage, kWh/year 

Q = flowrate, gal/min

TH = total head, ft 

t = pumping time, h/year 

F = constant, 3960 x 0.746 = 2954

E = overall pumping efficiency, decimal 

The overall efficiency depends on the type of 

wastewater and the specifics of pump and motor 

selection. In the absence of specific information on pump

and motor efficiency, the following overall pumping 

system efficiencies can be used: 

Table 5-30. Benefits of Land Treatment Systems

Sale of crops $/yr

 Muskegon, MI 900,000 – 1,000,000 

 San Angelo, TX 58,000 – 71,000

Lease of land $/acre·yr

a

 Bakersfield, CA 80 

 Coleman, TX 5 

 Manteca, CA 40 

 Mesa, CA 50 

 Winters, CA 20 

Sale of effluent $/acre·ftb

 Cerritos, CA 40 

 Irvine Ranch, CA 118 

 Las Virgines, CA 160 

 Marin MWD, CA 300 

acre x 0.4047 = ha. 

acre·ft x 0.123 = ha·m. 

Table 5-31. Options for Land Acquisition and Management at Selected SR Systems 

Location Area, acresa Acquisition Option Management Option 

Bakersfield, CA 2,400 Fee simple Leaseback to farmer 

Camarillo, CA 475 Contract Landowner accepts water 

Dickinson, ND 250 Contract Cash lease for water sale to farmer 

Lubbock, TX 4,000 Fee simple and contract Leaseback, farmer owns effluent 

Mesa, AZ 160 Fee simple Leaseback for cash rent 

Muskegon, MI 10,400 Fee simple Managed by county

Petaluma, CA 550 Contract Cash rent for irrigation equipment

Roswell, NM 285 Contract Cash lease for water sale to farmer 

San Antonio, TX 740 Fee simple Managed by city

Tooele, UT 1,200 Contract Cash lease for water sale to farmer a

 acre x 0.4047 = ha. 

5-22 
and Middlebrooks et al., (1979). Energy for crop

production is minor compared to energy for distribution. 

For example, energy requirements for corn production

are 51.3 MJ/ha (5.7 kWh/acre) and for alfalfa are 22.5

MJ/ha (2.5 kWh/acre). Fuel usage can be converted to

energy using 34,596 KJ/L (124,000 Btu/gal) for gasoline 

and 3,906 KJ/L (14,000 Btu/gal) for diesel (US EPAij, 

1978 and WPCF, 1981). 

5.5.11 Energy Conservation 

Sprinkler distribution systems are candidates for 

energy conservation. Impact sprinklers may require 45 to 

60 m (150 to 200 ft) of head to operate. Recent 

advances have been made in sprinkler nozzle design to 

allow operation at lower pressures without sacrificing 

uniformity of application. Use of drop nozzles with

pressure requirements of 15 m (50 ft) of head can result 

in significant energy conservation. 

Energy conservation is also possible in land treatment

systems through the use of surface distribution. A 

comparison of primary and secondary energy usage of

various land and aquatic treatment systems is presented

in Table 5-32 (Tchobanoglous et al., 1979). Primary 

energy is that fuel or power used directly in operations. 

Secondary energy is that used in the construction of

facilities or manufacturing of chemicals. 

Energy conservation through the use of land

application of wastes can also be realized through

savings in energy use for manufacturing of commercial 

fertilizer. A presentation of energy needs to produce 

fertilizer and the energy value of nutrients in wastewater 

is given in Table 5-33 (Middlebrooks et al., 1979 and 

WPCF, 1981). 

Table 5-32. Energy Requirements for Land and Aquatic Treatment Systems

Equivalent energy, 1,000 kWh/yeara

System Primary Energy Secondary Energy Total Energy

PT + SAT 187 102 289 

Ponds and wetlands 121 198 319 

PT + SR(surface) 187 135 322 

PT + OF 192 159 351 

Ponds and hyacinths 167 195 362 

PT + SR(spray) 327 173 500 

Note: PT = primary treatment; SAT = soil aquifer treatment; SR = slow rate and OF = overland flow. a

kWh x 3.6 = MJ.

Table 5-33. Energy Value of Nutrients in Wastewater

Nutrient 

Content of effluent, 

mg/La

Content of effluent, 

lb/acre·ftb

Energy to produce, transport and 

apply fertilizer, kWh/lbc

Energy value of nutrients in wastewater, 

kWh/acre·ftd

Nitrogen as N 20 54 2.79 190 

Phosphorus as P 10 27 0.10 13 

Potassium as K 15 38 0.10 10 a

mg/L = g/m3. b

lb/acre·ft x 3.69 = kg/ha·m. c

kWh/lb x 7.9 = MJ/kg. d

kWh/acre·ft x 29.3 = MJ/ha·m.

5.6 References 

Christensen, L.A. (1982) Irrigating with Municipal

Effluent, USDA, ERS-672, Washington, DC. 

Crites, R.W. (1981) Economics of Reuse, Proceedings 

of the Water Reuse Symposium II, Volume 3,

AWWA, p. 1745-1751. 

Crites, R.W. (1982) Land Treatment and Reuse of

Food Processing Waste, Proceedings of the

Industrial Wastes Symposia, Water Pollution Control 

Federation, 55th Annual Conference, St. Louis, MO. 

Crites, R.W. (1982) Innovative and Alternative

Treatment at Petaluma, CA, .Presented at the 

Hawaii Water Pollution Control Association Annual

Conference, Honolulu, HI.

Crites, R.W. and G. Tchobanoglous (1998) Small and

Decentralized Wastewater Management Systems, 

McGraw-Hill, New York, NY. 

Crites, R.W. (1998) Costs of Constructed Wetlands, 

Proceedings WEFTEC ’98, Orlando, FL. Water 

Environment Federation, Alexandria, VA. 

Crites, R.W., S.C. Reed, and R.K. Bastian (2000) Land

Treatment of Municipal and Industrial Wastewater, 

McGraw-Hill Book Co., New York, NY. 

5-23 
Dewsnup, R.L. and Jensen, D.W. (Eds.) (1973) A 

Summary Digest of State Water Laws, National 

Water Commission, Washington, DC. 

Loehr, R.C. (1974) Agricultural Waste Management–

Problems, Processes, and Approaches, New York:

Academic Press. 

Metcalf & Eddy, Inc. (1976) Land Application of

Wastewater in the Salinas-Monterey Peninsula

Area, U.S. Army Engineer District San Francisco,

CA. 

Middlebrooks, E.J. and C.H. Middlebrooks (1979) 

Energy Requirements for Small Flow Wastewater

Treatment Systems, USA CRREL, Special Report

79-7. 

Moser, M.A. (1978) A Method for Preliminary 

Evaluation of Soil Series Characteristics to

Determine the Potential for Land Treatment 

Processes, Proceedings of the Symposium on Land

Treatment of Wastewater, Hanover, NH. 

Nightingale, H.I. et al. (1983) Leaky Acres Recharge

Facility: A Ten-Year Evaluation, AWRA Water 

Resources Bulletin, Vol. 19, 3, p. 429. 

Reed, S.C. (1982) The Use of Clayey Sands for Rapid 

Infiltration Wastewater Treatment, USA CRREL IR 

805, p.55. 

Richard, D., T. Asano, and G. Tchobanoglous (1992) 

The Cost of Wastewater Reclamation in California, 

Department of Civil and Environmental Engineering,

University of California, Davis. 

Sills, M.A., et al. (1978) Two-Phase Evaluation of Land 

Treatment as a Wastewater Treatment Alternative – 

A Rational Approach to Federal and State Planning

and Design Requirements, Proceedings of the 

Symposium on Land Treatment of Wastewater,

Hanover, NH. 

Taylor, G.L. (1981) Land Treatment Site Evaluation in 

Southeastern Mountainous Areas, Bulletin of the 

Association of Engineering Geologists, 18: 261-266. 

Tchobanoglous, G., J.E. Colt, and R.W. Crites (1979) 

Energy and Resource Consumption in Land and

Aquatic Treatment Systems, Proceedings: Energy 

Optimization of Water and Wastewater Management 

for Municipal and Industrial Applications Conference,

USDOE, Volume 2, New Orleans. 

US DOI (1978) Drainage Manual, U.S. Department of 

the Interior, Bureau of Reclamation. 

US EPA (1976) Use of Climatic Data in Estimating

Storage Days for Soil Treatment Systems, EPA -

600/2-76-250, U.S. Environmental Protection 

Agency, Cincinnati, OH. 

US EPA (1977a) Annual and Seasonal Precipitation

Probabilities, EPA-600/2-77-182, U.S. 

Environmental Protection Agency, Cincinnati, OH. 

US EPA (1977b) Land Application of Wastewater and 

State Water Law: An Overview 

(Volume I), EPA-600/2-77-232, U.S. Environmental 

Protection Agency, Cincinnati, OH. 

US EPA (1978a) Land Application of Wastewater and 

State Water Law: State Analyses

(Volume II), EPA-600/2-78-175, U.S. Environmental 

Protection Agency, Cincinnati, OH. 

US EPA (1978b) Energy Conservation in Municipal 

Wastewater Treatment, EPA-430/9-77-011. 

US EPA (1978) Energy Conservation in Municipal

Wastewater Treatment, EPA-430/9-77-011. 

US EPA (1979a) Wastewater: Is Muskegon County’s

Solution Your Solution? EPA-905/2-76-004, U.S. 

Environmental Protection Agency, Washington, DC. 

US EPA (1979b) Cost of Land Treatment Systems, EPA

430/9-75-003, U.S. Environmental Protection 

Agency, Washington, DC. 

US EPA (1980) Design Manual - Onsite Wastewater 

Treatment and Disposal Systems, EPA 625/1-80-

012 U.S. Environmental Protection Agency, 

Cincinnati, OH. 

US EPA (1981a) The Role of Conservation Districts 

and the Agricultural Community in Wastewater Land

Treatment, EPA-430/9-77-011. 

US EPA (1981b) Process Design Manual for Land

Treatment of Municipal Wastewater, EPA 625/1-81-

013, U.S. Environmental Protection Agency, 

Cincinnati, OH. 

US EPA (1981c) Construction Costs for Municipal

Wastewater Conveyance Systems: 1973-1979, EPA 

430/9-81-003, U.S. Environmental Protection 

Agency, Washington, DC. 

US EPA (1982) Operation and Maintenance 

Considerations for Land Treatment Systems, EPA600/2-82-039.

US EPA (1995) Process Design Manual – Land

Application of Sewage Sludge and Domestic

Septage, EPA/625/R-95/001, U.S. Environmental

Protection Agency, Washington, DC. 

Water Pollution Control Federation (1981) Energy 

Conservation in the Design and Operation of

Wastewater Treatment Facilities, Manual of Practice

No. FD-2. 

5-24 
Chapter 6 

Preapplication Treatment and Storage

The level of preapplication treatment required prior to

any of the land treatment processes should involve both

engineering and economic decisions that recognize the

potential performance of the land treatment process and

the sensitivity of the receiver environment. An approach 

would be to start with the final effluent or percolate

quality requirements for the site and climatic conditions 

and, then determine the contribution the land treatment

processes can provide. A level of preapplication

treatment can then be adopted for those constituents 

that will not be removed or reduced to an acceptable 

concentration by the land treatment process. The 

method of preapplication treatment should then be

selected as the simplest and most cost-effective system

possible. 

6.1 EPA Guidance 

The level of preapplication treatment required should 

also be based on the degree of public access to the site

and/or on the type and end use of the crop grown. The

guidelines for preapplication treatment developed by the 

US EPA are summarized in Table 6-1. The level of

treatment increases as the degree of public access 

increases when the crop is for direct human 

consumption and when environmental sensitivity 

increases. The chemical and microbiological standards 

in general are based on water quality requirements for 

irrigation with surface water and on bathing water quality 

limits for the recreational case (Thomas and Reed,

1980). 

6.1.1 Slow Rate Systems 

SR systems may require preapplication treatment for 

several reasons, including public health protection 

relating to human consumption of crops and crop

byproducts that are eaten uncooked or direct exposure 

to applied effluent, prevention of nuisance conditions 

during storage, distribution system protection, or soil and

crop considerations and watershed considerations (e.g., 

TMDLs). Preliminary treatment, except for solids 

removal, is often de-emphasized because SR systems 

are capable of achieving final water quality objectives 

with minimal pretreatment. In many cases, SR systems 

are designed for regulatory compliance following

preliminary treatment so the potential for reuse can be 

realized. Systems designed to emphasize reuse

potential require greater flexibility in the handling of 

effluent, which can be achieved with higher pretreatment

levels. 

The treatment objective should be to maximize

nitrification if surface discharge is required and ammonia 

discharge requirements are stringent. Nitrification may 

be achieved using either primary or secondary treatment

prior to application. 

6.1.2 Soil Aquifer Treatment Systems 

Primary sedimentation or the equivalent is the

minimum recommended preapplication treatment for all

SAT systems. This level of treatment reduces wear on 

the distribution system, prevents unmanageable soil 

clogging, reduces the potential for nuisance conditions, 

and allows the potential for maximum nitrogen removal. 

For small systems, a short-detention-time pond is 

recommended. Long-detention-time facultative or 

aerobic ponds are not recommended because of their 

propensity to produce high concentrations of algae. The

algae produced in stabilization ponds will reduce

infiltration rates significantly. If facultative or stabilization 

ponds are to be used with SAT, it is recommended that 

an aquatic treatment or constructed wetland system be

used between the pond and the SAT basins to reduce

TSS levels (Crites and Tchobanoglous, 1998). 

6-1 
Table 6-1. Guidelines for Assessing the Level of Preapplication Treatment (Thomas and Reed, 1980)

I. Slow Rate Systems 

A. Primary treatment – acceptable for isolated locations with restricted public access and when limited to crops not for direct human 

consumption 

B. Biological treatment by lagoon or in-plant processes plus control of fecal coliform count to less than 1,000 MPN/100 ml – acceptable for 

controlled agricultural irrigation except for human food crops to be eaten raw 

C. Biological treatment by lagoons or in-plant processes with additional BOD or TSS removal as needed for aesthetics plus disinfection to a 

geometric mean of 125 E.coli per 100 mL and 33 enterococci per 100 mL (EPA water quality criteria for bathing waters) – acceptable for 

application in public access areas such as parks and golf courses 

II. Rapid Infiltration Systems (Soil Aquifer Treatment) 

A. Primary treatment – acceptable for isolated locations with restricted public access 

B. Biological treatment by lagoons or in-plant processes – acceptable for urban locations with controlled public access 

III. Overland Flow Systems 

A. Screening or comminution – acceptable for isolated sites with no public access 

B. Screening or comminution plus aeration to control odors during storage or application – acceptable for urban locations with no public access 

6.1.3 Overland Flow Systems 

Preapplication treatment before OF is provided to

prevent operating problems with distribution systems, to 

prevent nuisance conditions during storage and possibly 

to meet stream discharge requirements. Preapplication 

treatment to protect public health is not usually a

consideration with OF systems because public contact 

with the treatment site is usually controlled and no crops 

are grown for human consumption. 

Municipal wastewater contains rags, paper, hair and 

other coarse solids that can impair and clog orifices and

valves in surface and sprinkler distribution systems.

Comminution is generally not sufficient to eliminate 

clogging problems. Fine screening or primary 

sedimentation with surface skimming is necessary to

prevent operating difficulties. For small systems, Imhoff 

tanks or 1- to 2-day aerated detention ponds are

recommended. Static or rotating fine screens have also

been used successfully at Davis, CA. and Hall’s Summit, 

LA. (WPCF, 1989). For sprinkler distribution systems, 

screen sizes should be less than one-third the diameter

of the sprinkler nozzle. Static inclined screens with 1.5 

mm openings have been used successfully for raw 

wastewater screening (US EPA, 1981). 

Grit removal is advisable for wastewaters containing

high grit loads. Grit reduces pump life and can deposit in

low-velocity distribution pipelines. 

6.2 Types of Preapplication Treatment 

Preapplication treatment operations and processes 

can include fine screening, primary treatment, lagoons or

ponds, constructed wetlands, biological treatment, 

membranes, and disinfection. Removal efficiencies and

design criteria for these treatment operations and 

processes are documented in Crites and Tchobanoglous 

(1998). Because ponds and constructed wetlands are 

often compatible with land treatment systems, the

efficiencies of these preapplication treatment methods 

are described in the following sections. In addition, 

biological nutrient removal and membrane processes are

also discussed. 

6.2.1 Constituent Removals in Ponds 

Effluent from any conventional wastewater treatment 

process can be applied successfully to the land as long 

as the site and soils are compatible. In many cases, a

pond or lagoon will be the most cost-effective choice for 

treatment. Ponds can be used with land treatment for

basic treatment, flow equalization, for emergency 

storage, and where there are seasonal constraints on 

the operation of land treatment systems. In cases where

storage is needed, it will usually be most cost-effective to

combine the treatment and storage functions in a 

multiple cell pond system. Where odor control or high

strength wastes are a factor, the initial cell may be 

aerated and followed by one or more deep storage cells. 

In remote locations an anaerobic primary cell can be 

designed for the treatment of high-strength wastes and

solids removal and be followed by storage cells. The

treatment occurring in the storage cells will be similar to

that in a facultative pond. Basic design criteria for 

conventional pond systems are available from a number 

of sources (Crites and Tchobanoglous, 1998; Reed et 

al., 1995; US EPA, 1983; and Middlebrooks et al., 1982). 

The pond unit can be specifically designed for the

removal of a particular wastewater constituent. More

typically, the detention time in the pond component is 

established by the storage requirements for the system. 

The removal of various constituents that will occur within 

that detention time can then be calculated. If additional

removal is required, the cost-effectiveness of providing

more detention time in the pond can be compared to 

alternative removal processes. The removal of nitrogen

in the pond unit is particularly important because

nitrogen is often the Limiting Design Parameter (LDP) for 

slow rate systems. Any reduction of nitrogen in the pond

unit directly impacts on the design of the land treatment

component. 

6-2 
6.2.2 BOD and TSS Removal in Ponds 

BOD5 is usually not the LDP for design of the 

municipal land treatment component in any of the

processes. However, many regulatory agencies specify 

a BOD5 requirement for the wastewater to be applied, so

it may be necessary to estimate the removal that will 

occur in the pond components. There may be a

combination of an aerated or anaerobic cell followed by 

the storage pond. 

Aerated Ponds 

The BOD5 removal that will occur in aerated cells can 

be estimated with: 

n

o c

n

C k t

C

(1 )

1

+ = (6-1)

Where: 

Cn = effluent BOD5 from cell n, mg/L 

Co = influent BOD5 to system, mg/L 

kc = reaction rate constant (see Table 6-2) at 20o

C 

t = total hydraulic resident time, d 

n = number of cells 

The reaction rate constant, kc, is dependent on the 

water temperature, as shown in Equation 6-2: 

( 20)

20

− = T

cT k k θ (6-2)

Where: 

kcT = reaction rate const. at temperature T 

k20 = reaction rate const. at 20oC (see Table 6-2) 

θ = 1.036 

T = temperature of pond water, o

C 

The temperature of the pond can be estimated with the 

following equation: 

Af Q

AfT QT T a i

w +

+ = (6-3)

Where: 

Tw = pond temperature, oC 

Ta = ambient air temperature, o

C 

Ti = pond influent temperature 

A = surface area of pond, m2

f = proportionality factor = 0.5 

Q = wastewater flow rate, m3

/d 

The selection of an apparent reaction rate value from

Table 6-2 depends on the aeration intensity to be used. 

The “complete mix” value assumes high intensity

aeration [about 20 W/m3

 (100 HP/MG)], sufficient to 

maintain the solids in suspension. The “partial mix” value

assumes that there is sufficient air supplied to satisfy the 

oxygen demand [about 2 W/m3

 (10 HP/MG)], but that 

solids deposition will occur.

Table 6-2. Reaction Rates for Aerated Ponds, BOD5

Type of Aeration k at 20°C 

Complete mix

Partial mix

2.5 

0.276 

The suspended solids in the effluent from a complete 

mix aerated cell will be nearly the average concentration 

in the cell. The suspended solids in the partial mix pond

effluent will be lower, depending on the detention time. 

For a detention time of 1 day, assume the suspended

solids are similar to primary effluent [60 to 80 g/m3

(mg/L)]. 

Facultative Ponds 

The BOD5 removal that will occur in a facultative cell

can be estimated using Equation 6-4. 

e K t

C

C n p

0

= − (6-4)

Where: 

Cn = effluent BOD5, g/m3 (mg/L)

Co = influent BOD5, g/m3

 (mg/L)

Kp = plug flow apparent reaction rate constant (see Table 6-3) 

t = detention time, days

The apparent rate constant for plug flow also varies 

with temperature with a ө value of 1.09. 

Table 6-3. Variation of Plug Flow Apparent Rate Constant with 

Organic Loading Rate for Facultative Ponds (Neel et al., 1961)

Organic Loading Rate, 

kg/ha·day* kp, per day 

22 

45 

67 

90 

112 

0.045 

0.071 

0.083 

0.096 

0.129 

*kg/ha·day x 0.8928 = lb/acre·day. 

The TSS concentrations from facultative cells depend

on the temperature and detention time. Algae 

concentrations can reach 120 to 150 g/m3

 (mg/L) or 

more in warm temperatures and may be as low as 40 to 

60 g/m3

 (mg/L) in cooler temperatures (Stowell, 1976). 

Anaerobic Ponds 

Anaerobic ponds are rarely used with municipal 

wastewaters unless there is a large industrial waste 

component. The ponds are typically 3 to 4.5 m (10 to 15 

ft) deep. BOD5 loading rates may be as high as 500

kg/ha·day (450 lb/ac·day), detention times range from 20

to 50 days, depending on the climate, and a BOD5

conversion of about 70 percent is typical. Effluent TSS 

values range from 80 to 160 g/m3

 (mg/L). 

6-3 
A primary anaerobic cell is used at a number of

municipal pond systems in rural areas of the western 

provinces of Canada (Higo, 1966). The anaerobic cells 

are also designed for solids removal and retention and

are typically followed by one or more long-detention-time 

facultative cells. Effluent from these cells is comparable

to primary effluent. Detectable odors have been noted to

at least 305 m (1,000 ft) around these systems, so a 

remote location or other odor control is needed. 

6.2.3 Constituent Removals in Constructed 

Wetlands 

Constructed wetlands have been used to remove 

BOD5, TSS, nitrate-nitrogen, and metals, among other 

constituents, from wastewater (Crites and

Tchobanoglous, 1998; Reed et al., 1995; Reed 1999; 

USEPA 1999). Constructed wetlands can be free water 

surface (FWS) or subsurface flow (SF). Free water 

surface constructed wetlands are best suited to

preapplication treatment, especially for flows above 0.1 

mgd (387 m3

/d).

Area for BOD Removal 

The field area needed for a constructed wetland can 

be calculated using Equation 6-5. 

( )( )

(ln ln )

K y η

Q C C A o − e = (6-5)

Where: 

A = field area, m2 (acres)

Q = average flow, (in + out)/2 m3

/d (acre-ft/d) 

Co = influent BOD, mg/L 

Ce = effluent BOD, mg/L 

K = apparent removal rate constant 

= 0.678 d-1 for FWS wetlands at 20o

C 

= 1.104 d-1 for SF wetlands at 20oC 

y = water depth, m (ft) 

η = porosity

= 0.75 to 0.9 for FWS wetlands 

= 0.28 to 0.45 for SF wetlands 

The average flow should be the annual average flow

into the wetlands plus the effluent flow divided by two. 

The apparent K factor is temperature dependent and

Equation 6-2 can be used for different water 

temperatures, with the ө factor being 1.06. The porosity 

of FWS wetlands depends on the density of the 

vegetation, with 0.75 being appropriate for high plant 

densities and 0.85 being appropriate for moderate plant 

densities. Where open water areas are interspersed

with vegetated zones the porosity will be 0.8 to 0.9. For 

SF constructed wetlands the porosity depends on the

particle size of the gravel used. Coarse sand and

gravelly sand has a porosity of 0.28 to 0.35. Fine gravel, 

widely used in SF systems, has a porosity of 0.35 to 

0.38. Medium to coarse gravel has a porosity of 0.36 to

0.45 (Reed et al., 1995). These porosity values are

measured by a field test and are much higher then those

given in Figure 3-2, which are measured in a laboratory 

using a standard ASTM method. The values from Figure

3-2 are for in-situ soil and gravel deposits which have

been naturally consolidated, and they are not

appropriate for design of SF constructed wetlands. 

Area for Nitrate Removal 

Constructed wetlands can be effectively designed for 

nitrate removal for effluents containing high nitrate. 

Equation 6-6 can be used to predict nitrate reduction. 

For water temperatures of 1o

C or less, assume that 

denitrification effectively ceases. 

n

i f

k

C C t ln( / ) = (6-6)

Where: 

t = actual detention time, days Ci = influent nitrate concentration, g/m

C = effluent nitrate concentration, g/m

3

 (mg/L)

f

K

3

 (mg/L)

n = rate constant, use 1.0 for temperature of 20°C 

The temperature adjustment can be made using

Equation 6-2, using a ө value of 1.15. 

6.2.4 Nitrogen Losses in Storage Ponds 

The loss of nitrogen from ponds and water bodies has 

been recognized and predictive models are available 

(Reed, 1984). The removal of nitrogen in a pond is 

dependent on pH, temperature, and detention time.

Under ideal conditions up to 95 percent has been 

observed. Volatilization of the ammonia fraction is 

believed to be the major pathway responsible for longterm permanent losses. 

Because nitrogen is often the limiting design

parameter (LDP) for land treatment design, it is essential 

to determine (i.e., operationally monitor) the losses that 

will occur in any preliminary pond units for treatment or 

storage. This may influence the basic feasibility of a 

particular process, or control the amount of land needed. 

The equations presented below can be used for 

facultative ponds and for storage ponds. The nitrogen

losses in short detention time aerated ponds can usually 

be neglected. The procedure is based on total nitrogen 

in the system because numerous transformations from

one form of nitrogen to another are likely during the long

detention time. 

The first design equation is (Reed et al., 1995): 

exp { [ 60.6 ( 6.6)] } 0= −k t + pH − N

N nt

e (6-7)

Where: 

Ne = effluent total N, g/m3

 (mg/L) 

No = influent total N, g/m3

 (mg/L) 

knt = temperature-dependent reaction rate const., d-1

6-4 
= 0.0064 at 20o

C 

t = detention time, days

pH = median pH in pond during time t 

The temperature adjustment can be made using

Equation 6-2, using a theta value of 1.039. 

The second design equation is presented below (Reed 

et al., 1995): 

1 (0.000576 0.00028) exp [(1.08 0.042 )( 6.6)]

1 0 + − − − = t T T pH

Ne N

(6-8)

Terms are the same as for Equation 6-7.

Application of Equation 6-7 requires information on the

wastewater nitrogen concentration, the detention time, 

pH and temperature conditions to be expected. In a 

typical case the nitrogen concentration will vary from 

month to month so actual long-term data are desirable

for design. 

For the first iteration, the detention time should be

determined based on (a) any BOD removal required, or 

(b) by the storage time needed. If additional nitrogen

removal is necessary then the cost-effectiveness of 

providing more detention time can be compared to other 

alternatives. 

Equation 6-7 is based on plug flow kinetics and is valid

when a pond is discharging and the detention time is 

then the total detention time in the system. A value of 

one-half the detention time should be used for the filling

and storage (non-discharge) periods for storage ponds. 

The pH is controlled by the algae interactions with the 

carbonate buffering system in the pond. If possible, pH 

values should be obtained from an operating pond in the 

vicinity. The median pH values for four facultative ponds 

in the U.S. are given in Table 6-4 (US EPA, 1977; US 

EPA, 1977; and US EPA, 1977). A rough estimate of the 

pH to be expected can be obtained with: 

] (6-9) pH = 7.3 exp [ 0.005 (Alk )

Where: 

pH = median pH in the bulk liquid 

Alk = alkalinity of the influent (as CaCO3), g/m3 (mg/L)

Table 6-4. Typical pH and Alkalinity Values in Facultative Ponds

Location Annual Median pH

Annual Average 

Alkalinity,

g/m3

 (mg/L)

Peterborough, NH

Eudora, KS 

Kilmichael, MS 

Corinne, UT

7.1 

8.4 

8.2 

9.4 

85 

284 

116 

557 

6.2.5 Phosphorus Removal in Ponds 

Phosphorus removal in ponds is limited. Chemical 

addition using alum or ferric chloride has been used to 

reduce phosphorus to below 1 g/m3

 (mg/L) (Reed et al., 

1995). Application of chemicals can be on a batch or 

continuous-feed basis. For controlled release ponds the 

batch process is appropriate. The State of Minnesota

has 11 facultative pond systems that use the addition of 

liquid alum directly into secondary cells via motorboat to

meet a spring and fall discharge limitation of 1 g/m3

(mg/L) (Surampalli et al., 1993). 

For continuous-flow applications, a mixing chamber is 

often used between the last two ponds or between the 

last pond and a clarifier. In Michigan, both aerated ponds 

and facultative ponds have been used with continuousflow applications. Influent phosphorus concentrations for 

21 treatment facilities ranged from 0.5 to 15 g/m3

 (mg/L) 

with an average of 4.1 g/m3

 (mg/L) and the effluent 

target is 1 g/m3

 (mg/L) (Surampalli et al., 1993). 

6.2.6 Pathogen Removal in Ponds 

The design of systems that include a pond component 

should evaluate the bacteria and virus reductions that 

will occur in the pond. In some cases the reductions that 

will occur in a pond will produce acceptable levels so an 

extra disinfection step will not be required. At Muskegon,

MI, for example, the fecal coliforms in the storage pond

effluents were consistently below required levels so that 

chlorination was terminated (Reed, 1979). The effluent in 

this case is applied to corn, with poultry feed a major use

of the harvested corn. Water-quality changes through

the storage pond at Muskegon, MI, and in a pilot-scale

pond in Israel are summarized in Table 6-5 (US EPA, 

1976; Kott, 1978). 

6-5 
Removal of bacteria and virus in ponds is strongly 

dependent on temperature and detention time. Virus 

removal in model ponds is illustrated in Figure 6-1

(Sagik, 1978). Similar results were observed at 

operational facultative ponds in the southwest, southeast

and north central United States. In summer months, 

virus removal exceeded 2 log (i.e., 99 percent) in the first 

two cells of these systems. The overall removal on a 

year-round basis exceeded 1.5 log (i.e., 95 percent). 

Removal of fecal coliforms was even higher. 

Table 6-5. Changes of Microorganisms Concentration During Storage (US EPA, 1979)

Location Input Concentration, count/100 mL Output Concentration, count/100 mL 

Muskegon County, MI (winter): 

 Fecal coliform 1 x 106 1 x 103

Haifa, Israel

(winter, 73 days):

 Total coliform

 Fecal coliform

 Fecal streptococcus 

 Enterovirus 

2.3 x 107 

1.1 x 106 

1.1 x 106 

1.1 x 103

1.84 x 104 

2.4 x 103

5.0 x 102 

0 

Haifa, Israel

(summer, 35 days): 

 Total coliform 

 Fecal coliform

 Fecal streptococcus 

 Enterovirus 

1.4 x 107 

3.5 x 106

6.0 x 105

200 

2.3 x 104 

2.4 x 104

3.7 x 103

0 

Figure 6-1. Virus Removal in Ponds (Sagik, 1978).

Results very similar to those in Figure 6-1 have been 

demonstrated for fecal coliforms in facultative ponds in

Utah (Bowles et al., 1979). An equation was developed,

based on Chick’s Law which describes the die-off of 

fecal coliforms in a pond system as a function of time

and temperature: 

fc

i f

k

C C t ln( / ) = (6-10)

Where: 

t = actual detention time, d 

Ci = influent fecal coliforms, #/100 mL

Cf = final fecal coliforms, #/100 mL 

kfc = rate constant, use 0.5 for temperature of 20o

C 

Figure 6-2. Fecal Coliform Removal in Ponds – Detention Time vs. 

Liquid Temperature.

Removal of fecal coliform with time is shown in 

Figure 6-2. Temperature and detention times to achieve 

final concentrations of 200 CFU/100 mL for irrigation

standards and 1,000 CFU/100 mL for recreation water 

standards are shown in Figure 6-2. The detention time 

used in the equation is the actual detention time as 

measured by dye studies. In the ponds used for model

development the actual detention time ranged from 25 to

89 percent of the theoretical design detention time due

to short-circuiting. The geometric mean was 46 percent. 

If the actual detention time in the pond system is not 

known, it is suggested that this factor be applied when

using the equation to estimate fecal coliform die-off to

ensure a conservative prediction. 

6-6 
6.2.7 Biological Nutrient Removal 

Because both nitrogen and phosphorus can impact

receiving water quality, the discharge of one or both of

these constituents must often be controlled. Nitrogen 

may be present in wastewaters in various forms (e.g., 

organic, ammonia, nitrites, or nitrates). Most of the 

available nitrogen in both septic tank effluent and in

municipal wastewater is in the form of organic or

ammonia nitrogen. In wastewater treatment, about 20

percent of the total nitrogen settles out in sedimentation 

processes. During biological nitrogen removal treatment, 

ammonia nitrogen is converted to nitrate nitrogen, and

then to nitrogen gas (Crites and Tchobanoglous, 1998). 

Phosphorus is present in municipal wastewaters in

organic form, as inorganic orthophosphate, or as

complex phosphates. The complex phosphates 

represent about one-half of the phosphates in municipal

wastewater and result from the use of these materials in 

synthetic detergents. Complex phosphates are 

hydrolyzed during biological treatment to the

orthophosphate form (PO4

-3). Of the total average 

phosphorous concentration, about 10 percent is 

removed as particulate material during primary 

sedimentation and another 10 to 20 percent is 

incorporated into bacterial cells during biological

treatment. The remaining 70 percent is normally 

discharged with secondary treatment plant effluents. 

Although ponds can act as a pretreatment method, 

more aggressive biological processes, allowing

increased hydraulic loading rates and enhanced nitrogen

removal, may be required to comply with discharge

standards. Details on biological nutrient removal can be

found in Crites and Tchobanoglous (1998) and WEF

(1998). 

6.2.8 Membrane Processes 

With the development of various membranes for a 

wide range of applications, membrane treatment is 

rapidly becoming widespread and effectively competing

with conventional water treatment processes. Membrane

processes include microfiltration (MF), ultrafiltration (UF), 

nanofiltration (NF), reverse osmosis (RO), and 

electrodialysis (ED). Membrane treatment is generally

used for total dissolved solids (TDS) reduction and

removal of viruses, pathogens, and bacteria prior to the

reuse of the treated effluent. The principal applications of

the various membrane technologies for the removal of 

the constituents found in wastewater are summarized in 

Table 6-6. 

Table 6-6. Application of Membranes for the Removal of Constituents Found in Wastewater (Crites and Tchobanoglous, 1998)

Type of Membrane 

Constituents MF UF NF RO Comments 

Biodegradable organics √ √ √

Hardness √ √

Heavy metals √ √

Nitrate √ √

Priority organic pollutants √ √ √

Synthetic organic compounds √ √

TDS √ √

TSS √ √ Removed as pretreatment for NF and RO. 

Bacteria √ √ √ √ Used for membrane disinfection. 

Removed as pretreatment for NF and RO 

with MF and UF.

Protozoan oocysts and cysts √ √ √ √

Viruses √ √ Used for membrane disinfection. 

6.3 Design of Storage Ponds 

For SR and OF systems, adequate storage must be 

provided when climatic conditions require operations to

be curtailed or hydraulic loading rates to be reduced. 

Most SAT systems are operated year-round, even in

areas that experience cold winter weather. SAT systems 

may require cold weather storage during periods when

the temperature of the wastewater to be applied is near 

freezing and the ambient air temperature at the site is 

below freezing. Land treatment systems also may need

storage for flow equalization, system backup and

reliability, and system management, including crop

harvesting (SR and OF) and spreading basin

maintenance (SAT). Reserve application areas can be 

used instead of storage for these system management

requirements.

The approach used to determine storage requirements 

is to first estimate a storage volume requirement using a

water balance computation or computer programs 

developed to estimate storage needs based on observed 

climatic variations throughout the United States. The

final design volume is then determined by adjusting the 

estimated volume for net gain or loss due to precipitation 

and evaporation using a monthly water balance on the

storage pond. These estimating and adjustment

procedures are described in the following sections. As 

discussed in Section 6.2.1, ponds can offer additional

treatment benefits. These benefits should be determined

6-7 
and considered when calculating the final size of the

storage pond.

6.3.1 Estimation of Storage Volume Using 

Water Balance Calculations 

An initial estimate of the storage volume requirements 

may be determined using a water balance calculation

procedure, as described below: 

1. Determine the design monthly hydraulic loading rate. 

2. Convert the actual volume of wastewater available

each month to units of depth (cm) using the

following relationship: 

w

m

a A

Q W ( )(10 )

2

= (6-11)

Where: 

Wa = depth of available wastewater, cm 

Qm = volume of available wastewater for the month, m3

AW = field area, ha 

3. Formulate a water balance table listing the results 

for each month. In some instances, influent 

wastewater flow varies significantly with the time of

year. The values used for Qm should reflect monthly

flow variation based on historical records. 

4. Compute the net change in storage each month by

subtracting the monthly hydraulic loading from the

available wastewater in the same month. 

5. Compute the cumulative storage at the end of each

month by adding the change in storage during one

month to the accumulated quantity form the previous

month. The computation should begin with the

reservoir empty at the beginning of the largest

storage period. 

6. Compute the required storage volume using the 

maximum cumulative storage and the field area. 

The water balance calculation method is illustrated by 

Example 6-1.

Example 6-1. Storage Volume Requirements Using Storage Water 

Balance Calculations. 

Conditions 

1. Annual wastewater hydraulic loading rate, LW = 1.2 m/yr

2. Total yearly flow is 365,000 m3

/yr, with monthly flow rates given in

Column (2) of Table 6-7. 

3. Assume total land application area of 30.4 ha. 

Calculations 

1. Tabulate the design monthly hydraulic loading rate as indicated in

Column (1) of Table 6-7. 

2. Convert actual volume of wastewater available each month to 

units of depth (cm) with Equation 6-11. Results are tabulated in

Column (3) of Table 6-6. 

For example, April:

cm m

cm

m

ha

ha

m Wa 13.2

100

30.4 10,000

40,000

2

3

= ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

=

3. Compute the net change in storage each month by subtracting 

the monthly hydraulic loading rate from the available wastewater, 

as indicated in Column (4) of Table 6-7. 

4. Compute the cumulative storage at the end of the each month by

adding the change in storage during one month to the 

accumulated quantity from the previous month, as indicated in

Column (5) of Table 6-7. 

5. Calculate the required storage volume using the maximum 

cumulative storage. 

( )( ) 3

2

72,656 100

10,000 Re 23.9 30.4 m cm

m

ha

m quired Storage Volume cm ha = ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ =

6-8 
Table 6-7. Estimation of Storage Volume Requirements Using Water Balance Calculations

(1) (2) (3) (4) (5) 

Month LW, cm Wm, m3 Wa, cm 

Change in Storage, 

cm (3)-(2) 

Cumulative Storage, 

cm 

April 10 40,000 13.2 3.2 0 

May 10 42,500 14.0 4.0 3.2 

June 10 50,000 16.4 6.4 7.1 

July 10 42,500 14.0 4.0 13.6 

August 10 45,000 14.8 4.8 17.6 

September 10 35,000 11.5 1.5 22.4 

October 10 25,000 8.2 -1.8 23.9* 

November 10 15,000 4.9 -5.1 22.1 

December 10 15,000 4.9 -5.1 17.0 

January 10 15,000 4.9 -5.1 12.0 

February 10 15,000 4.9 -5.1 6.9 

March 10 25,000 8.2 -1.8 1.8 

* Maximum storage month.

6.3.2 Final Design of Storage Volume 

Calculations 

The estimated storage volume requirement obtained

by water balance calculation or computer programs must

be adjusted to account for net gain or loss in volume due 

to precipitation or evaporation. The required storage

volume should be determined by conducting a monthly 

water balance, which must include the net precipitation, 

evaporation, and seepage from the pond. This method

requires an iterative solution with some assumed initial 

conditions because the pond area is not known. The

overall storage volume must be increased to include

enough freeboard to retain an appropriate storm event

(i.e., at a minimum a 25y24h precipitation event. It is 

usually convenient to assume a depth for the initial 

calculation. This procedure is illustrated in the following 

example: 

Example 6-2. Calculations to Determine Final Storage Volume

Requirements 

Conditions 

1. Monthly evapotranspiration (ET) and precipitation (Pr) data 

indicated in Table 6-8, Columns (1) and (2). 

2. Assume seepage from pond is negligible. 

3. Initial conditions and estimated storage volume from Example 6-1. 

Calculations 

1. Using the initial estimated storage volume and an assumed 

storage pond depth compatible with local conditions, calculate a 

required surface area for the storage pond: 

s

s

s d

V est A ( ) = (6-12)

Where: 

As = area of storage pond, m2

Vs(est) = estimated storage volume, m3

ds = assumed pond depth, m 

For example, assume ds = 4 m 

2

3

18,164

4

72,656

m

m

m

As = =

2. Calculate the monthly net volume of water gained or lost from 

storage due to precipitation, evaporation, and seepage: 

( )( ) ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

Δ = − − cm

m Vs Pr E S As 100

(6-13)

Where: 

ΔVs = net gain or loss of storage volume, m3

Pr = monthly precipitation, cm 

E = monthly evaporation, cm 

S = monthly seepage, cm 

As = storage pond area, m2 

3. Estimated lake evaporation in the local area should be used for E, 

if available. Potential ET values may be used if no other data are 

available. Tabulate monthly values and sum to determine the net 

annual ΔVs. Results are tabulated in Column (3) of Table 6-8. 

4. Tabulate the volume of wastewater available each month (Qm), 

given in Example 6-1. 

