FHWA-WFL/TD-09-001 October 2008

Federal Highway Administration

U.S. Department of Transportation

Best Management Practices for

Chemical Treatment 

Systems for 

Construction Stormwater and Dewatering

October 2008

and Dewatering
Technical Report Documentation Page

1. Report No.

 FHWA-WFL/TD-09-001

2. Government Accession No. 3. Recipient’s Catalog No.

4. Title and Subtitle

Best Management Practices for Chemical Treatment Systems for 

Construction Stormwater and Dewatering

5. Report Date

 January 2009

6. Performing Organization Code

7. Author(s)

Richard A. McLaughlin, Ph.D. and Alex Zimmerman, CPESC

8. Performing Organization Report No.

9. Performing Organization Name and Address

 North Carolina State University

 101 Derieux Street, 2232 Williams Hall

 Raleigh, NC 27695

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

12. Sponsoring Agency Name and Address

 Federal Highway Administration

 Western Federal Lands Highway Division

 610 East 5th St.

 Vancouver, WA 98661

13. Type of Report and Period Covered

Final Report 2009

14. Sponsoring Agency Code

 HFL-17

15. Supplementary Notes

 COTR: Amit Armstrong, Ph.D., P.E.

This project was funded under the FHWA Federal Lands Highway Technology Deployment Initiatives and Partnership 

Program (TDIPP) and Coordinated Technology Implementation Program (CTIP).

16. Abstract

Chemical treatment systems (CTS) are implemented in areas where traditional, physical erosion and sediment control 

practices will not meet water quality goals for construction site runoff. The purpose of CTS is to reduce the amount of 

suspended sediment which would be released using conventional erosion control systems. The primary mechanism is the 

introduction of chemical fl occulants into runoff, resulting in a binding of the suspended clays and silts together into larger 

particles which settle more quickly or can be fi ltered from the stormwater. Flow control through CTS is of vital importance 

for the proper dosing of stormwater runoff. All normal hydrologic analyses must be done to insure that reasonable peak 

fl ows are accounted for along with typical fl ows from designed storm events. Once analysis is adequately addressed, then the 

project can deal with the complexities of design and dose rate requirements.

The overall objectives of this book are twofold. First, it is designed to provide a technically credible basis for best 

management practices for the use of CTS for turbidity reduction on road construction projects. Secondly, it is designed to 

identify the most important variables to address when selecting chemical treatment best management practices for a particular 

site.

17. Key Words

BEST MANAGEMENT PRACTICES, CHEMICAL 

TREATMENT SYSTEMS, STORMWATER, 

DEWATERING, WATER QUALITY, TURBIDITY

18. Distribution Statement

 No restriction. This document is available to the 

 public from the sponsoring agency at the website 

 http://www.wfl .fhwa.dot.gov/td/.

19. Security Classif. (of this report)

Unclassifi ed

20. Security Classif. (of this page)

Unclassifi ed

21. No. of Pages

12

22. Price

$0.00

 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
Best Management Practices for

Chemical Treatment Systems for

Construction Stormwater and Dewatering

Report Number: FHWA-WFL/TD-09-001

Technology Deployment Program

Western Federal Lands Highway Division

Federal Highway Administration

610 East 5th St.

Vancouver, WA 98661

Technology Deployment Report
SI* (MODERN METRIC) CONVERSION FACTORS

APPROXIMATE CONVERSIONS TO SI UNITS

Symbol When You Know Multiply By To Find Symbol 

LENGTH

in inches 25.4 millimeters mm 

ft feet 0.305 meters m 

yd yards 0.914 meters m 

mi miles 1.61 kilometers km

AREA

in2 square inches 645.2 square millimeters mm2 

ft2 square feet 0.093 square meters m2

yd2 square yard 0.836 square meters m2 

ac acres 0.405 hectares ha 

mi2 square miles 2.59 square kilometers km2

VOLUME

fl oz fl uid ounces 29.57 milliliters mL 

gal gallons 3.785 liters L 

ft3 cubic feet 0.028 cubic meters m3

yd3 cubic yards 0.765 cubic meters m3

NOTE: volumes greater than 1000 L shall be shown in m3

MASS

oz ounces 28.35 grams g 

lb pounds 0.454 kilograms kg 

T short tons (2000 lb) 0.907 megagrams (or “metric ton”) Mg (or “t”)