5. Calculate an adjusted field area to account for annual net 

gain/loss in storage volume. 

( ) ⎟

⎠

⎞ ⎜

⎝

⎛

⎟

⎟

⎞

⎜

⎜

⎛

ΣΔ + Σ =

cm

m

ha

m L

V Q A

W

s m

W

10,000 0.01

2

'

(6-14)

Where: 

AW' = adjusted field area, ha 

ΣΔVs = annual net storage gain/loss, m3

ΣQm = annual available wastewater, m3

LW = design annual hydraulic loading rate, cm 

For example: 

( )

ha

cm

m

ha

m cm

m m AW 28.4

120 10,000 0.01

24,104 365,000

2

3 3

' =

⎟

⎠

⎞ ⎜

⎝

⎛

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

− + =

Note: The final design calculation reduced the field area from 30.4 ha

to 28.4 ha. 

⎝ ⎠

6-9 
6. Calculate the monthly volume of applied wastewater using the 

design monthly hydraulic loading rate and adjusted field area: 

( )( ) ⎟

⎠

⎞ ⎜

⎝

⎛

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ = cm

m

ha

m VW LW AW 10,000 0.01

2 ' (6-15)

Where: 

VW = monthly volume of applied wastewater, m3 

LW = design annual hydraulic loading rate, cm 

AW' = adjusted field area, ha 

Results are tabulated in Column (5) of Table 6-8. 

7. Calculate the net change in storage each month by subtracting 

the monthly applied wastewater (VW) from the sum of available 

wastewater (Qm) and net storage gain/loss (ΔVs) in the same 

month. Results are tabulated in Column (6) of Table 6-8. 

8. Calculate the cumulative storage volume at the end of each 

month by adding the change in storage during one month to the 

accumulated total from the previous month. The maximum 

monthly cumulative volume is the storage volume requirement 

used for design. Results are tabulated in column (7) of Table 6-8. 

For this example, design Vs = 64,565 m3. 

9. Adjust the assumed value of storage pond depth (ds) to yield the 

required design storage volume using Equation 6-16. 

s

s

s A

V d = (6-16)

d m

m

m

d

s

s

3.55

18,164

64,565

2

3

=

=

If the pond depth cannot be adjusted due to subsurface constraints, 

then the surface area must be adjusted to obtain the required design

volume. However, if the surface area is changed, another iteration of 

the above procedure will be necessary because the value of net 

storage gain/loss (ΔVs) will be different for a new pond area. 

Table 6-8. Final Storage Volume Requirement Calculations

(1) (2) (3) (4) (5) (6) (7) 

Month ET, cm Pr, cm 

ΔVs Net 

gain/loss, m3 Qm, m3 VW, m3 ΔVs, m3

 (3)+(4)-(5) 

Cumulative 

Storage, m3

April 13.2 2 -2,034 40,000 28,400 9,566 0 

May 17.7 0.5 -3,124 42,500 28,400 10,976 9,566 

June 21.8 0.3 -3,905 50,000 28,400 17,695 20,541 

July 23.9 0 -4,341 42,500 28,400 9,759 38,236 

August 22.1 0 -4,014 45,000 28,400 12,586 47,995 

September 14.7 0.3 -2,616 35,000 28,400 3,984 60,581 

October 10.9 0.8 -1,835 25,000 28,400 -5,235 64,565* 

November 5.1 1.3 -690 15,000 28,400 -14,090 59,331 

December 2.5 2.5 0 15,000 28,400 -13,400 45,240 

January 2.3 3 127 15,000 28,400 -13,273 31,840 

February 5.1 2.8 -418 15,000 28,400 -13,818 18,567 

March 9.7 2.8 -1,253 25,000 28,400 -4,653 4,750 

Annual -24,104 365,000 340,800 

Maximum monthly cumulative volume. 

6.3.3 Storage for Overland Flow 

Storage facilities may be required at an OF system for 

any of the following reasons: 

1. Storage of water during the winter due to reduced 

hydraulic loading rates or system shutdown 

2. Storage of stormwater runoff to meet mass 

discharge limitations 

3. Equalization of incoming flows to permit constant 

application rates 

6.3.4 Storage Requirements for Cold 

Weather 

In general, OF systems must be shut down for the

winter when effluent quality requirements cannot be met 

due to cold temperature even at reduced application

rates or when ice begins to form on the slope. The

duration of the shutdown period and, consequently, the 

required storage period will, of course, vary with the local

climate and the required effluent quality. 

In studies at Hanover, NH, a storage period of 112 

days, including acclimation, was estimated to be 

required when treating primary effluent to BOD and TSS 

limits of 30 g/m3

 (mg/L). 

In areas of the country below the 40-day storage 

contour on Figure 5.2, OF systems generally can be 

operated year-round. However, winter temperature data

at the proposed OF site should be compared with those 

at existing systems that operate year-round to determine 

if all year operation is feasible. 

Storage is required at those OF sites where winter

loading rates are reduced below the average design 

rate. The required storage volume can be calculated

using Equation 6-17. 

V = (Qw)(Dw) – (As)(Lww)(Daw) (Metric) 

V = (Qw)(Dw) – (As)(Lww)(Daw)(7.48/106) (U.S. Customary) (6-17)

Where: 

V = storage volume, m3 (million gallons)

Qw = average daily flow during winter, m3

/d (mgd) 

6-10 
Dw = number of days in the winter period 

As = slope area, m2

 (ft2) 

Lww = hydraulic loading rate during winter, m/d (ft/d) 

Daw = number of operating days in winter period 

The duration of the reduced loading period at existing 

systems generally has been about 90 days. 

6.3.5 Storage for Stormwater Runoff 

Stormwater runoff from the overland slopes must be

considered because OF is a surface discharging system. 

Facilities that have a discharge must be covered by a 

multisector stormwater permit or obtain coverage under 

an individual NPDES permit. In such cases, stormwater

runoff may need to be stored and discharged at a later 

time when mass discharge limits would not be 

exceeded. A procedure for estimating storage

requirements for stormwater runoff is outlined below. 

1. Determine the maximum monthly mass discharge 

allowed by the permit for each regulated constituent. 

2. Determine expected runoff concentrations of 

regulated constituents under normal operation (no 

precipitation).

3. Estimate monthly runoff volumes from the system 

under normal operation by subtracting estimated 

monthly ET and percolation losses from design 

hydraulic loading. 

4. Estimate the monthly mass discharge under normal 

operation by multiplying the values from Steps 2 and 

3. 

5. Calculate the allowable mass discharge of regulated 

constituents resulting from storm runoff by 

subtracting the estimated monthly mass discharge in 

Step 5 from the permit value in 

Step 1. 

6. Assuming that storm runoff contains the same 

concentration of constituents as runoff during normal 

operation, calculate the volume of storm runoff 

required to produce a mass discharge equal to the 

value of Step 5. 

7. Estimate runoff as a fraction of rainfall for the 

particular site soil conditions. Consult the local 

NRCS office for guidance. 

8. Calculate the total rainfall required to produce a 

mass discharge equal to the value in Step 5 by 

dividing the value in Step 6 by the value in Step 7. 

9. Determine for each month a probability distribution 

for rainfall amounts and the probability that the 

rainfall amount in Step 8 will be exceeded. 

10. In consultation with regulatory officials, determine 

what probability is an acceptable risk before storm 

runoff storage is required and use this value (Pd) for 

design. 

11. Storage must be provided for those months in which 

total rainfall probability exceeds the design value 

(Pd) determined in Step 10. 

12. Determine the change in storage volume each 

month by subtracting the allowable runoff volume in 

Step 6 from the runoff volume expected from rainfall 

having an occurrence probability of Pd. In months 

when the expected storm runoff exceeds the 

allowable storm runoff, the difference will be added 

to storage. In months when allowable runoff 

exceeds expected runoff, water is discharged from 

storage. 

13. Determine cumulative storage at the end of each 

month by adding the change in storage during one 

month to the accumulated quantity from the previous

month. The computation should begin at the start of 

the wettest period. Cumulative storage cannot be 

less than zero. 

14. The required storage volume is the largest value of 

cumulative storage. The storage volume must be 

adjusted for net gain or loss due to precipitation and 

evaporation. 

If stored storm runoff does not meet the discharge

permit concentration limits for regulated constituents, 

then the stored water must be reapplied to the OF 

system. The amount of stored storm runoff is expected

to be small, relative to the total volume of wastewater 

applied, and therefore, increases in slope area should 

not be necessary. The additional water volume can be 

accommodated by increasing the application period as 

necessary. 

6.3.6 Storage for Equalization 

From a process control standpoint, it is desirable to

operate an OF system at a constant application rate and

application period. For systems that do not have storage

facilities for other reasons, small equalizing basins can 

be used to even out flow variations that occur in 

municipal wastewater systems. A storage capacity of 1-

day flow should be sufficient to equalize flow in most 

cases. The surface area of basins should be minimized 

to reduce intercepted precipitation. However, an 

additional half-day of storage can be considered to hold

intercepted precipitation in wet climates. 

For systems providing only screening or primary 

sedimentation as preapplication treatment, aeration

should be provided to keep the storage basin contents 

mixed and the surface zone aerobic. The added cost of 

aeration, in most cases, will be offset by savings 

resulting from reduced pump sizes and peak power 

6-11 
demands. The designer should analyze the costeffectiveness of this approach for the system in question. 

6.4 Operation of Storage Ponds 

The scheduling of inputs or withdrawals from storage

ponds will depend on the overall process, including

agricultural operations and the treatment functions 

expected for the pond unit. Storage units in an SAT 

system are typically only for emergency conditions and

should be used accordingly. These ponds should remain

dry during routine operations and then be drained as 

rapidly as possible after the emergency is resolved. In 

some cases a separate pond is not provided in SAT 

systems but extra freeboard is constructed into one or 

more of the infiltration basins. 

Storage ponds for OF systems may be bypassed in 

many cases during the late spring and summer months 

to avoid performance problems caused by algae. The 

storage pond contents are then gradually blended with 

the main wastewater stream so that the pond is drawn

down to the specified level at the start of the next 

storage period. In areas with non-continuous algal

blooms, the pond discharges should be coordinated with

periods of low algae concentration. 

Operation of storage ponds for SR systems will

depend on whether or not any treatment function has 

been assigned to the pond. If a specified level of

nitrogen or fecal coliform removal is expected, then the 

incoming wastewater should continue to flow into the

pond and the withdrawals should be sufficient to reach 

the required pond level at the end of the application 

season. When these factors are not a concern, or when 

it is desired to maximize the nitrogen application to the 

land, the main wastewater stream should bypass the 

storage and be applied directly. Regular withdrawals 

over the season can then draw down the pond. 

For SR systems emphasizing water reuse and urban

irrigation, steps may be needed to minimize algae in the

storage ponds. These steps can include pre-storage

treatment in constructed wetlands, post-storage 

treatment by constructed wetlands, dissolved air flotation

(DAF), filtration, or reservoir management that may 

include mixing, aeration, or selective depth removal of

the highest quality water. 

6.5 References 

Brown and Caldwell (2000) Screening of Feasible

Technologies, Prepared for the San Francisco

Public Utilities Commission. 

Bowles, D.S., E.J. Middlebrooks, and J.H. Reynolds 

(1979) Coliform Decay Rates in Waste Stabilization

Ponds, Journal WPCF, 51:87-99. 

Chudoba, P. and Pujol, R. (1998) A Three-Stage

Biofiltration Process: Performances of a Pilot Plant, 

Water Science Technology, 38(8-9)257-265. 

Crites, R.W. and G. Tchobanoglous (1998) Small and 

Decentralized Wastewater Management Systems, 

McGraw-Hill, New York, NY. 

Crites, R.W., S.C. Reed, and R.K. Bastian (2000) Land

Treatment Systems for Municipal and Industrial

Wastes, McGraw-Hill, New York, NY. 

Higo, T.T. (1966) A Study of the Operation of Sewage 

Ponds in the Province of Alberta, Department of

Public Health, Government of Alberta. 

Kott, Y. (1978) Lagooned Secondary Effluents as 

Water Source for Extended Agricultural Purposes, 

Water Research, 12(12):1101-1106. 

Middlebrooks, E.J. et al. (1982) Wastewater 

Stabilization Lagoon Design, Performance and

Upgrading, Macmillan Publishing Co., New York. 

Neel, J.K., J.H. McDermott, and C.A. Monday (1961) 

Experimental Lagooning of Raw Sewage, Journal

WPCF, 33(6):603-641. 

Reed, S.C. (1984) Nitrogen Removal in Wastewater 

Ponds, CRREL Report 84-13, Cold Regions 

Research and Engineering Laboratory, Hanover, 

NH. 

Reed, S.C., R.W. Crites, E.J. Middlebrooks (1995) 

Natural Systems for Waste Management and

Treatment, Second Edition, McGraw-Hill, New York, 

NY. 

Reed, S.C. (2001) Wetland Systems. Chapter 9 in: 

Natural Systems for Wastewater Treatment, WEF 

Manual of Practice, Second Edition, Water 

Environment Federation, Alexandria, VA. 

Pano, A. and E.J. Middlebrooks (1982) Ammonia

Nitrogen Removal in Facultative Wastewater 

Stabilization Ponds, Journal WPCF, 54(4):344-351. 

Sagik, B.P. (1978) The Survival of Human Enteric 

Viruses in Holding Ponds, Contract Report DAMD 

17-75-C-5062, United States Army Medical

Research and Development Command, Ft. Detrick,

MD. 

Stowell, R. (1976) A Study of Screening of Algae from

Stabilization Ponds, Masters Thesis, Department of 

Civil Engineering, University of California, Davis. 

Surampalli, R.Y., et al. (1993) Phosphorus Removal in 

Ponds, Proceedings of the 2nd International 

Association of Water Quality International Specialist

Conference, Oakland, CA.

6-12 
Thomas, R.E. and S.C. Reed (1980) EPA Policy on 

Land Treatment and the Clean Water Act of 1977, 

Journal WPCF, 52:452. 

US EPA (1976a) Use of Climatic Data in Estimating 

Storage Days for Soil Treatment Systems, EPA600/2-76-250, U.S. Environmental Protection 

Agency, Office of Research and Development, 

Cincinnati, OH. 

US EPA (1976b) Is Muskegon County’s Solution, Your 

Solution?, U.S. Environmental Protection Agency,

Region V, Chicago, IL. 

US EPA (1977a) Performance Evaluation of Existing

Lagoons, Peterborough, N.H., EPA-600/2-77-085,

U.S. Environmental Protection Agency, Cincinnati, 

OH. 

US EPA (1977b) Performance Evaluation of an Existing

Seven Cell Lagoon System, EPA 600/2-77-086, U.S. 

Environmental Protection Agency, Cincinnati, OH. 

US EPA (1977c) Performance Evaluation of an Existing 

Lagoon System at Eudora, Kan., EPA-600/2-77-167, 

U.S. Environmental Protection Agency, Cincinnati, 

OH. 

US EPA (1977d) Preliminary Survey of Toxic Pollutants

at the Muskegon Wastewater Management System, 

U.S. Environmental Protection Agency, ORD,

Washington, DC. 

US EPA (1979) Health Aspects of Land Treatment, US 

GPO 1979-657-093/7086, U.S. Environmental

Protection Agency, Cincinnati, OH. 

US EPA (1980) Enteric Virus Removal in Wastewater 

Lagoon Systems, Report IAG 79-0-X0728, U.S. 

Environmental Protection Agency HER, Cincinnati,

OH. 

US EPA (1981) Process Design Manual for Land

Treatment of Municipal Wastewater, EPA 625/1-81-

013, U.S. Environmental Protection Agency,

Cincinnati, OH. 

US EPA (1983) Design Manual – Municipal

Wastewater Stabilization Ponds, EPA-625/1-83-015,

U.S. Environmental Protection Agency, Cincinnati, 

OH. 

US EPA (1999) Manual: Constructed Wetlands 

Treatment of Municipal Wastewaters, EPA/625/R99/010, September 1999, National Risk 

Management Research Laboratory, Office of 

Research and Development, U.S. Environmental

Protection Agency, Cincinnati, OH. 

WPCF (2001) Natural Systems, Manual of Practice, 

No. FD-16, Water Pollution Control Federation, 

Alexandria, VA. 

6-13 
Chapter 7 

Distribution Systems

Design of the distribution system involves two steps: (1) 

selection of the type of distribution system, and (2) detailed 

design of system components. The three major types of 

distribution systems are surface, sprinkler, and drip 

systems. Only basic design principles for each type of 

distribution system are presented in this manual, and the 

designer has referred to several standard agricultural 

engineering references for further design details (e.g., Burt, 

1995; Pair, 1983). Factors that distinguish land treatment 

from conventional irrigation include: 

• Supplemental irrigation water source may be needed 

to meet crop water use requirements 

• Application generally occurs over a longer season than 

conventional irrigation. There is often abundant treated 

effluent available in the late summer and fall when 

irrigation requirements are decreasing. 

• Water use efficiency is not always the optimum 

approach for managing treated effluent. 

• A higher level of environmental monitoring is required 

including accurate flow measurements, controls on 

runoff, and documentation of water and constituent 

loading rates. 

• Additional factors control irrigation rate and frequency 

when compared to conventional irrigated agriculture. 

7.1 Types of Distribution Systems 

SR systems utilize all types of distribution systems. OF 

systems are generally sprinkler, spray or surface irrigation 

with gated pipe. The goal of a distribution for a SR systems 

is to obtain even distribution through the entire application 

area, while the goal of the OF distribution system is to 

spread the water evenly at the top of the slope, creating 

uniform flow across the slope. SAT (rapid infiltration) 

systems employ infiltration basins, which are often 

operated similar to level border irrigation systems. 

Table 7-1 contains the description, advantages and 

disadvantages of various system types. 

Table 7-1. Description, Advantages, and Disadvantages of Distribution Systems

Type Description Advantages/Disadvantages 

Surface Irrigation Broad Class of irrigation where water is 

 distributed over the soil surface by gravity. 

Wild Flooding Uncontrolled application to a vegetated surface 

via gravity or low head pumping 

Poor uniformity of application 

Not generally suitable for effluent application 

Furrow Application to a graded field via small ditches 

between crop rows

Primarily for row crops 

Careful leveling is required. 

Uniform application is difficult on coarse textured soils. 

Border Application to a leveled field in 20 – 100 foot 

wide strips, bordered by dikes. 

Primarily for grass or perennial crops 

Careful leveling is required. 

Uniform application is difficult on coarse textured soils. 

Remaining solids not distributed evenly.

Sprinkler Irrigation Application of water to the soil through sprinkling 

 or spraying 

Components can be sensitive to process water chemistry.

Almost eliminates runoff. 

Susceptible to wind drift. 

Highest pumping cost 

Good method for coarse textured soils or uneven ground 

Solid Set Permanently or semi-permanently installed 

sprinklers are used in blocks. 

Good for winter irrigation if subsurface piping is used. 

Harvest and tillage are difficult around the sprinkler risers. 

Rapid rotation among blocks is feasible to provide smaller applications. 

Hand Move Moveable sprinkler lateral segments cover field 

in sets. 

High labor 

Labor requirement to move sprinklers makes long sets common. 

Least expensive system 

End Tow Entire sprinkler laterals are towed to new set 

locations after each irrigation. 

Less labor than hand move sprinkler lines 

Labor requirement to move sprinklers makes long sets common. 

Requires sturdy laterals and care during moves 

Limited to grass or hay crops 

Wheel Line Engine moveable sprinklers cover field in sets. Less labor than hand move sprinkler lines 

Labor requirement to move sprinklers makes long sets common. 

Only suitable for low height crops and rectangular fields 

Inexpensive equipment 

Big Gun Large diameter orifices operating at high 

pressure spread water. Travelling hose reels 

allow big guns to irrigate strips over uneven 

ground. 

Requires high pressure for maximum area coverage 

Water impact can damage crops and soil at low pressure. 

Relatively high irrigation rate 

7-1 
Type Description Advantages/Disadvantages 

Center Pivot Mechanical sprinkler system with fixed central 

water supply moves in a circle to irrigate 20 to 

more than 400 acres. 

Moderate initial capital expense but less labor 

Flexible, efficient irrigation with proper design. 

Frequent light irrigation of fields is used in winter to minimize soil storage 

May not be suitable for boggy or sticky soils 

High instantaneous application rates 

Linear Move Mechanical sprinkler system with end or center 

feed water supply moves in a straight line to 

irrigate fields up to 5000 feet long. 

High initial capital expense but less labor 

Efficient irrigation with proper design 

May not be suitable for boggy or sticky soils 

High instantaneous application rates 

Covers large rectangular fields 

Micro Irrigation Water is applied to the soil surface as drops or 

 smaller streams through emitters. Preferred 

 term is drip irrigation. 

Emitter clogging limits utility of micro irrigation 

Some difficulties with animal damage 

High capital cost 

Precise control of irrigation water 

Popular for permanent crops 

Surface Drip Low flow emitters placed on the ground surface 

apply water to crop root zone but not between 

rows

Easier to observe emitter performance and system plugging than with 

subsurface emitters 

Subsurface Drip Emitters are buried 6 – 12 inches deep as a 

semi-permanent installation. 

More difficult to observe system performance 

Buried lines sometimes damaged by tillage operations 

Eliminates exposure to wastewater 

Micro-Spray Small spray heads or jets on stakes next to 

permanent crops 

Only suitable for permanent crops 

Easier to observe performance than with drip emitters 

Generally more resistant to plugging than drip emitters 

7.1.1 Surface Distribution 

With surface distribution systems, water is applied to the 

ground surface at one end of a field and allowed to spread 

over the field by gravity. Conditions favoring the selection 

of a surface distribution system include the following: 

1. Capital is not available for the initial investment 

required for more sophisticated systems. 

2. Surface topography of land requires little additional 

preparation to make uniform grades for surface 

distribution. 

The principal limitations or disadvantages of surface 

systems include the following: 

1. Land leveling costs may be excessive on uneven 

terrain. 

2. Uniform distribution cannot be achieved with highly 

permeable soils. 

3. Runoff control and a return system must be provided 

when applying wastewater. 

4. Periodic maintenance of leveled surfaced is required 

to maintain uniform grades. 

The two general types of surface distribution are the 

ridge and furrow and the diked border systems. Variations 

of these two types of methods can be found in standard 

references (e.g., Burt, 1995; Hart, 1975; Booher, 1974). 

7.1.2 Sprinkler Distribution 

Sprinkler distribution uses a rotating nozzle as opposed 

to spray distribution which refers to a fixed nozzle orifice. 

Most nozzles used in land treatment systems are of the 

sprinkler type. 

Sprinkler distribution systems simulate rainfall by creating 

a rotating jet of water that breaks up into small droplets that

fall to the soil surface. The advantages and disadvantages 

of sprinkler distribution systems relative to surface and 

micro distribution systems were summarized in Table 7-1. 

In this chapter, sprinkler systems are classified according

to their movement during and between applications 

because this characteristic determines the procedure for 

design. There are three major categories of sprinkler 

systems based on movement: (1) solid set, (2) move-stop,

and (3) continuous move. A summary of the various types 

of sprinkler systems under each category is given in 

Table 7-2 along with respective operating characteristics. 

7.1.3 Micro Irrigation Distribution 

Micro irrigation (also referred to as drip or trickle 

irrigation) includes surface and subsurface low-flow 

emission devices that supply water to the root zone of each 

individual plant. The three major categories of micro 

irrigation devices are: 

• surface drip emitters 

• subsurface drip emitters 

• micro-sprays

Drip emitters can be discreet devices manually inserted 

into drip lateral hose or can be manufactured integrally into

the lateral hose. Drip emitters can also be installed on short 

“pigtail” tubes coupled to the drip lateral hose. Thin wall 

hose with integrated emitters is sometimes referred to as 

"drip tape.” Micro-sprays are small, low flow spray or jet 

devices. The advantages and disadvantages of micro 

irrigation for distribution of effluent compared with surface 

and sprinkler irrigation methods were listed in Table 7-1. 

7-2 
Table 7-2. Sprinkler System Characteristics 

Type 

Typical application 

rate, in/h 

Labor required per 

application, h/acre 

Nozzle pressure range, 

lb/in2

Size of single system, 

acres Maximum grade, % 

Solid Set 

 Permanent 0.05-2.0 0.008-0.016 30-100 No limit 40 

 Portable 0.05-2.0 0.03-0.04 30-60 No limit 40 

Move-stop 

 Hand-move 0.01-2.0 0.08-0.24 30-60 2-40 20 

 End tow 0.01-2.0 0.03-0.06 30-60 20-40 5-10 

 Side roll 0.1-2.0 0.016-0.048 30-60 20-80 5-10 

 Stationary gun 0.25-2.0 0.03-0.06 50-100 20-40 20 

Continuous move 

 Traveling gun 0.25-1.0 0.016-0.048 50-100 40-100 20-30 

 Center pivot 0.25-1.0 0.008-0.024 15-60 40-160 15-20 

 Linear move 0.25-1.0 0.008-0.024 15-60 40-360 15-20 

7.2 General Design Considerations for All 

 Types of Distribution Systems 

The hydraulic loading rate will be determined based on 

the limiting design factor as shown in Chapters 8, 9, and 10 

depending on the treatment system. 

Design parameters that are common to all distribution 

systems are defined as follows: 

Depth of Wastewater Applied. The depth of wastewater 

applied is determined using the relationship: 

D = Lw/F (7-1)

Where: 

D = depth of wastewater applied per application, mm (in.) 

Lw = monthly hydraulic loading, per application mm/mo (in./mo) 

F = frequency of applications, applications/mo 

7.2.1 Application Frequency 

The application frequency is defined as the number of 

applications per month or per week. The application 

frequency used for design is a judgment decision made by 

the designer considering: (1) the objectives of the system, 

(2) the water and nutrient needs or tolerance of the crop, 

(3) the moisture retention properties of the soil, (4) the 

labor requirement of the distribution system, (5) the 

application characteristics of the type of distribution system, 

and (6) the capital cost of the distribution system. Some 

general guidelines for determining an appropriate 

application frequency are presented here, but consultation 

with a local farm adviser is recommended. 

Except for the water tolerant forage grasses, most crops, 

including forest crops, generally require a drying period 

after reaching saturation to allow aeration of the root zone 

to achieve optimum growth and nutrient uptake. Thus, 

more frequent applications are appropriate as the ET rate 

and the soil permeability increase. In practice, application 

frequencies range from once every 3 or 4 days for sandy 

soils to about once every 2 weeks for heavy clay soils. An 

application frequency of once per week is commonly used 

for most distribution methods, with continuous move 

sprinkler and micro irrigation methods being the exception.

Continuous move sprinkler and micro irrigation methods 

have a higher irrigation frequency, but still maintain 

adequate root zone aeration. Continuous move sprinkler 

irrigation systems usually apply water at a rate higher than 

the long-term infiltration rate of the soil. In order to take 

advantage of surface micro-storage and the high initial 

infiltration rate of most soils, continuous move sprinkler 

systems typically apply water for a brief period of time 

every 1 to 4 days. The smaller application amounts and 

brief application periods allow adequate root zone aeration 

to take place between irrigations. Micro irrigation systems 

usually apply water for several hours every day. Because 

of low average application rate and that the soil surface 

area is not saturated, micro irrigation practices allow for 

root zone aeration. 

The operating and capital costs of distribution systems 

can affect the selection of application frequency. With 

distribution systems that must be moved between 

applications (move-stop systems), it is usually desirable to 

minimize labor and operating costs by minimizing the 

number of moves and therefore the frequency of 

application. On the other hand, capital costs of the 

distribution system are directly related to the flow capacity 

of the system. Thus, the capital cost may be reduced by 

increasing the application frequency to reduce the capacity 

needed in each part of the distribution system. 

7.2.2 Application Rate 

Treated wastewater application rate is the rate at which 

water is applied to the field by the distribution system. In 

general, the application rate should be restricted by the 

infiltration rate of the soil and/or vegetated surface to 

prevent unpermitted runoff and tailwater return 

requirements. Specific guidelines relating application rates 

7-3 
to infiltration properties are discussed under the different 

types of distribution systems. 

7.2.3 Application Period 

The application period is the time necessary to apply the 

desired depth of water (D). Application periods vary 

according to the type of distribution system, but, in general, 

are selected to be convenient to the operator and 

compatible with regular working hours. For most 

distribution systems application periods are less than 24 h. 

7.2.4 Application Zone 

In most systems, wastewater is not applied to the entire 

field area during the application period. Rather, the field 

area is divided into application plots or zones and 

wastewater is applied to only one zone at a time. 

Application is rotated among the zones such that the 

entire field area receives wastewater within the time 

interval specified by the application frequency. Application 

zone area can be computed with the following: 

Aa = Aw/Na (7-2) 

Where: 

Aa = application zone area 

Aw = field area 

Na = No. of application zones 

The number of application zones is equal to the number 

of applications that can be made during the time interval 

between successive applications on the same zone as 

specified by the application frequency. 

For example, if the application period is 11 h, effectively 

two applications can be made each operating day. If the 

application frequency is once per week and the system is 

operated 7 d per week, then there are 7 operating days 

between successive applications on the same zone and the 

number of application zones is: 

Na = (2 applications/day)(7 operating days) = 14 

If the field area is 35 acres, then the application zone is: 

A 2.5acres

14

35 = =

7.2.5 System Capacity 

Whatever type of distribution system is selected, the 

maximum flow capacity of the system must be determined 

so that components, such as pipelines and pumping 

stations, can be properly sized. For systems with a 

constant application rate throughout the application period, 

the flow capacity of the system can be computed using the 

following formula: 

Q = CAaD/ta (7-3)

Where: 

Q = discharge capacity, L/s (gal/min) 

C = constant, 28.1 (453) 

Aa = total application area, ha (acres) 

D = gross depth of water applied during peak periods, cm (in.) 

ta = application period, h 

Values for water applied and application period on a perday basis are usually incorporated into the above formula. 

The effective amount of time available per day for 

application must take into account time lost in moving 

distribution equipment and system maintenance. 

7.3 Surface Distribution 

Ridge and furrow and graded border distribution are most 

often associated with slow rate systems. For overland flow, 

surface application can be used with either gated aluminum

pipe or bubbling orifices. For soil aquifer treatment, the 

common method of application is basin flooding. 

7.3.1 Ridge and Furrow Distribution 

The design procedure for ridge and furrow systems is 

empirical and is based on past experience with good 

irrigation systems and field evaluation of operating 

systems. The design variables for furrow systems (see 

Figure 7-1) include furrow grade, spacing, length, and 

stream size (flowrate). The furrow grade will depend on the 

site topography. A grade of 2 percent is the recommended 

maximum for straight furrows. Furrows can be oriented 

diagonally across fields to reduce grades. Contour furrows 

or corrugations can be used with grades in the range of 2 

to 10 percent. 

Figure 7-1. Typical Surface Distribution Methods – Ridge and Furrow. 

The furrow spacing depends on the water intake 

characteristics of the soil. The principal objective in 

selecting furrow spacing is to make sure that the lateral 

movement of the water between adjacent furrows will wet 

the entire root zone before it percolates beyond the root 

zone. Suggested furrow spacings based on different soil 

and subsoil conditions are given in Table 7-3. 

7-4 
The length of the furrow should be as long as will permit 

reasonable uniformity of application, because labor 

requirements and capital costs increase as furrows become

shorter. Suggested maximum furrow lengths for different 

grades, soils, and depths of water applied are given in 

Table 7-4. 

Table 7-3. Optimum Furrow Spacing

Soil condition Optimum 

spacing, in1

Coarse sands-uniform profile 12 

Coarse sands-over compact subsoils 18 

Fine sands to sandy loams-uniform 24 

Fine sands to sandy loams-over more compact 

subsoils 

30 

Medium sandy-silt loam-uniform 36 

Medium sandy-silt loam-over more compact 

subsoils 

40 

Silty clay loam-uniform 48 

Very heavy clay soils-uniform 36 

1

2.54 centimeters per inch. 

The furrow stream size or application rate is expressed 

as a flow rate per furrow. The optimum stream size is 

usually determined by trial and adjustment in the field after 

the system has been installed (Merriam and Keller, 1978). 

The most uniform distribution (highest application 

efficiency) generally can be achieved by starting the 

application with the largest stream size that can be safely 

carried in the furrow. Once the stream has reached the end 

of the furrow, the application rate can be reduced or cut 

back to reduce the quantity of runoff that must be handled. 

As a general rule, it is desirable to have the stream size 

large enough to reach the end of the furrow within one-fifth 

of the total application period. This practice will result in a 

theoretical application efficiency of greater than 90 percent

for most soils if tailwater is returned. 

Table 7-4. Suggested Maximum Lengths of Furrows, ft2

Average depth of wastewater applied, in1

Furrow grade, Clays Loams Sands 

% 3 6 9 12 2 4 6 8 2 3 4 5 

0.05 1000 1300 1300 1300 400 900 1300 1300 200 300 500 600 

0.2 1200 1540 1740 2030 720 1200 1540 1740 400 600 800 1000 

0.5 1300 1640 1840 2460 920 1200 1540 1740 400 600 800 1000 

1.0 920 1300 1640 1970 820 980 1200 1540 300 500 700 800 

2.0 720 890 1100 1300 590 820 980 1100 200 300 500 600 

1

2.54 centimeters per inch. 

2

 30.48 centimeters per foot.

The application period is the time needed to infiltrate the 

desired depth of water plus the time required for the stream 

to advance to the end of the furrow. The time required for 

infiltration depends on the water intake characteristics of 

the furrow. There is no standard method for estimating the 

furrow intake rate. The recommended approach is to 

determine furrow intake rates and infiltration times by field 

trials as described in Merriam and Keller, (1978). 

Design of supply pumps and transmission systems 

should be based on the maximum allowable stream size, 

which is generally limited by erosion considerations when 

grades are greater than 0.3 percent. The maximum 

nonerosive stream size can be estimated from the 

equation: 

qe = C/G (7-4)

Where: 

qe = maximum unit stream size, gpm. 

C = constant, 10 

G = grade, % 

For grades less than 0.3 percent, the maximum allowable

stream size is governed by the flow capacity of the furrow, 

estimated as follows: 

qc = CFa (7-5)

Where: 

qc = furrow flow capacity, gpm 

C = constant, 74 

Fa = cross-sectional area of furrow, ft2

For wastewater distribution, pipelines are generally used.

If buried pipelines are used to convey water, vertical riser 

pipes with valves are usually spaced at frequent intervals to

release water into temporary ditches equipped with siphon 

tubes or into hydrants connected to gated surface pipe 

(Figure 7-2). 

7-5 
Figure 7-2. Typical Gated Pipe Distribution Unit. 

The spacing of the risers is governed either by the head 

loss in the gated pipe or by widths of border strips when 

graded border and furrow methods are alternated on the 

same field. The valves used in risers are alfalfa valves 

(mounted on top of the riser) or orchard valves (mounted 

inside the riser). Valves must be sized to deliver the design

flow rate. 

Gated surface pipe may be aluminum or plastic. Outlets 

along the pipe are spaced to match furrow spacings. The 

pipe and hydrants are portable so that they may be moved 

for each irrigation. The hydrants are mounted on valved 

risers, which are spaced along the buried pipeline that 

supplies the wastewater. Operating handles extend through 

the hydrants to control the alfalfa or orchard valves located 

in the risers. Control of flow into each furrow is 

accomplished with slide gates or screw adjustable orifices 

at each outlet. Slide gates are recommended for use with 

wastewater. Gated outlet capacities vary with the available

head at the gate, the velocity of flow passing the gate, and 

the gate opening. Gate openings are adjusted in the field to

achieve the desired stream size. 

7.3.2 Graded Border Distribution 

The design variables for graded border distribution are: 

1. Grade of the border strip 

2. Width of the border strip 

3. Length of the border strip 

4. Unit stream size 

Graded border distribution can be used on grades up to 

about 7 percent. Terracing of graded borders can be used 

for grades up to 20 percent. Graded border irrigation may 

not be suitable for the application of wastewater with 

substantial amounts of settleable solids to grass or hay 

crops because of poor resulting solids distribution. 

The widths of border strips are often selected for 

compatibility with farm implements, but they also depend to 

a certain extent upon grade and soil type, which affect the 

uniformity of distribution across the strip. A guide for 

estimating strip widths is presented in Table 7-5 and Table 

7-6. 

The length of border strips should be as long as practical 

to minimize capital and operating costs. However, 

extremely long runs are not practical due to time 

requirements for patrolling and difficulties in determining 

stream size adjustments. Lengths in excess of 400 m 

(1,300 ft) are not recommended. In general, border strips 

should not be laid out across two or more soil types with 

different intake characteristics or water holding capacities, 

and border strips should not extend across slope grades 

that differ substantially. The appropriate length for a given 

site depends on the grade, the allowable stream size, the 

depth of water applied, the intake characteristics of the soil, 

and the configuration of the site boundaries. For 

preliminary design, the length of the border may be 

estimated using Table 7-5 and Table 7-6. 

Table 7-5. Design Guidelines for Graded Borders for Deep-Rooted Crops1,2,3

Soil type and Border strip, ft 

infiltration rate, 

in/h Grade, % 

Unit flow per foot 

of strip width, 

gal/min 

Average dept of 

water applied, in Width Length 

Sand 

 >1.0 0.2-0.4 50-70 4 40-100 200-300 

0.4-1.6 40-50 4 30-40 200-300 

0.6-1.0 25-40 4 20-30 250 

Loamy sand 

 0.75-1.0 0.2-0.4 30-50 5 40-100 250-500 

0.4-0.6 25-40 5 25-40 250-500 

0.6-1.0 13-25 5 25 250 

Sandy loam 

 0.5-0.75 0.2-0.4 25-35 6 40-100 300-800 

0.4-0.6 18-30 6 20-40 300-600 

0.6-1.0 9-18 6 20 300 

Clay loam 

 0.25-0.5 0.2-0.4 13-18 7 40-100 600-1000 

0.4-0.6 9-13 7 20-40 300-600 

7-6 
0.6-1.0 5-9 7 20 300 

Clay

 0.10-0.25 0.2-0.3 9-18 8 40-100 1200 1

2.54 centimeters per inch. 

2

30.48 centimeters per foot. 

3

3.785 liters per 1 US gallon. 

Table 7-6. Design Guidelines for Graded Borders for Shallow-Rooted Crops1,2,3

Border strip, ft 

Soil profile Grade, % 

Unit flow per foot of strip 

width, gal/min 

Average depth of 

water applied, in Width Length 

Clay loam, 0.15-0.6 25-35 2-4 15-60 300-600 

24 in deep 0.6-1.5 18-30 2-4 15-20 300-600 

 over permeable 

 subsoil 

1.5-4.0 9-18 2-4 15-20 300-600 

Clay, 24 in 0.15-0.6 13-18 4-6 15-60 600-1000 

 deep over 0.6-1.5 9-13 4-6 15-20 600-1000 

 Permeable 

 subsoil 

1.5-4.0 5-9 4-6 15-20 600 

Loam, 6 to 

18 in deep 

 over hardpan 

1.0-4.0 5-20 1-3 15-20 300-1000 

1

2.54 centimeters per inch. 

2

30.48 centimeters per foot. 

3

3.785 liters per 1 US gallon. 

The application rate or unit stream size for graded border 

irrigation is expressed as a flow rate per unit width of 

border strip. The stream size must be such that the desired

volume of water is applied to the strip in a time equal to, or 

slightly less than, the time necessary for the water to 

infiltrate the soil surface. When the desired volume of water 

has been delivered onto the strip, the stream is turned off. 

Shutoff normally occurs when the stream has advanced 

about 75 percent of the length of the strip. The objective is 

to have sufficient water remaining on the border after 

shutoff to apply the desired water depth to the remaining 

length of border limiting runoff or ponding at the bottom 

end. 

Use of a proper stream size is necessary to achieve 

uniform and efficient application. Too rapid a stream results 

in inadequate application at the upper end of the strip or in 

excessive ponding or surface runoff at the lower end. If the 

stream is too small, the lower end of the strip receives 

inadequate water or the upper end has excessive deep 

percolation. Actually achieving uniform distribution with 

minimal runoff requires a good deal of skill and experience 

on the part of the operator. The range of stream sizes given 

in Table 7-5 and Table 7-6 for various soil and crop 

conditions may be used for preliminary design. Wastewater 

with significant amounts of settleable solids should be 

applied at relatively higher flow rates to improve the 

distribution of solids on the field. Procedures given in the 

Border Irrigation chapter of the USDA NRCS National 

Engineering Handbook (USDA, 1980) may be used to 

obtain a more accurate estimate of stream size. 

The application period necessary to apply the desired 

depth of water may be determined from the following 

equation: 

ta = LD/Cq (7-6)

Where: 

ta = application period, h 

L = border strip length, ft 

D = depth of applied water, in 

C = constant, 96.3 

q = unit stream size, gpm/ft of width 

Opportunity Time (Shut-off Time) 

The majority of graded border systems used for 

wastewater land treatment are operated with diked ends, 

allowing no runoff. For this case, the duration of application 

is not a simple function of calculating the run time based on 

the flow rate and the area of the border strip. Uniform 

infiltration of water is achieved when the entire length of the 

system has equal opportunity to infiltrate. Equal opportunity

time occurs when the advance rate of the wetting front is 

equal to the recession of the water. The recession of water

is a function of the slope and percolation rate. A guideline 

to assist the applicator in achieving uniform distribution is to

set the flow rate so the total volume is applied when the 

wetting front advances 60 percent of the strip length for 

clay soil and 90 percent of the length for sandy soils. 

The percolation rate changes throughout the season and 

depends on the surface preparation. Unfortunately, the 

same flow rate will not supply equal distribution throughout

the season. 

The results of equal opportunity time at the head and tail 

of the strip are shown in Figure 7-3. Equal opportunity time 

is achieved when the advance time matches the recession 

time. With diked ends, the water which would normally 

runoff, ponds and adds to the opportunity time at the end of 

the strip. If the shut-off advance distance is left constant 

7-7 
and the flow rate is reduced, the head of the strip receives 

a greater opportunity time. In Figure 7-4, the opportunity at 

the head of the strip, T1, is greater than the opportunity 

time as the tail of the strip, T2. If the flow rate is reduced 

even further the wetting front will not even reach the end of 

the strip. If the flow rate is increased above the optimal, 

the tail end of the strip receives a greater opportunity time 

from the ponded water and T2 is greater than T1, as shown 

in Figure 7-5 (Burt, 1995). 

The conveyance and application devices used for border

distribution are basically the same as described for ridge 

and furrow distribution. Open ditches with several evenly 

spaced siphon tubes are often used to supply the required 

stream size to a border strip. When buried pipe is used for 

conveyance, vertical risers with valves are usually spaced 

at intervals equal to the width of the border strip and are 

located midway in the border strip. With this arrangement, 

one valve supplies each strip. Water is discharged from the 

valve directly to the ground surface, as indicated in 

Figure 7-6, and is distributed across the width of the strip 

by gravity flow. For border strip widths greater than 9 m (30 

ft), at least two outlets per strip are necessary to achieve 

good distribution across the strip. Hydrants and gated pipe 

can be used with border systems. Use of gated pipe 

provides much more uniform distribution at the head of 

border strips and allows the flexibility of easily changing to 

ridge and furrow distribution if crop changes are desired. 

7.3.3 Surface Distribution for Overland 

Flow 

Municipal wastewater can be surface applied to overland 

flow slopes, but industrial wastewater should usually be 

sprinkler applied if there are higher concentrations of BOD 

and solids. Surface distribution methods include gated 

aluminum pipe commonly used for agricultural irrigation, 

and slotted or perforated plastic pipe. Commercially 

available gated pipe can have gate spaces ranging from 

0.6 to 1.2 m (2 to 4 ft) and gates can be placed on one or 

both sides of the pipe. A 0.6 m (2-ft) spacing is 

recommended to provide operating flexibility. Slide gates 

rather than screw adjustable orifices are recommended for

wastewater distribution. Gates can be adjusted manually to 

achieve reasonably uniform distribution along the pipe. 

However, the pipe should be operated under low pressure, 

2 to 5 lb/in.2

, to achieve good uniformity at the application 

rates recommended in Chapter 9, especially with long pipe 

lengths. Pipe lengths up to 520 m (1,700 ft) have been 

used, but shorter lengths are recommended. For pipe 

lengths greater than 90 m (300 ft), inline valves should be 

provided along the pipe to allow additional flow control and 

isolation of pipe segments for separate operation. 

Distance Along Strip

Time

0

0

end

Diked End

No Runoff- Water ponded

at lower end

Recession

Advance

Lag

Time Shutoff Time

T1

T2

Figure 7-3. Equal Opportunity Time Along Entire Strip (Burt, 1995). 

7-8 
Distance Along Strip

Time

0

0

end

Diked End

No Runoff- Water ponded

at lower end

Recession

Advance

Lag

Time Shutoff Time

T1

T2

Figure 7-4. Greater Opportunity Time at Head of Strip: Flow Rate Too Small (Burt, 1995). 

7-9 
Distance Along Strip

Time

0

0

end

Diked End

No Runoff- Water ponded

at lower end

Recession

Advance

Lag

Time Shutoff Time

T1

T2

Figure 7-5. Greater Opportunity Time at Tail End of Strip: Flow Rate Too Large 

(Burt, 1995). 

.

Figure 7-6. Typical Discharge Valve for Border Strip Application. 

Example 7-1: Establish Preliminary Design Criteria for a Graded 

Border System 

Conditions 

Deep clay loam soil, finished grade, G: 0.3%, 

maximum monthly hydraulic loading, Lw: 12 in, 

application frequency, F : 3 times per month, field 

area, Aw: 120 acres, crop: pasture. 

Solution 

1. Calculate the depth of wastewater to be 

applied using Equation 7-1. 

D = Lw/F 

D = 12 in = 4 in 

 3 

2. Select border width and length from Table 7-6 

for design conditions for shallow-rooted 

crops. 

Width = 40 ft 

Length = 600 ft 

3. Select unit flow per width of strip, gpm from 

Table 7-6. 

q = 30 gpm/ft of width 

4. Calculate the period of application, ta, using 

Equation 7-6. 

ta = LD /96.3 q 

ta = (600 ft)(4)/ (96.3)(30) 

= 0.83 h 

7-10 
5. Determine number of applications per day

assuming a 12 h/d operating period. 

Number of applications = 12 h/d/ 0.83 

 application 

6. Determine the number of application zones. 

Application cycle is 10 day (30 d/mo)

3 cycles/mo 

Application zones = (10 d) (15 

applications/d) = 150 

7. Calculate the area per zone, Aa. 

Aa = Aw /number of zones 

= 120 acres

150 zones 

Aa = 0.8 acres 

8. Determine the number of border strips per 

application zone. 

Number of borders = Aa

(L)(W) 

= (0.8 acres)(43,560 ft2

/acre)

(600 ft)(40 ft) 

= 1.45, use 2 

9. Determine system flow capacity, Q. 

Q = (2 borders)(W)(q) = (2)(40 ft)(30 gpm/ft) 

= 2,400 gpm 

The system must be capable of supplying 

2,400 gpm during the maximum month. 

Slotted or perforated plastic pipe have fixed openings at 

intervals ranging from 0.3 to 1.2 m (1 to 4 ft). These 

systems operate under gravity or very low pressure and the 

pipe must be level to achieve uniform distribution. 

Consequently, such methods should be considered only for

small systems having relatively short pipe lengths that can

be easily leveled. The advantages and disadvantages of 

surface, spray, and sprinkler systems are compared in 

Chapter 9. 

7.3.4 Surface Distribution for Soil Aquifer 

 Treatment (SAT) 

Although sprinklers may be used, wastewater distribution

for SAT is usually by surface spreading. This distribution 

technique employs gravity flow from piping systems or 

ditches to flood the application area. To ensure uniform 

basin application, basin surfaces should be reasonably flat. 

Overflow weirs may be used to regulate basin water 

depth. Water that flows over the weirs is either collected 

and conveyed to holding ponds for recirculation or 

distributed to other infiltration basins. If each basin is to 

receive equal flow, the distribution piping channels should 

be sized so that hydraulic losses between outlets to basins 

are insignificant. Design standards for distribution systems 

and for flow control and measurement techniques are 

published by the American Society of Agricultural 

Engineers (ASAE). Outlets used at currently operating 

systems include valved risers for underground piping 

systems and turnout gates from distribution ditches. 

Basin layout and dimensions are controlled by 

topography, distribution system hydraulics, and loading 

rate. The number of basins is also affected by the selected 

loading cycle. As a minimum, the system should have 

enough basins so that at least one basin can be loaded at 

all times, unless storage is provided. 

The number of basins also depends on the total area 

required for infiltration. Optimum basin size can range from 

0.2 to 2 ha (0.5 to 5 ac) for small to medium sized systems 

to 2 to 8 ha (5 to 20 ac) for large systems. For a 24-ha (62-

ac) system, if the selected loading cycle is 1 day of 

wastewater application alternated with 10 days of drying, a 

typical design would include 22 basins of 1.3 ha (2.8 ac) 

each. Using 22 basins, two basins would be flooded at a 

time and there would be ample time for basin maintenance 

before each flooding period. 

At many sites, topography makes equal-sized basins 

impractical. Instead, basin size is limited to what will fit into 

areas having suitable slope and soil type. Relatively 

uniform loading rates and loading cycles can be maintained 

if multiple basins are constructed. However, some sites will 

require that loading rates or cycles vary with individual 

basins. 

In flat areas, basins should be adjoining and should be 

square or rectangular to maximize land use. In areas where

groundwater mounding is a potential problem, less 

mounding occurs when long, narrow basins with their 

length normal to the prevailing groundwater flow are used 

than when square or round basins are constructed. Basins 

should be at least 300 mm (12 in) deeper than the 

maximum design wastewater depth, in case initial 

infiltration is slower than expected and for emergencies. 

Basin walls are normally compacted soil with slopes 

ranging from 1:1 to 1:2 (vertical distance to horizontal 

distance). In areas that experience severe winds or heavy 

rains, basin walls should be planted with grass or covered 

with riprap to prevent erosion. 

If basin maintenance will be conducted from within the 

basins, entry ramps should be provided. These ramps are 

formed of compacted soil at grades of 10 to 20 percent and 

are from 3 to 3.6 m (10 to 12 ft) wide. Basin surface area 

for these ramps and for wall slopes should not be 

considered as part of the necessary infiltration area. 

7.4 Sprinkler Distribution 

Sprinkler distribution is common to SR systems, is 

generally used with industrial OF systems, and can be 

used with SAT systems. Forest SR, OF and many 

agricultural SR systems use solid set (stationary) sprinkler 

7-11 
distribution, whereas move-stop and continuous move 

sprinklers are restricted to SR systems. 

7.4.1 Design Application Rates 

For all SR sprinkler systems the design application rate 

cm/h (in./h) should be less than the infiltration rate of the 

surface soil to avoid surface runoff. For final design, the 

application rate should be based on field infiltration rates 

determined from previous experience with similar soils and 

crops or from direct field measurements. 

For solid set or move-stop sprinkler irrigation systems, 

the design application rate should be less than the 

saturated permeability or infiltration rate of the surface soil 

(see Chapter 3) to prevent runoff and uneven distribution. 

Application rates can be increased when a full cover crop is 

present (see Section 4.3.2.4). The increase should not 

exceed 100 percent of the bare soil application rate. 

Application rates for continuous move irrigation systems 

should not exceed the instantaneous infiltration rate and 

any available surface micro-storage during the period of 

water application. Recommended reductions in application

rate for sloping terrain are given in Table 7-7. A practical 

minimum design application rate is 0.5 cm/h (0.2 in./h). For

final design, the application rate should be based on field 

infiltration rates determined on the basis of previous 

experience with similar soils and crops or from direct field 

measurements. 

Table 7-7. Recommended Reductions in Application Rates Due to 

Grade [McCulloch et al, 1973] 

Percent Grade 

Application 

rate reduction 

0-5 0 

6-8 20 

9-12 40 

13-20 60 

Over 20 75 

Solid Set Systems 

Solid set sprinkler systems remain in one position during 

the application season. The system consists of a grid of 

mainline and lateral pipes covering the field to be irrigated. 

Impact sprinklers are mounted on riser pipes extending 

vertically from the laterals. Riser heights are determined by 

crop heights and spray angle. Sprinklers are spaced at 

prescribed equal intervals along each lateral pipe, usually 

12 to 30 m (40 to 100 ft). A system is called fully permanent 

or stationary when all lines and sprinklers are permanently 

located. Permanent systems usually have buried main and 

lateral lines to minimize interference with farming 

operations. Solid set systems are called fully portable when 

portable surface pipe is used for main and lateral lines. 

Portable solid set systems can be used in situations where 

the surface pipe will not interfere with farming operations 

and when it is desirable to remove the pipe from the field 

during periods of winter storage. When the mainline is 

permanently located and the lateral lines are portable 

surface pipe, the system is called semipermanent or 

semiportable.The primary advantages of solid set systems 

are low labor requirements and maintenance costs, and 

adaptability to all types of terrain, field shapes, and crops. 

They are also the most adaptable systems for climate 

control requirements. The major disadvantages are high 

installation costs and obstruction of farming equipment by 

fixed risers. 

Application Rate 

For solid set systems, the application rate is expressed 

as a function of the sprinkler discharge capacity, the 

spacing of the sprinklers along the lateral, and the spacing 

of the laterals along the main according to the following 

equation: 

R = qsC/SsSL (7-7)

Where: 

R = application rate, in./h 

qs = sprinkler discharge rate, gpm 

C = constant = 96.3 

Ss = sprinkler spacing along lateral, ft 

SL = lateral spacing along main, ft 

Detailed procedures for sprinkler selection and spacing 

determination to achieve the desired application rate are 

given in the references (e.g., Fry et al., 1971; NRCS 1983; 

and Pair et al., 1983). 

Sprinkler Selection and Spacing Determination 

Sprinkler selection and spacing determination involves 

an iterative process. The usual procedure is to select a 

sprinkler and lateral spacing, then determine the sprinkler 

discharge capacity required to provide the design 

application rate at the selected spacing. The required 

sprinkler discharge capacity may be calculated using 

Equation 7-7. 

Manufacturers' sprinkler performance data are then 

reviewed to determine the nozzle sizes, operating 

pressures, and wetted diameters of sprinklers operating at 

the desired discharge rate. The wetted diameters are then 

checked with the assumed spacings for conformance with 

spacing criteria. Recommended spacings are based on a 

percentage of the wetted diameter and vary with the wind 

conditions. Recommended spacing criteria are given in 

Table 7-8. 

The sprinkler and nozzle size should be selected to 

operate within the pressure range recommended by the 

7-12 
manufacturer. Operating pressures that are too low cause 

large drops which are concentrated in a ring a certain 

distance away from the sprinkler, whereas high pressures 

result in fine drops which fall near the sprinkler. Sprinklers 

with low design operating pressures are desirable from an 

energy conservation standpoint. 

Table 7-8. Recommended Spacing of Sprinklers [McCulloch et al., 

1973] 

Wind Speed 

Km/h (mi/h) Spacing, % of wetted diameter 

0-11 (0-7) 40 (between sprinklers) 

65 (between laterals) 

11-16 (7-10) 40 (between sprinklers) 

60 (between laterals) 

>16 (>10) 30 (between sprinklers) 

50 (between laterals) 

Lateral Design 

Lateral design consists of selecting lateral sizes to deliver

the total flow requirement of the lateral with friction losses 

limited to a predetermined amount. A general practice is to 

limit all hydraulic losses (static and dynamic) in a lateral to 

20 percent of the operating pressure of the sprinklers. This 

will result in sprinkler discharge variations of about 10 

percent along the lateral. Since flow is being discharged 

from a number of sprinklers, the effect of multiple outlets on 

friction loss in the lateral must be considered. A simplified 

approach is to multiply the friction loss in the entire lateral 

at full flow (discharge at the distal end) by a factor based 

on the number of outlets. The factors for selected numbers 

of outlets are presented in Table 7-9. For long lateral lines, 

capital costs may be reduced by using two or more lateral 

sizes that will satisfy the head loss requirements. Elevation 

losses or gains should be incorporated into the hydraulic 

loss calculations. Flexible flow-regulating sprinkler nozzles 

can be used in difficult terrain or design conditions. 

Table 7-9. Pipe Friction Loss Factors to Obtain Actual Loss in Line 

with Multiple Outlets 

Numbers of outlets Value of F 

1 1.000 

2 0.634 

3 0.528 

4 0.480 

5 0.451 

6 0.433 

7 0.419 

8 0.410 

9 0.402 

10 0.369 

15 0.379 

20 0.370 

25 0.365 

30 0.362 

40 0.357 

50 0.355 

100 0.350 

The following guidelines should be used when laying out 

lateral lines: 

1. Where possible, run the lateral lines across the 

predominant land slope and provide equal lateral 

lengths on both sides of the mainline. 

2. Avoid running laterals uphill where possible. If this 

cannot be avoided, the lateral length must be 

shortened to allow for the loss in static head. 

3. Lateral lines may be run down slopes from a 

mainline on a ridge, provided the slope is relatively 

uniform and not too steep. With this arrangement, 

static head is gained with distance downhill, allowing 

longer or smaller lateral lines to be used compared 

to level ground systems. 

4. Lateral lines should run as nearly as possible at right 

angles to the prevailing wind direction. This 

arrangement allows the sprinklers rather than 

laterals to be spaced more closely together to 

account for wind distortion and reduces the amount 

of pipe required. 

Example 7-2: Establish Preliminary Design Criteria for Solid Set 

Sprinkler System 

Conditions 

Infiltration rate: 0.6 in/h, depth of wastewater 

applied, D : 2 in., crop: forage grass, applications 

zone area, Aa : 10 acres, average wind speed : 5 

mph. 

Solution 

1. Determine design application rate, R. 

Assume an 8 h application period. 

R = D

ta = 2 in

 8 h 

= 0.25 in/h ( < 0.6 in/h) 

2. Select sprinkler and lateral spacings. 

use Ss = 60 ft 

SL = 60 ft 

R D/ta 

= 2 in/8 h 

3. Calculate required sprinkler discharge 

rearranging Equation 7-7. 

qs = R SsSL

 96.3 

qs = (0.25)(60)(60)

 96.3 

= 9.3 gpm 

4. Select sprinkler nozzle size, pressure, and 

wetted diameter to provide necessary

discharge. 

Use a 7/32 in. nozzle at 50 lb/in.2

 pressure. 

Wetted diameter = 125 ft 

5. Check selected spacing against criteria in 

Table 7-8 for the average wind speed. 

Sprinkler spacing, Ss = 60

 125 

 = 48%> 40% 

7-13 
Lateral spacing, SL = 60

 125 

 = 48%< 65% 

6. Change sprinkler spacing to 50 ft (OK at 

40%), and lateral spacing to 80 ft (OK at 

64%). Recalculate qs = 10.4 gpm The same 

nozzle is satisfactory if the pressure is 

increased to 55 lb/in2

. Wetted diameter is 127 

ft. 

7. Determine system flow capacity, Q. 

Q = AaR = (10 acres)(0.25 in/h)(27,154 

gal/acre•in)( 1 hr )/60 min = 1,131 gpm 

7.4.2 Solid Set Forest Systems 

Solid set irrigation systems are the most commonly used

systems in forests. Buried systems are less susceptible to 

damage from ice and snow and do not interfere with forest 

management activities (thinning, harvesting, and 

regeneration). Solid set sprinkler systems for forest crops 

have some special design requirements. Spacing of 

sprinkler heads must be closer and operating pressures 

lower in forests than other vegetation systems because of 

the interference from tree trunks and leaves and possible 

damage to bark. An 18-m (60-ft) spacing between 

sprinklers and a 24-m (80-ft) spacing between laterals has 

proven to be an acceptable spacing for forested areas. This 

spacing, with sprinkler overlap, provides good wastewater 

distribution at a reasonable cost. Operating pressures at 

the nozzle should not exceed 379 kPa (55 lb/ in2

 ), 

although pressures up to 586 kPa (85 lb/in2

 ) may be used 

with mature or thickbarked hardwood species. The 

sprinkler risers should be high enough to raise the sprinkler 

above most of the understory vegetation, but generally not 

exceeding 1.5-m (5-ft). Low-trajectory sprinklers should be

used so that water is not thrown into the tree canopies, 

particularly in the winter when ice buildup on pines and 

other evergreen trees can cause the trees to be broken or 

uprooted. 

A number of different methods of applying wastewater 

during subfreezing temperatures in the winter have been 

attempted. These range from various modifications of 

rotating and nonrotating sprinklers to furrow and 

subterranean applications. General practice is to use lowtrajectory, single nozzle impact-type sprinklers, or lowtrajectory, double nozzle hydraulic driven sprinklers. 

Installation of a buried solid set irrigation system in 

existing forests must be done with care to avoid excessive 

damage to the trees or soil. Alternatively, solid set systems 

can be placed on the surface if adequate line drainage is 

provided (see Figure 7-7). For buried systems, sufficient 

vegetation must be removed during construction to ensure 

ease of installation while minimizing site disturbance so 

that site productivity is not decreased or erosion hazard 

increased. A 3-m (10-ft) wide path cleared for each lateral 

meets these objectives. Following construction, the 

disturbed area must be mulched or seeded to restore 

infiltration and prevent erosion. During operation of the land 

treatment system, a 1.5-m (5-ft) radius should be kept 

clear around each sprinkler. This practice allows better 

distribution and more convenient observation of sprinkler 

operation. Water distribution patterns will still not meet 

agricultural standards, but this is not as important in forests 

because the roots are quite extensive. 

Figure 7-7. Forest Solid Set Sprinkler Irrigation at Clayton County. 

7.4.3 Solid Set Overland Flow Systems 

Sprinkler distribution systems recommended for OF 

systems are discussed in Chapter 9. High pressure, 50 to 

80 lb/in2

, impact sprinklers have been used successfully 

with food processing wastewaters containing suspended 

solids concentration >500 mg/L. The position of the impact 

sprinkler on the slope is also discussed in Chapter 9. 

Spacing for low-pressure fixed spray heads at the top of 

the overland flow slopes should meet the same criteria as 

spacing for rotating sprinklers. 

The spacing of the sprinkler along the slope depends on 

the design application rate and must be determined in 

conjunction with the sprinkler discharge capacity and the 

diameter of coverage. The relationship between OF 

application rate and sprinkler spacing and discharge 

capacity is given by the following equation: 

R = q (7-8)

 Ss

Where: 

R = OF application rate, gpm/ft of slope width 

q = sprinkler discharge rate, gpm 

Ss = sprinkler spacing, ft 

The sprinkler spacing should allow for some overlap of 

sprinkler diameters. A spacing of about 80 percent of the 

wetted diameter should be adequate for OF. Using the 

7-14 
applied, the system is turned off and the sprinklers (or 

sprinkler) are moved to another position in the field for the 

next application. Multiple sprinkler move-stop systems 

include portable hand-move systems, end tow systems, 

and wheel line (also known as side-roll) systems. Single 

sprinkler move-stop systems include stationary gun 

systems. Diagrams of operation for the different types of 

move-stop sprinkler systems are shown in Figure 7-8. 

design OF application rate and the above criteria for 

overlap, a sprinkler can be selected from a manufacturer's 

catalog. 

7.4.4 Move-Stop Sprinkler Systems 

With move-stop systems, sprinklers (or a single sprinkler)

are operated at a fixed position in the field during 

application. After the desired amount of water has been 

Figure 7-8. Move-Stop Sprinkler Systems.

7-15 
Portable Hand Move Systems 

Portable hand move systems consist of a network of 

surface aluminum lateral pipes connected to a main line 

which may be portable or permanent. The major 

advantages of these systems include low capital costs and

adaptability to most field conditions and climates. They may

also be removed from the fields to avoid interference with 

farm machinery. The principal disadvantage is the high 

labor requirement to operate the system. 

End Tow Systems 

End tow systems are multiple-sprinkler laterals mounted 

on skids or wheel assemblies to allow a tractor to pull the 

lateral intact from one position along the main to the next. 

The pipe and sprinkler design considerations are identical 

to those for portable pipe systems with the exception that 

pipe joints are stronger than hand-moved systems to 

accommodate the pulling requirements. 

The primary advantages of an end tow system are lower 

labor requirements than hand-moved systems, relatively 

low system costs, and the capability to be readily removed 

from the field to allow farm implements to operate. 

Disadvantages include crop restrictions to movement of 

laterals and cautious operation to avoid crop and 

equipment damage. 

Wheel Line 

Wheel line or side-roll systems are basically lateral lines 

with sprinklers that act as the axle for a series of large 

diameter wheels. The lateral line is aluminum pipe, typically

100 to 125 mm (4 to 5 in) in diameter and up to 406 m 

(1,320 ft) long. The wheels are aluminum and are 1.5 to 2.1 

m (5 to 7 ft) in diameter (see Figure 7-9). The end of the 

lateral is connected by a flexible hose to hydrants located 

along the main line. The unit is stationary during application 

and is moved between applications by an integral engine 

powered drive unit located at the center or end of the 

lateral. 

The principal advantages of wheel line systems are lower

labor requirements and overall cost than hand-move 

systems, and freedom from interference with farm 

implements. Disadvantages include restrictions to crop 

height and field shape, and misalignment of the lateral 

caused by uneven terrain. 

Stationary Gun Systems 

Stationary gun systems are wheel-mounted or skidmounted single sprinkler units, which are moved manually 

between hydrants located along the laterals. The 

advantages of a stationary gun are similar to those of 

portable pipe systems with respect to capital costs and 

versatility. In addition, the larger nozzle of the gun-type 

sprinkler is relatively free from clogging. The drawbacks to 

this system are similar to those for portable pipe systems in 

that labor requirements are high due to frequent sprinkler 

moves. Power requirements are relatively high due to high 

pressures at the nozzle, and windy conditions adversely 

affect distribution of the fine droplets created by the higher 

pressures. 

Figure 7-9. Side-Wheel Roll Sprinkler System. 

Design Procedures 

The design procedures regarding application rate, 

sprinkler selection, sprinkler and lateral spacing, and lateral 

design for move-stop systems are basically the same as 

those described for solid set sprinkler systems. An 

additional design variable for move-stop systems is the 

number of units required to cover a given area. The 

minimum required number of units is a function of the area 

covered by each unit, the application frequency, and the 

period of application. More than the minimum number of 

units can be provided to reduce the number of moves 

required to cover a given area. The decision to provide 

additional units should be based on the relative costs and 

availability of equipment and labor. 

7.4.5 Continuous Move Systems 

Continuous move sprinkler systems are self-propelled 

and essentially move continuously during the application 

period. The three types of continuous move systems are 

(1) traveling gun, (2) center pivot, and (3) linear move. 

Diagrams showing the operation of continuous move 

sprinkler systems are shown in Figure 7-10. 

Traveling Gun Systems 

Traveling gun systems are self-propelled, single large 

gun sprinkler units that are connected to the supply source 

by a hose 63 to 127 mm (2.5 to 5 in) in diameter. Two 

types of travelers are available, the hose drag-type and the 

reel-type. The hose drag traveler is driven by a hydraulic or

gas-driven winch located within the unit, or a gas-driven 

winch located at the end of the run. In both cases, a cable 

anchored at the end of the run guides the unit in a straight 

7-16 
Figure 7-10. Continuous Move Sprinkler Systems.

7-17 
path during the application. The flexible rubber hose is 

dragged behind the unit. The reel-type traveler (see 

Figure 7-11) consists of a sprinkler gun cart attached to a 

take-up reel by a semi-rigid polyethylene hose. The gun is 

pulled toward the take-up reel as the hose is slowly wound 

around the hydraulic powered reel. Variable speed drives 

are used to control travel speeds. Typical lengths of run 

range between 201 to 403 m (660 and 1,320 ft), and 

spacings between travel lanes range between 50 to 100 m 

(165 and 330 ft). After application on a lane is complete, 

the unit shuts off automatically. Some units also shut off the 

water supply automatically. The unit must be moved by 

tractor to the beginning of the next lane. 

Figure 7-11. Reel-Type Traveling Gun Sprinkler. 

The more important advantages of a traveling gun 

system are low labor requirements and relatively clog-free 

nozzles. They may also be adapted to fields of somewhat 

irregular shape and topography. Disadvantages are high 

power requirements, hose travel lanes required for hose 

drag units for most crops, and drifting of sprays in windy 

conditions. Traveling gun systems are generally more 

suited to systems with low operating hours per year. 

In addition to the application rate and depth of 

application, the principal design parameters for traveling 

guns are the sprinkler capacity, spacing between travel 

lanes (see Table 7-10), and the travel speed. 

Table 7-10. Recommended Maximum Lane Spacing for Traveling Gun 

Sprinklers

Wind speed, mi/h 

Lane spacing, 

% of wetted diameter 

0 80 

0-5 70-75 

5-10 60-65 

>10 50-55 

The minimum application rate of most traveling gun 

sprinklers is about 5.8 mm/h (0.23 in./h), which is higher 

than the infiltration rate of the less permeable soils. 

Therefore, the use of traveling guns on soils of low 

permeability without a mature cover crop is not 

recommended. The relationship between sprinkler 

capacity, lane spacing, travel speed, and depth of 

application is given by the following equation: 

D = qs

C (7-9)

 (st)(Sp) 

Where: 

D = depth of water applied, in 

qs = sprinkler capacity, gpm 

St = space between travel lanes, ft 

Sp = travel speed, ft/min 

C = conversion constant, 1.60 

The typical design procedure is as follows: 

1. Select a convenient application period, h/d, allowing at least 1 h 

between applications to move the gun. 

2. Estimate the area to be irrigated by a single unit. This value 

should not exceed 80 acres (32 ha). 

3. Calculate the sprinkler discharge capacity using Equation 7-7. 

qs = (435)(D)(A) (7-10)

 Ct 

Where: 

qs = sprinkler discharge capacity, gpm 

D = depth of wastewater applied per application, in 

A = area irrigated per unit, acres 

C = cycle time between applications, d 

t = operating period, h/d 

4. Select a sprinkler size and operating pressure from 

manufacturer's performance tables that will provide the estimated 

discharge capacity.

5. Calculate the application rate using Equation 7-8. 

R = 96.3 Q (7-11)

 r2

Where: 

R = application rate, in/h 

Q = sprinkler capacity, gpm 

r = sprinkler wetted radius, ft 

6. Compute the lane spacing as a percentage of the wetted diameter 

against spacing criteria in Table 7-10. 

7. Adjust sprinkler selection and lane spacing as necessary to be 

compatible with soil intake rate. 

8. Calculate the travel speed using Equation 7-9 as rearranged: 

 Sp = 1.6qs

 D St

9. Calculate the area covered by a single unit. 

A = St(travel distance, ft/d)(cycle, d)

 43,560 ft2/acre 

10. Determine the total number of units required. 

Units required = field area

 unit area 

7-18 
11. Determine the system capacity, Q 

Q = (qs)(number of units) 

Example 7-3: Establish Preliminary Design Criteria for Reel Type 

Traveling Gun System 

Conditions 

Loam soil, infiltration rate : 0.4 in/h, depth of 

wastewater applied, D : 3 in, field area : 100 acres, 

application cycle : every 10 d, average wind speed 

: 5 mph. 

Solution 

1. Select a 15 h/d application period 

2. Estimate 25 acres/unit 

3. Calculate the sprinkler discharge capacity

qs = (435)(3)(25)

 (10)(15) 

= 217.5 gpm 

4. Select a sprinkler with a 230 gpm capacity

and a wetted diameter of 340 ft. 

5. Calculate the application rate 

R = 96.3(230)

 (170)2

= 0.24 in./h ( < 0.4 in./h, OK) 

6. Lane spacing should be less than 70% to 

75% of wetted diameter 

St = 0.7 (340) = 238 ft 

use 240 ft 

7. Calculate the travel speed 

Sp = (1.6)(230)

 (3)(240) 

= 0.5 ft/min 

8. Calculate the area covered by a single unit 

A = (240)(0.5)(15 h)( h)(10 d)

 43,560 

= 24.8 acres 

9. Calculate the number of units required 

Units required = 100 acres 

 24.8 acres/unit 

= 4.03 

use 4 units 

10. Calculate the system capacity, Q 

Q = (qs)(number of units) = (230 gpm)(4) = 920 

gpm 

Center Pivot Systems 

Center pivot systems consist of a truss supported lateral 

with multiple sprinklers or spray nozzles that are mounted 

on self-propelled, continuously moving tower units (see 

Figure 7-12 and Figure 7-13) rotating about a fixed pivot in 

the center of the field. Sprinklers on the lateral may be 

high-pressure impact sprinklers; however, the trend is 

toward use of low-pressure spray nozzles or other lowpressure sprinkling devices to reduce energy requirements. 

Water is supplied by a buried main to the pivot, where 

power is also furnished. The lateral is usually constructed 

of 150 to 200 mm (6 to 8 in.) steel pipe 60 to 780 m (200 to 

2,600 ft) in length. A typical system with a 393 m (1,288 ft) 

lateral is centered on a 64 ha (160-ac) parcel. The circular 

pattern reduces coverage to about 52 ha (130 ac), although 

systems with swing out corner laterals or high-pressure 

corner guns are available to irrigate a portion of the 

corners. 

The tower units are driven electrically or hydraulically and 

may be spaced from 24 to 76 m (80 to 250 ft) apart. Control 

of the travel speed is achieved by varying the average 

speed of the end tower motor. Most systems run the end 

tower motor for an adjustable percentage of a short interval 

(1 to 2 minutes), while a few systems control the speed 

directly. Cable or other guidance mechanisms are 

employed to sense the alignment of the towers and actuate 

the inner tower motors to keep up with the outer tower. 

Figure 7-12 Center Pivot Sprinkler Unit. 

Figure 7-13. Center Pivot Irrigation System. 

An important limitation of the center pivot system is the 

required variation in sprinkler discharge rates along the 

length of the pivot lateral. Because the area circumscribed 

by a given length of pivot lateral increases with distance 

from the pivot point (as does the ground speed of the unit), 

the discharge per unit of lateral length provided by the 

7-19 
sprinklers must increase with distance from the center to 

provide a uniform depth of application. Increasing the 

discharge rate can be accomplished by decreasing the 

spacing of the sprinklers along the lateral and increasing 

the discharge capacity of the individual sprinklers. The 

resulting application rates at the outer end of the pivot 

lateral can be so high as to be unacceptable for many soils. 

Since center pivot sprinkler systems typically apply water 

on a more frequent basis and for shorter durations than 

move-stop sprinkler systems, short term soil infiltration and 

surface storage characteristics are more important than the 

long-term infiltration rate. On a short term basis, the 

infiltration rate normally decreases exponentially with the 

amount of water infiltrated. In addition, infiltration rates 

normally decrease over the season due to surface soil 

sealing from sprinkler droplet impact. Figure 7-14 shows a 

graphical representation of water application, infiltration 

rate, and potential runoff with center pivot irrigation. 

Potential runoff will become actual runoff if there is not 

sufficient surface storage to retain the excess water. 

Figure 7-14. Intersection Between an Elliptical Moving Application 

Rate Profile Under a Center-pivot Lateral and a Typical Infiltration 

Curve. 

Equation 7-12 can be used to describe short-term 

infiltration characteristics of soils (Keller and Bleisner, 

1990). The coefficients for Equation 7-12 can be 

determined by fitting a curve (or regression of the 

logarithms) of sprinkling infiltration test data which 

measures depth to ponding at various application rates as 

shown in Figure 7-15 (Reinders and Louw, 1985). Soil 

surface and moisture conditions should be as close to 

anticipated field conditions as possible. 

Figure 7-15. Schematic of the Revolving – Sprinkler Infiltrometer. 

Di = kp(Tp)

p (7-12)

Where: 

Di = depth infiltrated for average sprinkle application rate at 

time of ponding 

Kp = time-to-ponding coefficient dependent on soil and water 

characteristics at the time of the test and the 

measurement units used 

P = time-to-ponding exponent dependent on soil and water 

characteristics at the time of the test 

A variety of sprinkler spacing packages are available 

from the manufacturers along with various types of impact 

sprinklers, rotating plate sprinklers, and fixed sprays. The 

rotating plate sprinklers and fixed sprays can also be 

placed on offset booms to increase the wetted width and 

thereby decrease application rates. The selection of the 

sprinkler package should take into account the soil 

infiltration rate curve, slope, wind conditions, potential for 

soil compaction, and pressure requirements. Typical 

relative application rates for various types of application 

packages are shown in Figure 7-16. The center pivot flow 

rate and application rate near the end of the center pivot 

can be calculated using Equations 7-12 and 7-13, 

respectively. 

Figure 7-16. Comparison of Relative Application Rates Under Various 

Center Pivot Sprinkler Packages. 

7-20 
The flow capacity of a center pivot system is given by 

Equation 7-10. 

Q = 1,890 D A (7-13)

Where: 

Q = flow capacity, gpm 

D = average daily depth of wastewater application, in/d 

A = area of application, acres 

The average application rate at the end of the center 

pivot lateral is given by Equation 7-14. 

I = 2πL • D (7-14)

 W T 

Where: 

I = average application rate of the last sprinklers, in/h (mm/h) 

L = center pivot length, ft (m) 

D = average daily depth of wastewater application, in/d (mm/d) 

W = wetted width of the last few sprinklers or sprays (including 

offset boom length, if offset booms are used), ft (m) 

T = average operating hours per day

Surface storage is dependent upon slope, crop, and 

cultural practices. Some preliminary values for surface 

storage as a function of slope are shown in Table 7-11

(Rogers et al, 1994). 

Table 7-11. Typical Values for Surface Storage

Slope Storage (in.) 

0 – 1% 

1% - 3% 

3% - 5% 

>5% 

0.5 

0.3 

0.1 

0.0 

Operating center pivots at a higher rotation rate will 

decrease the depth of application per irrigation. This takes 

greater advantage of surface storage and higher early 

instantaneous infiltration rates to reduce runoff. If the 

coefficients for Equation 7-9 can be estimated from 

infiltrometer or other data and surface storage is estimated 

from Table 7-11, the application time that will not cause 

runoff can be calculated with Equation 7-12. The maximum

rotational time that will not cause runoff can then be 

calculated using Equation 7-13. (Keller and Bleisner, 1990). 

SS = I (Ta) _ Kp (Ta)

p (7-15)

 60 

Where: 

SS = Surface Storage 

I = Average application rate near end of center pivot 

Ta = Time of application to pond and fill surface storage 

Kp = Time to ponding coefficient from Eq. 7-9. 

P = Time to ponding exponent from Eq. 7-9. 

Solve for Ta by convergent trial and error. 

Tcr = 2πL (7-16)

 60 (W) 

 Ta

Where: 

Tcr = Critical maximum rotation time which will not cause runoff 

L = Length of center pivot lateral 

W = Wetted width of sprinklers at end of center pivot lateral 

(including offset booms) 

Ta = Time of application to pond and fill surface storage from 

Eq.7-15 

A sprinkler package with a sufficient wetted width should 

be selected such that the calculated time of rotation for no 

runoff is greater than 24 hours at a minimum. Short rotation

times can cause crops to be shallow rooted, and the more 

frequent wetting can increase mold disease in some crops. 

Ideally, design rotation times should be 48 hours or greater. 

Sprinkler packages should be selected to minimize or 

eliminate estimated runoff. If good soil infiltration test data 

are not available, it is usually best to rely upon local 

experience in the selection of sprinkler packages. 

Figure 7-17 can also be used to obtain a rough idea of the 

feasibility of center pivot irrigation if only soil texture is 

known. 

Figure 7-17. Anticipated Center Pivot Performance versus Soil 

Texture. 

Water droplet kinetic energy can adversely affect 

infiltration rates as an irrigation season progresses. For 

soils that have low structural cohesion or are otherwise 

susceptible to sealing, water droplet energy should be 

considered when selecting a sprinkler package. Water 

sprinkler or spray devices have relatively smaller nozzles 

droplet energy is typically lower for fixed sprays than for 

7-21 
sprinklers. Water droplet energy is also lower when and/or 

are operated in the higher end of their pressure ranges. 

A limitation of center pivots is mobility under certain soil 

conditions. Some clay soils can build up on wheels and 

eventually cause the unit to stop. Drive wheels can lose 

traction on slick (silty) soils and can sink into soft soils and 

become stuck. Runoff exacerbates these conditions. As a 

result, high flotation tires are used and low tire pressures 

are recommended according to the data in Table 7-12.

Table 7-12. Recommended Soil Contact Pressure for Center Pivots

Percent fines Pounds per square inch 

20 

40 

50 

25 

16 

12 

Linear Move Systems 

Linear move systems are constructed and driven in a 

similar manner to center pivot systems, except that the unit 

moves continuously in a linear path rather than a circular 

path. Complete coverage of rectangular fields can thus be 

achieved while retaining all the advantages of a continuous 

move system. Water can be supplied to the unit through a 

flexible hose that is pulled along with the unit or it can be 

pumped from an open center ditch constructed down the 

length of the linear path. Slopes greater than 5 percent 

restrict the use of center ditches. Manufacturers should be 

consulted for design details. 

Application rate under a linear move system is a function

of the system flow, wetted width of the sprinkler package, 

and the system length as shown in Equation 7-17. 

Equation 7-15 can then be used to calculate the maximum 

time of application for a linear move system for no runoff, 

where time of application is equal to wetted width divided 

by travel speed. Flow, wetted width, total travel distance, 

and travel speed are all factors which can be adjusted 

during the planning process to arrive at a linear move 

system design which minimizes potential runoff. 

I = C Q (7-17)

 L W 

Where: 

I = average application rate, mm/h (in/h) 

C = unit conversion factor = 1 (96.3) 

Q = system flow rate, L/h (gpm) 

L = linear move length, m (ft) 

W = wetted width of the sprinklers or sprays (including offset 

boom length, if offset booms are used), m (ft) 

7.5 Micro Irrigation Distribution System 

 Planning and Design 

Micro irrigation encompasses drip or trickle irrigation and 

micro-spray irrigation systems. Micro irrigation systems 

usually deliver water to emission devices immediately 

adjacent to individual plants. Flow rates of micro irrigation 

emission devices range from 2 L/h (0.5 gal/h) for low flow 

emitters to 120 L/h (30 gal/h) for the largest micro-sprays. 

Micro irrigation is not typically used for large-scale 

wastewater land treatment systems. It is most commonly 

used for landscape irrigation with effluent that has been 

treated to tertiary levels (oxidation, filtration, and 

disinfection). Micro irrigation can be used to distribute 

wastewater with lower degrees of treatment than tertiary, 

but much more care is then needed in equipment selection 

and operation. Micro irrigation is gaining increased 

attention as a distribution method for wastewater from 

small and onsite treatment systems. Micro irrigation is also

used for such specialized applications such as landscape 

irrigation around treatment plants and to provide water for 

odor biofilters. Micro irrigation has little to offer for OF and 

conventional SAT systems. 

There are a number of very good references for micro 

irrigation design (e.g., Keller and Bliesner, 1990). Rather 

than cover that material extensively, the information 

provided in this chapter will give an overview of micro 

irrigation design issues with special attention to the 

prevention of plugging. 

7.5.1 Soil Wetting 

Micro irrigation devices typically only wet a portion of the 

horizontal cross sectional area of the soil (see Figure 7-18). 

The target percentage of area wetted is generally 33 

percent to 67 percent for wide spaced crops such as trees 

and vines (Keller and Bliesner, 1990). Yields can suffer at 

wetted areas lower than 33 percent while some of the 

benefits such as reduced water use and fewer weeds 

diminish at values above 67 percent. The minimum target 

percentage for closely spaced crops is also 33 percent, but

the higher density of emission devices often translates into

a wetted area of over 67 percent. Field tests with emission 

devices are usually the best way to determine wetted width

for a given type of device at the planned irrigation site. 