TEMPERATURE (exact degrees)

°F Fahrenheit 5 (F-32)/9 Celsius °C

or (F-32)/1.8

ILLUMINATION 

fc foot-candles 10.76 lux lx 

fl foot-Lamberts 3.426 candela/m2 cd/m2

FORCE and PRESSURE or STRESS 

lbf poundforce 4.45 newtons N 

lbf/in2 poundforce per square inch 6.89 kilopascals kPa

APPROXIMATE CONVERSIONS FROM SI UNITS

Symbol When You Know Multiply By To Find Symbol

LENGTH

mm millimeters 0.039 inches in 

m meters 3.28 feet ft 

m meters 1.09 yards yd 

km kilometers 0.621 miles mi 

AREA mm2

 square millimeters 0.0016 square inches in2

m2 square meters 10.764 square feet ft2

m2 square meters 1.195 square yards yd2

ha hectares 2.47 acres ac 

km2

 square kilometers 0.386 square miles mi2 

VOLUME

mL milliliters 0.034 fl uid ounces fl oz 

L liters 0.264 gallons gal 

m3 cubic meters 35.314 cubic feet ft3

m3 cubic meters 1.307 cubic yards yd3

MASS

g grams 0.035 ounces oz 

kg kilograms 2.202 pounds lb 

Mg (or “t”) megagrams (or “metric ton”) 1.103 short tons (2000 lb) T 

TEMPERATURE (exact degrees)

°C Celsius 1.8C+32 Fahrenheit °F

ILLUMINATION

lx lux 0.0929 foot-candles fc 

cd/m2 candela/m2 0.2919 foot-Lamberts fl 

FORCE and PRESSURE or STRESS

N newtons 0.225 poundforce lbf 

kPa kilopascals 0.145 poundforce per square inch lbf/in2

*SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. 

(Revised March 2003)
5

List of Acronyms

BMPs Best management practices

CTS Chemical treatment systems 

DADMAC Diallyldimethyl ammonium chloride

EPA Environmental Protection Agency 

ESC Erosion and sediment control 

NPDES National Pollutant Discharge Elimination System 

NTU Nephelometric Turbidity Unit

PAM Polyacrylamide

SWPPP Stormwater Pollution Prevention Plan 

TSS Total Suspended Solids
6

Table of Contents

Section 1 Introduction .................................................................................................... 7

Section 2 Rationale for Choosing Chemical Treatment Systems (CTS) ........................... 7

Section 3 Design for CTS ................................................................................................ 8

Approvals ..........................................................................................................................8

Criteria for Chemical Treatment Product Use ......................................................................8

Treatment System Design Elements .....................................................................................8

Sizing Criteria ..................................................................................................................9

Location of CTS ..............................................................................................................11

Section 4 Stormwater Treatment (Use of CTS) .............................................................. 11

Inspection and Maintenance .............................................................................................11

Discharge Compliance .....................................................................................................11

Operator Training ...........................................................................................................11

Standard BMPs ..............................................................................................................12

Section 5 Maintenance And Decommissioning ............................................................ 12

Sediment Removal and Disposal ......................................................................................12

Adjustment of Settling and Retention Ponds ......................................................................12

Remove All Equipment and Chemicals from the Site and Store in a Safe Manner ................12

Section 6 Monitoring Report of Chemical Treatment Systems ...................................... 12

References ..................................................................................................................... 13

Appendix A: List of Chemicals Typically Used for Treating Turbidity ........................... 14

Polymers ..........................................................................................................................14

Other Additives ...............................................................................................................14

Appendix B: Examples of Chemical Treatment Systems and Costs ............................... 15

Estimating Total Monthly System Costs Based on Th ree Reasonable Scenarios .......................18

Scenario One .......................................................................................................................18

Scenario Two .......................................................................................................................20

Scenario Th ree .....................................................................................................................20
7

Section 1 Introduction

Chemical treatment systems (CTS) are implemented in areas where traditional, physical erosion and sediment 

control practices will not meet water quality goals for construction site runoff . Th ey are not intended to replace 

traditional erosion and sediment control (ESC) practices, which are the most important and cost-eff ective 

approaches to reducing sediment loads in stormwater discharge. 