7-22 
Figure 7-18. Comparison of Wetting Profiles in Sandy Soil. 

7.5.2 Micro Irrigation Design Criteria 

In addition to wetted width, the most important micro 

irrigation system design criteria are as follows: 

• Efficiency of filtration 

• Permissible variations of pressure head 

• Base operating pressure to be used 

• Degree of control of flow or pressure 

• Relation between discharge and pressure a the pump 

or hydrant supplying the system 

• Allowance for temperature correction for long path 

emitters 

• Chemical treatment to dissolve or prevent deposits 

• Use of secondary safety screening 

• Incorporation of flow monitoring 

• Allowance for reserve system capacity or pressure to 

compensate for reduced flow due to clogging 

Of the above criteria, the filtration and chemical treatment

criteria are critical when wastewater is to be used in the 

micro irrigation system. 

7.5.3 General System Layout 

Agricultural scale micro irrigation distribution systems 

normally include mainlines, submains, laterals, and 

emitters. Sometimes manifolds are also utilized to control 

flow and pressure to a number of laterals off a submain. 

Landscape or small scale micro irrigation may only have 

submain and lateral piping. A typical layout for an 

agricultural micro irrigation system is shown in Figure 7-19. 

Figure 7-19. Typical Micro Irrigation System Layout. 

7.5.4 Emission Device Flow 

 Characteristics 

Flow from emission devices can usually be characterized 

by the following equation: 

Q = KHx (7-18)

Where: 

Q = flow 

K = discharge coefficient 

H = pressure head 

X = emitter discharge exponent 

The most common types of emission devices based on 

flow characteristics are long path, turbulent flow, orifice, 

and pressure compensating. Flow exponents range from 

zero for fully compensating devices to 0.5 for orifice and 

turbulent flow devices to approximately 0.7 for smooth long 

path devices. The flow exponents are very important in the

design of micro irrigation systems for discharge uniformity. 

Low flow exponents generally provide higher uniformity and 

greater latitude in system design, especially for systems on

undulating terrain. 

Coefficient of manufacturing variability is important in the

overall uniformity of application. Flow rate coefficients of 

variability less than 0.05 are generally considered 

excellent, while coefficients greater than 0.11 are 

considered poor. 

7.5.5 Selection of Emission Devices to 

 Minimize Plugging 

When micro irrigation systems are used to distribute 

effluent, the selection of the proper emission device can be

critical for preventing plugging. The best emission devices

are those which have automatic flushing features built into 

7-23 
them. The relative resistance to plugging of various types 

of emitters is shown in Table 7-13. 

Susceptibility to gradual plugging can usually be 

overcome with an aggressive chemical treatment and 

flushing program, except in the case of porous pipe. 

It should be noted that the flow rate for an emission 

device is determined by the size of the flow path within the 

emission device. An 8 L/h emitter will have a larger flow 

path than a 2 L/h emitter, and therefore be much more 

resistant to plugging. Distribution systems for effluent 

should always use emission devices with the highest 

possible flow rates that still meet the basic system design 

criteria. 

Inline drip emitters or drip tape can be especially 

sensitive to plugging because of the low flow rates of each 

emitter. Emission devices incorporating inlet filtering, 

automatic flushing, and larger flow paths are strongly 

recommended when considering inline or tape products. 

Manufacturer’s specific recommendations should also be 

considered in the selection of emission devices and the 

corresponding filtration and water treatment for any specific 

application. 

Table 7-13. Relative Resistance to Plugging for Various Emission Devices 

Emitter Type 

Resistance to Catastrophic 

Particulate Plugging Resistance to Gradual Plugging 

Multiple Flexible Orifice (continuous flushing) High Moderate 

Compensating Diaphragm – turbulent path (continuous flushing) Moderately High Moderately High 

Micro-Sprays Moderate High 

Compensating Diaphragm – straight path or groove Moderate Moderately Low

Long Path Turbulent Moderate Moderate 

Long Path Straight or Spiral Moderately Low Low

Porous Pipe* High Very Low

*Not recommended for use in any wastewater irrigation system. 

7.5.6 Submain, Manifold and Lateral 

 Design 

The distribution piping should be designed to minimize 

overall costs (capital and energy) and maintain a high 

uniformity. Pressure regulator valves or devices are 

normally installed either at the beginning of the submain or 

at the inlet to the manifold. Piping downstream of the last 

pressure regulation point should be designed to keep the 

minimum emitter flow rate greater than 90 percent of the 

average emitter flow rate. Lateral length and diameter are 

usually key factors for emission uniformity. When barbed 

emitters or couplings are used, it is important to include 

minor losses caused by the barbs in the laterals. There are 

graphical and numerical solutions available in micro 

irrigation design guides that combine emitter flow 

characteristics with losses in laterals, manifolds, and 

submains to enable calculation of average and minimum 

flow rates. 

Laterals should also be designed with automatic flush 

valves or a flushing manifold at the ends of the laterals to 

enable regular flushing and prevent the buildup of 

sediments in the lateral. This is critical for the long term 

prevention of plugging in effluent distribution systems. 

7.5.7 Subsurface Drip Irrigation System 

Considerations 

Subsurface drip irrigation is appealing because the 

laterals are out of the way for cultural practices and less 

susceptible to physical damage. With subsurface drip 

irrigation, wetting of the ground surface is minimal. This can

be a desirable aesthetic consideration for disposal/reuse of 

treated effluent. 

The main disadvantage of subsurface drip irrigation is 

that emitter performance is not readily observable, so 

plugging can become serious before the irrigator 

recognizes the problem. Subsurface emitters can also be 

susceptible to root intrusion, and laterals can be subject to 

root pinching. Emitters impregnated with herbicide to 

prevent root intrusion are commercially available. Root 

intrusion can also be prevented by regular shock 

chlorination as discussed later in this section. 

7.5.8 Subsurface Drip Irrigation for Small 

and Onsite Systems 

There is an increasing level of interest in using drip 

irrigation components for the subsurface distribution of 

effluent from small and on-site wastewater treatment 

systems. These systems typically have septic tank or other 

sedimentation treatment followed by intermittent sand 

filtration or other small scale secondary treatment. The 

effluent is then applied below grass or landscape areas to 

provide supplemental irrigation and disposal. The emission

device selection and system design considerations are the

same as discussed in this section. One of the differences 

for small and on-site systems is that relatively higher flow 

rate emitters can be used. A second difference is that 

emission devices should be designed to prevent root 

intrusion through chemical impregnation or physical 

7-24 
features. The designer may also want to consider sleeving

the laterals in larger PVC or polyethylene perforated drain 

pipes for easy replacement if the laterals become 

irreversibly plugged. 

7.5.9 Micro-Spray System Considerations 

In comparison to drip emitters, micro-sprays have a direct 

area of coverage. The area of spray coverage plus 

subsurface lateral movement of water should provide 

adequate coverage of the root zone of the crop at maturity. 

Micro-sprays are commonly used for trees and landscape 

beds in place of multiple drip emitters. The proper 

functioning of micro-sprays is easier to observe than for 

drip emitters, and micro-sprays are generally less 

susceptible to gradual plugging than drip emittershe main 

disadvantage of micro-sprays is that the mounting stakes 

are generally more susceptible to damage than individual 

drip emitters. 

7.5.10 Filtration 

Primary wastewater treatment must be provided as an 

absolute minimum prior to any micro irrigation system 

filters. Partial or full secondary treatment is also highly 

recommended. High-rate automatic sand media filtration is 

the filtration of choice for effluent micro irrigation systems. 

For systems smaller than 10 L/s (150 gpm), more 

advanced biological treatment followed by automated disk 

filters may be satisfactory. Screen filters are only 

recommended for highly treated effluent, and should be 

very significantly oversized. 

In general, filtration should be provided to 74 micron (200 

mesh) equivalent screen size. Small systems with emitters

which are highly resistant to plugging can use somewhat 

coarser filtration depending upon the manufacturer’s 

recommendations. Filter units should be oversized and 

should have plenty of backflush flow capacity. For 

automated filter banks, three or more filter units per bank 

will provide better backflushing performance than two unit 

banks. 

7.5.11 Chemical Treatment to Prevent 

 Plugging 

Chemical water treatment should be provided for all 

effluent micro irrigation systems except possibly tertiary 

effluent with adequate residual chlorine. Chemical 

treatment is used to prevent and dissolve organic (algae 

and bacterial slime) and minerals deposits which can form 

in lateral lines and emission devices. Chlorine and acids 

are most commonly used for chemical treatment. 

Hydrogen peroxide can be substituted for chlorine when 

high concentrations of oxidant are needed to restore 

system capacity. 

For tertiary treated wastewater, maintaining 1.0 mg/L of 

free residual chlorine at the ends of laterals is generally 

adequate to prevent plugging. For primary or secondary 

effluent, the most effective strategy is to inject sufficient 

chlorine to bring the concentration of free chlorine at the 

ends of the laterals to 10 mg/L during the last 20 minutes of

the irrigation cycle or to at least 2 mg/L during the last hour 

of an irrigation cycle (Tajrishy, 1993). If a micro irrigation 

system has to be restored from a gradual buildup of 

organic material in the emission devices, concentrations of

up to 100 mg/L chlorine can be temporarily used to treat 

the system. Liquid sodium hypochlorite is generally the 

preferred form of chlorine because of safety and handling 

considerations. 

Depending upon water chemistry, acid injection may also 

be needed. Acid injection may be needed to keep effluent 

pH below 7.5 during chlorination to maintain chlorine 

effectiveness. Acid is also sometimes used on an 

intermittent basis to dissolve mineral precipitates. During 

intermittent acid treatment, the pH may be reduced to a 

range of 3 to 4. Care must be taken during intermittent acid

treatment to keep the pH above the level specified by the 

manufacturer where emitter damage could occur. 

Positive displacement chemical injection pumps or 

differential pressure venturi tube injectors are the most 

common devices used for chemical injection. 

7.5.12 Water Use and Scheduling 

Irrigation water needs are based on ET and leaching 

fraction in a similar manner as for sprinkler or surface 

irrigation. With micro irrigation, there is less evaporative 

loss from the soil surface and a lower leaching requirement 

than for other types of irrigation. When scheduling micro 

irrigation, the evapotranspiration can be estimated by 

multiplying the ET for a crop with full coverage by the 

percentage of the area that is actually wet or shaded by the 

crop, whichever is greater. Micro irrigation systems typically 

irrigate the entire area daily, rotating through each flow 

zone for several hours to apply the appropriate depth of 

water. 

7.5.13 Other Operational Considerations 

Regular flushing of micro irrigation laterals is very 

important for preventing the buildup of solids and 

sediments in the laterals. For larger systems, flush 

manifolds with automatic valves connected to the ends of a 

group of laterals are preferred. These can be operated 

briefly at the beginning and/or end of every irrigation. For 

smaller systems, automatic flush caps can be installed on 

the end of every lateral. Monthly manual flushing should 

also be performed for laterals with automatic end flush 

caps because the automatic flush caps do not flush at full 

operating flow and pressure. 

One other operational issue for the irrigation of crops 

using effluent with elevated salinity is that light rains during 

the growing season can move salts into the root zone. For 

7-25 
this reason, the irrigation system should be turned on 

during light rains to help flush salts away from the roots. 

7.6 Pumping Stations and Mainlines 

Different types of pumping stations are used for 

transmission, distribution, and tailwater pumping. 

Transmission pumping of either raw or treated wastewater 

usually involves a conventional wastewater pumping 

station. Distribution pumping of treated wastewater can 

involve either a conventional wastewater pumping station 

or structure built into a treatment/storage pond. Tailwater 

pumping is used with surface distribution systems and may 

also be used with some sprinkler distribution systems. 

The number of pumps to be installed depends on the 

magnitude of the flow and the range of flows expected. 

Unless there is storage available for many days of 

operation, the pumps should have capacity equal to the 

maximum expected inflow with at least one pump out of 

service. Pumps should be selected with head-capacity 

characteristics that correspond as nearly as possible to the

flow and head requirements of the overall system (Sanks 

et al., 1989). 

The horsepower required for pumping can be estimated 

using Equation 7-19. 

Hp = QH (7-19)

 3960 e 

Where: 

Hp = horsepower required, hp 

Q = flow, gpm 

H = total head, ft 

3960 = conversion factor 

e = pumping system efficiency

Efficiencies range from about 40 to 50 percent when 

pumping raw wastewater up to a range of 65 percent to 80 

percent when pumping primary or secondary effluent. 

7.7 Distribution Pumping 

Distribution pumping stations can be located next to 

preapplication treatment facilities or can be built into the 

dikes of treatment/storage ponds (see Figure 7-20). 

Depending on the method of distribution the pumps may 

discharge under pressure. Peak flows depend on the 

operation plan and the variation in application rates 

throughout the operating season. For example, if the land 

application site is to receive wastewater for only 8 h/d, the 

pumps must be able to discharge at least three times the 

average daily flow rate (24/8 = 3). 

The basis of the pump design is the total head (static 

plus friction) and the peak flow requirements. Flow 

Figure 7-20. Distribution Pumps in the Side of a Storage Pond Dike. 

requirements are determined based on the hours of 

operation per day or per week and the system capacity 

(see next section). Details of pumping station design are 

available in standard references (Sanks et al., 1989; 

Hydraulic Institute, 1983). 

7.8 Tailwater Pumping 

Most surface distribution systems will produce some 

runoff that is referred to as tailwater. When partially treated

wastewater is applied, tailwater must be contained within 

the treatment site and reapplied. Thus, a tailwater return 

system is an integral part of an SR system using surface 

distribution methods. A typical tailwater return system 

consists of a sump or reservoir, a pump(s), and return 

pipeline (see Figure 7-21). 

The simplest and most flexible type of system is a 

storage reservoir system in which all or a portion of the 

tailwater flow from a given application is stored and either 

transferred to a main reservoir for later application or 

reapplied from the tailwater reservoir to other portions of 

the field. Tailwater return systems should be designed to 

distribute collected water to all parts of the field, not 

consistently to the same area. If all the tailwater is stored, 

pumping can be continuous and can commence at the 

convenience of the operator. Pumps can be any convenient

size, but a minimum capacity of 25 percent of the 

distribution system capacity is recommended. If a portion of

the tailwater flow is stored, the reservoir capacity can be 

reduced but pumping must begin during tailwater collection. 

Cycling pump systems and continuous pumping systems 

can be designed to minimize the storage volume 

requirements, but these systems are much less flexible 

than storage systems. 

7-26 
Figure 7-21. Typical Tailwater Pumping Station. 

The principal design variables for tailwater return 

systems are the volume of tailwater and the duration of 

tailwater flow. The expected values of these parameters for

a well-operated system depend on the infiltration rate of the 

soil. Guidelines for estimating tailwater volume, the 

duration of tailwater flow, and suggested maximum design 

tailwater volume are presented in Table 7-14. 

Runoff of applied wastewater from sites with sprinkler 

distribution systems should not occur because the design 

application rate of the sprinkler system is less than the 

infiltration rate of the soil-vegetation surface. However, 

some runoff from systems on steep (10 to 30 percent) 

hillsides should be anticipated. In these cases, runoff can 

be temporarily stored behind small check dams located in 

natural drainage courses. The stored runoff can be 

reapplied with portable sprinkling equipment. 

7.9 Mainlines 

Mainlines are pressurized pipelines that transmit the 

wastewater from the pumping station to the application site. 

The considerations in mainline design are velocity and 

friction loss. Velocities should be in the range of 1 to 1.5 

m/s (3 to 5 ft/s) to keep any solids in suspension without 

developing excessive friction losses. Optimum velocities 

and pipe sizes depend on the cost of energy and the cost 

of pipe. 

Mainlines are usually buried. Pipe materials for 

conveyance of pressurized effluent are usually PVC 

(polyvinyl plastic) or ductile iron. Under some low pressure 

conditions reinforced concrete pipe (RCP) may also be 

used. 

Table 7-14. Recommended Design Factors for Tailwater Return Systems

Permeability Class PermeabilityRate, in/h Texture range 

Maximum duration of 

tailwater flow, % of 

application time 

Estimated tailwater 

volume, % of 

application volume 

Suggested maximum 

design tailwater 

volume, % of 

application volume 

Very slow to slow 0.06-0.2 Clay to clay loam 33 15 30 

Slow to moderate 0.02-0.06 Clay loam to silt loam 33 25 50 

Moderate to 

moderately rapid 

0.6-6 Silt loams to sandy

loams 

75 35 70 

7.10 References 

Booher, L.J.,( 1974) Surface Irrigation,. FAO Agricultural 

Development Paper NO. 94, Food and Agricultural 

Organization of the United Nations, Rome. 

Burt, C.M., (1995) The Surface Irrigation Manual. 

Waterman Industries, Inc., Exeter, CA. 

Dillon, R.C., Hiler, E.A., and Vittetoe, G., (1972). Centerpivot Sprinkler Design Based on Intake Characteristics,

ASAE Trans. 15: 996-1001. 

Fry, A.W. and A. S. Gray, (1971). Sprinkler Irrigation 

Handbook, 10th Ed., Rain Bird Sprinkler Manufacturing 

Corporation, Glendora, CA. 

Hart, W.E., (1975). Irrigation System Design, Colorado 

State University, Department of Agricultural 

Engineering, Ft. Collins, CO. 

Hydraulic Institute, (1983) Hydraulic Institute Standards, 

Cleveland, OH. 

Keller, J. and Bliesner, R. D., (1990) Sprinkle and Trickle 

Irrigation, Chapter 14, Van Nostrand Reinhold, New 

York, NY. 

King, B.A., and Kincaid, D.C., (1997) Optimal Performance 

from Center Pivot Sprinkler Systems, University of 

Idaho Cooperative Extension System Bulletin 797. 

McCulloch, A.W. et al, (1973) Lockwood-Ames Irrigation 

Handbook, Lockwood Corporation, Gering, NB. 

Merriam, J.L. and Keller, J., (1978) Irrigation System 

Evaluation: A Guide for Management, Utah State 

University, Logan, UT 

Pair, C.H. et al, (1983) Irrigation, Fifth Ed., Irrigation 

Association, Silver Spring, MD 

7-27 
Reinders, F. B. and Louw, A..A.. (1985) The Measurement 

of Infiltration as a Design Input for Mechanized 

Irrigation Systems. S.A. Irrigation 7(1):9-21. 

Rogers, D.H., et al. (1994) Sprinkler Package Effects on 

Runoff, Cooperative Extension Service, Kansas State 

University, Publication L-903. 

Sanks, R.L., G. Tchobanoglous, B.E. Bosserman, D. 

Newton, and G.M. Jones (1989) Pumping Station 

Design, Butterworth Publishers, Stoneham, MA. 

Tajrishy, Massoud A.M., Pretreatment Requirements of 

Secondary Effluent for Drip Irrigation. Dissertation, UC 

Davis, 1993. 

U.S. Department of Agriculture, Soil Conservation Service,

(1980) Border Irrigation, Irrigation, Chapter 4, Natural 

Resources Conservation Service National Engineering

Handbook, Section 15. 

U.S. Department of Agriculture, Soil Conservation Service,

(1983) Sprinkler Irrigation, Irrigation, Chapter 11 in 

NRCS National Engineering Handbook, Section 15. 

7-28 
Chapter 8 

Process Design – Slow Rate Systems

The process design approach to slow rate (SR) 

systems for land treatment of municipal wastewater, 

must address water, nutrient and oxygen balances.

These balances are discussed in this chapter. The

expected treatment performance and removal

mechanisms were described in Chapter 2. 

8.1 System Types 

Slow rate (SR) land treatment involves the controlled 

application of wastewater or to a vegetated land surface.

There are two basic types of SR systems: 

Type 1 – maximum hydraulic loading, i.e.: apply the 

maximum amount of water to the least possible land

area; a “treatment” system. 

Type 2 – optimum irrigation potential, i.e.: apply the

least amount of water that will sustain the crop or 

vegetation; an irrigation or “water reuse” system with

treatment capacity being of secondary importance. 

Many of the system components (vegetation, 

preapplication treatment, transmission, distribution, etc.) 

may be identical for both types. A Type-1 SR “treatment 

system” may be limited by soil permeability or by 

nitrogen loading. The Type-1 system utilizes deep 

percolation of treated wastewater for additional capacity 

beyond evapotranspiration. To optimize reuse, the 

capacity of a Type-2 SR is limited by crop water or

nutrient requirements. 

In general, industrial operations with easily degraded 

wastes and municipalities in the humid parts of the 

country will seek to minimize land and distribution

system costs, and will implement Type-1 systems. In the 

arid parts of the world, where the water has a significant

economic value, it is often cost-effective to design a 

Type-2 system. 

8.2 Land Area Determination 

The Limiting Design Parameter (LDP) for a slow rate 

system can be determined after completing a series of

constituent balances including a water balance, organic 

loading, and nutrient balance. 

For Type-1 systems, the maximum deep percolation 

rate or drainage determines the hydraulic loading. The

percolation rate and the hydraulic loading are

determined as: 

Lh = Etc – P + Pw (8-1)

Where: 

Lh = hydraulic loading rate, cm/mo

ETc = crop evapotranspiration, cm/mo 

P = precipitation, cm/mo 

Pw = deep percolation rate, cm/month 

If a Type-1 system is being designed, the design

percolation rate, Pw, is a function of the limiting 

permeability or hydraulic conductivity in the soil profile. 

The hydraulic conductivity can be measured in the field, 

as described in Chapter 3. If published data on soil

permeability are used, a safety factor of 4 to 10 percent 

of the published value should be used. (See Example 8-

1.) 

If a Type-2 system is being designed, then the Pw is

the amount of water required to leach salts out of the 

root zone so plant growth will not be inhibited. Limiting 

permeability is discussed in Chapter 3 and leaching is 

described in Section 8.4. 

In a Type-1 system, the limiting permeability may 

determine a hydraulic loading rate in excess of the crop

water tolerance, so care must be taken to ensure proper 

growing conditions. 

The monthly value of the design percolation rate

depends on crop management, precipitation, and

freezing conditions: 

• Crop management. Downtime must be allowed

for harvesting, planting, and cultivation as

applicable. 

• Precipitation. Downtime for precipitation is 

already factored into the water balance

computation. No further adjustments are

necessary. Where rainfall runoff occurs during 

periods of non-operation, the runoff may be

subtracted from the total precipitation. 

• Freezing temperature. Subfreezing temperatures may cause soil frost that reduces 

infiltration rates. Operation is usually stopped

when this occurs. The most conservative 

approach to adjusting the monthly percolation 

rate for freezing conditions is to allow no

operation for days during the month when the 

mean temperature is less than 0°C (32 °F). A

less conservative, but acceptable, approach is to 

use a lower minimum temperature. The 

recommended lowest mean temperature for 

operation is –4°C (25°F). For forested sites,

operation can often continue during subfreezing

8-1 
conditions, with special attention to prevent

freezing in the distribution system. 

• Seasonal crops. When a single annual crop is 

grown, wastewater is not normally applied 

during the winter season, although applications

may occur after harvest and before the next 

planting. 

Procedures for determining the storage days needed 

based on climatic factors are presented in Chapter 6.

The additional agronomic factors listed above can be

determined from local experience in the area once the

type of crop is tentatively identified. It is necessary to

select the general type of vegetation at an early stage of 

design so that the crop uptake of nitrogen or other

constituents can be estimated. 

Example 8-1: Water Balance for Type-1 SR System 

Given: Type-1 system in a humid climate with soils having

a limiting permeability of 2 cm/hr. Flow is 1,000 

m3

/d. Storage needs are 3 mo/yr, precipitation is 

50 cm/yr and ET is 40 cm/yr. Conduct a

preliminary water balance and initial land area 

requirements evaluation. 

Solution: Hydraulic loading rate is based on the 2 cm/hr soil 

permeability. Use a safety factor of 7 percent 

(midpoint between 4 and 10 percent). 

1. Determine annual percolation: 

Percolation is 2 cm/hr x 24 hr/d x 0.07 = 3.36 cm/d

Assume 1 application per week for 9 months (9 mo x 4.33 wk/mo

= 39 weeks) 

39 weeks x 3.36 cm/wk = 131 cm/yr 

2. Determine water balance for application area: 

 Lh = ETc –P + Pw

 Lh = 40 cm/yr – 50 cm/yr + 131 cm/yr = 121 cm/yr

3. Determine land required for application: 

Annual flow = 1,000 m3

/d x 365 = 365,000 m3/yr 

Although the storage reservoir will accumulate 10 cm/yr from excess 

rainfall, the percolation from the storage reservoir is assumed equal to 

the gain from rainfall. 

Area = 365,000 m3

/yr ÷ 1.21 m/yr = 301,600 m2

Area = 301,600 m2/10,000 m2/ha = 30.16 ha 

An estimate of the design precipitation on an annual

basis is suitable for preliminary calculations during site 

planning. Monthly values are needed for final design. 

The monthly precipitation should be based on a 5-year 

return period analysis. When monthly precipitation data 

are not available a 10-year return period may be

distributed monthly based on the ratio of average

monthly-to-average-annual precipitation.

The design ET rate is a critical component in the water 

balance for both crop production and water quality 

concerns. In the latter case, a high water loss due to ET 

will tend to increase the concentration of constituents in 

the remaining percolate. See Chapter 4 for discussion

and procedures for estimating ET for a particular crop. 

A further modification is necessary to account for 

water losses to percolation and evaporation in the 

conveyance and distribution systems. This overall 

efficiency of a distribution system ranges from about 75 

percent to over 95 percent. The final water balance 

equation for the irrigation case (Type-2 system) is: 

ES

(1 LR) L (ETc P) h

− = − ⋅ (8-2)

Lh = hydraulic loading, cm/month 

P = design precipitation, cm/month 

ETc = crop evapotranspiration, cm/month 

ES = distribution system efficiency, fraction 

(0.65 to 0.75 for surface systems)

(0.70 to 0.85 for sprinklers) 

LR = leaching requirement, fraction, defined in Equation 8-10 

The land area required can be calculated using Equation 

8-3. 

A = Q/C Lh (8-3)

Where: 

A = field area, ha

Q = Annual flow, m3

/yr

C = conversion factor, 10,000 m2

/ha 

Lh = hydraulic loading rate, m/yr 

8.2.1 Oxygen Balance 

The plant/soil system removes biodegradable organics 

through filtration, adsorption, and biological reduction 

and oxidation. Most of the biological activity occurs near 

the surface where organics are filtered by the soil and

oxygen is present to support biological oxidation. 

However, biological activity continues with depth. 

The BOD loading rate is defined in Equation 2-1 as

the average BOD applied over the field area in one

application cycle. The oxygen demand created by the 

BOD is balanced by the atmospheric reaeration of the 

soil profile during the drying period. 

Excess organic loading can result in (1) odorous 

anaerobic conditions (2) untreated organics passing

through the soil profile, (3) reduced environments 

mobilizing oxidized forms of iron and manganese and/or 

(4) increases in alkalinity via carbon dioxide dissolution. 

Prevention from excess loading of organics is a function 

of maintaining an aerobic soil profile, which is managed 

by organic loading, hydraulic loading, drying time, 

oxygen flux, and cycle time. 

Aerobic conditions and carbon dioxide venting can be 

maintained by balancing the total oxygen demand with

oxygen diffusion into the soil. McMichael and McKee

(1966) reviewed methods for determining oxygen 

diffusion in the soil after an application of wastewater. 

They discussed three principal mechanisms for 

reaeration: (1) dissolved air carried in the soil by 

percolating water, (2) the hydrodynamic flow of air 

resulting from a “piston-like” movement of a slug of 

8-2 
water, and (3) diffusion of air through the soil pores.

Dissolved oxygen in wastewater has an insignificant

impact on high BOD waste streams. The “piston-like” 

effect may have a substantial impact on the oxygen 

available immediately after drainage, but quantifying the 

exact amount is dependent on the difficult to model

dynamics of draining soils. McMichael and McKee 

(1966) solved the non-steady state equation of oxygen 

diffusion based on Fick’s law. They used the equation as

a tool for determining the flux of oxygen (mass of O2 per 

area) that diffuses in the soil matrix over a given time. 

The flux of oxygen across the soil surface does not 

address the destination of the oxygen, but as long as a

gradient exists the oxygen will continue to diffuse into

the soil pores. The gradient is based on the oxygen 

concentration at the soil surface and the initial 

concentration in the soil. McMichael and McKee (1966) 

assumed total depletion of oxygen in the soil matrix. 

Overcash and Pal (1979) assumed a more conservative 

140 g/m3

 based on a plant growth limiting concentration 

(Hagen et al. eds., 1967). 

The total oxygen demand (TOD) is the sum of the

BOD and the nitrogenous oxygen demand (NOD) and

plant requirement. The NOD is defined as: 

NOD = 4.56 x Nitrifiable Nitrogen (8-4) 

Nitrifiable nitrogen is the ammonium concentration, 

which is often insignificant when compared to high BOD 

waste streams.

Equation 8-6 can be rearranged to solve for time: 

t = π · [No2/2(Co2-Cp)]

 2 (8-7) 

 Dp 

Cycle time is a function of required aeration time plus

the time for the soil to reach field capacity. The time to

reach field capacity is estimated with the infiltration time 

calculated by dividing the depth applied by the steady 

state infiltration rate. 

ti = 3600 · d/I (8-8) 

tI = time to infiltrate, hours 

d = depth, cm 

I = steady state infiltration rate, cm/s 

There are numerous variables involved in determining 

the oxygen balance, all which must be evaluated on a 

site-specific basis. An important point to note is that 

supplemental irrigation water without a significant

oxygen demand can increase the required cycle time

due to increasing drain and reaeration time. The time 

required for the upper zone of the soil to drain is a

function of climatic conditions and the depth of the

wastewater applied. To achieve the desired loading in 

surface applications mixing, of supplemental water is 

often required because of larger applications. Most 

surface applications can not apply less than 7.6 cm (3

inches) in a uniform manner. 

8.2.2 Nitrogen Balance 

Nitrogen loading is commonly the LDP. However, 

when the wastewater contains a high carbon to nitrogen

(C:N) ratio, significant denitrification and immobilization

occur. The main concern associated with the land

application of wastewater with high nitrogen

concentrations is the potential for nitrate to be

transported into the groundwater. 

Nitrogen in wastewater goes through transformations 

when applied to the soil matrix. The transformations are 

both chemical and biological and are a function of

temperature, moisture, pH, C:N ratio, plant interactions, 

and equilibrium with other forms of nitrogen. 

Because of large influence of organic carbon on 

available nitrogen, a factor has been developed to

account for nitrogen lost to denitrification, volatilization, 

and soil storage. 

Table 8-1 contains the nitrogen loss factor as a 

function of the C:N. Actual losses are dependent on 

other factors including climate, forms of the nitrogen

applied, and application method. 

TOD = BOD + NOD (8-5)

From the TOD the time required to diffuse an

equivalent amount of oxygen can be determined. The 

diffusion equation follows:

No2 = 2(Co2-Cp) · [Dp·t/π] 1⁄2 (8-6) 

No2 = flux of oxygen crossing the soil surface (g/m2

) 

Co2 = vapor phase O2 concentration above the soil surface 

(310 g/m3

) 

Cp = vapor phase O2 concentration required in soil to prevent 

adverse yields or root growth (140 g/m3

) 

t = aeration time; t = Cycle time – infiltration time 

Dp = effective diffusion coefficient 

Dp = 0.6 (s)(Do2) 

where s = fraction of air filled soil pore volume at field 

capacity

Do2 = oxygen diffusivity in air (1.62 m2

/d) 

8-3 
Table 8-1. Nitrogen Loss Factor for Varying C:N Ratios 

C:N ratio Example f 

>8 Food processing wastewater 0.5 - 0.8 

 1.2-8 Primary treated effluent 0.25 - 0.5 

 0.9-1.2 Secondary treated effluent 0.15 - 0.25 

 <0.9 Advanced treatment effluent 0.1

Adapted from Reed et al., 1995. 

While existing inorganic and organic nitrogen in the 

soil may supply short-term crop needs, nitrogen

deficiencies and resulting reduced yield and nitrogen 

uptake will result if the gross applied nitrogen does not 

exceed crop demand. Also, depletion of the soil organic 

reserves will reduce soil health. Combining the crop 

uptake and the nitrogen loss factor will estimate the 

desired nitrogen loading. For additional information see

Chapter 4. 

Ln = U/(1-f) (8-9) 

Where: 

Ln = Nitrogen loading, kg/ha (lb/acre)

f = nitrogen loss factor (

Table 8-1) 

U = Estimated crop uptake as a function of yield, kg/ha

(lb/acre) (Chapter 4) 

8.3 Total Acidity Loading 

Natural biochemical reactions maintain the soil pH

near neutral. A range of wastewater pH between 3 and

11 has been applied successfully to land treatment 

systems. Extended duration of low pH can change the 

soil fertility and lead to leaching of metals. When the

acidity is comprised of mostly organic acids, the water 

will be neutralized as the organics are oxidized. 

The acidity of wastewater can be characterized by the 

total acidity with units of mg CaCO3/L. The total acidity 

represents the equivalent mass as CaCO3 required to 

adjust the pH to a specific pH, commonly defined as 7.0. 

The soil buffer capacity is reported as mg CaCO3/kg or 

tons CaCO3/acre. The buffer capacity represents the soil

response to neutralize an equivalent amount of acidity. A 

balance between the total acidity applied in the

wastewater and the buffer capacity of the soil can

indicate the capacity of the soil to effectively neutralize 

the acid in the wastewater. The buffer capacity of the soil

is restored after organic acids are cleaved. 

Most field crops grow well in soils with a pH range of 

5.5 to 7.0. Some crops like asparagus or cantaloupes 

with a high calcium requirement prefer a soil pH greater 

than 7.0. If the pH of the soil begins to drop, liming is

recommended to return the pH to the desirable range for 

crop production. Likewise, if the pH increases, sulfuric

acid addition may be recommended. Chapter 4 contains 

the range optimal soil pH of various crops. 

Because of the soil capability to treat large amounts of 

organics acids, it is recommended that the pH of 

wastewater only be adjusted for extreme pH conditions 

(pH < 5.0 and > 9). If the mineral (non-organic) cause of 

the high or low pH is a threat to crops or groundwater, 

adjustment may be necessary. 

8.4 Salinity

Municipal WWTP treated effluent has a TDS of 150-

380 mg/l of TDS over the source water. In non-oxidized

wastestreams, approximately 40 percent of the dissolved

solids will consist of volatile dissolved solids that will be 

removed in the treatment process or will degrade in the

soil. Plant macronutrients, such as nitrogen,

phosphorous and potassium; and minerals, such as 

calcium and magnesium, are part of the fixed dissolved

solids (FDS) and are partially removed in land 

application systems that incorporate growing and

harvesting of crops. The remaining inorganic dissolved 

solids are either leached from the soil profile or 

precipitate out into non-soluble forms. When inorganic 

dissolved solids accumulate in the soil, an increase in 

the osmotic stress in plants may result in reduced yields 

or failed germination. 

Salt removal by plants is estimated using the ash

content of the harvested crop and can be calculated

similarly to nutrient uptake. Ash content is approximately 

10 percent of the dry weight. Often salts in excess of 

crop uptake are applied and leaching of salts is required

to limit salt build-up in the root zone. 

The leaching requirement is the ratio of the depth of 

deep percolation to the depth of the applied water (see 

Equation 8-10). The same ratio exists between the

concentration of the conservative salts applied and the 

concentration of conservative salts in the percolate. The 

EC of water can reliably indicate the salt concentration 

when little or no dissolved organics are present. The 

equation is only valid when weathering and precipitation

of salts are insignificant (Hoffman, 1996). 

d

a

a

d

C

C

D

D LR = = (8-10)

Where: 

LR = leaching fraction, unitless 

Dd = drainage depth, m 

Da = depth applied, m

Ca = concentration of salt applied, dS/m 

Cd = concentration of salt in drainage, dS/m 

8-4 
If Equation 8-10 is solved for Cd, the salt concentration 

of the drainage is equal to the concentration of the salt 

applied divided by the leaching fraction as presented in

Equation 8-11. 

LR

C C d

a = (8-11)

All terms are described above. 

The leaching requirement is determined based on the 

crop sensitivity presented in Chapter 4. The average root

zone salts calculated based on solving the continuity 

equation for salt throughout the root zone (Hoffman and

van Genchten, 1983): 

[ ] Z/δ

a

ln L (1 L)e Z LR

δ

L

1

C

C − • + − ⋅ = + (8-12)

Where: 

C = mean rootzone salt concentration, dS/m 

Ca = salt concentration of applied water, dS/m 

LR = leaching fraction as defined in EQ 8-10 

Z = root zone depth,m 

δ = empirical constant = 0.2Z 

To determine the desired EC value of drainage, both 

the crop sensitivity to salinity and the groundwater 

quality should be reviewed. The groundwater uses,

quality, and flux beneath the site should be reviewed to 

determine the impact of the leachate of groundwater. 

High EC values can be offset by small leaching depths 

resulting in insignificant loading to the groundwater.

Also precipitation of minerals continues to occur below 

the root zone reducing the loading to groundwater. 

The salinity thresholds presented in Chapter 4 are

based on EC extracts of the soil (ECe) normally 

measured under trial conditions of 50 percent leaching. 

The average root zone salinity is adjusted to the ECe by 

dividing by a factor of two. The osmotic stress of 50

percent leaching fraction is accounted by subtracting C

at a given leaching fraction by the C at 50 percent 

leaching. Hoffman (1985) found the best agreement 

when comparing this model to published ECe threshold 

values. The results of this model are presented in Figure

8-1. 

Figure 8-1. Leaching Requirement as a Function of Applied Salinity 

and ECe of Crop Salinity Threshold.

Example 8-2. Type-2 SR Design Loading Rate and Required Area 

Given:

Secondary treated wastewater is used to irrigate sudan grass and 

winter wheat in Merced, CA. The historical yield of the area is 8 

tons/acre and for sudan and 75 bushels/acre for winter wheat and an 

additional 1.5 tons/acre of straw. The field configuration and soil type

allow for uniform distribution with a minimum of application of 10 cm

(3.9 inches) with 12 hour sets. 

Waste Stream Soil

Flow = 3,785 m3/d (1.0 mgd) Total pore space = 42% 

BOD5 = 40 mg/L Field capacity = 0.18 mm/mm

Nitrifiable ammonia = 4 mg/L Steady state infiltration = 18.3 

cm/d 

Total nitrogen = 15 mg/L 

EC = 1.2 dS/m 

Solution:

Oxygen Balance 

The total oxygen demand (TOD) is the sum of the

BOD and the nitrogenous oxygen demand (NOD) and

plant requirement. 

Using Equation 8-5, the total oxygen demand can be

determined. 

40 mg/L + 4 mg/L x 4.56 = 58.2 mg/L TOD 

8-5 
At a hydraulic loading rate of 10 cm the organic 

loading is 58 kg/ha (52 lb/acre) or 5.8 g/m2

. The time 

required to diffuse an equivalent amount of oxygen can 

be determined with Equation 8-7. 

t = π π ● [No2/2(Co2-Cp)] 2 

 Dp 

Where: 

Dp = effective diffusion coefficient 

Dp = 0.6 (s)(Do2) 

Where: 

s = fraction of air filled soil pore volume at field capacity

Do2 = oxygen diffusivity in air (1.62 m2

/d) 

Dp = 0.6 ● (0.42-0.18) · 1.62 m2

/d = 0.388 m2/d 

t = π (0.388 m2/d) ● [5.8 g/m2/2(310 g/m3-140/g/m3)] 2 = 0.002 days

The small time required for diffusion of secondary 

treated wastewater shows that drain time is more critical 

than the diffusion time for small application depths of

treated municipal effluent. Equation 8-8 can be used to

estimate the time to reach field capacity. 

ti = 

18.3 cm/d

10 cm = 0.54 d 

The minimum cycle time is the sum of the application 

time, the diffusion time, and the drain time. The resulting

minimum cycle time is just over 1 day. The oxygen

balance then limits application to 10 cm every third set or 

1.5 days. 

Total Area for oxygen balance = 

1.5 days x 3,785 m3

/d ÷ 0.1 m = 56,780 m2 = 5.7 ha

The frequent irrigation suggested by the small oxygen 

demand does not consider the water logging from a 

crop.

Nitrogen Balance Based on Crop Removal 

The nitrogen loading is determined by the nitrogen

uptake and estimates of nitrogen losses. The C:N ratio

can be estimated from the BOD:N ratio. The result is a

C:N ratio of 2.6. The corresponding nitrogen loss factor 

from 

Table 8-1 is 0.25. Table 4-9 lists the average N 

percentage of sudan as 1.36 percent N. A 8 ton/acre 

harvest will require 245 kg-N/ha (218 lb-N/acre). Winter 

wheat at 75 bushel/acre at 60 lb/bushel is equivalent to

4,000 kg/ha (4,500 lb/acre). At 2.08 percent nitrogen,

wheat removes an additional 105 kg/ha (94 lb/acre). If 

the 1.5 tons of straw per acre is also removed an 

additional 22 kg/ha (20 lb/acre) of nitrogen is removed. 

Equation 8-8 provides the nitrogen limited loading. 

Ln = U/(1-f) 

Where: 

Ln for sudan = 245/(1-0.25) = 327 kg-N/ha 

Ln for winter wheat = 127/(1-0.25) = 169 kg-N/ha 

At a total nitrogen content of 15 mg/L, the sudan grass 

nitrogen requirement is met with a application of 2.18 m 

(86 inches). The winter wheat requires an application of 

1.13 m (44 inches). The minimum area for a nitrogen 

balance could be achieved when the area was double

cropped and a total of 3.31 meters was applied. 

Total Area for nitrogen balance = 

3,785 m3/d x 365 d/yr ÷ 3.31 m/yr = 417,000 m2 = 41.7 ha 

A hydraulic load of 3.31 m per year exceeds the crop 

irrigation requirements and a Type-2 SR system could 

be designed around 42 ha, if considerations for 

percolation and crop water-logging are made. 