Th e purpose of CTS is to reduce the amount of suspended sediment which would be released using 

conventional erosion control systems. Th is sediment consists of clays and fi ne silts which are very slow to settle even 

under ideal conditions in settling basins. Th e primary mechanism is the introduction of chemical fl occulants into 

runoff , resulting in a binding of the suspended clays and silts together into larger particles which settle more quickly 

or can be fi ltered from the stormwater. 

Flow control through CTS is of vital importance for the proper dosing of stormwater runoff . All normal 

hydrologic analyses must be done to insure that reasonable peak fl ows are accounted for along with typical fl ows 

from designed storm events. Once analysis is adequately addressed, then the project can deal with the complexities 

of design and dose rate requirements.

Proper dosing, mixing, and settling time are needed for CTS to be eff ective. Also, matching the right fl occulant 

to a specifi c sediment and water chemistry is important. In addition, disposal and fi nal stabilization of the 

fl occulated materials must be planned for in advance and monitored during system operation.

Th ese best management practices (BMPs) focus on the design and use of active CTS, and do not directly 

address the use of passive systems. Active systems involve treating pumped stormwater using chemicals that are 

metered into the fl ow at a known dose rate. Passive systems use the fl ow of stormwater to dissolve the fl occulant 

from a solid form (blocks, granules, socks, etc.) prior to a mixing and settling system. While the use of passive 

systems is not generally discouraged, this document is focused on active systems only.

Section 2 Rationale for Choosing Chemical Treatment Systems (CTS)

Sedimentation ponds are commonly used to treat construction site runoff prior to discharge, but they are only 

eff ective at removing larger particles by gravity settling. Smaller particles, such as clay and fi ne silt, tend to remain in 

suspension for a longer duration than typical design retention times for sedimentation ponds. Chemical treatment 

can reliably provide exceptional reductions of turbidity and associated pollutants and should be considered where 

turbid discharges to sensitive waters cannot be prevented using other traditional BMPs.

Chemical treatment involves the application of chemicals to stormwater to aid in the reduction of turbidity 

caused by fi ne suspended sediment. Th e technology is used to treat stormwater from temporary construction sites, 

as opposed to permanent stormwater treatment facilities.

Typically, chemical treatment (fl occulant) is limited to waters with turbidity limits or other water quality 

standards. However, at times, there may be no regulatory reason to deal with turbid water, but there may be 

aesthetic, social, or political reasons to reduce sediment discharge and resulting turbidity in receiving waters.

Th e following are situations where CTS may be needed:

1. Sediment Retention Pond — Chemical treatment is an enhancement option when a pond of a required 

size or design cannot be constructed or is otherwise not suffi cient to control turbidity. Th is may occur 

because of topographical constraints, diffi cult foundation conditions, or the presence of natural habitats 

of ecological value.

2. Physical Characteristics of Sediment Retention Pond — In some situations a pond of a required volume 

can be accommodated but the design of the pond cannot be optimized in terms of shape, depth, location 

of inlet and outlet, or energy attenuation of the infl ow. 

3. Soil Type — Most soils contain suffi cient clay and silt to produce substantial turbidity in runoff . 

However, some soil types produce suspended sediment in stormwater runoff which is particularly 

diffi cult to settle in typical sediment retention ponds due to particle size and charge. 
8

4. Sediment Generation Potential of Earthwork Area — In areas with highly erodible soils or steep long 

slopes, there is a high risk of increased erosion and sediment runoff from rainstorm events. 

5. Use of the Earthwork Site & Construction Schedule — Some common uses of earthwork sites, 

particularly repeated machinery movements (e.g., on haul roads) can result in high sediment loadings in 

stormwater. Large areas of disturbance which cannot be stabilized with ground covers due to operational 

constraints will likely generate signifi cant turbidity in stormwater runoff . 

6. Performance of the Sediment Retention Pond — If a sediment retention pond does not perform 

adequately, addition of chemical fl occulants may improve performance. 

7. Construction Dewatering — Dewatering activities from construction sites, such as pumping 

accumulated water from excavation areas, can produce highly turbid discharge water, as distinguished 

from stormwater.

Section 3 Design for CTS

Approvals

1. Th e use of chemical treatment must have the advanced, written approval of the appropriate permitting 

authority in your particular state. For Federally authorized projects, this will be the Environmental 

Protection Agency (EPA) or an EPA designated agency.

2. Th e intention to use chemical treatment shall be indicated on the notice of intent for coverage under the 

construction general permit. Chemical treatment systems should be designed as part of the construction 

Stormwater Pollution Prevention Plan (SWPPP) or non-National Pollutant Discharge Elimination 

System (NPDES) equivalent, not after the fact. 

3. Chemical treatment may be used to correct problem sites (i.e., CTS were not originally planned). Th e 

contractor must submit a plan to use CTS and receive formal written approval from the appropriate 

permitting authority prior to use. 

Criteria for Chemical Treatment Product Use

Chemically treated stormwater discharged from construction sites must be non-toxic to aquatic organisms. Th e 

following protocol should be used to evaluate chemicals proposed for stormwater treatment at construction sites. 

Authorization to use a chemical in the fi eld based on this protocol does not relieve the applicant from responsibility 

for meeting all discharge standards and receiving water quality criteria.

1. Treatment chemicals must be approved for use by the local or state permitting authority. Petroleumbased emulsions or carriers are prohibited.

2. Treatment chemicals must have already passed aquatic toxicity testing protocols, and so do not need to 

be reevaluated. Contact the appropriate permitting authority for a list of treatment chemicals that have 

been, or may be approved for use.

3. Prior to authorization for fi eld use, jar tests shall be conducted in order to demonstrate that turbidity 

reduction necessary to meet the receiving water quality criteria can be achieved. Test conditions, 

particularly the dosage, should be indicative of fi eld conditions. Although these small-scale tests cannot 

be expected to reproduce actual performance under all fi eld conditions, they are indicative of treatment 

capability and indicative of various chemical dose rates required for eff ective treatment.

Treatment System Design Elements

Good erosion and sediment control practices should always be part of the overall stormwater management 

plan and treatment system design in order to minimize erosion and sediment loading. Th e design and operation 
9

of a chemical treatment system should take into consideration the factors that determine optimum, cost-eff ective 

performance. It is important to recognize the following:

1. Th e right chemical must be used at the right dosage. Th ere is an optimum dosage rate for every 

combination of sediment and chemical. Dosing at lower or higher rates will result in reduced 

performance of the system. Th is is a situation where the adage “adding more is always better” is not 

the case. As stated previously, it is important to match a specifi c chemical to specifi c soil types. When 

mixing a dry concentrated fl occulant solution for metering into the pumped stormwater during 

treatment, be sure to add the fl occulant granules or powder slowly, providing equal and uniform wetting

to an agitated or circulating tank of water. Adding the powder too quickly may produce gelatinous 

masses or “fi sh eyes” that will not dissolve. Flocculants may be provided as a concentrated solution or an 

emulsion, negating this concern. Various chemicals require diff erent mixing times resulting in various 

fl oc sizes and settling rates, so it is important to follow the manufacturer’s recommendations regarding 

handling, mixing, storage and dispersion of all chemicals. 

2. A pH-adjusting chemical may be needed in the CTS to bring the pH into the chemical fl occulant 

manufacturer’s recommended operating range. Th e pH adjusting chemical or gas must be mixed thoroughly 

into the stormwater to insure proper dispersion and contact. Th is can be achieved in various ways after the 

chemical is introduced to the fl ow of the turbid water, including metering the chemical into the pump 

intake or routing the treated fl ow through corrugated pipe, static mixers, and/or tanks with baffl es.

3. Th ere must be a post-treatment settling or fi ltration system to remove the fl occulated sediment. 

Chemically treated stormwater should never be directly discharged from the construction site. Settling 

basins designed to allow suffi cient settling time are commonly used, preferably with surface discharge 

and porous baffl es. Where space is limited, mechanical sand fi lters can remove the fl ocs and pump 

the sediment backwash sludge to isolated contained storage areas for decanting and fi nal stabilization 

or disposal. Th e treated stormwater can be pumped into geotextile sediment bags. Th ese will usually 

remove the fl ocs, but in doing so they will often clog relatively quickly and may need to be replaced 

frequently. Th is must be considered when determining the costs and the maintenance requirements of 

the CTS. 