Salinity 

The leaching fraction is a function of the crop and the

water quality. Figure 4-3 shows that 10 percent yield

reduction occurs at 5.9 dS/m for sorghum and 7.0 dS/m 

for wheat. The most restrictive crop is sorghum. Using 

an ECe of 5.9 dS/m and an applied EC of 1.1 dS/m, 

Figure 8-1 suggests a leaching requirement less than 

0.05. To ensure productivity a leaching fraction of 0.05

should be used. 

Water Balance 

Crop coefficients gathered from local extension service 

are utilized in the water balance below. The area used to

calculate the irrigation requirement including irrigation 

efficiency and leaching requirement is adjusted until the

irrigation requirement meets the flow. 

8-6 
1 2 3 4 5 6 7 8 9 1

0

10 11 12 

Wastewater Precipitation Normal Winter Wheat 30 Acres Sudan 9

0

 90 Acres Water 

Volume 5-yr ETo k ETc Irrigation k ETc Irrigation Balance 

Month days MG in. in. In in MG In in MG MG 

January 31 31.0 3.56 1.0 1 1.0 0.0 0.0 0.0 0.0 0.0 31.0

February 28 28.0 3.14 1.5 1 1.5 0.0 0.0 0.0 0.0 0.0 28.0

March 31 31.0 2.97 3.2 1 3.3 0.4 0.3 0.0 0.0 0.0 30.7

April 30 30.0 1.77 4.7 0.0 0.0 0.0 0.8 3.8 2.5 6.0 24.0

May 31 31.0 0.91 6.6 0.0 0.0 0.0 1.1 6.9 7.4 18.2 12.8

June 30 30.0 0.19 7.9 0.0 0.0 0.0 1.1 8.3 10.0 24.5 5.5

July 31 31.0 0.02 8.5 0.0 0.0 0.0 1.1 8.9 11.0 26.9 4.1

August 31 31.0 0.03 7.2 0.0 0.0 0.0 1.1 7.6 9.3 22.7 8.3

September 30 30.0 0.33 5.3 0.0 0.0 0.0 1.1 5.6 6.5 15.8 14.2

October 31 31.0 0.99 3.4 0.0 0.0 0.0 1.1 3.6 3.2 7.8 23.2

November 30 30.0 2.10 1.4 0.2 0.3 0.0 0.0 0.8 1.1 0.0 0.0 30.0

December 31 31.0 2.83 0.7 1 0.7 0.0 0.0 0 0.0 0.0 31.0

TOTAL 365 365.0 18.8 51.4 0.4 0.3 49.9 121.8

Figure 8-2. Example Spreadsheet Used to Calculate the Irrigation Requirements Including Irrigation Efficiency and Teaching Requirements.

Notes:

Are Associated with Columns 

1 Wastewater flow based on design flow x number of days per month (in this case 1 MGD) 

2 Monthly precipitation with a 5-yr return period 

3 Normal monthly ETo 

4 Crop coefficient from local extension office 

5 ETc = k x ETo 

6 Irrigation Requirement = Precipitation -[k x ETo x (1 + Leaching Fraction) ÷ Irrigation Efficiency]

7 Irrigation Requirement converted to volume = inches x .027152 x acres = MG 

8 -11 Same as 5 –6 

12 Total wastewater volume - crop requirement 

A Type-2 system can be managed with a crop rotation 

plan allowing for a portion of the available area to be

fallow at all time. The fallow area can receive water 

during harvesting and planting when applications are not 

possible. During the summer, application could be

applied to the fallow portion that will be planted in wheat 

the subsequent fall. During the winter months, one or 

two applications per month can be applied to wheat with

the remainder going on the fallow ground where the 

sudan will be planted. The crop rotation will allow for 

application all winter. 

8.5 Design Considerations 

The design procedure is outlined in Figure 8-2 (US

EPA., 1981). Additional design consideration of buffer 

zone,

storage requirements, distribution system, and crop

selection must also be addressed for both Type-1 and

Type-2 systems.

8.5.1 Buffer Zone Requirements 

The objectives of buffer zones around land treatment

sites are to control public access, and in some cases, 

improve project aesthetics. There are no universally

accepted criteria for determining the width of buffer 

zones around SR treatment systems. In practice, the 

widths of buffer zones range from zero for remote 

systems to 200 ft or more for systems using sprinklers 

near populated areas. In many states, the width of buffer 

zones is prescribed by regulatory agencies and the 

designer should determine if such requirements exist. 

8-7 
SITE CHARACTERISTICS

(Chapter 5)

PROCESS PERFORMANCE

(Chapter 2)

CROP SELECTION

(Chapter 4)

LOADING RATES

(Chapter 8.2)

FIELD AREA

(Chapter 8.2)

DISCHARGE

DISTRIBUTION

(Chapter 7)

SUBSURFACE

SYSTEM MONITORING

(Chapter 8.6)

WASTEWATER

CHARACTERISTICS

(Chapter 2)

WATER QUALITY

REQUIREMENTS

(Chapter 2)

PREAPPLICATION TREATMENT

(Chapter 6)

STORAGE

(Chapter 6)

DRAINAGE AND RUNOFF

CONTROL

(Chapter 7)

SURFACE WATER

CROP MANAGEMENT

(Chapter 8.6.8)

Figure 8-3. Slow Rate Design Procedure.

8-8 
The requirements for buffer zones in forest SR

systems are generally less than those of other 

vegetation systems because forests reduce wind speeds 

and, therefore, the potential movement of aerosols. 

Forests also provide a visual screen for the public. A 

minimum buffer zone width of 50 ft should be sufficient 

to meet all objectives, if the zone contains trees with a

dense leaf canopy. 

8.5.2 Storage Requirements 

A detailed discussion and calculation procedures for 

storage are presented in Chapter 6. When storage is a

component in a SR system, it may be advantageous not 

to bypass the pond in the application season to allow 

reductions in coliforms and nitrogen to occur as 

described in Chapter 6. Algal production in storage

ponds should not affect SR operations. In fact, algae will

incorporate the inorganic nitrogen into cells as inorganic 

nitrogen, which will reduce the leaching potential of the 

nitrogen 

8.5.3 Crop Selection 

The type of crop selected will directly influence the 

land area required, if crop uptake is a critical factor in

determining the design hydraulic loading. In most cases, 

crop selection will be one of the first design decisions in 

SR design. See Chapter 4 for discussion of crop 

selection procedures. 

8.5.4 Distribution System 

It is necessary for Type-2 irrigation systems to decide 

on the method of distribution that will be used, at an

early stage of design. The system efficiency (see 

Equation 8-2) is a significant factor in determining the Lh

and the amount of land that can be irrigated. An early 

decision on distribution method is less critical for Type-1

treatment system. Distribution systems are discussed

further in Chapter 7. 

8.5.5 Application/Irrigation Scheduling 

A regular, routine application schedule is usually 

adopted for Type-1 SR treatment systems for 

operational convenience. Sprinklers with an application

rate of 0.2 to 0.3 in/hr are often employed in SR 

systems. This will not usually exceed the intake rate of 

most soils, so surface runoff is avoided. It is then typical 

to operate the sprinkler unit continuously for a sufficient

number of hours to achieve the design loading. The

application is then repeated at regular cycle intervals. 

Operation can either be manual, automated with time 

switches or some combination.

The scheduling of a Type-2 SR irrigation system is

dependent on the climate and the crop to be grown. The

purpose is to maintain sufficient moisture in the root

zone to sustain plant growth. The water available for 

plant use is defined as the difference between the field 

capacity and the wilting point (see Chapter 3). 

The usual range of the deficit that is allowed ranges 

from 30 to 50 percent of the available water in the root

zone, depending on the crop type and the stage of 

growth, and soil type (Figure 3-2). An irrigation event is 

scheduled when the soil moisture reaches the

predetermined deficit. Ideally irrigation maintains soil

moisture level for optimum plant growth. This can be 

measured using soil moisture sensors or estimated

based on ETc. Soil moisture sensors can be used in a 

completely automated system to start-up, shutdown and

shift applications from field to field. 

The amount of water to be applied in each irrigation

event can be determined with: 

ES

(1 LR) I I T D

− = ⋅ (8-13)

Where 

IT = total depth of water to be applied during an irrigation, cm 

ID = soil moisture deficit to be replaced, cm 

LR = leaching requirement as defined in EQ 8-10 

ES = irrigation efficiency, fraction 

8.6 Crop, Soil and Site Management 

Requirements 

Site management is a critical part of operating and

monitoring a land application system. Detailed 

monitoring and observations provide information for 

documenting and evaluating performance of a facility’s 

land application program. 

This section addresses routine land application site 

monitoring including: 

• Documentation of flow and water quality; 

• Use of supplemental irrigation water; 

• Soil conditions; 

• Soil sampling and analysis;

• Groundwater sampling and analysis; 

• Crop yield and biomass data collection; and 

• Maintenance and routine inspection observations. 

In all of these areas, interrelated data gathering, shortterm and long-term observations, and some analysis of

basic data is required to maximize the usefulness of the 

information. Data organization, calculations, analysis,

and record keeping are critical to the success of a 

monitoring program. 

8.6.1 Basic Structure of a Monitoring 

Program 

The personnel responsible for operating the land

application system often conduct monitoring. During site 

8-9 
monitoring, the system operator will collect data required 

to document operations and will make both quantitative

and qualitative observations. These observations may 

include details regarding functioning of the physical 

infrastructure, as well as crop management issues, 

including both field management, such as disking or 

leveling, and irrigation. During the course of monitoring, 

the observer will learn more about the behavior of the 

land application system. This often leads to developing

improved operating procedures based on experience 

and can be invaluable for solving temporary problems 

that occur within the land application site. 

The monitoring and operations activities described 

above fall in the general category of “process control.” 

These observations are made in order to develop and

implement protocols for managing the land application 

system. This can include changing irrigation practices; 

scheduling harvesting, replanting, and other crop

management activities; scheduling preventative

maintenance and repair; and expanding or improving the

system.

A second, equally important monitoring objective is to 

provide system operations documentation for regulatory

oversight and compliance. Often, process control

monitoring and regulatory reporting requirements are 

similar in scope. Table 8-2 provides examples of typical

conditions that address site monitoring for process 

control. Regulatory requirements vary from state to 

state, and often within states, so the individual state 

agency should beto state, and often within states, so the

individual state agency should be contacted. Process 

control observations are often gathered more frequently 

than regulatory monitoring requirements for short-term

decision-making. Those short-term decisions may 

require more complex evaluation and decision-making

than the more straight-forward task of documenting 

compliance.

For a land application site with more than one field, 

field-by-field flows must also be recorded to determine

loading rates. Process control monitoring also requires 

that irrigation amounts (including both effluent and

supplemental irrigation water) be measured on a daily 

basis so that a decision about where to apply facility 

flows for the following day can be made. This decision

must also incorporate additional information as well as a

more complex analysis that takes into account time of

last irrigation, soil moisture status in the field, current

and projected weather conditions, cropping patterns, and 

scheduling needs for other fields within the land

application program. 

8.6.2 Water Monitoring 

Permits issued to a facility for land application routinely 

require measurement of flow and detailed observations 

to document timing and distribution of flows. Monitoring

of supplemental water flow, if used, is also required for 

land application systems. A supplemental irrigation water 

supply is required when effluent cannot be used to meet

all irrigation water requirements. Table 8-3 summarizes

monitoring for flow and water quality that may be

required as part of a monitoring plan. 

Sampling locations must be selected to allow 

collection of samples from a location that is 

representative of the flow to be monitored. Effluent 

quality can change from point to point within the

distribution system, particularly when storage is a 

component. Facility personnel should consider these

changes when selecting a sampling point for regulatory

compliance or to calculate field loading rates. For

Table 8-2. Suggested Minimum Process Control Monitoring

Sampling Category Operational Management 

Effluent • Total daily flow (gallons) 

BOD, TSS, FDS, Total N, SAR 

Field-by-Field Loadings • Monthly effluent application, inches 

• Daily climate data (precipitation, evapotranspiration) 

• Calculation of loading rate for LDP

Soil Testing • Annual pH, EC, TKN, K, NH3-N, ESP (Sample each field, 3 depths per application zone, composite 

samples from a minimum of 3 locations) 

• Annual available P, available K for crop nutrient supply analysis 

Crop Sampling • Date, biomass, and crop harvested

• Annual tissue ash weight, total N

Groundwater • Quarterly NO3-N, pH, EC, water level for each well 

• Annual Ca, Mg, Na, K, Cl, SO4, HCO3, CO3 for each well 

Routine Inspection Needs • Pumping system operating pressures, field operating pressures, proper operation of irrigation system, 

leaks along pipeline, ponding, crop health, runoff, etc. 

Definitions: Biochemical Oxygen Demand (BOD), Total suspended solids (TSS), Electroconductivity (EC), Total Kjeldahl Nitrogen (TKN), NitrateNitrogen (NO3-N), NH3-N, Ammonia Nitrogen (NH4-N)

8-10 
operations monitoring, sampling in more than one

location within a distribution system is performed to

evaluate changes or problems such as uneven

distribution. 

Samples can be either grab or composite and sample

collection can be performed either manually or using 

automated sampling equipment. Samples meant to 

represent a single point in time and give a “snapshot” of 

conditions at that instant are usually collected via grab

sampling. Grab sampling involves filling containers 

manually. 

8.6.3 Flow Measurement 

Detailed measurements of effluent flow are required to

determine irrigation volumes and field constituent 

loading rates. Flow monitoring and sampling for water 

quality analysis are typically conducted at a central, 

accessible location. Ideally, there should be one exit 

location identified for sampling. Table 8-4 outlines 

methods used to measure effluent flows and 

summarizes the advantages and disadvantages of these

methods. 

Table 8-3. Suggested Minimum Effluent Monitoring

Parameter Flow Water Quality

Effluent • Daily or monthly facility flow • Monthly nitrogen (TKN, NO3-N, NH3-N), FDS, salt ions, 

BOD, other parameters known to be of concern and 

present 

Lagoon or storage 

pond 

• Water level in relation to maximum and minimum 

operating levels 

• Monthly nitrogen species, salt ions, BOD, other 

parameters known to be of concern and present (If all 

water passes through the pond, the pond water quality

should be used rather than effluent quality into the

pond.) 

Field by field 

application amounts 

• Effluent application 

• Visible inspection for runoff, equipment malfunctioning, 

erosion, crop condition 

• Constituent loading can be calculated from flows and 

constituent concentrations 

Pumps and pipelines • Visible inspection for leaks 

• Pressure checks to identify leaks, other equipment 

failures, need for maintenance 

• Vibration in pumps and excess heat 

Climate • Daily or weekly precipitation and temperature 

• Daily or weekly evapotranspiration

Table 8-4. Flow Measurement Alternatives

Method Alternatives Advantages/Disadvantages 

Intrusive flow

meters 

• Impeller, paddle wheel 

• Hot wire anemometer 

• Intrusive devices can clog with solids or from biological growth; 

higher friction loss/pressure drop 

• Low pH or high EC can cause failure of sensing components 

resulting in higher maintenance 

Non-intrusive flow

meters 

• Magnetic 

• Ultrasonic/Doppler 

• These sensors have no parts in the flow

• Higher capital cost: often, these are used at main pump station and

alternate methods are used for individual fields

Open channel flow

measurements 

• Weir-type • Requires controlled channel to establish proper conditions for 

measurement 

• Simple, reliable operation; measurements can be recorded 

Incoming water 

supply correlation

• Discharge volume is estimated as a 

percentage of incoming water consumption 

• Supply water is clean, relatively simple to measure using meters 

• A correlation between incoming flow, in-plant loss, and effluent 

discharge is required 

Pump run time and 

output calculation 

• Flow for individual fields can be estimated 

proportionally from total flow

• Requires a master pump station flow meter or some calibration 

• Irrigation fields must be maintained so they operate according to 

specifications 

• Primarily applicable to sprinkler irrigation systems or surface 

irrigation using siphon tubes or gated pipe 

In-field methods • Rain gauge/catch cans in individual fields 

• Use of soil water measurements to calculate 

net irrigation 

• Measures net irrigation (amounts actually applied) rather than gross 

irrigation 

• Assumptions in water budget method make method approximate; 

calibration required. Measurement of soil moisture at bottom of root 

zone provides useful information related to leaching 

• Rain gauges are applicable to sprinkler irrigation only

8-11 
Direct flow measurement devices provide reliable data 

when properly installed and maintained (including

periodic inspection, preventative maintenance, and

calibration). The type of measurement device or 

flowmeter selected depends upon the flow conveyance

used in the facility. 

The type of meter installed should allow measurement 

of both the instantaneous and record the total volume – 

this type of meter is known as a totalizing flowmeter. 

Flow measurement requires sufficient straight length of

pipe or channel to develop uninterrupted, smooth nonturbulent flow to provide consistent and reliable data. 

Typically, a straight length of approximately ten (10) 

diameters should be available upstream of the flowmeter 

and the piping should remain straight for approximately 

four (4) pipe diameters downstream. 

8.6.4 In-Field Distribution of Irrigation

Water 

For land application systems, total flow and the

distribution of effluent among irrigation fields (for facilities 

with multiple fields) should be measured. This is required

to calculate hydraulic and other constituent loadings for 

the land application area. The type of application method

(pumped conveyance, surface irrigation, sprinklers, etc.) 

influences the choice of in-field distribution monitoring

method. The most commonly used flow measurement 

methods are listed in Table 8-4 and described in this 

section. These typically involve either direct 

measurement of flow at the field inlet; estimating the flow 

based on readings taken at the field inlet, estimating 

application amounts based on readings taken of soil

moisture, or direct measurement of the amounts applied 

in the field. 

For systems where effluent is pumped to the field(s),

the direct measurement flowmeters described in the 

previous section are appropriate for in-field flow 

measurement. Use of hour-meters and estimation of flow 

from pump discharge and system pressure data are also

feasible for estimating in-field distribution of water. Use 

of on-going pressure measurements in conjunction with 

this method is recommended because suspended solids 

may affect system pressures and water delivery by 

restricting flow in the pipelines or plugging sprinkler 

nozzles or gated pipe openings. Monitoring pressures in

the field can be combined with performing on-going

maintenance/inspection of the irrigation system. 

For a facility using surface irrigation methods, with

either gated pipe openings or siphon tubes for 

transferring water from the irrigation ditches to the field

sections, these can be calibrated to allow measurement 

of flow to the different portions of the field. Gated 

openings are holes in horizontal pipe sections to allow 

water to spill out into the field and siphon tubes are

smaller diameter tubing laying in the irrigation ditch to 

convey the water by siphoning. Estimates of field flows 

must take into account the loss and return or “tailwater” 

flow, if return of the tailwater from the end of the irrigated

area is practiced. 

For facilities applying with sprinkler type systems, net 

irrigation, can be measured using rain gauges placed

within the fields. This method is a simple and effective 

way to measure the actual water applied to different

areas. Rain gauges are installed in land application 

fields and are typically read weekly, although some

facilities use daily measurements. Since the 

measurement technology is simple and inexpensive,

several rain gauges should be installed at each site for 

comparison. For fields that receive both effluent and

supplemental irrigation water, field notes regarding dates 

and hours of water flow from these two sources must be 

used to separate these water sources. Background

rainfall amounts are recorded separately, usually at a

nearby location not receiving irrigation, and subtracted 

from the total recorded in the field locations. 

8.6.5 Soil Monitoring and Testing 

Soil testing and analysis is an important part of land

application site monitoring. Soils data are used for three 

primary purposes in land application systems, as follows: 

• Assessment of nutrient supply for crops; 

• Evaluation of treatment efficiency of the soil plant

system;

• Assessment of the land application site condition 

over time. 

A well-designed soil sampling program addresses both 

environmental and agricultural production objectives. 

Your state land grant university should be consulted for 

extraction solutions and analytical methods for your local

area. Basic monitoring parameters and the use of the 

measurements are summarized in Table 8-5. 

The most common soil sampling methods for land

application systems rely on removal of a soil core or soil

sample within land application fields. Sampling depths 

vary and your local land grant university has 

recommendations. Generally pastures are samples 0-4”

and row crop fields 0.6”. Increasingly, in-situ

measurements of soil aeration status and moisture

content have been used. These latter methods are 

8-12 
Table 8-5. Soil Monitoring Parameters

Parameters Sampling considerations 

General Measure following harvest of each

crop: 

• Make a composite sample 

from a minimum of 3 locations 

per application zone, 

depending on field size 

pH, EC, Organic matter, • Basic soil test to assess 

general condition

TKN, NO3-N, NH3-N, PO4, • Nutrient analysis to asses 

loading impacts 

Na, Ca, Mg, HCO3, • Salt analysis to calculate the 

Sodium Adsorption Ratio and 

Exchangeable Percentage 

Available K, Available P, SO4, • Nutrient analysis to assess soil 

fertility (SR and OF systems 

look for K deficiency) 

CO3, Cl • Additional ions to complete a 

salt balance. This need not be 

done at every sampling event. 

customarily used for more research-oriented purposes 

and are included here for completeness. Soil sampling 

is commonly done once or twice during cropping years 

at multiple depths and at multiple locations in the field.

Often samples from different locations in the field are

composited so that average conditions can be assessed.

It is recommended that soil samples be collected before

planting and following harvest for evaluation of the

nutrient requirements and uptake of crops. 

Since soil moisture monitoring is primarily performed

for operational purposes, rather than regulatory 

compliance, the frequency and depths of sampling can

be selected based on site-specific needs. Soil moisture

depth monitored below the root can be used to

document the presence of leaching. 

8.6.6 Vadose Zone Sampling 

The unsaturated soil from the soil surface to

groundwater is the vadose zone. Monitoring or sampling

of the vadose zone can be accomplished by sampling 

soil or soil-water. Vadose zone samples are too variable 

and therefore of little value to measure performance of 

land treatment. 

Vadose zone monitoring has been used to assess land 

application programs primarily for research purposes. 

Vadose zone monitoring is more complex than

monitoring of other media in a land application system 

because both water movement and solution 

concentrations must be measured. In fact, vadose zone

monitoring is often considered to be primarily a research

tool because considerable analysis is required to

properly interpret results and measurement methods are 

intricate and susceptible to error due to installation 

method and operation. Use of these techniques for 

operational management or regulatory compliance does 

not appear to be as useful as other methods for 

addressing soil and groundwater conditions. 

Common techniques used to measure vadose zone

properties are summarized in Table 8-6. Additional 

technical information is available in ASTM standards

(ASTM 1992). All but one of the methods in Table 8-6 is 

designed to measure concentrations of constituents in

the water in the vadose zone soil pores. Key differences

among methods include ability to measure water flow as 

well as water quality, disturbance required to install the 

device, and the need to install replicate sensors to

address measurement variability. The different types of 

lysimeters used to measure soil water constituent 

concentrations are summarized in Table 8-6. 

Soil sampling can be included in a list of vadose zone 

sampling methods because this can yield basic

monitoring information. Soil concentrations of

constituents of interest are measured and a water 

budget developed using techniques discussed

previously can provide an estimate of water flow. 

Changes in soil concentrations at a given depth over 

time can be used to assess whether a land application

site is managed properly. 

Suction lysimeters are relatively simple to operate. 

Samples are collected from the device by applying a

vacuum (generally for 24 hours prior to sampling), which

draws soil solution into the lysimeter, and samples can 

then be collected. The sample is analyzed to determine 

concentrations but interpretation of this “simple” result is 

complex. Suction lysimeters often appear to be a lowcost monitoring choice because the basic sampling

equipment is relatively inexpensive. This is often not the

case when replicate installations to provide 

representative results and the requirement to provide an

accompanying water flow measurement are included in 

the cost of monitoring. 

The more capital-intensive pan and basin lysimeters 

are improvements over the suction lysimeter method

because these provide a solution sample that has been 

collected as a result of downward flow of water. These

provide both a sample for chemical analysis and an

estimate of water flow based on the volume of water 

collected. These sensors are often considered to be a

permanent installation because of the relatively complex

installation procedure. The disadvantage of pan

lysimeters is that the sample can exceed holding time for 

some constituents because it is not necessarily 

withdrawn as soon as it appears in the sampler. In

addition, if the soil profile is disturbed by the installation, 

the movement and water quality changes represented by

the sample may not reflect that of the undisturbed soil

profile.

8-13 
Table 8-6. Vadose Zone Sampling/Monitoring Alternatives

Method Description Advantages/Disadvantages 

Soil Sampling Soil samples are collected and analyzed for pH, 

EC, Cl, NO3-N 

Simple and reliable 

Samples totals, not just solution fraction 

Destructive sample 

Requires a soil water balance calculation to determine whether flow occurs 

Suction 

Lysimeter

A porous ceramic tube is placed in the soil so 

soil solution samples can be collected and 

analyzed 

Inexpensive, simple technique to implement 

Extracts soil solution that is not mobile 

Known to have large measurement variability

Requires a soil water balance calculation to determine whether flow occurs 

Pan Lysimeter A small collection pan (1-5 ft2) is buried at a 

selected depth so that soil solution samples 

can be collected via gravity drainage for 

analysis 

Extracts soil solution during flow events 

Provides a measure of both flow and water quality

Installation can approximate undisturbed conditions 

Moderate variability among replicate samples 

Basin Lysimeter A large collection pan (50-400 ft2) is

constructed and covered with soil so that soil 

solution samples can be collected via gravity

drainage for analysis 

Extracts soil solution during flow events 

Provides a measure of both flow and water quality

Installation creates disturbed soil conditions 

Large sample decreases variability

Wick Lysimeter A porous wick designed to match the soil water

retention characteristics of the soil is buried at a 

selected depth so that solution samples can be 

collected using a low negative pressure. 

Extracts soil solution at near zero water potential 

Installation can approximate undisturbed conditions 

Requires a soil water balance calculation to determine whether flow occurs 

8.6.7 Groundwater 

Groundwater monitoring is required at most land 

application sites. Details regarding the establishment of 

a program, monitoring well construction, hydrogeologic 

evaluation, and monitoring methods follow agency

guidelines and industry standards. 

8.6.8 Crop Management and Biomass 

Removal 

Crop management is an important part of operating

and maintaining a land application system. A healthy 

and productive crop is required to remove nutrients and 

salts. Plant material quality is an indicator of the

biological integrity of the site. Although it is of secondary 

importance, the value of crops harvested from the site 

may provide an additional incentive to assure that proper 

attention is paid to the land application fields. Attention 

to crop needs, including irrigation water and nutrients, 

will result in better management for agricultural

production, water treatment, and environmental

protection objectives. 

Much of crop management is accomplished in the

same way for a land application site and conventional

agricultural operations. Because effluent supplies 

organic fertilizer, crop responses to effluent irrigation 

differ from those in a conventional irrigation

water/inorganic commercial fertilizer scenario. Daily 

monitoring (addressed in the next section) is required to

assess whether each crop is healthy enough or whether 

some management action must be taken. 

Recommendations for routine monitoring of crops are

provided in Table 8-7. Local county representatives and 

land grant universities should be contacted to help in

developing crop management plans. Careful daily 

observations are important for ongoing management 

activities and should be maintained in a field log for

reference. The actual measurements required for crop

monitoring include biomass removal and tissue sampling

to determine constituent levels removed. Because 

nutrient uptake is the primary function of the crop, 

analysis for nitrogen is recommended. Salt management 

at land application sites includes a number of soil 

processes, salt loading and crop uptake need not match 

as closely as nitrogen levels. 

8.6.9 Routine Maintenance and Inspection 

Thorough daily inspections to identify operational

problems and gather data to make irrigation and

cropping decisions are recommended as part of routine 

monitoring. Each facility should develop a customized

inspection form. Table 8-8 provides an example 

Inspection form useful for guiding daily inspections. 

It is common that a routine inspection form also 

incorporates collection of meter readings, pressure

checks, times that various activities take place, etc. This 

is an appropriate combination of tasks and should be 

encouraged. Because land application treatment is a

biological process, it is somewhat unpredictable and

observations used to adjust management according to 

actual field conditions are important. In addition, results 

and observations made during inspection are an

appropriate topic at periodic facility staff meetings or 

informal meeting of field or maintenance personnel. 

8-14 
Table 8-7. Example Crop Monitoring Parameters

Parameter Description 

Crop management chronology Dates of cropping activities should be logged including date of planting, date of harvest, dates of primary

tillage operations, application of fertilizer, observations of crop health

Biomass removed This can be accomplished by counting bales, bushels, trucks or other field-scale measurements. Water 

content should be determined so that data can be converted to dry weight. 

Constituents removed Sample crops for TKN, NO3-N 

Salts can be evaluated if appropriate for a specific site. 

Table 8-8. Routine Maintenance Inspection Checklist for Land Application Sites

Feature Condition Recommended Action 

Facility Discharge Check amount of flow, evidence of unusual conditions 

Lagoon or Pond Pond level, odor, scum on surface, presence of excessive solids 

Main Pump Station Current operations, flow, pressure, odor, leaks, mechanical concerns 

Transmission Piping Leaks, odor, pressure at intermediate locations 

Booster Pumps Current operations, flow pressure, odor, leaks, mechanical concerns 

Fields irrigated For each field: list irrigation run times, effluent or supplemental water supply, odor 

Fields condition For each field: assess irrigation uniformity, runoff, erosion, irrigation system condition, 

odor, solids on surface 

Crop condition For each field: general crop health, need for farming activities 

Samples Collected List samples taken 

8.7 References 

American Society of Agronomy. 1986. Methods of Soil 

Analysis, Part 1, Physical and Mineralogical

Methods 2nd edition, A. Klute, Editor, Madison, WI. 

Crites, R. W., S. C. Reed, and R. K. Bastian. 2000.

Land Treatment Systems for Municipal and Industrial

Wastes. McGraw-Hill. New York, NY. 

Hagen, R. M., H. R. Haise, T. W. Edminster, eds. 1967. 

Irrigation of Agriculture Lands, Agronomy Series No.

11. Madison, WI. 

Hoffman, G. J. and M. van Genuchten. 1983. “Water

Management of Salinity Control.” Limitation to

Efficient Water Use in Crop Production, Chapter 2C. 

H. Taylor, W. Jordan, and T. Sinclair, eds. ASA. 

Monograph, pp 73-85. 

Hoffman, G. J. 1985. Drainage Required to Manage

Salinity. Journal of Irrigation and Drainage Division. 

ASCE 111. pp 199-206. 

Hoffman, G. J. 1996. “Leaching Fraction and Root Zone

Salinity Control”, Agricultural Salinity Assessment

and Management. ASCE No. 71. K. K. Tanji, ed. 

Corrected Edition. ASCE. New York, NY. 

McMichael, F. C. and J. E. McKee. 1956. Wastewater 

Reclamation at Whittier Narrows. State Water 

Quality Control Board. Publication No. 33. 

US EPA 1981. Process Design Manual for Land 

Treatment of Municipal Wastewater, EPA-625/1-81-

013, U.S. Environmental Protection Agency, CERI, 

Cincinnati, OH. 

US EPA. (1982). Handbook for Chemical and Sample 

Preservation of Water and Wastewater, EPA-600/4-

82-029, Washington, DC. 

US EPA. (1983). Methods for Chemical Analysis of

Water and Waste, EPA-600/4-79-020, Washington, 

DC. 

US EPA. (1995). Groundwater Well Sampling, Standard 

Operating Procedure 2007.

8-15 
Chapter 9 

Process Design – Overland Flow Systems

The process design approach to overland flow (OF) 

systems for land treatment of municipal wastewater is 

discussed in this chapter. The expected performance

and removal mechanisms are described in Chapter 2.

Because OF systems discharge, permit conditions and

rainfall runoff must be considered in the design. 

9.1 System Concept 

Overland flow (OF) is defined as the controlled

application of wastewater onto grass-covered, uniformlygraded, gentle slopes, with relatively impermeable 

surface soils. The process was first applied in the United

States for industrial wastewaters in Napoleon, OH and

Paris, TX (Bendixen et al., 1969; Gilde et al., 1971). 

Early application of the process for municipal

wastewaters occurred in England, where it was termed

“grass filtration,” and in Melbourne, Australia (Scott and

Fulton, 1979; US EPA, 1975). Many of these OF

systems have been in continuous and successful

operation since the late 19th century. Research efforts by 

EPA (US EPA, 1976) and the U.S. Army Corps of 

Engineers (Peters et al., 1978; Carlson et al., 1974) and 

the performance of operational systems (Peters et al., 

1981; US EPA, 1979; US EPA., 1981) led to modeling 

efforts and the development of rational design criteria

(Jenkins et al., 1978; US EPA, 1981; Smith and 

Schroeder, 1982). 

9.1.1 Site Characteristics 

Overland flow is best suited for use at sites having

surface soils that are slowly permeable (clays), or that

have a restrictive layer, such as a hardpan or claypan at 

depths of 0.3 to 0.6 m (1 to 2 ft). Moderately permeable 

soils can be used if the subsurface layer is compacted to

restrict deep percolation and ensure a sheet flow down 

the graded slope. 

Overland flow may be used at sites with grades 

between 1 and 12 percent. Slopes can be constructed 

on level terrain by creating a 2 percent slope. Grades 

steeper than 10 percent should be terraced (slopes of 2 

to 8 percent built up, followed by a steep drop and

another terrace) so that erosion (from heavy rainfall and 

heavy wastewater application) is minimized. For the 

desired slope range of 2 to 8 percent, the actual slope

does not affect the treatment performance (Jenkins et

al., 1978). The slope must be graded so that it is smooth

and of nearly constant grade. This is especially true

near the upper reaches of the slope to prevent 

channeling of wastewater and poor treatment. Site 

grades less than 2 percent may require special

measures to avoid ponding of water on the slope. The 

potential for short-circuiting and erosion is higher for 

slopes greater than 8 percent. 

9.1.2 System Configuration 

The general system layout should match as closely as

possible the natural topography at the site to minimize

expensive earthwork. The total field area for treatment is 

determined by methods described later in this chapter.

Individual treatment slopes are laid out on a topographic 

map of the site until the field area requirements are

satisfied. The individual slopes must be connected with a 

network of ditches for collection of treated runoff and

stormwater runoff for conveyance to the final system 

discharge point. 

The choice of the system layout is also influenced by

the type of wastewater distribution. High-solids-content 

wastewaters typically are applied using high-pressure

sprinklers to ensure uniform distribution of the solids on

the treatment slope. Low-pressure systems involving

gated pipe or sprinklers have been used successfully for

screened, primary, secondary or pond effluents. The

various possibilities for both high- and low-pressure 

types are illustrated in Figure 9-1 (Jenkins et al., 1978). 

Chapter 7 contains design details on both types of 

distribution systems.

Figure 9-1. Distribution Alternatives for Overland Flow.

Most industrial systems are of the type shown in 

Figure 9-1 (a) or (b), with the sprinklers for type (b)

9-1 
located at the one-third point down the slope so that all 

the wastewater applied is contained on the treatment 

surface. Empirical criteria were developed through trialand-error experience, so that slope lengths from 30 to 45 

m (100 to 150 ft) would provide adequate treatment for 

most wastewaters. If, for example, a sprinkler with a 30 

m (100 ft) diameter wetted circle is located at the onethird point on a 45 m (150 ft) long slope, the “average” 

travel distance for all the applied wastewater would then

be 30 m (100 ft). Solids content of less than 100 g/m3

typically allows the use of low-pressure systems. A

slotted or gated pipe at the top of a 30 m (100 ft) slope

should provide the same degree of treatment as the 45

m (150 ft) slope with the pressure sprinklers at the onethird point. Low-pressure systems are not suitable for 

high-solids content wastewater because deposition of

the solids will occur in the immediate vicinity of the 

application point, results in excess accumulation and

either maintenance requirements or incomplete

treatment and the production of odors. 

9.1.3 Performance Standards and System 

Capabilities 

OF systems can be designed to achieve high levels of 

treatment. OF can be used as a pretreatment step to a

water reuse system or can be used to achieve

secondary treatment, advanced secondary treatment, or 

nitrogen removal, depending on discharge requirements. 

Most OF systems have an outlet to surface water for the 

treated runoff and therefore require NPDES discharge

permits. For municipalities depending on WQS the

permit will limit BOD and TSS, and that is the basis for 

the design approach presented in this chapter. If the 

permit contains other requirements (i.e.: nitrification of

ammonium, phosphorus removal, etc.), then the

following multi-step procedure can be used to determine 

the limiting design parameter (LDP) for the system: 

1. Determine the slope length, loading rates, etc. for 

BOD removal. 

2. Estimate the slope length and loading rate for other 

parameters. 

3. Select the parameter that results in the lowest 

application rate as the LDP.

The effluent quality from properly designed and

operated OF systems can consistently produce effluents 

with 10 g/m3

 (mg/L) BOD and 15 g/m3 (mg/L) TSS 

(WEF, 2001). OF systems can be designed to nitrify to 1 

g/m3

 (mg/L) of ammonium-nitrogen and can produce

effluent total nitrogen concentrations of 5 g/m3

 (mg/L)

(WEF, 2001). In concept, the system can be thought of 

as a plug-flow, attached-growth biological reactor with a

vegetated surface (Martel, 1982). The near-surface soil

and surface deposits and the grass stems and roots 

provide a matrix for the microbial components that result 

in the bulk of the treatment. The grass also serves as a

sink for nutrients as well as water removal by 

evapotranspiration. 

Vegetation on the treatment slopes is essential to 

regulate and retard the flow, minimize velocity, and

minimize erosion, short-circuiting and channeling. The

choice of vegetation is more limited for OF systems as 

compared to SR systems because perennial, watertolerant grasses are the only feasible possibilities for OF

systems, as described in Chapter 4. Reed canarygrass, 

tall fescue and other similar grasses can withstand daily 

saturation and flourish under frequently anaerobic 

conditions. 

In some respects the OF process offers more flexibility 

and control of effluent quality than SAT and SR systems 

do. For most SAT or SR systems there is no access to

the wastewater once it is applied to the soil. All of the 

responses and constraints have to be anticipated and 

programmed into the design because there will be

limited opportunities to control the responses once the

system is operational. In contrast, most of the 

wastewater is continuously accessible in an OF system 

and this allows greater flexibility in operational 

adjustments. 

9.2 Design Procedures 

The procedure for design of OF systems is to establish 

the limiting design parameter; select the application rate, 

application period, and slope length; calculate the 

hydraulic loading rate; and calculate the field area

required. The storage volume, if any, must also be 

determined, and the field area increased to account for 

stored volume. Because BOD is often the LDP for 

municipal systems, the design approach discussed in 

this section is tailored for BOD removal. Design

considerations for systems limited by nitrogen and total 

suspended solids are also described below. 

9.2.1 BOD5

Laboratory and field research at the University of 

California at Davis has resulted in the development and

validation of a rational design procedure for OF when

BOD is the limiting design parameter (Smith, 1981; 

Smith and Schroeder, 1982 and 1983). The design

model assumes first-order, plug-flow kinetics which can 

be described with the following equation: 

exp( )

0

n

z

q

kz A

C

C R − = − (9-1)

Where: 

Cz = BOD5 concentration of runoff at a distance (z) downslope, 

g/m3

 (mg/L)

R = background BOD5 concentration, typically 5 g/m3

 (mg/L) 

Co = BOD5 concentration of applied wastewater, g/m3

 (mg/L) 

A = empirically-determined coefficient dependent on the value of q 

9-2 
k = empirically-determined exponent (less than one) 

z = distance downslope, m or ft 

q = application rate, m3

/hּm (downslope) (gal/minּft (downslope)) 

n = empirically-derived exponent 

The equation is presented graphically in Figure 9-2 for 

primary effluent (Smith and Schroeder, 1985). It has 

been validated for screened raw wastewater and primary 

effluent, as shown in Table 9-1 (Smith and Schroeder,

1982). The equation has not been validated for industrial

wastewater with BOD values of 400 g/m3

 (mg/L) or

more. The OF process does not produce an effluent free 

of suspended and organic material. This is because the 

effluent from an OF slope will approach a nonzero,

steady-state concentration value regardless of slope 

length. The 5 g/m3

 (mg/L) BOD residual or background

concentration is due to the release of natural decaying 

organic material and solids from the soil-plant system 

rather than a component of the influent BOD (Reed et 

al., 1995; Tedaldi and Loehr, 1991). For facultative pond

effluent, the application rate should not exceed 0.10

m3

/hּm (0.12 gal/minּft). 

Figure 9-2. Overland-Flow Application Rates and Slope Length.

Application Rate 

The application rate is defined as the flowrate applied 

to the slope per unit width of slope. The application rate 

used for design of municipal OF systems depends on 

the limiting design factor (usually BOD), the 

preapplication treatment, and the climate. The removal 

of BOD for various application rates and different types 

of wastewater is presented in Table 9-2 (Crites and

Tchobanoglous, 1998). A range of suggested application

rates is presented in Table 9-3 for different climates and

levels of required removal (Crites and Tchobanoglous,

1998; Reed et al., 1995). 

Application Period 

Application periods usually range from 6 to 12 h/d for 5

to 7 d/wk. For municipal wastewater an 8 h/d application

period is typical. For industrial wastewaters the 

application period can be as short as 4 h/d. 

Occasionally, municipal OF systems can operate 24 h/d 

for relatively short periods. The ability to nitrify is 

impaired with an application schedule beyond 12 h on

and 12 h off (Kruzic and Schroeder, 1990). The typical 8

h on and 16 h off schedule allows the total field area to

be divided into three subareas and for the system to

operate 24 h/d when required. 

Slope Length 

Slope lengths in OF practice have ranged typically 

from 30 to 60 m (100 to 200 ft). The longer the slope the 

greater the removal of BOD, TSS, and nitrogen. The

recommended slope length depends on the method of 

application. For gated pipe or spray heads where the

wastewater is applied at the top of the slope, a slope

length of 36 to 45 m (120 to 150 ft) is recommended. For 

high-pressure sprinkler application, the slope should be 

between 45 to 61 m (150 and 200 ft). The minimum 

slope length for sprinkler application should be the

wetted diameter of the sprinkler plus about 20 to 21 m 

(65 to 70 ft) (Crites and Tchobanoglous, 1998). 

Hydraulic Loading Rate 

A rational approach to design is to first select the 

application rate and then determine the hydraulic loading 

rate. Using the application rate approach allows for the

designer to consider varying the application rate and

application period to accomplish a reduction or increase 

in hydraulic loading. The relationship between the 

application rate and the hydraulic loading rate is 

presented in Equation 9-2.

Z

qPF LW = (9-2) 

9-3 
Where: 

LW = wastewater hydraulic loading rate, m/d (in/d) 

q = application rate per unit width of slope, m3/minּm 

(gal/minּft) 

P = application period, h/d 

F = conversion factor, 60 minּh (96.3 minּft2

ּin/hּgal) 

Z = slope length, m (ft) 

Hydraulic loading rates have generally ranged from 20 

to 100 mm/d (0.8 to 4 in/d). 

Table 9-1. Comparison of Actual and Predicted OF Effluent BOD Concentrations Using Primary and Raw Municipal Wastewater

BOD5 Concentration (g/m3

)

c

Location Applied Wastewater 

Application Rate 

(m3

/hּm)a Slope Length (m)

b Actual Predicted 

Hanover, NH Primary 0.25 30.5 17 16.3 

Primary 0.37 30.5 19 17.5 

Primary 0.12 30.5 8.5 9.7 

Ada, OK Primary 0.10 36 8 8.2 

Raw 0.13 36 10 9.9 

Easley, SC Raw 0.21 53.4 23 9.6 a

m3/hּm x 1.34 = gal/minּft. b

m x 3.28 = ft. c

g/m3 = 1 mg/L. 

Table 9-2. BOD Removal for Overland Flow Systems

BOD Concentration (g/m3

)

c

Location Municipal Wastewater Type 

Application Rate* 

(m3

/hּm)a Slope Length (m)

b Influent Effluent 

Ada, OK Raw wastewater 0.09 36.6 150 8 

Primary effluent 0.12 36.6 70 8 

Secondary effluent 0.24 36.6 18 5 

Easley, SC Raw wastewater 0.26 54.9 200 23 

Pond effluent 0.28 45.7 28 15 

Hanover, NH Primary effluent 0.15 30.5 72 9 

Secondary effluent 0.09 30.5 45 5 

Melbourne, Australia Primary effluent 0.29 250 507 12 

*Application rate is average flow, m3/h, divided by the width of the slope, m. a

m3/hּm x 1.34 = gal/minּft. b

m x 3.28 = ft. c

g/m3 = 1 mg/L. 

Table 9-3. Application Rates Suggested for BOD Removal in Overland Flow Design, m3

/hּm (gal/minּft)

Preapplication 

Treatment 

Stringent Requirements 

and Cold Climates* 

Moderate Requirements 

and Climates†

Least Stringent

Requirements and 

Warm Climates‡

Screening/ primary 0.08–0.12 (0.11–0.16) 0.19–0.29 (0.25–0.39) 0.30–0.45 (0.40–0.60) 

Aerated cell 

(1-day detention)

0.09–0.12 (0.12–0.16) 0.19–0.39 (0.25–0.52) 0.39–0.48 (0.52–0.64) 

Secondary 0.19–0.24 (0.25–0.32) 0.24–0.39 (0.32–0.52) 0.39–0.48 (0.52–0.64) 

*Stringent requirements: BOD = 10 g/m3, TSS = 15 g/m3. †

Moderate requirements: BOD and TSS ≤ 20 g/m3. ‡

Least stringent requirements: BOD and TSS ≤ 30 g/m3. 

Organic Loading Rate. Organic loading rates for OF

are typically less than 100 kg/haּd (90 lb/acreּd). The

oxygen transfer efficiency through the thin water film 

(usually 5 mm or 0.2 in) limits the aerobic treatment 

capacity of the OF process to the above rates. The 

organic loading rate can be calculated using

Equation 9-3.

0.1( )( ) LBOD = Lw C0 (9-3)

Where: 

LBOD = BOD loading rate, kg/haּd (lb/acreּd) 

0.1 = conversion factor (0.225 in U.S. customary units) 

Lw = hydraulic loading rate, mm/d (in/d) 

C0 = influent BOD5 concentration, g/m3

 (mg/L)

When the BOD of the applied wastewater exceeds 

about 800 g/m3

 (mg/L), the treatment efficiency becomes 

impaired by the oxygen transfer efficiency. Effluent 

recycle has been used to reduce the concentration to

around 500 g/m3 (mg/L) and achieve 97 percent BOD 

removal at a BOD loading rate of 56 kg/haּd (50 

lb/acreּd) (Perry et al., 1981). It should be noted that 

Figure 9-2 has only been validated to 400 g/m3 (mg/L) 

BOD. 

9-4 
9.2.2 Total Suspended Solids 

With the exception of algae, wastewater solids will not 

be the LDP for overland flow design. Suspended and 

colloidal solids are effectively removed because of the

low velocity and the shallow depth of flow on the 

treatment slope. Maintenance of a thick grass cover and

elimination of channel flow are essential for solids 

removal. The removal of suspended matter is relatively 

unaffected by cold weather or other process loading 

parameters (US EPA, 1981). 

When lagoons or storage ponds are used in overland

flow systems the presence of algae in the wastewater 

may result in high suspended solids in the final effluent 

because of the inability to remove some types of algae 

(Witherow and Bledsoe, 1983). Many small-diameter,

free floating species of algae and diatoms have little or 

no tendency to aggregate and are particularly difficult to

remove. Examples are the green algae Chamdomonas

and Chlorella and the diatoms Anomoeoneis. In contrast,

the green algae Protococcus has a “sticky” surface and 

is effectively removed on the OF slope. Because control 

of algal species in ponds may be a problem, it may be

necessary to isolate or bypass the ponds with the algal 

blooms. Therefore, during periods of algal blooms, 

storage ponds for OF systems should be off-line and

only used when absolutely necessary. Once the algal 

bloom periods have passed, the affected pond cell can

be returned to service. 

If overland flow is otherwise best suited to a site with

an existing pond system, design and operational

procedures are available to improve algae removal. The

application rate should not exceed 0.10 m3

/hּm (0.13 

gal/minּft) for such systems, and a nondischarge mode

of operation can be used during algae blooms. In the

nondischarge mode, short application periods (15 to 30 

min) are followed by 1- to 2-h rest. The OF systems at

Heavener, OK and Sumrall, MI operate in this manner 

during algae blooms (Crites and Tchobanoglous, 1998). 

9.2.3 Nitrogen 

There are many mechanisms that remove nitrogen in 

OF systems, but the major pathways are

nitrification/denitrification, crop uptake, and adsorption of 

ammonium on materials with cation exchange capacity 

(CEC). Nitrification/denitrification, which accounts for 

most of the nitrogen removal, depends on adequate

detention time, temperature, and BOD/nitrogen ratios 

(Reed et al., 1995). Denitrification appears to be most 

effective when screened raw or primary effluent is 

applied, because of the high BOD/nitrogen ratio. Soil 

temperatures below 4°C (39°F) will limit the nitrification 

reaction. 

Up to 90 percent removal of ammonium was reported 

at application rates of 0.10 m3

/hּm (0.13 gal/minּft) at

the OF system at Davis, CA (Kruzic and Schroeder, 

1990). Slope lengths of 45 to 60 m (150 to 200 ft) may 

be required to achieve this level of ammonia removal.

At Garland, TX, nitrification studies were conducted

with secondary effluent to determine if a 2-g/m3

 (mg/L) 

summer limit for ammonia and a 5-g/m3

 (mg/L) winter 

limit could be attained. Removal data for the two periods 

are presented in Table 9-4 for different application rates 

(Zirschky et al., 1989). Winter air temperatures ranged 

from 3° to 21°C (26° to 70°F). The recommended

application rate for Garland was 0.43 m3

/hּm (0.56 

gal/minּft) for a slope length of 60 m (200 ft) with 

sprinkler application (Zirschky et al., 1989).

Table 9-4. Ammonia Concentrations (in g/m3) in OF Systems in Garland, TX

Length Downslope (m)b

Month Application Rate (m3/hּm) a 46 61 91 

Summer 0.57 1.51 0.40 0.12 

Mar. – Oct. 0.43 0.65 0.27 0.11 

0.33 0.14 0.03 0.03 

Winter 0.57 2.70 1.83 0.90 

Nov. – Feb. 0.43 1.29 0.39 0.03 

0.33 0.73 0.28 0.14 a

m3/h·m x 1.34 = gal/min·ft. b

m x 3.28 = ft. 

Note: Summer-applied ammonia nitrogen = 16.0 g/m3

; winter-applied ammonia nitrogen = 14.1 g/m3. 

9.3 Land Area Requirements 

The field area, the area of land to which wastewater is 

actually applied, for OF depends on the flow, the 

application rate, the slope length, and the period of 

application. The total land area required for an OF

system should include land for preapplication treatment, 

administration and maintenance buildings, service roads,

buffer zones, and storage facilities. If there is no

seasonal storage, the field area can be calculated using

Equation 9-4.

qPF

QZ A = (9-4)

9-5 
Where: 

A = field area, ha (acres) 

Q = wastewater flowrate, m3

/d (gal/min) 

Z = slope length, m (ft) 

q = application rate, m3

/hּm (gal/minּft)] 

P = period of application h/d 

F = conversion factor, 10,000 in SI units (726 in U.S. units) 

If wastewater storage is a project requirement, the 

application field area is determined using Equation 9-5.

Equation 9-5 was developed using an application rate of

0.048 m3

/hּm (0.06 gal/minּft). 

DL F

Q V

A

W

+ S = 365 (9-5)

Where: 

A = field area, ha (acres) 

Q = wastewater flow, m3

/d (ft3/d) 

Vs = net loss or gain in storage volume due to precipitation, 

evaporation, and seepage, m3

/yr (ft

3

/yr) 

D = number of operating days per year

Lw = hydraulic loading rate, cm/d (in/d)

F = conversion factor, 100 in SI units (3630 in U.S. units) 

9.4 Design Considerations 

Considerations for design of overland flow systems 

include winter operation, storage of wastewater required 

for rainfall runoff or crop harvesting, distribution systems,

runoff collection and permit requirements for rainfall 

runoff, slope design and construction, and vegetation 

selection.

9.4.1 Winter Operation 

In general, OF systems shut down for cold winter 

weather when effluent quality requirements cannot be

met because of cold temperatures or when ice begins to

form on the slope. Sometimes the reduction of the 

application rate can allow the operation to continue

during cold weather. If a shutdown is required, 

wastewater must be stored. The most conservative

approach would be to assume a storage period that is

equal in length to that required for SR systems (Chapter 

6 and 8). At wastewater and soil temperatures above

8°C (50°F), the BOD removal efficiency is independent 

of temperature (Smith and Schroeder, 1982). In low 

temperature studies in New Hampshire, the following 

relationship between effluent BOD and temperature was 

developed (Jenkins et al., 1978): 

0.226 6.53 53 2 EBOD = T − T + (9-6)

Where: 

EBOD = effluent BOD, g/m3

 (mg/L)

T = soil temperature, °C 

Equation 9-5 was developed for an application rate of 

0.048 m3

/hּm (0.06 gal/minּft). At a soil temperature of

less than 3.9°C (39°F) the effluent BOD will exceed 30 

g/m3

 (mg/L), based on Equation 9-6. 

Wastewater applications should cease when an ice

cover forms on the slope. Operation of sprinkler systems 

can be very difficult at air temperatures below freezing. 

In locations where night-time air temperatures fall below 

0°C (32°F) but daytime air temperatures exceed 2°C 

(36°F), a day-only operation may be chosen in which all 

the field area is used within 10 to 12 hours. 

9.4.2 Storage of Rainfall Runoff 

A detailed discussion and calculation procedures for 

storage are presented in Chapter 6. Research and field 

studies at a number of systems have found that rainfall 

runoff either during or after wastewater applications did 

not significantly affect the concentration of the major 

constituents in the runoff (Smith and Schroeder, 1982; 

US EPA, 1981). This must be considered as part of total 

maximum daily load (TMDL) requirements. 

Based on work at the Davis, CA, overland flow system 

stormwater discharges are the result of natural organics 

and litter on the slope and not wastewater constituents 

and in fact were less than the losses from control slopes 

where no wastewater had been applied.

9.4.3 Distribution Systems 

Municipal wastewater can be surface-applied to OF

slopes; however, industrial wastewater should be

sprinkler-applied. Surface application using gated pipe 

offers lower energy demand and avoids aerosol 

generation. Slide gates at 0.6-m (2-ft) spacings are 

recommended over screw-adjusted orifices. Pipe lengths 

of 100 m (300 ft) or more require in-line valves to allow 

adequate flow control and isolation of pipe segments for 

separate operation.

With the orifice-pipe or fan-spray types of low-pressure 

distribution, the wastewater application is concentrated 

along a narrow strip at the top of each slope. As a

consequence, a grass-free application strip 1.2 to 2 m (4

to 6 ft) wide should be provided with these types of

distribution systems to allow operators to inspect the 

area easily and to access the outlets without damaging 

wet slopes. Gravel is a suitable material for this 

unvegetated strip, but it tends to work into the soil and 

requires replacement over time. 

Sprinkler distribution is recommended for wastewater 

with BOD or TSS levels of 300 g/m3 (mg/L) or more. 

Impact sprinklers located about one-third of the way 

down the slope are generally used. Wind speed and

direction must be considered in spacing between 

sprinklers (Reed et al., 1995). 

9-6 
9.4.4 Runoff Collection 

The purpose of the runoff collection channels is to 

transport the treated runoff and storm runoff to a final

discharge point and allow runoff to flow freely off the 

slopes. The collection channels are usually vegetated 

with the same species of grasses growing on the slopes 

and should be graded to prevent erosion. Runoff

channels should be graded to no greater than 25 percent 

of the slope grade to prevent cross flow on the slope.

In humid regions, particularly where the topography is

quite flat and the runoff channels have small grades,

grass covered channels may not dry out entirely. This 

may increase channel maintenance problems and

encourage mosquito populations. In these cases, 

concrete or asphalt can be used to construct the

channels. Small channels are normally V-shaped, while

major conveyance channels have a trapezoidal crosssections.

In addition to transporting treated effluent to the final 

discharge point, the runoff channels must also be 

capable of transporting all stormwater runoff from the 

slopes. The channels should be designed, as a 

minimum, to carry runoff from a storm with a 25-yearreturn frequency. Both intensity and duration of the 

storm must be considered. A frequency analysis of 

rainfall intensity must be performed and a rainfall-runoff 

relationship developed to estimate the flowrate due to

storm runoff that must be carried in the channels. In 

most cases, it is desirable to provide a perimeter 

drainage channel around the OF site to exclude offsite

stormwater from entering the OF drainage channels.

9.4.5 Slope Design and Construction 

The OF site is divided into individual treatment slopes

each having the selected design length. Site geometry 

may require that the slope lengths vary somewhat.

Slopes should be grouped into a minimum of four or five

hydraulically-separated, approximately-equal application 

zones to allow operating and harvesting or mowing 

flexibility. This arrangement allows one zone to be taken 

out of service for mowing or maintenance while 

continuing to operate the system at design application 

and loading rates (WEF, 2001). 

Smooth, uniform sheet flow down the slope is critical 

to consistent process performance, so emphasis must 

be placed on the proper construction of the slopes.

Naturally occurring slopes, even if these are the required

length and grade, seldom have the uniform grade and

overall smoothness required to prevent channeling, 

short-circuiting and ponding. Therefore, it is necessary to 

completely clear the site of all vegetation and to regrade

it into a series of OF slopes and runoff collection 

channels. The first phase of the grading operation 

should be accomplished within a grade tolerance of 0.03

m (0.1 ft). If buried piping is used, this grading phase is 

generally followed by the installation of the distribution

piping and appurtenances. 

After the slopes have been formed in the first grading 

operation, a farm disk should be used to break up the

clods, and the soil should then be smoothed with a land 

plane. Usually a grade tolerance of plus or minus 0.015 

m (0.05 ft) can be achieved with three passes of the land 

plane. Surface distribution piping may be installed at this 

stage. 

Soil samples of the regraded site should be taken and 

analyzed by an agricultural laboratory to determine the

amount of lime (or gypsum) and fertilizer that are needed 

to optimize crop establishment. The appropriate

amounts should then be added prior to seeding. A light 

disk should be used to eliminate any wheel tracks on the 

slopes as final preparation for seeding. 

9.4.6 Vegetation Selection and 

Establishment 

The various grass mixtures used for overland flow

systems are described in Chapter 4. An OF cover crop

should have the following characteristics: perennial 

grasses; high moisture tolerance; long growing season;

high nutrient uptake; and suited for the local climate and

soil conditions, and possibly market potential. In the

northern humid zones, various combinations of orchard 

grass, Reed canarygrass, tall fescue and Kentucky 

bluegrass have been most successful since this mixture

contains species that produce high biomass and are 

rhizomatous. Including rhizomatous species in the 

mixture is important to prevent channeling of water 

running down the slope. The use of a nurse grass such

as annual ryegrass is recommended because it will grow 

quickly and protect the soil surface while the other 

grasses establish. 

A Brillion seeder is capable of doing an excellent job of 

seeding the slopes on newly prepared sites that contain 

bare soils. The Brillion seeder carries a precision device 

to drop seeds between cultipacker-type rollers so that 

the seeds are firmed into shallow depressions. This 

allows for quick germination and protection against 

erosion. When reseeding existing sites, a no till seeder 

can be used. This seeder slices the soil surface and 

drops seed into the slices. Hydroseeding may also be

used if the range of the distributor is sufficient to provide

coverage of the slopes so that the vehicle does not have

to travel on the slopes. Traffic on the slopes in the

direction of the water flow should be avoided whenever 

possible to keep channelization to a minimum. Vehicle

access should be in the cross-slope direction and 

allowed only when the soil is dry. If a vehicle creates ruts 

9-7 
over 2.5 cm (1 inch) in depth, then field traffic should 

stop. 

A good vegetative cover is essential prior to 

application of wastewater. Grass planting should be

undertaken only during the optimum periods for planting

in particular, and the overall construction schedule must

be adjusted accordingly. In arid and semiarid climates,

portable sprinklers may be necessary to provide 

moisture for germination and growth of the grass. The

wastewater distribution system should not be used until 

the grass is established to avoid erosion of the bare soil. 

The construction contract should have a contingency to

cover reseeding or erosion repair in the case of intense

rainfall during the period between final site grading and

grass establishment. 

As a general rule, wastewater should not be applied at 

design rates until the grass has grown enough to receive

one cutting. Cut grass from the first cutting may be left 

on the slope to help build an organic mat as long as the 

clippings are relatively short (0.3 m, < 1 ft). Long

clippings tend to remain on top of the cut grass, thus 

shading the surface and retarding regrowth. 

A period of slope aging or maturing and acclimation is

required following initial startup before process 

performance will approach satisfactory levels. During

this period, the microbial population on the slopes is 

increasing and the slime layers are forming. The initial 

acclimation period may be as long as 3 to 4 months. If a 

variance to allow discharge during this period cannot be

obtained, provisions should be made to store and/or 

recycle the effluent until effluent quality improves to the 

required level. 

An acclimation period also should be provided 

following winter storage periods for those systems in 

cold climates. Acclimation following winter shutdown

should require less than a month. Acclimation is not

necessary following shutdown for harvest unless the 

harvest period is extended to more than 2 or 3 weeks 

due to inclement weather. 

9.5 System Monitoring and Management 

The primary objective of the OF system is to produce a

treated effluent that is within the permit requirements. 

Therefore, a monitoring program and a preventive 

maintenance program are necessary to ensure 

continued compliance with discharge requirements. A 

detailed description of crop, soil, and site management 

requirements for land treatment systems is given in

Chapter 8. 

9.5.1 Crop Management 

After the cover crop has been established, the slopes 

will need little maintenance work. Grass should be cut

two or three times a year. Removal of cut grass from the 

slopes is optional, especially if the system is designed 

for BOD/TSS removal. Removal from the slope is mainly 

to allow the new grass to grow and to avoid 

decomposition byproducts from being discharged off the 

slope. Other advantages are that additional nutrient 

removal is achieved, channeling problems may be more

readily observed, and revenue can be generated from 

the sale of hay. Before harvesting, each slope must be 

allowed to dry out so that equipment can travel over the 

soil surface without leaving ruts. If a vehicle creates ruts 

over 2.5 cm (1 inch) in depth, access to the site should

cease. Ruts could develop into channeling, especially if 

oriented downslope, and ruts across the slope may 

create a mosquito problem. The drying time necessary

before mowing is usually about 1 to 2 weeks; however, 

this can vary depending on the soil and climatic

conditions. After mowing and conditioning, the hay 

should be dried before raking and baling. This may take

another week or so depending on the weather.

However, during unusually wet years, site conditions 

limit vehicle access and mobility. Under these 

circumstances, weather permitting, hay can be shredded

on the treatment slopes and left in place with no baling

or removal (Tedaldi and Loehr, 1991). 

If the necessary drying times can not be met, the cut 

grass can be collected and stored. Two methods include

bale wrapping and storing cut grass in plastic silage

bags. The bale wrappers tightly seal each bale in a

sturdy, UV resistant plastic to resist sun damage and

adverse weather conditions. Wrapped bales undergo a 

fermentation process that prevents spoilage from yeasts, 

aerobic bacteria, molds, and insects, while maintaining a 

high protein and nutrient content. A bale wrapper is

shown in Figure 9-3. Alternatively, unbaled hay can be 

compacted tightly into silage bags (Figure 9-4). The 

airtight environment encourages anaerobic conditions to 

produce feed quality silage low in nitrates and free from

pest contamination. These methods allow storage of

grasses with high moisture content, minimizing the time 

needed for drying cut grass. Both, wrapped bales and

silage bags may be stored away from the treatment 

slopes, allowing the application of wastewater to 

continue without too much off-time for drying and 

conditioning of cut vegetation. 

9-8 
Figure 9-3. Bale wrappers tightly seal each bale of hay in plastic for 

storage. (Courtesy of New Holland.) 

Figure 9-4. Plastic silage bags for storing cut hay. (Courtesy of AgBag, International, Ltd.)

Monitoring programs for soils and vegetation are the 

same for OF as for SR systems (Chapter 8). If the grass 

is used as fodder, samples may be required during each 

harvest and may be analyzed for various nutritional

parameters such as protein, fiber, total digestible 

nutrients, phosphorus, nitrate, and dry matter. 

9.6 References 

Bendixen, T.W., R.D. Hill, F.T. DuByne, and G.G. 

Robeck (1969) Cannery Waste Treatment by Spray 

Irrigation-Runoff, Journal WPCF, 41: 385. 

Carlson, C.A., et al. (1974) Overland Flow Treatment of 

Wastewater, USA, WES Misc., Paper Y-74-3, 

Vicksburg, MS.

Crites, R.W. and G. Tchobanoglous (1998) Small and

Decentralized Wastewater Management Systems, 

McGraw-Hill, New York, NY.

Gilde, L.C., A.S. Kester, J.P. Law, C.H. Neeley, and

D.M. Parmelee (1971) A Spray Irrigation System for 

Treatment of Cannery Wastes, Journal WPCF, 43:

2011. 

Jenkins, T.F., et al. (1978) Pilot Scale Study of Overland

Flow Land Treatment in Cold Climates, In:

Proceedings: Developments in Land Methods of

Wastewater Treatment and Utilization – Melbourne,

Australia, Pergamon Press, New York, Progress in

Water Technology, 11 (4-5): 207. 

Jenkins, T.F., et al. (1978) Performance of Overland

Flow Land Treatment in Cold Climates, In:

Proceedings State of Knowledge in Land Treatment

of Wastewater, Vol.2, USA, CRREL, Hanover, NH. 

Kruzic, A.J. and E.D. Schroeder (1990) Nitrogen

Removal in the Overland Flow Wastewater 

Treatment Process – Removal Mechanisms, Res. J.

Water Pollution Control Federation, 62(7): 867-876. 

Martel, C.J. (1982) Development of a Rational Design 

Procedure for Overland Flow Systems, CRREL 

Report 82-2, CRREL, Hanover, NH. 

Peters, R.E., et al. (1978) Field Investigations of 

Advanced Treatment of Municipal Wastewater by 

Overland Flow, Vol.2, Proceedings of the 

International Symposium on Land Treatment of 

Wastewater, USACOE, CRREL, Hanover, NH. 

Peters, R.E., C.R. Lee and D.J. Bates (1981) Field 

Investigations of Overland Flow Treatment of 

Municipal Lagoon Effluent, USA, WES, Tech. Report 

EL-81-9, Vicksburg, MS. 

Perry, L.E., E.J. Reap, and M. Gilliand (1981) Pilot 

Scale Overland Flow Treatment of High Strength

Snack Food Processing Wastewaters, Proceedings 

National Conference on Environmental Engineering,

ASCE, EED, Atlanta, GA. 

Reed, S.C., R.W. Crites and E.J. Middlebrooks (1995) 

Natural Systems for Waste Management and

Treatment, Second Edition, McGraw-Hill, New York, 

NY. 

Scott, T.M. and D.M. Fulton (1979) Removal of 

Pollutants in the Overland Flow (Grass Filtration) 

System, Progress in Water Technology, II (4 and 

5):301-313. 

Smith, R.G. and E.D. Schroeder (1982) Demonstration 

of the Overland Flow Process for the Treatment of 

Municipal Wastewater – Phase II Field Studies, Dept

of Civil Engineering, University of California, Davis,

Report to California State Water Resources Control

Board.

9-9 
Smith, R.G. and E.D. Schroeder (1983) Physical Design 

of Overland Flow Systems, Journal WPCF, 55(3):

255-260. 

Smith, R.G. and E.D. Schroeder (1985) Field Studies of 

the Overland Flow Process for the Treatment of Raw 

and Primary Treated Municipal Wastewater, Journal 

WPCF, 57(7): 785-794. 

Tedaldi, D.J. and R.C. Loehr (1991) Performance of an 

Overland Flow System Treating Food-Processing

Wastewater, Research Journal WPCF, 63: 266. 

US EPA (1975). Land Application of Wastewater in

Australia, EPA 430/9-75-017, U.S. Environmental 

Protection Agency, OWPO, Washington, DC.

US EPA (1976). Overland Flow Treatment of Raw 

Wastewater with Enhanced Phosphorus Removal, 

EPA-660/2-76-131, U.S. Environmental Protection 

Agency, ORD. 

US EPA (1979). Municipal Wastewater Treatment by

the Overland Flow Method of Land Application, EPA 

600/2-79-178, U.S. Environmental Protection 

Agency, RSKERL, Ada, OK. 

US EPA (1981). Process Design Manual for Land

Treatment of Municipal Wastewater, EPA 625/1-81-

013, U.S. Environmental Protection Agency, CERI, 

Cincinnati, OH. 

US EPA (1981). Development of a Rational Basis for 

Design and Operation of the Overland Flow

Process, Proceedings: National Seminar on

Overland Flow Technology for Municipal

Wastewater, EPA 600/9-81-022, U.S. Environmental 

Protection Agency, Washington, DC. 

US EPA (1981). Overland Flow Treatment of Poultry 

Processing Wastewater in Cold Climates, EPA 

600/S1-81-234, U.S. Environmental Protection

Agency, RSKERL, Ada, OK. 

WEF (2001) Natural Systems for Wastewater Treatment, 

Draft, Manual of Practice, Alexandria, VA. 

Zirschky, J. et al. (1989) Meeting Ammonia Limits Using

Overland Flow, Journal WPCF, 61: 1225-1232.

9-10 
Chapter 10 

Process Design – Soil Aquifer Treatment

The process design of soil aquifer treatment (SAT) 

systems is generally governed by the infiltration rate into 

and permeability through the soil to a defined outlet 

(e.g., groundwater for recharge).. SAT systems utilize 

the highest hydraulic loading rate of any land treatment 

system. The site selection criteria for SAT are also more

stringent. The typical design procedure for soil aquifer 

treatment is outlined as follows: 

1. Characterize the soil and groundwater conditions

with field measurements. 

2. Predict the hydraulic pathway of percolate, based on

the site hydrogeology and discharge requirements to

adjacent surface water or groundwater. 

3. Select the infiltration rate from field test data (see

Chapter 5). 

4. Determine the overall treatment requirements by 

comparing wastewater characteristics to the water 

quality requirements, including potential restrictions

on the system imposed by downstream users. 

5. Select the appropriate preapplication treatment level 

appropriate for the site and the treatment needs (see

Chapter 6). 

6. Calculate the annual hydraulic loading rate based on

the treatment needs, the infiltration rate, and the

preliminary wet/dry ratio. 

7. Calculate the land requirements. 

8. Check the potential for groundwater mounding and 

determine the need for underdrains (see Chapter 3). 

9. Select the hydraulic loading cycle and the number of

basin sets. 

10. Calculate the application rate and check the final 

wet/dry ratio.

11. Lay out the basins and design berms, structures,

etc. 

12. Determine monitoring requirements and locate

monitoring wells. 

10.1 Treatment Requirements 

Soil aquifer treatment is an especially effective 

process for BOD, TSS, and pathogen removal and can

provide significant removals of nitrogen, phosphorus,

metals, and trace organics. Removal mechanisms of 

wastewater constituents such as BOD, suspended 

solids, nitrogen, phosphorus, heavy metals, 

microorganisms, and trace organics are discussed in 

Chapter 2. Typical results from various operating

systems are discussed for BOD, TSS, nitrogen, 

phosphorus, and trace organics. 

BOD and Suspended Solids 

Particulate BOD and suspended solids are removed

by filtration at or near the soil surface. Soluble BOD may 

be adsorbed by the soil or may be removed from the 

percolating wastewater by soil biota. BOD and 

suspended solids removals are generally not affected by 

the level of preapplication treatment. However, high

hydraulic loadings of wastewaters with high

concentrations of BOD and suspended solids can cause

clogging of the soil. 

BOD loadings on industrial SAT systems range from

112 to 667 kg/haּd (100 to 600 lb/acּd). BOD loadings 

beyond 336 kg/haּd (300 lb/acּd) require careful

management to avoid production of adverse odors.

Suspended solids loadings of 112 to 224 kg/haּd (100

to 200 lb/acּd) or more require frequent disking or

scarifying of the basin surface to avoid sealing of the 

surface soil. Typical values of BOD loadings and BOD 

removals for SAT systems are presented in Table 10-1 

(Crites and Tchobanoglous, 1998). 

Table 10-1. BOD Removal for Soil Aquifer Treatment Systems (Crites and Tchobanoglous, 1998)

Location 

Applied Wastewater BOD, 

lb/ac·d* 

Applied Wastewater BOD, 

mg/L 

Percolate Concentration, 

mg/L 

Removal, 

% 

Boulder, CO 48† 131† 10† 92 

Brookings, SD 11 23 1.3 94 

Calumet, MI 95† 228† 58† 75 

Ft. Devens, MA 77 112 12 89 

Hollister, CA 156 220 8 96 

Lake George, NY 47 38 1.2 97 

Milton, WI 138 28 5.2 81 

Phoenix, AZ 40 15 0 – 1 93 – 100 

Vineland, NJ 43 154 6.5 96 

*Total lb/ac·yr applied divided by number of days in the operating season. †

COD basis. 

Conversion units: 1 lb/ac·d = 1.12 kg/ha·d; 1 mg/L = 1 g/m3

.

10.1.1 

10-1 
10.1.2 Nitrogen 

Nitrogen removal has been observed during SAT at 

many sites recharging effluent containing ammonianitrogen. A common hypothesis for this nitrogen removal 

in SAT is the two-step process of autotrophic nitrification

and heterotrophic denitrification. Recharge basins are

typically operated to consist of a wetting cycle when 

water is applied followed by a drying cycle. Due to the 

net positive charge of the ammonium ion, it is adsorbed

onto the soil in the upper region of the vadose zone

during the wetting cycle. As the soil dries and air/oxygen

enters the soil, the oxidation of ammonia to nitrate by 

autotrophic nitrifiers may occur. This process results in a 

high nitrate concentration at the beginning of the

following wetting cycle. This nitrate, which tends to be

more mobile, is transported with the percolating water 

deeper into the vadose zone. Once the nitrate reaches 

an anoxic zone, heterotrophic denitrification may convert 

the nitrate to nitrogen gas in the absence of oxygen

(Gable and Fox, 2000). The nitrogen gas then migrates 

through unsaturated soil back to the surface where it is 

lost to the atmosphere. Some volatilization of the 

ammonia can also occur at the soil surface. 

Both nitrification and denitrification are accomplished

by soil bacteria. The optimum temperature for nitrogen 

removal is 30°C to 35°C (86°F to 95°F). Both processes 

proceed slowly between 2°C and 5°C (36°F and 41°F) 

and stop near 0°C (32°F). Nitrification rates decline 

sharply in acidic soil conditions and reach a limiting 

value at approximately pH 4.5. The denitrification 

reaction rate is reduced substantially by pH values below

5.5. Thus, both soil temperature and pH must be 

considered if nitrogen removal is important. 

Furthermore, alternating aerobic and anaerobic 

conditions must be provided for significant nitrogen 

removal. Because aerobic bacteria deplete soil oxygen 

during flooding periods, resting and flooding periods 

must be alternated to result in sequencing aerobic and 

anaerobic soil conditions. 

Nitrogen removal is also a function of detention time, 

BOD:N ratio (adequate organic carbon source), and

anoxic conditions. Experiments with secondary effluent

at Phoenix, AZ, showed for effective nitrogen removal 

(80 percent or more), the liquid loading rate should not 

exceed 150 mm/day (6 in/d) (Lance et al., 1976). When

primary effluent is used, the maximum hydraulic 

application rate is recommended not to exceed 200

mm/day (8 in/day). Nitrogen removal by denitrification 

requires both adequate organic carbon, which acts as a

“food” source for microorganisms, and adequate

detention time. The potential limitation on the amount of 

nitrogen removal can be approximated using the

following equation: 

2

− 5 = TOC N (10-1)

Where: 

N = change in total nitrogen, g/m3

 (mg/L) 

TOC = total organic carbon in the applied wastewater, g/m3

(mg/L) 

The 5 g/m3 (5 mg/L) of residual TOC, in Equation 10-1, 

is typical for municipal wastewater after passage through

about 1.5 m (5 ft) of soil. The coefficient 2 in the 

denominator of Equation 10-1 is based on experimental 

data where 2 g of wastewater carbon were required to

denitrify 1 g of wastewater nitrogen (US EPA, 1980). In 

terms of BOD:N ratio, a ratio of 3:1 or more is 

recommended to ensure adequate carbon to drive the

denitrification reaction. 

The two-step nitrification-denitrification process is 

consistent with field observations. However, few SAT

systems have the BOD:N ratios that can sustain 

heterotrophic denitrification. Most secondary effluents 

applied to SAT systems have BOD:N ratios of

approaching 1, where a BOD:N ratio of greater than 3 

(occurring in most primary effluents) is necessary to

sustain high nitrogen removal efficiencies. Additionally, 

most SAT systems have carbon (C) to nitrogen ratios of

1, where typically a C:N ratio greater than 2 is needed to 

carry out optimal heterotrophic denitrification 

(Kopchynski et al., 1999). These conditions would result 

in nitrogen removal efficiencies of about 30 percent, 

whereas, much higher nitrogen removal efficiencies 

have been observed in SAT systems. This would

suggest that some other mechanisms are responsible for 

the additional nitrogen removal. The anaerobic 

ammonium oxidation (Anammox) process is proposed

as a sustainable mechanism for denitrification in SAT 

systems (Gable and Fox, 2000). 

Anammox is an anaerobic, autotrophic bacterial

process that occurs when both nitrate and ammonium 

are present (Van de Graaf et al., 1995, 1996, 1997).

The nitrate is reduced to nitrogen gas while the nitrate 

oxygen is used for the oxidation of ammonium. Since the

process is autotrophic, no organic carbon is required. 

The infiltration process provides an ideal environment for 

the growth of Anammox microorganisms. While the true

mechanisms of Anammox are still being researched and 

defined, recent tests provide evidence that some type of 

anaerobic ammonium oxidation could be occurring in

SAT systems (Gable and Fox, 2000; Woods et al., 1999;

Van de Graaf et al., 1997). 

Experience with nitrification has been that rates of up

to 67 kg/haּd (60 lb/acּd) can be achieved under 

favorable moisture and temperature conditions. Total 

nitrogen loadings should be checked to verify that these

are not in excess of the 56 to 67 kg/haּd (50 to 60 

10-2 
lb/acּd) range. Ammonia will be retained in the upper 

soil profile when temperatures are too low [below 2.2°C 

(36°F)] for nitrification. Recent field studies at an SAT 

site in Truckee, CA, demonstrated that predictable and

consistent biological nitrogen removal occurred both in 

multiple years of treating normally fluctuating flows and 

loadings and during a short term study in which effluent 

total nitrogen concentrations were increased up to 80 

percent (Woods et al., 1999). Typical removals of total 

nitrogen and percolate concentration of nitrate nitrogen

and total nitrogen are presented in Table 10-2. To 

determine the nitrogen loading rate from the hydraulic 

loading rate, use: 

D

L CF L w

n = (10-2)

Where: 

Ln = nitrogen loading rate, kg/haּd (lb/acּd) 

LW = wastewater hydraulic loading rate, m/yr (in/yr) 

C = wastewater nitrogen concentration, g/m3 (mg/L) 

F = conversion factor, 10 kgּm2

/gּha (0.226 lbּL/mgּacּin)

D = number of operating days per year

Table 10-2. Nitrogen Removal for Soil Aquifer Treatment Systems*

Applied Total Nitrogen Percolate, mg/L 

Location lb/acּd mg/L Nitrate-N Total N Total N Removal, % 

Calumet, MI 20.7 24.4 3.4 7.1 71 

Dan Region, Israel 28.9 13.0 6.5 7.2 45 

Ft. Devens, MA 37.0 50.0 13.6 19.6 61 

Hollister, CA 14.9 40.2 0.9 2.8 93 

Lake George, NY 12.5 12.0 7.0 7.5 38 

Phoenix, AZ 40.0 18.0 5.3 5.5 69 

W. Yellowstone, MT 115.6 28.4 4.4 14.1 50 

*Adapted from Crites (1985a). 

Conversion units: 1 lb/ac·d = 1.12 kg/ha·d; 1 mg/L = 1 g/m3.

Phosphorus 

Phosphorus removal in SAT is accomplished by

adsorption and chemical precipitation. The adsorption

occurs quickly and the slower occurring chemical

precipitation replenishes the adsorption capacity of the 

soil. Typical phosphorus removals for SAT are presented 

in Table 10-3, including travel distances through the soil. 

If phosphorus removal is critical, a phosphorus 

adsorption test using the specific site soil can be

conducted (Reed and Crites, 1984). To conduct an 

adsorption test, about 10 g of soil is placed in containers 

solution. After periodic shaking for up to 5 days the

solution is decanted and analyzed for phosphorus. The 

difference in concentrations is attributed to adsorption

onto the soil particles. The detailed procedure is 

presented (US EPA 1975). Actual phosphorus retention 

at an SAT site (long term) will be 2 to 5 times greater 

than the values obtained in the 5-day phosphorus 

adsorption test (US EPA, 1981). An equation to predict

phosphorus removal is presented in Section 2.8.2. 

Phosphorus removal can also be tested using 

mathematical models detailed in Ryden et al. (1982) and 

Enfield (1978). 

Table 10-3. Phosphorus Removal for Soil Aquifer Treatment Systems*

Distance of Travel, ft 

Location 

Average Concentration in 

Applied Wastewater, mg/L Vertical Horizontal 

Average Concentration in 

Renovated Water, mg/L Removal, % 

Boulder, CO† 6.2† 8 – 10 0 0.2 – 4.5 40 – 97 

Brookings, SD‡ 3.0‡ 2.6 0 0.45 85 

3.5† Calumet, MI 10 – 30 0 – 400 0.1 – 0.4 89 – 97 †

3.5† § 5580§ 0.03 99 

Ft. Devens, MA‡ 9.0‡ 50 100 0.1 99 

Hollister, CA‡ 10.5‡ 22 0 7.4 29 

2.1‡ Lake George, NY 10 0 < 1 >52 ‡

2.1‡ § 1970§ 0.014 99 

8 – 11† Phoenix, AZ 30 0 2 – 5 40 – 80 †

7.9† 20 100 0.51 94 

4.8‡ Vineland, NJ 6.5 – 60 0 1.54 68 ‡

4.8‡ 13 – 52 850 – 1700 0.27 94 

*Adapted from US EPA (1981). †

Total phosphate measured. ‡

Soluble phosphate measured. 

§

Seepage. 

Conversion units: 1 mg/L = 1 g/m3

; 1 ft = 0.305 m.

10.1.3 

10-3 
10.1.4 Trace Organics 

Trace organics can be removed by volatilization, 

sorption, and degradation. Degradation may be either 

chemical or biological; trace organic removal from the 

soil is primarily the result of biological activity. Removal 

rates depend on the constituent, the applied

concentration, the loading rate, and the presence of 

easily degradable organics to serve as a primary 

substrate (Crites, 1985b). 

If local industries contribute large concentrations of 

synthetic organic chemicals and the SAT system

overlies a potable aquifer, industrial pretreatment should

be considered. Further, since chlorination prior to land 

application causes formation of chlorinated trace

organics that may be more difficult to remove, 

chlorination before application should be avoided

whenever possible. 

SAT systems have been utilized for the removal of 

endocrine disrupting chemicals found in municipal 

wastewaters (Conroy et al., 2001; Quanrqud et al., 

2002). Endocrine disruptors originate from industrial,

agricultural, and domestic sources. These include a

combination of natural hormones, pharmaceutical

products, and industrial chemicals such as 

polychlorinated biphenyls, organochlorine pesticides,

phenoxyacid herbicides, phthalates and tirazines.