4. Th e settling basin will require periodic maintenance, so access should be readily available to clean 

accumulated sediment. Where baffl es are used, most of the accumulation will occur in the inlet area 

of the basin and this can be the main access point. Mechanical sand fi lter backwash should be isolated 

from stormwater and must be prevented from discharging into surface waters.

Sizing Criteria

Th e combination of the sediment basin or other stormwater detention area and treatment capacity should be 

large enough to treat stormwater during multiple day storm events. Local permitting authorities may have fl ow 

control requirements regulating the volume of discharge during storm events and establishing sediment basin size, 

volume, and drawdown design criteria. Bypass should be provided around the chemical treatment system – into 

a settling pond – to accommodate extreme storm events. Primary settling should be encouraged in the sediment 

basin/storage pond. A forebay with access may be benefi cial for maintenance and operational function. 

Th ere are two opposing considerations in sizing batch treatment cells. A larger cell is able to treat a larger 

volume of water each time a batch is processed. However, the larger the cell the longer the time required to empty 

the cell. A larger cell may also be less eff ective at fl occulation, therefore requiring a longer settling time. 

Th e simplest approach to sizing the treatment cell is to multiply the allowable discharge fl ow rate by the desired 

drawdown time. A 4-hour drawdown time allows one batch per cell per 8-hour work period, given 1 hour each 

for operations and for fl occulation followed by 2 hours of settling. Th e permissible discharge rate governed by 

potential downstream eff ects can be used to calculate the recommended size of the treatment cells. Flow through 

and mechanical treatment systems are limited by pump and fi lter size as well as backwash duration. When sizing a 

mechanical system, fi lter maintenance and backwash duration must be considered to properly size the operational 
10

volume of the CTS. Th e following discharge fl ow rate limits apply, absent any local requirements:

1. If the discharge is direct or indirect to a stream, the discharge fl ow rate should not exceed 50 percent of 

the peak fl ow rate for all events between the 2-year and the 10-year, 24-hour event. 

2. If discharge is occurring during a storm event equal to or greater than the 10-year storm, the allowable 

discharge rate is the peak fl ow rate of the 10-year, 24-hour event.

3. Discharge to a stream should not increase the stream fl ow rate by more than 10 percent.

4. If the discharge is directly to a lake or major receiving water, or to an infi ltration system, there is no 

discharge fl ow limit.

5. If the discharge is to a municipal storm drainage system, the allowable discharge rate may be limited 

by the capacity of the public system. It may be necessary to clean the municipal storm drainage system 

prior to the start of the discharge to prevent scouring solids from the drainage system.

6. Runoff rates may be calculated using the Rational Method, unless another method is required by the 

local fl ood control agency, NPDES permitting authority, or agency that issued the grading permit.

Costs

Th e costs of a system and its operation will be highly variable depending on a wide range of factors. Some of 

these are listed below:

• Volume and pumping rate of water being treated.

• Turbidity levels of the source water and reduction in turbidity needed.

• Types of systems allowed by the permitting authority.

• Water chemistry, especially pH.

To provide some estimates of potential costs for a CTS, a detailed analysis of three diff erent pumping rates is 

provided in Appendix B. Th is was done for a system that involved a fl occulant (chitosan) and sand fi ltration. As 

the pumping rate increases, the cost per gallon drops considerably. At a little less than a million gallons per month, 

the cost is $0.021 per gallon. Th is drops to $0.009 per gallon as the rate approaches 5 million gallons per month. 

A system of this type is likely the most expensive due to its complexity and the cost of the chitosan. Substituting 

another chemical additive or polymer, such as polyacrylamide (PAM), in the same system may reduce costs, 

assuming they have similar performance. Again, remember that the right chemical at the right dosage must be used. 

Soil analysis with jar testing along with regulatory guidance will determine the correct polymer/additive that will 

meet the necessary requirements.

An alternative system involves only a settling basin after the chemical is introduced to the pumped water. Th is 

system is much simpler and has been shown to work well in many circumstances. Th e fl occulant is pumped directly 

into the intake of the water pump and metered in at a rate to achieve the desired concentration. Th e water pump 

and hoses provide initial mixing and contact before discharge into the settling basin. By eliminating the sand 

fi ltration and controller modules and switching to a lower cost polymer/additive, the treatment cost per gallon is 

reduced by about 40%. Th is assumes there is room for a settling basin and does not include the basin construction 

cost. If the turbid water is in a holding pond, the treated water could be returned to the pond until the turbidity 

was reduced to the desired level, then released. 

For small quantities of water, a variation on the above system is to pump the water into a geotextile bag 

(sediment bag). Again, the fl occulant would be introduced into the pump intake. Th e resulting fl ocs have been 

found to stay inside typical sediment bags. However, the bags tend to clog, and the project budget would have to 

take into account the use and disposal of these. It is not possible to estimate accurately how many bags would be 

used because it depends on the amount of pumping and the turbidity of the pumped water. Nevertheless, many 

more bags would be used if there was no chemical treatment of the pumped water.
11

Location of CTS

In most cases, the sediment basin collecting stormwater will be at the lowest point on the project. CTS should 

be placed adjacent to the basin to allow convenient pumping. Usually they are placed close to the site perimeter 

to keep out of the way of construction activities. An access road that is reasonably all-weather needs to be installed 

to provide access to the system due to the need for frequent maintenance of these systems. Th e discharge from the 

CTS needs to be stabilized so that no erosion or scour occurs at the discharge point. A generalized layout is shown 

in Appendix B.

Section 4 Stormwater Treatment (Use of CTS)

Inspection and Maintenance

Chemical treatment systems must be operated and maintained by individuals with expertise in their use. 

Chemical treatment systems should be monitored continuously while in use. Test results must be recorded in a daily 

log kept on site, and all records turned over to the contracting agency at completion of CTS operation and upon 

request of the local permitting authority. Th e following monitoring should be conducted:

1. Monitoring — Minimal operational daily logs will include the following:

a. pH conductivity (as a surrogate for alkalinity), turbidity, and temperature of the untreated 

stormwater. 

b. Rainfall (start of treatment shift).

c. Total volume treated and discharged (for active CTS, not feasible for passive systems).

d. Discharge time duration and fl ow rate. 

e. Type and amount of chemical used for pH adjustment.

f. Amount of polymer used for treatment.

g. Settling time (applies to batch treatments).

2. Compliance Monitoring — Th e following should be recorded:

a. pH and turbidity of the treated stormwater. 

b. pH and turbidity of the receiving water. 

Discharge Compliance

Treated stormwater must be sampled and tested for compliance with pH and turbidity limits. Th e sampling 

frequency may be established by the water quality standards or a site-specifi c discharge permit. Sampling and testing 

for other pollutants may also be necessary at some sites. Generally, the following apply:

1. Turbidity must be no more than 5 NTUs (Nephelometric Turbidity Unit), a nationwide multi-sector 

standard, above background turbidity. Background is measured in the receiving water, upstream from the 

treatment process discharge point. 

2. pH must be within applicable water quality standards and not cause a change in the pH of the receiving 

water of more than 0.2 standard units. It is often possible to discharge treated stormwater that has 

a lower turbidity than the receiving water and that matches the pH. Treated stormwater samples 

and measurements should be taken from the discharge pipe or another location representative of the 

nature of the treated stormwater discharge. Samples used for determining compliance with the water 

quality standards in the receiving water should not be taken from the treatment pond for decanting. 

Compliance with the water quality standards is determined in the receiving water. 

Operator Training
12

Each contractor who intends to use chemical treatment should be trained by an experienced system operator. 

Standard BMPs 

Erosion and sediment control BMPs should be implemented throughout the site to prevent erosion and 

discharge of sediment. 

Section 5 Maintenance And Decommissioning 

Sediment Removal and Disposal 

1. Sediment should be removed from the storage or treatment cells as necessary. Typically for systems using 

fl occulants, sediment removal is required at least once during a wet season and at the decommissioning 

of the cells. Also, when a sediment collection area has reached 1/3 capacity, the sediment should be 

removed and taken to a location where it can be stabilized (vegetated) or buried to prevent off -site 

transport. If sediment removal is not necessary during the life of the project, the sediment ponds can 

simply be fi lled in at decommissioning.