Following conventional secondary treatment, percolation 

through approximately 36 m (120 ft) of unconsolidated

sediments to the local aquifer reduced residual

estrogenic activity by >95 percent (Table 10-4) (Quanrud

et al., 2002). The fate of micropollutants originating from 

pharmaceuticals and active ingredients in personal care 

products have been studied at two groundwater 

recharge facilities in Arizona (Drewes et al., 2001a).

Preliminary studies indicate that groundwater recharge

offers a high potential to remove acidic drugs such as 

lipid regulators and analgesics. Other compounds such

as antiepileptic drugs and X-ray contrast agents showed

no clear indication of removal during travel times of more

than six years. 

Additional studies of long-term SAT at field sites in 

Mesa, AZ, indicate that substantial removal of effluent

organic matter can occur. Identified trace organics were 

efficiently removed as a function of travel time to very 

low concentrations or below detection limits. Drewes et 

al (2001b) found that the character of bulk organics 

present in final SAT water resembled the character of 

natural organic matter present in drinking water. 

Table 10-4. Fractional Attenuation of Estrogenic Activity

(Relative to Primary Effluent) During Secondary Treatment 

and Soil Aquifer Treatment

Sample Location Fractional Removal 

Primary 0.00 

Secondary Unchlorinated 0.62 

Secondary Chlorinated 0.65 

Secondary Dechlorinated 0.65 

Storage Pond 0.68 

0.8m (2.5 ft) 0.77 

3.1 m (10 ft) 0.83 

5.2 m (17 ft) 0.83 

18.3 m (60 ft) 0.93 

36.6 m (120 ft) 0.99 

10.2 Aquifer Characteristics 

The geohydrological aspects of the SAT site are more 

critical than for the other processes, and a proper 

definition of subsurface conditions and the local

groundwater system is essential for design. Therefore, 

site selection is critical to the success of an SAT project.

Important factors in subsurface evaluation and selection

are the soil depth, soil permeability and aquifer

transmissivity, depth to groundwater, groundwater flow 

direction, and distance to outlet. In addition, due to high

loading rates of applied wastewater in SAT, the effects 

of groundwater mounding and the transport of percolate

within an aquifer should be considered. 

 Soils Investigation 

Potential sites are located using the methods detailed

in Chapter 5. SAT sites require deep, permeable soil

without a shallow groundwater. Once a potential site is 

located, it is necessary to investigate the soil profile. 

Soil investigations can include backhoe pits, soil borings, 

and groundwater wells. 

Backhoe pits are excavated normally to a depth of 2.4 

to 3 m (8 to 10 ft). Pits should be located on each major 

soil type and landscape aspect. The number of pits will 

vary with the site size. For example, an 8-ha (20-ac) site 

may need 6 to 10 backhoe pits to define the variability of 

the soil profile within the treatment zone. Backhoe pits 

are excavated so that a soil scientist can walk into the pit 

and can observe the soil profile. The various soil

horizons can be identified visually, and the presence of 

fractured near-surface rock, hardpan, redoximorphic 

features, layers or lenses of gravel or clay, or other 

anomalies can be identified and recorded. If the pit 

extends into groundwater, it can also be used for inplace testing of lateral soil permeability. Soil samples 

can be taken from each soil layer and analyzed for 

particle size, pH, and 

10.2.1

10-4 
EC. Once observations are complete, level benches can 

be excavated at different depths in the soil profile 

(coinciding with different soil layers) to allow infiltration 

testing (US EPA, 1984). 

Soil borings are used to characterize the deeper soils 

[greater than 3 m (10 ft)] and to determine depth to 

bedrock and groundwater. All borings should penetrate

below the water table if it is within 9 to 15 m (30 to 50 ft)

of the surface. Fewer borings are needed typically than

backhoe pits, with 1 soil boring per 2 ha (5 ac) being

typical. Backhoe pits should be used to characterize

soils typical on a site. Generally this requires pits in each 

landscape position represented on the site. 

 Groundwater Investigations 

The depth to groundwater, thickness and permeability 

of the aquifers, and groundwater quality are important to 

determine. Because of the expense of drilling wells, the 

site and the SAT process should be well established as 

the preferred wastewater management alternative prior 

to drilling. Existing onsite and nearby wells should be

surveyed and sampled, and well logs should be

analyzed prior to drilling onsite wells. Once the SAT site 

appears to be acceptable, groundwater wells should be 

drilled. The EPA recommends three wells for a complete

SAT site investigation (US EPA, 1984). If the general

groundwater flow direction has been identified, the wells

should be located so that one is in the middle of the

basin area, one is upgradient, and the third well is 

downgradient near the project boundary. A triangulation

(pump-out) test can be used to characterize groundwater 

flow and direction. 

 Infiltration Test 

A critical element of SAT site evaluation is to conduct 

field measurements of infiltration rates, permeability, and 

transmissivity. The limiting rate of hydraulic flow in an

SAT system may be the basin surface, a subsurface

layer, or the lateral flow away from the site. All three 

elements must be considered and measured. The

surface and subsurface permeability can be measured 

using infiltration tests located at the elevation that will 

correspond to the basin surface and at critical depths in 

the subsurface. 

The backhoe pits and soil borings can be used to 

estimate the presence of restriction to vertical flow and

to locate layers that need to be tested for infiltration rate 

(permeability or hydraulic conductivity). There are a 

number of infiltration tests, but the preferred tests for 

SAT systems are the flooded basin technique and the 

cylinder infiltrometer (see Section 3.8.1). 

 Groundwater Mounding 

During SAT, the applied wastewater travels initially 

downward to the ground water, resulting in a temporary

groundwater mound beneath the infiltration site. 

Mounds continue to rise during the flooding period and 

only recede during the resting discharge period. 

Excessive mounding will inhibit infiltration and reduce

the effectiveness of treatment. For this reason, the 

capillary fringe above the groundwater mound should

never be closer than 0.6 m (2 ft) to the bottom of the 

infiltration basin. This distance corresponds to a water 

table depth of about 1 to 2 m (3 to 7 ft), depending on 

the soil texture. The distance to groundwater should be

1.5 to 3 m (5 to 10 ft) below the soil surface within 2 to 3 

days following a wastewater application. An analysis that 

can be used to estimate the mound height that will occur 

at various loading conditions is discussed in Chapter 3.

The Hantusch method can be used to estimate whether 

a site has adequate natural drainage or whether 

mounding will exceed the recommended values without

constructed drainage. 

10.3 Hydraulic Loading Rates 

Selecting the appropriate design hydraulic loading rate

is the most critical step in the process design procedure.

As indicated in Chapter 5, an adequate number of 

measurements must be made of the infiltration rate and

of the subsurface permeability. The hydraulic loading 

rate is a function of the site-specific hydraulic 

characteristics, including infiltration, percolation, lateral

flow, and depth to groundwater, as well as quality of the

applied wastewater and the treatment requirements. 

Design Infiltration Rate 

The tests for infiltration rate described in Chapter 5 

should be reviewed and an appropriate test selected. 

Using Equation 3-2 or 3-3 in Chapter 3, the mean 

infiltration rate is then calculated from the field data. 

During preliminary design the infiltration rate can be 

estimated from the NRCS permeability data which is 

based on soil texture. For final design, however, actual 

field data should be used. 

 Wet/Dry Ratio 

Intermittent application is critical to the successful

operation of all land treatment systems. The ratio of 

wetting to drying in successful SAT systems varies, but

is always less than 1.0. Typical wet/dry ratios are 

presented in Table 10-5 (Crites et al., 2000). For primary

effluent the ratios are generally less than 0.2 to allow for 

adequate drying and scarification/removal of 

10.2.2

10.2.3

10.2.4

10.3.1 

10.3.2

10-5 
the applied solids. For secondary effluent, the ratio 

varies with the treatment objective, from 0.1 or less 

where nitrification or maximum hydraulic loading is the

objective, to 0.5-1.0 where nitrogen removal is the

treatment objective. These drying periods are necessary

to restore the infiltration capacity and to renew the 

biological and chemical treatment capability of soil 

system.

Table 10-5. Typical Wet/Dry Ratios for SAT Systems (Crites et al., 2000)

Location Preapplication Treatment Application Period, days Drying Period, days Wet/Dry Ratio 

Barnstable, MA Primary 1 7 0.14 

Boulder, CO Secondary 0.1 3 0.03 

Calumet, MI Untreated 2 14 0.14 

Ft. Devens, MA Primary 2 14 0.14 

Hollister, CA Primary 1 14 0.07 

Lake George, NY Secondary 0.4 5 0.08 

Phoenix, AZ Secondary 9 12 0.75 

Vineland, NJ Primary 2 10 0.20 

Design Hydraulic Loading Rate 

The design hydraulic loading rate for SAT systems 

depends on the design infiltration rate and the treatment

requirements. The procedure is to calculate the hydraulic 

loading rate based on a percentage of the test infiltration 

rate. This value is then compared to the loading rate

based on treatment requirements and the lower rate is 

selected for design. The most commonly used

measurements for infiltration rates are the basin

infiltration test and the cylinder infiltrometer (see 

Chapter 5). 

The saturated vertical hydraulic conductivity is a 

constant with time, whereas infiltration rates decrease as 

wastewater solids clog the soil surface. Thus, vertical

conductivity measurements overestimate the wastewater 

infiltration rates that can be maintained over long periods 

of time. For this reason, and to allow adequate time for 

drying periods and for proper basin management, annual

hydraulic loading rates should be limited to a fraction of 

the measured clear water permeability of the most 

restrictive soil layer. 

Basin infiltration tests are the preferred method. 

However, the small area compared to the full-scale 

basin, allows a larger fraction of the wastewater to flow 

horizontally through the soil from the test site than from 

the operating basin. Therefore, test infiltration rates are 

higher than the rates operating systems would achieve. 

Thus, design annual hydraulic loading rates should be 

no greater than 7 to 10 percent of measured basin test 

infiltration rates (US EPA, 1981.

Cylinder infiltrometers greatly overestimate operating

infiltration rates. When cylinder infiltrometer 

measurements are used, annual hydraulic loading rates 

should be no greater than 2 to 4 percent of the minimum 

measured infiltration rates. Annual hydraulic loading 

rates based on air entry permeameter test results should 

be in the same range. 

Typical hydraulic loading rates for SAT systems and

the relationship between the actual loading rates and the 

loading rates determined by operating basin infiltration

rates and cylinder infiltrometer rates are shown in

Table 10-6 (US EPA, 1981). Design guidance for 

hydraulic loading rates is summarized in Table 10-7

(Crites et al., 2000). Where high wet/dry ratios and mild 

climates are expected, the upper end of the range of 

values in Table 10-7 can be used. Conversely, where

long drying periods are needed, the lower end of the

range should be used. 

Table 10-6. Typical Hydraulic Loading Rates for SAT Systems (Crites et al., 2000)

Annual Loading Rate 

Location 

Actual Annual Loading Rate, 

ft/year % of operating basin infiltration rate % of cylinder infiltrometer rate 

Boulder, CO 100 – 160 10 – 38 4 – 10 

Brookings, SD 78 – 118 16 – 24 — 

Ft. Devens, MA 95 13 2 

Hollister, CA 50 24 3 

Phoenix, AZ 200 27 — 

Vineland, NJ 70 — 1.6 

Conversion unit: ft = 0.3048 m. 

10.3.3 

10-6 
Table 10-7. Suggested Hydraulic Loading Rates Based on Different Field Measurements

Field Measurement Annual Loading Rate 

Basin infiltration test 7 to 10% of minimum measured infiltration rate 

Cylinder infiltrometer and air entry permeameter measurements 2 to 4% of minimum measured infiltration rate 

Vertical hydraulic conductivity measurements 4 to 10% of conductivity of most restricting soil layer 

10.4 Land Area Requirements 

The application area for SAT systems can be 

determined using Equation 10-3. 

Lw

Q A (0.0001)(365) = (metric)

Lw

Q A (3.06)(365) = (U.S. customary) (10-3)

Where: 

A = application area, ha (acres) 

Q = average design flow, m3

/day (mgd) 

Lw = annual hydraulic loading, m/yr (ft/yr) 

365 = days/yr 

0.0001 = metric conversion, haּm to m3

/day

3.06 = U.S. customary conversion, acreּft to mgd 

Other land requirements include area for buffer zones, 

preapplication treatment, access roads, berms, and

storage (if necessary). Buffer zones can be used to

screen SAT sites from public view. Access roads and 

ramps, typically 3 to 3.6 m (10 to 12 ft) wide, are needed 

so that maintenance equipment for surface scarification

can enter each basin. Climatic storage is generally

unnecessary for SAT systems. The equivalent of short

storage for emergencies can be attained by making the

basins deep enough so that some storage can be 

realized. Area for future expansion should also be 

considered. 

10.5 Hydraulic Loading Cycle 

Loading cycles are selected to maximize either the

infiltration rate, nitrogen removal, or nitrification. To 

maximize infiltration rates include drying periods that are

long enough for soil reaeration and for drying and 

oxidation of filtered soils. 

Loading cycles used to maximize nitrogen removal 

vary with the level of preapplication treatment and with

the climate and season. In general, application periods 

must be long enough for soil bacteria to deplete soil

oxygen, resulting in anaerobic conditions. 

Nitrification requires short application periods followed

by longer drying periods. Thus, hydraulic loading cycles

used to achieve nitrification are essentially the same as 

the cycles used to maximize infiltration rates.

Recommended hydraulic loading cycles are

summarized in Table 10-8 (Crites et al., 2000).

Generally the shorter drying periods in Table 10-8

should only be used in mild climates. In cold climates the 

longer drying periods should be used. 

Number of Basin Sets 

The number of basins or sets of basins depends on

the topography and the hydraulic loading cycle. The

decision on the number of basins and the number to be

flooded at one time affects both the distribution system 

hydraulics and the final wet/dry ratio. As a minimum, the 

system should have enough basins so that at least one 

basin can be flooded at all times. The minimum number

of basins required for continuous wastewater application 

is presented in Table 10-9 as a function of the loading

cycle (Crites et al., 1998). 

Table 10-8. Suggested SAT Loading Cycles

Loading Cycle Objective Applied Wastewater Season Application period*, days Drying Period, days 

Maximize infiltration rates Primary Summer 1 – 2 5 – 7 

Winter 1 – 2 7 – 12 

Secondary Summer 1 – 3 4 – 5 

Winter 1 – 3 5 – 10 

Maximize nitrogen removal Primary Summer 1 – 2 10 – 14 

Winter 1 – 2 12 – 16 

Secondary Summer 7 – 9 10 – 15 

Winter 9 – 12 12 – 16 

Maximize nitrification Primary Summer 1 – 2 5 – 7 

Winter 1 – 2 7 – 12 

Secondary Summer 1 – 3 4 – 5 

Winter 1 – 3 5 – 10 

*Regardless of season or cycle objective, application periods for primary effluent should be limited to 1 to 2 days to prevent excessive soil clogging. 

10.5.1 

10-7 
10.6.1

10.6.2

10.5.2 Application Rate 

The application rate is set by the annual loading rate 

and the loading cycle. The application rate is used to 

determine the required hydraulic capacity of the piping to

the basins. The application rate is calculated as follows: 

1. Add the application period to the drying period to

obtain the total cycle time, days. 

2. Divide the number of application days per year, 

usually 365 except where storage is planned, by the 

total cycle time to obtain the number of cycles per 

year. 

3. Divide the annual hydraulic loading by the number of 

cycles per year to obtain the loading per cycle. 

4. Divide the loading per cycle by the application period

to obtain the application rate, cm/d (ft/d). 

The discharge rate to the basins can then be

determined using Equation 10-4. 

Q = 6.94AR (metric)

Q = 18.9AR (U.S. customary) (10-4)

Where: 

Q = discharge capacity, m3

/min (gpm)

A = basin area, ha (acres) 

R = application rate, m/day (in/d) 

6.94 = metric conversion constant 

18.9 = U.S. customary conversion constant 

Table 10-9. Minimum Number of Basins Required for Continuous 

Wastewater Application

Loading Application 

Period, days

Cycle Drying 

Period, days

Minimum Number of 

Infiltration Basins 

1 5 – 7 6 – 8 

2 5 – 7 4 – 5 

1 7 – 12 8 – 13 

2 7 – 12 5 – 7 

1 4 – 5 5 – 6 

2 4 – 5 3 – 4 

3 4 – 5 3 

1 5 – 10 6 – 11 

2 5 – 10 4 – 6 

3 5 – 10 3 – 5 

1 10 – 14 11 – 15 

2 10 – 14 6 – 8 

1 12 – 16 13 – 17 

2 12 – 16 7 – 9 

7 10 – 15 3 – 4 

8 10 – 15 3 

9 10 – 15 3 

7 12 – 16 3 – 4 

8 12 – 16 3 

9 12 – 16 3 

10.6 Design Considerations 

Issues to be addressed during SAT system design 

include wastewater distribution, basin layout, surfaces, 

and drainage, and flow equalization or storage. 

 Distribution 

Although sprinklers may be used, wastewater

distribution is usually accomplished by surface

spreading. This distribution technique employs gravity 

flow from piping systems or ditches to flood the 

application area. To ensure uniform basin application, 

basin surfaces should be reasonably flat. At the SAT

system in Truckee, CA, with a 12.1 ha (30 ac) leach 

field, wastewater effluent is distributed throughout eight 

leach fields with 29,000 m (75,000 ft) of perforated

plastic piping buried at a depth of 1.5 to 1.8 m (5 to 6 ft)

(Woods et al., 1999). 

Overflow weirs may be used to regulate basin water 

depth. Water that flows over the weirs is either collected

and conveyed to holding ponds for recirculation or 

distributed to other infiltration basins. If each basin is to 

receive equal flow, the distribution piping channels 

should be sized so that hydraulic losses between outlets 

to basins are insignificant. Outlets used at currently 

operated systems include valved raisers for underground 

piping systems and turnout gates from distribution 

ditches. 

 Basin Layout 

Basin layout and dimensions are controlled by 

topography, distribution system hydraulics, and loading

rate. At many sites, topography makes equal-sized

basins impractical. Instead, basin size is limited to what 

will fit into areas having suitable slope and soil type. 

Relatively uniform loading rates and loading cycles can 

be maintained if multiple basins are constructed. 

However, some sites will require that loading rates or

cycles vary with individual basins. 

In flat areas, basins should be adjoining and should be 

square or rectangular to maximize land use. In areas 

where ground water mounding is a potential problem, 

less mounding occurs when long, narrow basins with

their length normal to the prevailing ground water flow 

are used than when square or round basins are 

constructed. Basins should be at least 30 cm (12 in)

deeper than the maximum design wastewater flooding

depth, in case initial infiltration is slower than expected

and for emergencies. Basin dikes and berms are 

normally compacted soil with slopes ranging from 1:1 to

1:2 (vertical distance to horizontal distance). Basin dikes 

and berms should be planted with grass or covered with 

rip rap to prevent erosion.

Entry ramps should be provided for all basins. These

ramps are formed of compacted soil at grades of 10 to

20 percent and are from 3 to 3.7 m (10 to 12 ft) wide.

Basin surface area for these ramps and for wall slopes 

should not be considered as part of the necessary

infiltration area. 

10-8 
The basin surface may be bare or covered with

vegetation. Vegetation covers tend to remove

suspended solids by filtration and maintain infiltration 

rates. However, vegetation also limits the application 

depth to a value that avoids drowning of vegetation,

increases basin maintenance needs, requires an 

increased application frequency to promote growth, and 

reduces the soil drying rate. Gravel covered basins are 

not recommended. The long-term infiltration capacity of 

gravel covered basins is lower than the capacity of sand 

covered basins, because sludge-like solids collect in the 

voids between gravel particles and because gravel

prevents the underlying soil from drying (Bouwer et al., 

1980). 

The type of drainage used must be incorporated into 

the basin design. See Section 10.9 for a discussion on 

drainage. If underdrains are required, basin design must

consider placement of drains and drain outlet 

characteristics.

Storage and Flow Equalization 

Although SAT systems usually are capable of 

operating during adverse climatic conditions, storage

may be needed to regulate wastewater application rates 

or for emergencies. Flow equalization may be required if 

significant daily or seasonal flow peaking occurs. 

Equalization also may be necessary to store wastewater 

between application periods, particularly when only one

or two infiltration basins are used and drying periods are

much longer than application periods. 

One example of flow equalization at an SAT site 

occurs at the Milton, WI, system. Milton discharges 

secondary effluent to three lagoons. One of these

lagoons is used as an infiltration basin, the other two

lagoons are used for storage. In this way, Milton is able 

to maintain a continuous flow into the infiltration basin 

(US EPA., 1979). 

In contrast, the City of Hollister formerly equalized flow

with an earthen reservoir that was ahead of the 

treatment plant headworks. In addition, one infiltration

basin was kept in reserve for primary effluent during

periods when wastewater flows were excessive (US

EPA, 1978). 

10.6.4 Construction Considerations 

Construction of rapid infiltration basins must be 

conducted carefully to avoid compacting the infiltrative

surface. Basin surfaces should be located in cut

compacted in the berms. The berms need not be higher

sections, with excavated material being placed and than

1 to 1.3 m (3 to 4 ft) in most cases. Erosion of the berm 

slopes should be avoided because erodible material is 

often fine-textured and can blind or seal the infiltrative 

surface.

10.7 Cold Weather Operation 

In regions that experience cold weather, longer loading 

cycles may be necessary during winter months.

Nitrification, denitrification, oxidation (of accumulated 

organics), and drying rates all decrease during cold

weather, particularly as the temperature of the applied

wastewater decreases. Longer application periods are

needed for denitrification so that the application rate is 

reduced as the rate of nitrogen removal decreases.

Similarly, longer resting periods are needed to 

compensate for reduced nitrification and drying rates. 

Ponds in cold climates can be used as preliminary 

treatment during the winter months. Ice may form in the 

SAT basin, but will float under normal conditions, so

applications of warmer wastewater can continue. In

addition, proper thermal protection is needed for pumps, 

piping, and valves (Crites et al., 2000). 

SAT systems that operate successfully during cold

winter weather without any cold weather modifications 

can be found in Victor, MT, Calumet, MI, and Lake

George, NY. However, some modifications have been

used to improve cold weather treatment in other 

communities. Basin surfaces that are covered with grass 

or weeds should be mowed during fall. Mowing followed

by disking should prevent ice from freezing to vegetation

near the soil surface. Floating ice helps insulate the

applied wastewater, whereas ice that freezes at the soil

surface prevents infiltration. Problems with ice freezing 

to vegetation have been reported at Brookings, SD, 

where basins were not mowed. Applied wastewater 

froze on top of the existing ice, preventing infiltration

completely (Dornbush, 1978). 

Another cold weather modification involves digging a 

ridge and furrow system in the basin surface. Following

wastewater application, ice forms on the surface of the 

water and forms bridges between the ridges as the water 

level drops. Subsequent loadings are applied beneath 

the surface of the ice, which insulates the wastewater

and the soil surface. For bridging to occur, a thick layer 

of ice must form before the wastewater surface drops 

below the top of the ridges. This modification has been

used successfully in Boulder, CO, and Westby, WI. 

The third type of basin modification involves the use of 

snow fencing or other materials to keep a snow cover

over the infiltration basins. The snow insulates both

applied wastewater and soil. 

At Truckee, CA the SAT distribution system consists 

of subsurface perforated piping, similar to an onsite

leachfield (Woods et al., 1999). 

10.6.3 

10-9 
10.8 Drainage 

SAT systems require adequate drainage to maintain

infiltration rates and treatment efficiencies. The

infiltration rate may be limited by the horizontal hydraulic 

conductivity of the underlying aquifer. Also, if there is

insufficient drainage, the soil will remain saturated and

reaeration will be inadequate for oxidation of ammonia 

nitrogen to occur. 

Renovated water may be isolated to protect either or

both the groundwater and the renovated water. In both

cases, there must be some method of engineered

drainage to keep renovated water from mixing with

native groundwater. 

Natural drainage often involves flow through the 

subsurface to surface waters. If water rights are 

important, the engineer must determine whether the

renovated water will drain to the correct watershed or 

whether wells or underdrains will be needed to convey 

the renovated water to the required surface water. In all 

cases, the engineer needs to determine the direction of 

subsurface flow due to drainage from SAT basins.

Outlet devices must be stabilized to assure no loss of

soil material around drainage outlets. 

Subsurface Drainage to Surface 

Waters 

If natural subsurface drainage to surface water is

planned, soil characteristics can be analyzed to 

determine if the renovated water will flow from the 

recharge site to the surface water. For subsurface 

discharge to a surface water to occur, the width of the 

infiltration area must be limited to values equal to or less 

than the width calculated in the following equation

(Bouwer, 1974): 

dL

KDH W = (10-5)

Where: 

W = total width of infiltration area in direction of groundwater flow, m (ft) 

K = permeability of aquifer in direction of groundwater flow, m/d 

(ft/d) 

D = average thickness of aquifer below the water table and 

perpendicular to the direction of flow, m (ft)

H = elevation difference between the water level of the water 

course and the maximum allowable water table below the 

spreading area, m (ft) 

d = lateral flow distance from infiltration area to surface water, m 

(ft) 

L = annual hydraulic loading rate (including rainfall input), m/d 

(ft/d) 

Examples of these parameters are shown in 

Figure 10-1. 

Figure 10-1. Definition Sketch for Lateral Drainage from SAT Systems 

Underdrains.

For SAT systems located in areas where both the

water table and the impermeable layer underneath the 

aquifer are relatively close to the soil surface, renovated 

water can be collected by underdrains. In such areas,

when drains can be installed at depths of 5 m (16 ft) or 

less, underdrains are more effective and less costly than

wells for removing renovated water from the aquifer. 

SAT systems using underdrains may consist of two 

parallel infiltration strips with a drain midway between 

the strips or a series of strips and drains. These two

types of configurations are shown in Figures 10-2 and

10-3 (US EPA, 1974a). In the first system, the drains are 

left open at all times during the loading cycle. If the 

second system is used, the drains below the strips 

receiving wastewater are closed and renovated water is 

collected from drains beneath the resting strips. When

infiltration beds are rotated, the drains that were closed

before are opened and those that were open are closed. 

This procedure allows maximum underground detention

times and travel distance. 

Procedures for estimating underdrain spacings are 

provided in Chapter 3. When designing a drainage 

system, different values of ‘d’ should be selected and

used to Calculate ‘S’, so that the optimum combination 

of ‘d’, ‘H’, and ‘S’ can be determined. Detailed

information on drainage may be found in the US Bureau

of Reclamation “Drainage Manual” and in the American

Society of Agronomy manual, “Drainage for Agriculture.” 

Simulation methods for design and evaluation of 

drainage systems for wastewater land treatment sites 

are also available. One such water management model, 

DRAINMOD, can be used for describing the 

performance of an artificially drained land treatment

system over a long period of climatological record

(Skaggs et al., 1982; Skaggs, 1991). The model is a

computer simulation program which predicts, on an

hour-by-hour, day-by-day basis, the response of the 

water table and the soil water regime above it to rainfall, 

10.8.1 

10-10
evapotranspiration, given intensities of surface and

subsurface drainage, controlled drainage, subirrigation 

and sprinkler, or surface irrigation. The model keeps 

track of the amount of water irrigated, water table

depths, drainage volumes and evapotranspiration, on a

daily basis, with monthly and yearly summaries. Thus, a

given drainage design and irrigation strategy can be 

analyzed for a long period of climatological record to

determine their suitability. More specifically, the effects 

of drain spacing, surface drainage, application

frequency, and loading rates on water table depth, 

drainage outflow volumes, and required wastewater 

storage volumes can be analyzed. An economic analysis 

can be conducted to demonstrate how the model can be

used to optimize the design of wastewater irrigationdrainage systems. 

Figure 10-2. Centrally Located Underdrain.

Figure 10-3. Underdrain System Using Alternating Infiltration and 

Drying Strips.

 Recovery Wells 

Soil aquifer treatment systems that utilize unconfined

and relatively deep aquifers should use wells if 

necessary to improve drainage or to remove renovated

water for reuse. Wells are used to collect renovated

water directly beneath the SAT sites at both Phoenix, 

AZ. and Fresno, CA. Wells are also involved in the reuse

of recharged wastewater at Whittier Narrows, CA; 

however, the wells pump groundwater that happens to 

contain reclaimed water, rather than pumping specifically

for renovated water. 

The arrangement of wells and recharge areas varies;

wells may be located midway between two recharge

areas, may be placed on either side of a single recharge 

strip, or may surround a central infiltration area. Well 

design is described in detail in Campbell and Lehr 

(1973). 

 Aquifer Storage 

Use of highly treated wastewater for aquifer storage is 

an increasingly important practice in many regions of the 

world where conventional freshwater resources are

limited and local aquifers are overused. There are

several advantages to storing treated wastewater

underground: (1) the cost of artificial recharge may be 

less than the cost of equivalent surface reservoirs; (2) 

the aquifer serves as an eventual distribution system 

and may eliminate the need for surface pipelines or

canals; (3) water stored in surface reservoirs is subject 

to evaporation, to potential taste and odor problems 

caused by algae and other aquatic growth, and to 

pollution; (4) suitable sites for surface reservoirs may not 

be available or environmentally acceptable; and (5) the 

storage of treated wastewater within an aquifer may also

provide psychological and aesthetic secondary benefits 

as a result of the transition between reclaimed 

wastewater and groundwater (Metcalf and Eddy, 1991). 

Locating the extraction wells as great a distance as 

possible from the spreading basins increases the flow 

path length and residence time of the applied 

wastewater. These separations in space and time 

contribute to the assimilation of the treated wastewater 

with the other aquifer contents. 

To minimize potential health risks, careful attention 

must be paid to groundwater recharge operations when 

a possibility exists to augment substantial portions of

potable groundwater supplies (Metcalf and Eddy, 1991).

Long-term loading of aquifers can pose a serious threat

to groundwater quality, especially in dry climates with

static or very slow moving aquifers. Chemicals of

concern include salts, pesticide residues and nitrates,

disinfection byproducts (DBPs), pharmaceutically active 

chemicals, pathogens, and DBP precursors such as 

humic substances and other dissolved organic matter 

which produce a new suite of DBPs when groundwater 

is abstracted again and chlorinated or otherwise

disinfected for potable use. Fujita et al. (1996) identified

dissolved organic carbon characteristics and evaluated 

specific trace organic monitoring techniques, which allow 

operators of groundwater recharge programs to acquire 

information about the movement and mixing of 

wastewater introduced into aquifer systems. All 

significant aquifer recharge projects should have a 

groundwater impact analysis to allow the best possible 

predictions of how the project will affect groundwater 

quality and water table levels, how the situations can

best be handled, and what damage and liability aspects 

can be expected (Bouwer et al, 1999). 

10.8.2

10.8.3

10-11
10.9 References 

Bouwer, H. (1974) Infiltration-Percolation Systems, In:

Proceedings of the Symposium on Land Application

of Wastewater, Newark, DE, p.85. 

Bouwer, H., et al. (1980) Rapid-Infiltration Research at 

Flushing Meadows Project, Arizona, Journal WPCF

52(10): 2457-2470.

Bouwer, H., P. Fox, and P. Westerhoff (1999) 

Integrating Water Management and Re-use: Causes

for Concern?, Water Quality International, 

January/February, pp. 19-22. 

Campbell, M.D. and Lehr, J.H. (1973) Water Well

Technology, McGraw-Hill, New York, NY. 

Conroy, O., K.D. Turney, K.E. Lansey, and R.G. Arnold

(2001) Endocrine Disruption in Wastewater and

Reclaimed Water, In: Proceedings of the Tenth

Biennial Symposium on Artificial Recharge of

Groundwater, Tucson, AZ, pp. 171-179.

Crites, R.W. (1985a) Micropollutant Removal in Rapid 

Infiltration, in T. Asano (ed.), Artificial Recharge of 

Groundwater, Butterworth Publishers, Stoneham,

MA, pp. 579-608. Crites, R.W. (1985b) Nitrogen 

Removal in Rapid Infiltration Systems, Journal of

Environmental Engineering Division ASCE, 111 (6): 

865-873. 

Crites, R.W. and G. Tchobanoglous (1998) Small and

Decentralized Wastewater Management Systems, 

McGraw-Hill, New York, NY. 

Crites, R.W., S.C. Reed, and R.K. Bastian (2000) Land

Treatment Systems for Municipal and Industrial

Wastes, McGraw-Hill, New York, NY. 

Davis, S.N. (1969) Flow Through Porous Media, R.J.M.

DeWeist, Editor, Academic Press, New York, NY. 

Dornbush, J.N. (1978) Infiltration Land Treatment of 

Stabilization Pond Effluent, Technical Progress 

Report 3, South Dakota State University, Brookings, 

SD. 

Drewes, J., A. Sollner, A. Sarikaya, M. Reinhard, P. Fox, 

and W. Montgomery-Brown (2001a) Membrane 

Treatment versus Soil-Aquifer Treatment for Indirect 

Potable Reuse – Performance, Limitations, and

Concerns, American Water Works Association,

Membrane Conference Proceedings.

Drewes, J., T. Heberer, and K. Reddersen (2001b) Fate 

of Pharmaceuticals During Groundwater Recharge, 

In: Proceedings of the Tenth Biennial Symposium on

Artificial Recharge of Groundwater, Tucson, AZ, pp.

181-190. 

Enfield, C.G. (1978) Evaluation of Phosphorus Models 

for Prediction of Percolate Water Quality in Land

Treatment, Proceedings of the International 

Symposium on Land Treatment of Wastewater,

Volume 1, CRREL, Hanover, NH, p.153.

Fujita, Y., W. Ding, and M. Reinhard (1996) 

Identification of Wastewater Dissolved Organic 

Carbon Characteristics in Reclaimed Wastewater 

and Recharged Groundwater, Water Environment 

Research, 68 (5): 867-876. 

Gable, J.E. and P. Fox (2000) Nitrogen Removal

During Soil Aquifer Treatment By Anaerobic 

Ammonium Oxidation (ANAMMOX), Proceedings of 

the Joint Conference Held by WEF and AWWA, San

Antonio, TX. 

Kopchynski, T., P. Fox, and M. Berner (1999) Pilot 

Scale Studies to Determine Mechanisms of DOC 

and Nitrogen Removal in Soil Aquifer Treatment 

(SAT) Systems, Submitted to Water Research. 

Lance, J.C., F.D. Whisler, and R.C. Rice (1976) 

Maximizing Denitrification During Soil Filtration of

Sewage Water, Journal of Environmental Quality, 5: 

102. 

Metcalf and Eddy, Inc. (1991) Wastewater Engineering 

Treatment, Disposal, and Reuse, Third Edition, 

McGraw-Hill, Inc. 

Quanrad, D., Q. Conroy, K. Turney, K. Lansey, and R. 

Arnold (2002) Fate of Estrogenic Activity in 

Reclaimed Water During Soil Aquifer Treatment, 

Water Sources Conference Proceedings, American 

Water Works Association, Las Vegas, NV.

Reed, S.C. and R.W. Crites (1984) Handbook of Land

Treatment Systems for Industrial and Municipal 

Wastes, Noyes Publications, Park Ridge, NJ. 

Ryden, J.C., J.K. Syers, and I.K. Iskandar (1982) 

Evaluation of a Simple Model for Predicting

Phosphorus Removal by Soils During Land 

Treatment of Wastewater, U.S. Army Corps of 

Engineers, CRREL, Special Report 82-14. 

Skaggs, R.W. and A. Nassehzadeh-Tabrizi (1982) 

Drainage Systems for Land Treatment of 

Wastewater, Journal of the Irrigation and Drainage

Division, Proceedings of the American Society of 

Civil Engineers, Vol. 108, No. IR3, pp. 196-211. 

Skaggs, R.W. (1991) Modeling Plant and Soil Systems, 

Agronomy Monograph No. 31, pp. 205-243. 

US EPA (1974a). Renovating Secondary Effluent by 

Groundwater Recharge with Infiltration Basins, In: 

Conference on Recycling Treated Municipal

Wastewater Through Forest and Cropland, EPA10-12
660/2-74-003, U.S. Environmental Protection 

Agency. 

US EPA (1975) Kinetic Model from Orthophosphate

Reactions in Mineral Soils, EPA-660/2-75-022, U.S. 

Environmental Protection Agency, Office of 

Research and Development, Ada, OK. 

US EPA (1978) Long-Term Effects of Land Application 

of Domestic Wastewater: Hollister, California, Rapid

Infiltration Site, EPA-600/2-78-084, U.S. 

Environmental Protection Agency. 

US EPA (1979). Long-Term Effects of Land Application 

of Domestic Wastewater: Milton, Wisconsin, Rapid

Infiltration Site, EPA-600/2-79-145, U.S. 

Environmental Protection Agency.

US EPA (1980) Summary of Long-Term Rapid 

Infiltration System Studies, EPA-600/2-80-165

Metcalf and Eddy, Inc. (1991) Wastewater 

Engineering: Treatment, Disposal, and Reuse, Third 

Edition, McGraw-Hill, Inc. 

US EPA (1981). Process Design Manual for Land 

Treatment of Municipal Wastewater, EPA-625/1-81-

013, U.S. Environmental Protection Agency, CERI, 

Cincinnati, OH. US EPA (1984) Process Design

Manual for Land Treatment of Municipal 

Wastewater, Supplement on Rapid Infiltration and

Overland Flow, EPA 625/1-81-0139, Center for 

Environmental Research Information (CERI), U.S. 

Environmental Protection Agency, Cincinnati, OH. 

Van de Graaf, A., A. Mulder, P. De Brujin, M. Jetten, L. 

Robertson, and G. Kuenen (1995) Anaerobic 

Oxidation of Ammonium Is a Biologically Mediated

Process, Applied and Environmental Microbiology, 

61(4): 1246-1251. 

Van de Graaf, A., P. De Brujin, L. Robertson, M. Jetten, 

and G. Kuenen (1996) Autotrophic Growth in

Anaerobic Ammonium-oxidizing Mircro-organisms in

a Fluidized Bed Reactor, Microbiology, 142: 2187-

2196. 

Van de Graaf, A., P. De Brujin, L. Robertson, M. Jetten, 

and G. Kuenen (1997) Metabolic Pathway of 

Anaerobic Ammonium Oxidation on the Basis of 15N 

Studies in a Fluidized Bed Reactor, Microbiology, 

143: 2415-2421. 

Woods, C., H. Bouwer, R. Svetich, S. Smith, and R. 

Prettyman (1999) Study Finds Biological Nitrogen

Removal in Soil Aquifer Treatment System Offers 

Substantial Advantages, Water Environment 

Federation, WEFTEC ’99, New Orleans, CA. 

10-13
Chapter 11 

Industrial Wastewater Land Application

Land treatment, in many ways, was rediscovered for 

treatment of industrial wastewater. In 1934, corn and

pea canning wastewater was reported to be applied 

successfully using the ridge and furrow method in

Hampton, Iowa (Bolton, 1947). In addition to food

processing wastewaters, pulp and paper, chemical, 

fertilizer, meat processing, dairy, brewery, and winery 

wastewaters have been land applied successfully for 

many years (Crites, 1982; Ludwig et al., 1951; US EPA, 

1973). This chapter is adapted from Chapter 13 of Land

Treatment Systems for Municipal and Industrial Wastes 

(Crites et al., 2000). 

11.1 Types of Industrial Wastewaters 

Applied 

11.1.1 Food Processing 

Because of the rural location of many food processing

facilities, and because waste from food processing

facilities is suitable for application to land, this 

technology has been used widely. Vegetable processing

in New York (Adamczyk, 1977), citrus processing in 

Florida (Wright, 1993) and potato processing in Idaho

(Smith, 1977) are industrial wastewaters and areas 

where land application is the treatment process of 

choice. Soup and tomato processing wastewater were

two of the first food processing wastewaters that were 

treated by spray-runoff or overland flow (Bendixen, 

1969; Gilde, 1971; US EPA, 1973). Winery wastewaters 

were treated successfully using rapid infiltration (Coast

Laboratories, 1947; Crites et al., 1981). Additional

sources of information can be found for brewery wastes 

(Crites et al., 1978; Keith et al., 1986), vegetables 

(Beggs et al., 1990; Canham, 1958; Lane, 1955; Luley, 

1963; Madison et al., 1993), soup (Law et al., 1970), fruit 

(Crites et al., 1974; Luley, 1963; Ludwig, 1951; Crites et 

al., 1994) coffee and tea (Loehr et al., 1988; Molloy, 

1964), dairy products (Breska et al., 1957; Lawton et al., 

1959; McKee, 1955; Scott, 1962), meat processing 

(Henry et al., 1954; Schraufnagel, 1962), and winery

stillage and wastewater (Crites, 1996). 

11.1.2 Pulp and Paper 

There have been many types of pulp and paper mill 

wastewaters that have been land applied successfully 

(Wallace, 1976). Much of the literature on land 

application of pulp and paper wastewater dates from the

1950s and 1960s (Billings, 1958; Blosser et al., 1964;

Flower, 1969; Koch et al., 1959; Meighan, 1958;

Parsons, 1967; Voights, 1955). Experiments with 

insulation board mill wastewater resulted in the

demonstration that BOD loading rates over 2,240 

kg/haּd (2,000 lb/acּd) caused vegetation to be killed

(Phillip, 1971). 

11.1.3 Other Industrial Wastes 

Other industrial wastewaters that have been land 

applied include chemical (Overcash et al., 1979; 

Woodley, 1968), fertilizer, tannery (Parker, 1967),

pharmaceutical (Coloves, 1962), explosives (Lever, 

1966), wood distillation (Hickerson et al., 1960) and oily 

wastewaters. 