2. Sediment remaining in the cells between batches may enhance the settling process and could reduce the required 

chemical dosage in the primary system.

3. When decommissioning, sediment must be stabilized away from drainages, which can include being 

incorporated into the roadway or being stabilized in-place. 

Adjustment of Settling and Retention Ponds

If stormwater detention ponds have been modifi ed for use as sediment treatment ponds, then they must be 

restored to fl ow control mode as originally designed (e.g., baffl es be removed, designed volume restored etc.).

Remove All Equipment and Chemicals from the Site and Store in a Safe Manner

All equipment and chemicals that were used on the site must be removed and stored in a designated and safe 

place.

Section 6 Monitoring Report of Chemical Treatment Systems

Th e use of CTS typically involves relatively high expenditures in areas of higher than average sensitivity. 

Because CTS are a relatively new technology for the construction industry, it is important to provide consistent 

reporting on these systems in order to properly evaluate them. Th e following are elements which must be included 

in the monitoring reports for all CTS. 

• Rainfall: amounts and time.

• Amounts and types of chemical used (range of dosing rates & total amounts used).

• Volume treated.

• Volumes of fl ow in and out of CTS.

• Infl uent/effl uent: pH, turbidity.

• Water quality of receiving waters: name, type, temperature, turbidity, pH.

• Schematic diagram and dimensions of treatment system used.

• Maintenance performed.

• Compliance data: thresholds both met and exceeded.
13

References

Auckland Regional Council (2004). DRAFT: Th e Use of Flocculants and Coagulants to Aid Suspended Sediment 

Settlement in Earthworks Runoff - Trials, Methodology and Design, Technical Publication No. 227, DRAFT June 

2004, ISSN 1175-205X, ISBN 1-877353-31-0, http://www.arc.govt.nz/library/l35022_2.pdf

California Regional Water Quality Control Board – Central Valley Region (2005). Monitoring Requirements 

for Storm Water Treatment Systems that Utilize Chemical Additives to Enhance Sedimentation, Letter to 

Project Owners/Developers, 3 p. http://www.waterboards.ca.gov/centralvalley/HomePageAttachments/

AdvTrtmnt2005.pdf

Caltrans (2003). BMP SE-11, in: Stormwater Quality Handbooks - Construction Site Best Management Practices 

(BMPs) Manual, State of California Department of Transportation (Caltrans), January 2003. http://www.dot.

ca.gov/hq/construc/stormwater/CSBMPM_303_Final.pdf

Caltrans (2004). BMP NS-02, Dewatering Operations, State of California Department of Transportation (Caltrans), 

Updated March 2004. http://www.dot.ca.gov/hq/construc/stormwater/NS02Update.pdf

City of Redmond (2005). Summary Report: Field Experience with Alternative Construction Stormwater Treatment 

Technologies, HDR/EES, February, 2005. 

Oregon Department of Environmental Quality (2004). BMP#34 – Flocculants & Coagulants, In: Best Management 

Practices for Stormwater Discharges Associated with Construction Activities, Oregon DEQ Northwest Region 

Document, August, 2004. http://www.oregondeq.com/nwr/WQConstructionBMPs.pdf

Washington State Department of Ecology (2005). BMP C250: Construction Stormwater Chemical Treatment, 

in: Stormwater Management Manual for Western Washington, Volume II – Construction Stormwater Pollution 

Prevention, Washington State Department of Ecology, February 2005. http://www.ecy.wa.gov/pubs/0510030.pdf

McLaughlin, R. A. (2006). SoilFacts: Using Baffl es to Improve Sediment Basins. N.C. State University Extension 

SoilFacts Publication AGW-439-59. http://www.soil.ncsu.edu/publications/Soilfacts/AGW-439-59/

AGW_439_59.pdf

McLaughlin, R. A. (2007). SoilFacts: Chemical Treatment to Control Turbidity on Construction Sites. N. C. State 

University Extension SoilFacts Publication AGW-439-62. http://www.soil.ncsu.edu/publications/Soilfacts/ 

AG-439-62/AG-439-62_lo_res.pdf

North Carolina Department of the Environment and Natural Resources (2006). Erosion and Sediment 