11.2 Water Quality and Pretreatment 

Requirements 

All wastewaters to be land applied must be

characterized before the limiting design parameter (see

Chapter 2) can be determined. The limiting design

parameter is based upon the fact that soil has a finite

assimilative capacity for inorganic and organic 

constituents. That capacity must not be exceeded if an 

environmentally sound and economically feasible land

treatment system is to result. A variety of parameters 

can limit waste application rates. Examples include

nitrate leached from the site to groundwater; synthetic 

organic compounds in surface water, groundwater, and

crops; salts that inhibit seed germination or alter soil 

structure; or metals that may be toxic to plants (Loehr et 

al., 1985). In-plant source control or pretreatment to

reduce the concentrations of specific constituents may 

be required or the size of the land treatment system

must be expanded to assimilate the most restrictive

constituent. 

11.2.1 Wastewater Constituents 

Industrial wastewaters may contain significant

concentrations and wide variations of constituents such

as BOD, COD, TSS, TDS, nitrogen, pH, organic 

compounds, and metals. Ranges of concentrations in

land-applied wastewaters are summarized in Table 11-1 

(US EPA, 1973). The impact and importance of these 

constituents are described in the following. 

BOD 

The degradable organic matter, as measured by the 

BOD test, can be present in very high concentrations in 

industrial wastewater. Because the soil mantle is very

efficient in the removal of BOD, it is often more costeffective to apply the wastewater to the land than to

remove it by pretreatment.

11-1 
Table 11-1. Characteristics of Various Industrial Wastewaters Applied to Land 

Constituent Food Processing Pulp and Paper Dairy

BOD, g/m3 200 – 10,000 60 – 30,000 4,000 

COD, g/m3 300 – 15,000 

TSS, g/m3 200 – 3,000 200 – 100,000 

Fixed Dissolved Solids (FDS), 

g/m3 1,800 2,000 1,500 

Total Nitrogen, g/m3 10 – 100 90 – 400 

pH, units 3.2 – 12 6 – 11 5 – 7 

Temperature, °C 63 91 

Conversion units: g/m3 = mg/L.. 

Organics in the form of sugars are more readily

degradable than starchy or fibrous material.

Consequently, those industrial wastewaters that contain

predominantly sugars, such as food processing

wastewaters, may be applied at a higher organic loading

rate than wastewaters from the pulp and paper industry, 

which often contain starchy or fibrous organic material

that are resistant to degradation. 

Total Suspended Solids 

Suspended solids may include coarse solids, such as 

peelings and chips, or fine solids such as pulp or silt. 

The presence of high concentrations of suspended

solids in a wastewater does not restrict its application to

a land treatment system because suspended solids can 

normally be separated quite simply by physical 

pretreatment. Failure to provide adequate suspended 

solids removal, however, can lead to operational

problems with clogging of sprinkler nozzles or nuisance

problems with solids settlement in surface irrigation 

systems. Surface buildup as a result of uneven

distribution or high concentrations of TSS can lead to 

reduced infiltration rates and inhibition of plant growth in 

ponded areas of irrigated fields. 

Total Inorganic Dissolved Solids

Salts, correctly measured only by the total inorganic 

(fixed, not volatile) solids test, are important to land 

treatment systems because there are no effective 

removal mechanisms for salt. The plants will take up a

minor amount of TDS (usually the macronutrients and

micronutrients) and some compounds will precipitate in

the soil (metal complexes and phosphate compounds). 

As a result of the minimal removal, mineral salts either 

build up in soil concentration or are leached to the 

groundwater. Industrial wastewaters with very high

inorganic solids concentrations are generally not suitable

for land application unless special provisions are made

to collect soil drainage. 

It is very important to measure the inorganic dissolved 

solids in the industrial process water because the 

standard total dissolved solids (TDS) test will include the 

organic acids, alcohols and other dissolved organic 

compounds that may be present in the wastewater. As 

an example, a milk processing wastewater was tested 

for fixed dissolved solids (FDS), TDS, electrical

conductivity (EC) for both the wastewater and the 

shallow groundwater (after slow-rate land treatment).

The results are summarized in Table 11-2 (Crites et al., 

2000). The ratios of FDS/TDS and FDS/EC are

presented for both waters and for upgradient shallow 

groundwater. A typical ratio of FDS/EC in clean water is 

0.64 (Westcot et al., 1984). As the wastewater infiltrates 

through the soil, a significant portion of the TDS, in the

form of organic material, is removed. Initially, the organic 

portion consists of 48 percent of the TDS and exceeds 

1,000 g/m3

 (mg/L). The slow-rate land treatment process 

reduces the organic TDS to 200 g/m3

 (mg/L),

approximately 17 percent of the TDS. The FDS portion

of the wastewater increases from 53 percent of the TDS

to 83 percent after treatment, resulting in a buildup of 

inorganic salts in the groundwater. 

Table 11-2. Comparison of Inorganic and Total Dissolved Solids Measurements in Milk Processing Wastewater and Shallow Groundwater

Water Source 

Fixed Dissolved 

Solids (FDS), g/m3

TDS, g/m3 EC, g/m3 FDS/TDS ratio FDS/EC ratio 

Process Wastewater 1,203 2,250 1,680 0.53 0.71 

Shallow Groundwater 1,000 1,200 1,700 0.83 0.58 

Upgradient 

Groundwater 

200 300 310 0.67 0.64 

Conversion units: g/m3 = mg/L. 

.

11-2 
Nitrogen 

Industrial wastewaters from livestock, potato, dairy, 

meat-packing, and explosives production may be high in

nitrogen. For these wastewaters, nitrogen is often the 

limiting design factor. The C:N ratio does not have to be 

in as close a balance for land treatment as it does for 

suspended growth systems, however, C:N ratios beyond 

30:1 will affect crop growth or biological nutrient removal 

because of the competition for available nitrogen. 

pH 

The pH of industrial wastewater can vary 

tremendously, even hourly, depending on the type of 

wastewater and the cleaning agents used. A range of pH 

between 3 and 11 has been applied successfully to the 

land (Crites, 1982). If the low pH is from the presence of 

organic acids, land treatment will have a neutralizing

effect as the organic acids are oxidized or degraded.

Temperature 

High-temperature industrial wastewater, such as spent 

cooking liquors from pulping operations, can sterilize

soil, thereby precluding the growth of vegetation and

reducing the treatment capability of the soil mantle 

(Guerri, 1971). High-temperature wastewaters should, 

therefore, be cooled prior to land application. 

Color 

The color in most industrial wastewaters is associated

with degradable organic material and is effectively 

removed as the wastewater percolates through the soil 

mantle. In some wastewaters, such as spent sulfite 

liquor, the color is due to inert compounds such as 

lignins. It has been observed that the color from inert

compounds can move through the soil (Blosser et al., 

1964). Groundwater contamination is of concern from 

land application of industrial wastewaters with color 

resulting from inert components. 

Metals 

Heavy metals are effectively removed by most soil

systems. Metals can be the limiting design factor in slowrate and rapid infiltration systems and the rate of 

retention in the soil may affect the longevity of a soil

system due to buildup in the soil. 

Sodium 

The sodium adsorption ratio (SAR), and the problems 

caused by high values, are defined in Chapter 2. Some 

industrial wastewaters that use caustic for cleaning may 

have a high sodium adsorption ratio and may require

pretreatment for correction. Municipal systems should

consider industrial discharges to the system (e.g., in cold

climates de-icing salts may cause a problem). 

11.2.2 Pretreatment Options 

Options for pretreatment of industrial wastewaters may 

need to be evaluated because of more stringent

discharge and land application limits. Pretreatment for 

industrial wastewaters may range from fine screening to 

biological treatment. The more typical of the 

pretreatment operations and processes are described in

the following. 

Fine Screening 

Fine screening is usually a minimum level of

pretreatment prior to land application of industrial

process/rinse water. Fine screens can range from fixed 

parabolic inclined screens to rotary drum screens (Crites 

et al., 1998). Coarse solids that can clog sprinkler heads 

or settle out at the head end of flood irrigation checks 

can be removed economically using fine screens. 

Screens also protect downstream pumps or other 

pretreatment units from large objects that may get 

washed into the wastewater stream. 

Ponds 

Ponds can range from anaerobic to deep facultative to 

aerated. Aerated lagoons or ponds are quite common to

the pulp and paper industry and to many food

processing wastewaters. Ponds can be used to equalize

the flows, reduce peak organic loadings, and store the 

wastewater for short periods of time. A sedimentation 

pond or lagoon can be a lined basin or concrete basin. 

The ponds can be designed by overflow rate or 

detention time. Sludge may be allowed to accumulate for 

season operations and cleared out after the season

concludes. If significant winter storage is required and 

the wastewater has a relatively high BOD, pretreatment

will usually be needed to reduce the BOD to 100 g/m3

(mg/L) or less (US EPA, 1973) to avoid odor production.

Alternatively, the storage pond can be aerated to avoid 

odor production. 

Adjustment of pH 

If the pH of the wastewater is outside the range of 4 to

9 due to inorganic acids or bases, pH adjustment may

be needed. Sometimes an equalization pond will serve 

to let the wastewater self-neutralize, particularly if large 

swings in the wastewater pH occur diurnally. Generally 

the pH will attenuate quickly as a result of land treatment 

and adjustment is not normally needed. 

Cooling 

High-temperature wastewaters [above 66°C (150°F)] 

should be cooled so that adverse effects on vegetation

and soil do not occur. High-temperature wastewaters 

can also have detrimental effects on plastic pipelines. If 

11-3 
the wastewater temperature needs to be reduced, either 

ponding or cooling towers can be used. 

Dissolved Air Flotation 

Dissolved air flotation (DAF) is a unit process in which 

pressurized flow containing tiny air bubbles is introduced

at the bottom of a special tank or clarifier (Crites et al., 

1998). The dissolved air will float suspended solids and 

the DAF unit will remove the solids through a float 

skimming device. Sedimentation also occurs in DAF

units so that the settled solids must be removed. DAF 

units are most effective for treating settleable solids and

fats, oil and grease (FOG). 

Constructed Wetlands 

Constructed wetlands are being used for pretreatment

of industrial wastewaters (Crites, 1996; Crites et al., 

1998; Reed et al., 1995). Treatment of livestock 

wastewater with constructed wetlands after treatment

through ponds is becoming more prevalent (Hunt et al., 

1995). Removals of various constituents through the

settling basin and first cell of a wetland receiving dairy 

wastewater in Mercer Co., KY are summarized in 

Table 11-3 (Hunt et al., 1995). 

Table 11-3. Water Quality Parameters in the Settling Basin and First Cell of a Wetland Receiving Dairy Wastewater, Mercer Co., KY

Constituent Settling Basin, g/m3 Influent, g/m3 Effluent, g/m3

Percent 

Reduction 

DO 0.5 0.6 0.8 — 

BOD 465 452 158 66 

TSS 3,516 1,132 408 88 

VSS 2,085 898 357 83 

TP 113.8 71.6 47.1 59 

SP 60.5 26.5 15.0 75 

TKN 197.0 107.5 123.8 37 

NH3-N 78.8 32.8 10.3 87 

Conversion units: g/m3 = mg/L. 

Dairy wastewater has been treated using constructed 

wetlands using a detention time of 7.7 days, a hydraulic 

loading rate of 39.4 mm/d (1.55 in/d), and a mass COD 

loading rate of 554 kg/haּd (494 lb/acּd) (Moore et al., 

1995). 

Anaerobic Digestion 

Anaerobic digestion can be used to reduce the organic 

content of wastewater and produce methane gas (also 

known as biogas). Anaerobic digestion can be

conducted in a variety of reactors and using a variety of 

processes (Crites et al., 1998). Typically a BOD of about 

2,500 g/m3

 (mg/L) or higher is needed in an industrial

wastewater to make anaerobic digestion attractive. 

Anaerobic digestion using some of the low-rate methods 

is generally favored in the food processing industry. 

11.3 Design Considerations 

Design considerations specific to industrial 

wastewaters include higher solids and organic loadings,

nitrogen transformations, and the control and attenuation 

of pH. 

11.3.1 BOD Loading Rates and Soil 

Reaeration 

An important design consideration specific to industrial 

wastewater is an accurate assessment of solids and 

organic loadings. Oxygen exchange into soils greatly 

depends on air-filled pore spaces because the diffusion

coefficient of oxygen is over 10,000 times more rapid in 

air than in water. As a result, if organic loadings are

intermittent and atmospheric oxygen is allowed to diffuse

directly into the soil, high organic loading rates can be 

sustained without the generation of odors (Reed et al., 

1995). 

Research at Cornell on acclimated soils of SR systems 

receiving food processing wastewater documented that

organic loading rates on a COD basis can exceed 4,480 

and 19,094 kg/haּd (4,000 and 17,000 lb/acreּd) for 

soil temperatures of 16°C and 28°C (61°F and 82°F),

respectively (Jewell et al., 1975). Field sampling of the

groundwater at application rates exceeding 8,960 

kg/haּd (8,000 lb/acreּd) of COD was less than 0.8 

percent of the applied COD (Jewell et al. 1978). Based

on the experience in New York State, guidelines have 

been established that organic loading rates should not

exceed 560 kg/haּd (500 lb/acreּd) based on BOD 

(Adamczyk, 1977). BOD loading rates for various food

processing slow rate systems are summarized in

Table 11-4 (Crites et al., 1998; Reed et al., 1984). 

11-4 
Table 11-4. BOD Loading Rates at Existing Industrial Slow-Rate Systems

Location Industry BOD Loading Rate, kg/haּday (lb/acreּday)

Almaden, McFarland, CA. Winery stillage 470 (420) 

Anheuser-Busch, Houston, TX. Brewery 403 (360) 

Bisceglia Brothers, Madera, CA. Winery stillage 312 (279) 

Bronco Wine, Ceres, CA. Winery 143 (128) 

Citrus Hill, Frostproof, FL. Citrus 447 (399) 

Contadina, Hanford, CA. Tomato processing 103 (92)

Frito-Lay, Bakersfield, CA. Potato processing 94 (84) 

Harter Packing, Yuba City, CA. Tomato processing 393 (351) 

Hilmar Cheese, Hilmar, CA. Cheese processing 249 (222) 

Ore-Ida Foods, Plover, WI. Potato processing 213 (190) 

Tri Valley Growers, Modesto, CA. Tomato processing 224 (200) 

In OF treatment, organic loading rates and BOD 

concentrations must be limited to avoid overloading the

oxygen transfer to the attached microorganisms. The 

initial work by Campbell Soup Company (Gilde et al., 

1971) indicated that excellent BOD removals could be

expected at applied BOD concentrations of about 800

g/m3

 (mg/L) (Crites, 1982). When higher strength

wastewaters were applied at similar loading rates [16 to 

36 mm/d (0.6 to 1.4 in/d)], however, an oxygen transfer 

problem began to develop. To overcome this problem, 

pretreat or recycling of the treated effluent can be used

(Crites, 1982). If a recycle operation is used, the

collection system should include a sump from which the 

treated runoff can be returned to the distribution system.

Nitrogen Transformations 

Permit limits in the past have focused on ammonia, 

nitrate, and total Kjeldahl nitrogen (TKN), with the

assumption that organic nitrogen measured in the TKN 

test is biodegradable. It is recognized that 

nonbiodegradable organic nitrogen exists and that the

TKN test, a chemical digestion procedure, is not always 

a good indicator of the biodegradability of an organic 

nitrogen compound. Although nonbiodegradable organic 

nitrogen may remain after exposure to rigorous 

anaerobic and aerobic treatment, studies support the

premise that this form of TKN does not pose the same

hazards to the environment as biodegradable organic 

nitrogen (Kobylinski et al., 1995). The presence of 

nonbiodegradable organic nitrogen may, however, 

impact the ability of an industrial land treatment system 

to comply TKN limits written into NPDES permits. 

Industrial wastewaters have a common tendency to

have very high C:N ratios, which may effect the 

biological nutrient removal processes of the treatment

system. Incubation studies conducted on various 

industrial wastewaters demonstrated the effect of C:N 

ratios on the mineralization of organic nitrogen. The data 

presented in Table 11-5 indicate that wastewaters with 

relatively low C:N ratios maintain a higher mineralization 

potential than wastewaters with high C:N ratios (King, 

1984). In this review wastewaters with C:N ratios greater 

than 23:1 displayed negative mineralization values,

indicating inefficient conversion of organic nitrogen into 

inorganic forms of nitrogen. 

11.3.2 pH Control and Attenuation 

Many food-processing wastewaters have a low pH that 

can range from 3.7 to 6, as the result of the presence of 

organic acids. The action of the soil microbes in 

oxidizing the organic acids and the soil buffering

capacity usually result in a relatively rapid attenuation of 

the pH. A review of sites receiving winery stillage waste 

with a typical pH of 3.7 found that the soil pH was 

reduced from 6.7 to 5.8 in the topsoil [0 to 15 cm (0 to 6 

in)], but only from 7.1 to 6.6 at the 0.6 m (2 ft) depth, and 

only from 7.45 to 7.16 at the 1.8 m (6 ft) depth (Crites et

al., 1981). 

Table 11-5. Nitrogen Mineralization of Industrial Wastewaters

Wastewater C:N Organic-N Mineralized (%) 

Textile Sludge 

Vacuum Filtered Solids 2.5 43 

Solids from Lagoon 4.4 9 

Wood Processing Wastes 

Paper Mill Sludge 82.2 -45 

Fiberboard Mill Sludge 23.0 -12 

Poultry Processing Waste 

Waste-Activated Sludge 3.0 52 

Fermentation Waste 

Sludge from Brewery Wastewater Treatment Plant 2.4 46 

Sludge from Enzyme Production 8.0 24 

11-5 
11.4 Slow-Rate Land Treatment 

The procedure for design of slow-rate land treatment

systems is presented in Chapter 8. The preferred

method of wastewater distribution is sprinkler application 

(irrigation). Although surface application methods (flood 

or furrow irrigation) have been used successfully, a

number of disadvantages have been observed. The 

applied solids tend to settle out near the point of 

application, producing a nonuniform distribution of solids 

and organics through the field. Flood or furrow irrigation 

also results in saturated flow through the soil and may 

reduce the effectiveness of treatment for some

constituents and result in anaerobic conditions that can

cause leaching of iron and manganese. Relatively lowcost methods of sprinkler application, such as center 

pivots, are usually preferred. See Chapter 7 for details 

on sprinkler application. Two brief case studies are

included here. 

11.4.1 Typical Examples 

Slow-rate land treatment is the most popular method

of industrial wastewater land treatment. Two examples 

of food processing wastewater land application are 

presented in the following illustrating a year-round 

application in Idaho and a seasonal application of tomato

processing wastewater in California. 

Potato Process Water— Idaho 

Bruner et al., 1999 reported the J.R. Simplot Company 

Food Group has operated a potato processing plant in 

Aberdeen, Idaho since 1973. This facility produces a 

variety of fried potato products. The 330-day processing 

season begins on about September 1 and ends on about

July 31 each year. The current average daily flow from

the facility is about 2,650 m3

/d (0.7 Mgal/d, for an annual

flow of about 874,427 m3

 (231 million gallons). All water 

used for potato processing is recycled through sprinkler 

irrigation on to a 190 ha (469 acre) agricultural receiver 

site containing silt loam soil and grass as the receiver

crop. Groundwater is about 10 to 20 m (30 to 60 ft) 

below the ground surface at this site. 

Process water is generated during the washing, 

cutting, blanching, and cooling of the potatoes. Water 

used to wash soil from the potatoes in the raw product 

receiving area is screened to remove potato vines,

rocks, and small potatoes, and then is diverted to a set 

of settling basins. The settled effluent is land applied on

a designated area of the facility's agricultural land, and

the overflow from the basins is pumped to the land 

application site with the process water stream. Water 

used within the processing plant is screened and then 

directed to a primary clarifier. The underflow potato 

solids from the clarifier are mechanically separated using 

centrifuges and are fed to cattle. Excess oil from the

fryers is removed by a separate clarifier and recycled off 

site. 

Southern Idaho has a semi-arid climate, with an 

annual average precipitation of about 23 centimeters (9

inches). The growing season for grass occurs during the 

months of April through October. Under intensely 

managed conditions, grass on land application sites in

southern Idaho typically consumes about 107

centimeters (42 inches) of water annually. 

The objective of Simplot's potato process water 

irrigation system is to provide a cost-effective, reliable,

and environmentally sound beneficial reuse of the water,

nitrogen, and other crop nutrients. The challenging

aspects of this system have been the management of 

applied salts and organics to protect groundwater 

quality, and to minimize odors. 

A view of the side roll sprinkler system is shown in 

Figure 11-1. 

Figure 11-1. Side roll sprinklers apply potato processing wastewater

throughout the winter at Aberdeen, Idaho. (Courtesy of Cascade Earth 

Science.)

Tomato Processing System in California 

Tomato processing wastewater has been land applied 

at a number of sites in California’s Central Valley for 

many years. Operations include direct land application to

open land; furrow, flood and sprinkler irrigation of 

agricultural crops; and provision of irrigation water to 

private farmers for pasture application. One site has 36 

ha (90 acres) for the direct land application of 3,875

m3/d (1.0 Mgal/d). Wastewater is passed through a fine

screen and applied to border strips for flood irrigation. 

BOD and TSS concentrations have averaged 1,700 g/m3

(mg/L) and 300 g/m3

 (mg/L), respectively, resulting in a 

BOD loading of 190 kg/haּd (170 lb/acreּd) and a TSS 

loading rate 33 kg/haּd of (30 lb/acreּd). The regulatory 

agency has placed a limit of 224 kg/haּd (200

11-6 
lb/acreּd) of BOD to avoid the generation of odors. 

Upgradient and downgradient groundwater monitoring 

wells have been sampled regularly and have

demonstrated improvement of water quality after land

application and no adverse impacts on quality of the 

groundwater (Beggs et al., 1990). 

11.5 Overland Flow Treatment 

The procedure for design of overland flow land

treatment systems is presented in Chapter 9. Overland

flow systems receiving high-strength wastewater are

recommended to use sprinkler application to distribute

the solids and organics evenly. Two brief case studies 

are included here. 

11.5.1 Typical Examples 

Overland flow has been used to treat a variety of food

processing wastewaters including apple, tomato, potato, 

soup, meat packing, poultry, peanuts, and pimientos 

(Crites, 1982). Two examples are presented briefly to 

illustrate a year-round system and a seasonal system. 

In the year-round example the treated runoff is discharge 

to surface water. In the more seasonal operation, the

treated runoff is reused for crop irrigation.

Soup Producer in Texas 

One of the oldest and best-known overland flow 

systems is the Campbell Soup Company's Paris, TX 

operation. Developed in the 1960s, the Paris site has 

had its origins documented (Gilde et al., 1971),

performance evaluated (Law et al., 1970), microbiology 

investigated (Vela, 1974), and long-term effects studied

(Tedaldi, 1991 and 1992).

The original 120 ha (300 acre) site was expanded to 

360 ha (900 acres) by 1976. The original slopes ranged 

from 1 to 12 percent, but those from 2 to 6 percent 

demonstrated the best performance, least erosion and 

least ponding. Before application, the wastewater is 

screened to remove large solids, and grease is 

skimmed. No storage of the screened wastewater occurs 

and the screened wastewater is pumped continuously 

from a 375-m3

 (99,075-gal) sump to spray the 

application slopes. The overland flow terraces are 60 to 

90 m (200 to 300 ft) long. The hydraulic loading rate was 

15 mm/d (0.6 in/d). The slopes are seeded to a mixture 

of Reed canarygrass, tall fescue, red top and perennial

ryegrass. Wastewater is applied using standard

agricultural impact-type solid set sprinklers [8.0-mm 

(0.315-in) nozzle diameter]. Application periods are 6 to

8 hr/d for 5 d/wk. Long-term operation and performance

data collected at the site indicate that the OF system

consistently achieved very high removal efficiencies from 

a surface discharge standpoint. The performance of the

system is summarized in Table 11-6 (Crites, 1982; Gilde 

et al., 1971; Law et al., 1970). 

Tomato Processor in California 

A 129 ha (320 acre) overland flow treatment system

was constructed near Davis, California in 1969 to treat 

15,100 m3/d (4 Mgal/d) of tomato processing 

wastewater. Screened wastewater is pumped to the 

overland flow field and sprinkled onto constructed 2.5

percent slopes. The slopes are 53 m (175 ft) long based

on the experience at Paris, TX. Reed canarygrass 

predominates as the vegetation. The cannery operates 3

to 4 months during the summer (July through midOctober) fresh processing season and, for the past few 

years, operates a remanufacturing processing season

from October through March. The solid-set sprinklers are

shown in Figure 11-2. 

Table 11-6. Performance of Paris, TX, Overland Flow System

Constituent Influent Effluent Percent Removal

BOD, g/m3 572 3.1 99.5 

COD, g/m3 806 45 94.4 

TSS, g/m3 245 38 84.5 

Total N, g/m3 17.2 2.8 83.7 

Total P, g/m3 7.4 4.3 41.9 

Chloride, g/m3 44 43 2.3 

pH, units 4.4 – 9.3 6.6 — 

Conversion units: g/m3 = mg/L. 

11-7 
Figure 11-2. Solid set sprinklers apply tomato processing wastewater 

to overland flow slopes. 

Treated runoff averages 7,550 m3/d (2 Mgal/d). The 

treated runoff is reused for crop irrigation on a nearby 

ranch. The performance of the overland flow system is 

summarized in Table 11-7.

11.6 Soil Aquifer Treatment 

The design of soil aquifer treatment systems is

described in Chapter 10. Few SAT systems exist for 

industrial wastewater. The reasons include the difficulty 

in siting SAT systems and the typical high strength of

industrial wastewater, which requires a high level of

treatment. 

The few SAT systems that exist are at the low end of

the hydraulic loading rate range for municipal 

wastewater. The loading rates for BOD, TSS, and

nitrogen, however, are generally quite high. 

Table 11-7. Performance of Overland Flow System at Davis, CA.

Constituent Influent Effluent Percent Removal

BOD, g/m3

 (mg/L) 1,490 17 98.9 

TSS, g/m3 (mg/L) 1,180 25 97.9 

pH, units 4.5 8.16 — 

Source: Brown and Caldwell files, Sacramento, CA. 

11.6.1 Cheese Processing Wastewater in 

California

Hilmar Cheese Company has been producing cheese 

products and land-applying the process water at their 

plant near the Town of Hilmar, five miles south of 

Turlock, CA, since 1985. The land use surrounding the 

plant site is primarily agricultural, with a mixture of

fodder, orchard, and pasture crops being grown. The 

soils in the area are characteristically sandy, and there is 

a relatively shallow groundwater table (3 m or 10 ft). 

The land has been leveled for surface irrigation. 

The area used for soil aquifer treatment has been

expanded with each increase in process water flow,

reaching 56 ha (140 acres) by 1998. The process water 

flowrate is 2,840 m3/d (0.75 Mgal/d). The average 

loading rate is 65 mm/wk (2.6 in/wk) because the 

application area is rotated between wastewater 

applications for about 6 months and cropping with either 

corn or barley for 6 months. The BOD loading rate can 

range from 89 to 734 kg/haּd (80 to 655 lb/acreּd), with 

248 kg/haּd (222 lb/acreּd) being typical. 

A comparison of the process water characteristics and 

the monitoring well groundwater quality is presented in

Table 11-8 (Nolte and Associates, 1996). As shown in

Table 11-8 the upgradient groundwater has much higher 

nitrate-nitrogen values as a result of areawide

fertilization practices. The downgradient wells have 

much lower nitrate-nitrogen as a result of denitrification. 

Hilmar Cheese is reclaiming byproducts from the cheese

production including the whey protein and lactose.

However, it should be noted that TKN, EC, TDS and

FDS increased significantly. An ultrafiltration system

concentrates the remaining fats and proteins into a slurry 

that is used for cattle feed (Struckmeyer, 1999). 

11.6.2 Winery Wastewater in California 

Winery wastewater is characterized by low pH, 

relatively high BOD, and a low nutrient content. Land 

application using soil aquifer treatment has been

practiced successfully at a number of California wineries

for many years (Coast Laboratories, 1947; Crites, 1987; 

Crites et al., 1974). 

A Central Valley winery was constructed in 1974 with a 

soil aquifer treatment system for treatment and disposal

of process water. Products include wine and wine 

coolers. Washwater is collected into a central sump and

pumped to a series of seven individual infiltration basins. 

Washwater flows vary by the season, being highest 

during the August to October crush period. Annual

average washwater flows are 760 m3/d (0.2 Mgal/d).

Operation of the infiltration system is cyclical.

Washwater is loaded onto one basin at a time for a

period of several days and then the washwater is moved

11-8 
to the next basin. The basins cover 4 ha (10 acres) and

are rectangular. In the late winter, when the flows are

reduced, about half the basins are taken out of service

and planted to an annual cereal crop, such as oats, 

wheat or barley. During July, after the crop is harvested,

the basins are ripped to a depth of 2-m (6-ft). The basins

are then disked and leveled for the next washwater 

application (Crites, 1987). 

The washwater quality varies with the season. BOD 

values are highest during the crush [up to 4,700 g/m3

(mg/L)] and lowest during the spring [about 300 g/m3

(mg/L)], with an average of 950 g/m3

 (mg/L). The total 

nitrogen concentration averages 33 g/m3

 (mg/L) and the 

BOD to nitrogen ratio averages 28:1. The pH ranges 

from 4.1 to 7.9. The low values of pH occur during the

crush, but do not have an adverse effect on either the 

soil or the groundwater (Crites, 1987). 

Table 11-8. Treatment Performance for Hilmar Cheese Soil Aquifer Treatment System

Constituent Process Water Upgradient Groundwater Downgradient Groundwater 

BOD, g/m3 2,852 2 2 

TKN, g/m3 93 1.1 9.3 

Nitrate-N, g/m3 18 35 0.4 

EC, dS/m 1,688 650 1,100 

TDS, g/m3 2,727 480 600 

FDS, g/m3 1,155 340 540 

Conversion units: g/m3 = mg/L. 

11.7 References 

Adamczyk, A.F. (1977) Land Disposal of Food

Processing Wastewaters in New York State, In: 

Land as a Waste Management Alternative, Loehr, 

R.C. (ed.), Ann Arbor Science Publishers, Ann 

Arbor, MI. 

Beggs, R.A. and R.W. Crites (1990) Odor Management 

for Land Application of Food Processing 

Wastewater, Proceedings of the 6th International

Symposium on Agricultural and Food Processing

Wastes, Chicago, IL. 

Bendixen, T.W., et al. (1969) Cannery Waste Treatment

by Spray Irrigation-Runoff, Journal WPCF, 41: 385. 

Billings, R.M. (1958) Stream Improvement through

Spray Disposal of Sulphite Liquor at the KimberlyClark Corporation, Niagara, Wisconsin, Mill, 

Proceedings of the 13th Industrial Waste 

Conference, Purdue University, 96: 71. 

Blosser, R.O. and E.L. Owens (1964) Irrigation and 

Land Disposal of Pulp Mill Effluents, Water and 

Sewage Works, 111: 424.

Bolton, P. (1947) Disposal of Canning Plant Wastes by 

Irrigation, Proceedings of the Third Industrial Waste 

Conference, Purdue University, Lafayette, IN. 

Breska, G.J., et al. (1957) Objectives and Procedures 

for a Study of Spray Irrigation of Dairy Wastes,

Proceedings of the 12th Industrial Waste 

Conference, Purdue University, 94: 636.

Bruner, D J., S.B. Maloney and H. Hamanishi (1999) 

Expansion of a Spray Irrigated Land Application

System for a Year-Round Potato Processing Facility 

in Idaho, Cascade Earth Science, Pocatello, ID. 

Canham, R.A. (1958) Comminuted Solids Inclusion with 

Spray Irrigated Canning Waste, Sewage & Industrial

Wastes, 30: 1028. 

Coast Laboratories (1947) Grape Stillage Disposal by 

Intermittent Irrigation, Prepared for Wine Institute, 

San Francisco, CA. 

Colovos, G.C. and N. Tinklenberg (1962) Land Disposal

of Pharmaceutical Manufacturing Wastes, Biotech.

Bioengineering. 4: 153. 

Crites, R.W. (1982) Land Treatment and Reuse of Food

Processing Waste, Presented at the 55th Annual 

Conference of the Water Pollution Control

Federation, St. Louis, MO. 

Crites, R.W. (1987) Winery Wastewater Land

Application, Proceedings of a Conference on

Irrigation Systems for the 21st Century, Irrigation

and Drainage Division, American Society of Civil

Engineering, Portland, OR. 

Crites, R.W. (1996) Constructed Wetlands for 

Wastewater Treatment and Reuse, Presented at the 

Engineering Foundation Conference, Environmental 

Engineering in the Food Processing Industry, XXVI, 

Santa Fe, NM. 

Crites, R.W., et al. (1978) Treatment of Brewery Spent 

Grain Liquor by Land Application, Proceedings of

the Third Annual Conference on Treatment and 

Disposal of Industrial Wastewater and Residues,

Houston, TX. 

11-9 
Crites, R.W. and R.C. Fehrmann (1981) Land

Application of Winery Stillage Wastes, Industrial

Wastes, 27: 14. 

Crites, R.W., C.E. Pound, and R.G. Smith (1974) 

Experience with Land Treatment of Food Processing

Wastewater, Proceedings of the Fifth National 

Symposium on Food Processing Wastes, Monterey, 

CA. 

Crites, R.W. and R.G. Stratton (1994) Land Application

of Pineapple Process Water for Reuse, Presented at

the Hawaii WPCA, Honolulu, HI. 

Crites, R.W. and G. Tchobanoglous (1998) Small and

Decentralized Wastewater Management Systems,

McGraw-Hill, New York, NY. 

Crites, R.W., S.C. Reed, and R.K. Bastian (2000) Land

Treatment Systems for Municipal and Industrial

Wastes, McGraw-Hill, New York, NY. 

Flower, W.A. (1969) Spray Irrigation for the Disposal of 

Effluents Containing Deinking Wastes, TAPPI, 52:

1267. 

Gilde, L.C., et al. (1971) A Spray Irrigation System for 

Treatment of Cannery Wastes, Journal WPCF, 43:

2011. 

Guerri, E.A. (1971) Sprayfield Application Handles

Spent Pulping Liquors Efficiently, Pulp & Paper, 45: 

93-95. 

Henry, C.D., et al. (1954) Sewage Effluent Disposal

Through Crop Irrigation, Sewage & Industrial 

Wastes, 26: 123. 

Henry, C.L. and S.A. Wilson (1988) Denitrification

Following Land Application of Potato Processing

Wastewater, Agronomy Abstracts, American Society 

of Agronomy, Madison, WI. 

Hickerson, R.D. and E.K. McMahon (1960) Spray

Irrigation of Wood Distillation Wastes, Journal

WPCF, 32: 55. 

Hunt, P.G., et al. (1995) State of the Art for Animal 

Wastewater Treatment in Constructed Wetlands,

Proceedings of the Seventh International 

Symposium on Agricultural and Food Processing

Wastes, ASAE, Chicago, IL. 

Jewell, W.J. and R.C. Loehr (1975) Land Treatment of 

Food Processing Wastes, Presented at the 

American Society of Agricultural Engineering, Winter

Meeting, Paper No. 75-2513, Chicago, IL. 

Jewell, W.J., et al. (1978) Limitations of Land Treatment 

of Wastes in the Vegetable Processing Industries,

Cornell University, Ithaca, NY. 

Keith, L.W. and W.D. Lehman (1986) Land Treatment of 

Food Processing Wastewater—Case History, 

Utilization, Treatment, and Disposal of Waste on 

Land, Soil Science Society of America, Madison, WI.

King, L.D. (1984) Availability of Nitrogen in Municipal, 

Industrial, and Animal Wastes, Journal of 

Environmental Quality, 13 (4): 609-612.

Kobylinski, E.A., Davey, J.W., and Shamskhorzani, R. 

(1995) Nonbiodegradable Organic Nitrogen is an

Enigma for Regulations, In: Proceedings of the WEF

68th Annual Conference and Exposition, Miami

Beach, FL., No. 3, pp. 501-511. 

Koch, H.C. and D.E. Bloodgood (1959) Experimental

Spray Irrigation of Paperboard Mill Wastes, Sewage 

& Industrial Wastes, 31: 827. 

Lane, L.C. (1955) Disposal of Liquid and Solid Wastes 

by Means of Spray Irrigation in the Canning and 

Dairy Industries, Proceedings of the 10th Industrial 

Waste Conference, Purdue University, 89: 508. 

Law, J.P., R.E. Thomas, and L.H. Myers (1970)

Cannery Wastewater Treatment by High-Rate Spray 

on Grassland, Journal Water Pollution Control

Federation, 42: 1621-1631.

Lawton, G.W., et al. (1959) Spray Irrigation of Dairy 

Wastes, Sewage & Industrial Wastes, 31: 923. 

Lever, N.A. (1966) Disposal of Nitrogenous Liquid

Effluent from Modderfontein Dynamite Factory, 

Proceedings of the 21st Industrial Waste

Conference, Purdue University, 121: 902. 

Loehr, R.C. and M.R. Overcash (1985) Land Treatment 

of Wastes: Concepts and General Design, ASCE; 

Journal of Environmental Engineering, 111 (2): 141-

160. 

Loehr, R.C., et al. (1988) Full-Scale Land Treatment of 

Coffee Processing Wastewater, Journal Water 

Pollution Control Association, 60 (11): 1948-1952. 

Ludwig, H., et al. (1951) Disposal of Citrus Byproducts

Wastes at Ontario, California, Sewage & Industrial

Wastes, 23: 1255-1266. 

Luley, H.G. (1963) Spray Irrigation of Vegetable and

Fruit Processing Wastes, Journal WPCF, 35: 1252. 

McKee, F.J. (1955) Spray Irrigation of Dairy Wastes,

Proceedings of the 10th Industrial Waste 

Conference, Purdue University, 89: 514.

Madison, M and M. Henderson (1993) Zero Discharge

All-Weather Land Application with Soil Storage, 

Proceedings of the 66th Annual Conference of the 

Water Environment Federation, Anaheim, CA. 

11-10
Meighan, A.D. (1958) Experimental Spray Irrigation of 

Strawboard Wastes, Proceedings of the 13th

Industrial Waste Conference, Purdue University, 96:

456. 

Molloy, D.J (1964) 'Instant' Waste Treatment, Water 

Works Wastes Engineering, 1: 68. 

Nolte and Associates (1996) Report of Waste 

Discharge, Hilmar Cheese Company, Sacramento,

CA. 

Overcash, M.R. and D. Pal (1979) Design of Land

Treatment for Industrial Wastes, Theory and

Practice, Ann Arbor Science Publishers, Ann Arbor, 

MI. 

Parker, R.R. (1967) Disposal of Tannery Wastes, 

Proceedings of the 22nd Industrial Waste

Conference, Purdue University, 129: 36.

Parsons, W.C. (1967) Spray Irrigation of Wastes from 

the Manufacture of Hardboard, Proceedings of the

22nd Industrial Waste Conference, Purdue 

University, 129: 602. 

Philipp, A.H. (1971) Disposal of Insulation Board Mill 

Effluent by Land Irrigation, Journal WPCF, 43: 1749. 

Reed, S.C. and R.W. Crites (1984) Handbook on Land

Treatment Systems for Industrial and Municipal 

Wastes, Noyes Data, Park Ridge, NJ. 

Reed, S.C., R.W. Crites and E.J. Middlebrooks (1995) 

Natural Systems for Waste Management and

Treatment, Second Edition, McGraw-Hill, New York, 

NY. 

Schraufnagel, F.H. (1962) Ridge-and-Furrow Irrigation 

for Industrial Waste Disposal, Journal WPCF, 34: 

1117. 

Scott, R.H. (1962) Disposal of High Organic Content 

Wastes on Land, Journal WPCF, 34: 1117. 

Smith, J.H. et al. (1977) Treatment of Potato Processing 

Wastewater on Agricultural Land: Water and Organic 

Loading, and the Fate of Applied Plant Nutrients, In:

Land as a Waste Management Alternative, Loehr, 

R.C. (ed.), Ann Arbor Science Publishers, Ann 

Arbor, MI. 

Struckmeyer, T. (1999) Personal Communication, Vice

President Hilmar Cheese Company, Hilmar, CA. 

Tedaldi, D.J. and R.C. Loehr (1991) Performance of an 

Overland Flow System Treating Food-Processing

Wastewater, Research Journal Water Pollution 

Control Federation, 63, 266. 

Tedaldi, D.J. and R.C. Loehr (1992) Effects of WasteWater Irrigation on Aqueous Geochemistry Near

Paris, Texas, Ground Water, 30 (5): 709-719. 

US EPA (1973) Wastewater Treatment and Reuse by 

Land Application, Volume II, U.S. Environmental 

Protection Agency, EPA-660/2-73-006b, 

Washington, DC. 

Vela, G.R. (1974) Effect of Temperature on Cannery 

Waste Oxidation, Journal Water Pollution Control 

Federation, 46 (1): 198-202. 

Voights, D. (1955) Lagooning and Spray-Disposal of 

Neutral Sulfite Semi-Chemical Pulp Mill Liquors, 

Proceedings of the 10th Industrial Waste 

Conference, Purdue University, 89: 497.

Wallace, A.T. (1976) Land Disposal of Liquid Industrial

Wastes, In: R.L. Sanks and T. Asano, Land 

Treatment and Disposal of Municipal and Industrial

Wastewater, Ann Arbor Science, Ann Arbor, MI. 

Westcot, D.W. and R.S. Ayers (1984) Irrigation Water 

Quality Criteria, In: Asano, T. and G.S. Pettygrove, 

Irrigation with Reclaimed Municipal Wastewater — A

Guidance Manual, California State Water Resources 

Control Board, Report No. 84-1. 

Woodley, R.A. (1968) Spray Irrigation of Organic 

Chemical Wastes, Proceedings of the 23rd Industrial

Waste Conference, Purdue University, 132: 251. 

Wright, J.F. (1993) Land Application of Citrus

Wastewater, Florida Department of Environmental 

Protection, State of Florida.

11-11