Control Planning and Design Manual. Section 6.84: Flocculants. http://www.dlr.enr.state.nc.us/pages/ 

manualsandvideos.html

Sojka, R. E., D. L. Bjorneberg, J. A. Entry, R. D. Lentz and W. J. Orts (2007). Polyacrylamide in Agriculture and 

Environmental Land Management. Adv. Agron. 92: 75-162. 
14

Appendix A: List of Chemicals Typically Used for Treating Turbidity

Th ere are many chemicals which are used to reduce suspended sediment in water. Each has its own benefi ts, 

costs, and risks for a particular application. In most cases, simple “shake” or batch tests are conducted to determine 

which chemical or combination of chemicals is most eff ective. Using any of these in CTS may be subject to local, 

state, or federal requirements for maximum use rates, aquatic toxicity data, or effl uent toxicity testing. Th ese 

requirements should be identifi ed prior to selecting which fl occulant to use on the site. Th e following are chemicals 

which have been used or tested in CTS for stormwater or similar environmental applications. Th e list is not 

intended to be exhaustive but to provide examples of the most common options in CTS. Th e list is separated into 

two sections: one for polymers and one for other additives.

Polymers

Chitosan — A cationic polymer made from chitin, which is derived from crab, shrimp, and other crustacean 

shells, can be used in CTS. Although a cationic polymer such as chitosan can be toxic to fi sh (as the gills of a fi sh 

have a negative charge), free polymer is unlikely to be released through a CTS described herein because it binds 

quickly to the suspended sediment in the untreated runoff . Even if free chitosan were released to surface water, it 

would immediately bind to any sediment in the surface water further decreasing the likelihood of adversely aff ecting 

aquatic life. In the state of Washington, where chitosan has been used widely on all types of construction projects 

since 2000, including DOT projects, there have been no incidences of harm to the environment.

Polyacrylamide (PAM) — A synthetic polymer, PAM is used to describe a wide variety of chemicals based on 

the acrylamide unit. When linked in long chains, some portion of the acrylamide units can be modifi ed to result 

in a net positive, neutral, or negative charge on the PAM molecule. Th e positively charged, or cationic, PAMs are 

often not used for turbidity control because they can be toxic to fi sh and other aquatic organisms if they enter water 

bodies in suffi cient concentrations. As is the case with chitosan, this eff ect has been shown to be greatly reduced 

in turbid water. Th e negatively charged, or anionic, PAMs are much less toxic to aquatic organisms and are widely 

used for erosion control in furrow irrigation agriculture. PAMs are also used in erosion control products. Th e 

reader should assume that all references to “PAM” in this document are to the anionic forms. In addition, only 

food-grade PAM is used because it contains very low (<0.05%) amounts of free acrylamide, which can be toxic but 

only at much higher concentrations.

Other Additives

DADMAC — Diallyldimethyl ammonium chloride is a cationic monomer which can bind the negatively 

charged sediment particles into fl ocs which can settle. Th is chemical can be polymerized into long-chain molecules 

commonly referred to as “poly-DADMAC.” DADMAC exhibits a strong aquatic toxicity and its use should be 

carefully considered against other eff ective options that are signifi cantly less toxic.

Gypsum — A naturally occurring mineral, gypsum is deposited widely around the earth. It is made up of 

calcium sulfate and water in the formula Ca(SO4)•2(H2O).

Alum — An aluminum sulfate material (Al2(SO4)3•16H2O), alum can be used for water clarifi cation. It is 

often more effi cient than gypsum but can acidify treated water if overdosed. It is widely used in the water treatment 

industry.

Aluminum and Iron Chlorides — Al and Fe cations bridge negatively charged sediment particles, causing them 

to coagulate and settle.
15

Appendix B: Examples of Chemical Treatment Systems and Costs

240,000 gpd Chitosan-Enhanced Sand Filter System Costs (Winter 2007)

Sand fi lter (48" diameter, 4-pod system auto backwash 400 gpm output) $3,500/Mo.

Sand (#30 grade crushed silica + under rock) $2,500/once only

Mobilization cost $500/once only

Demobilization cost $500/once only

Chitosan $9.00/10,000 gallons treated at 1 ppm

Chitosan $27.00/10,000 gallons treated at 3 ppm1

20,000-gal pretreatment tank $1,500/Mo.

Mobilization cost $500/once only

Demobilization cost $500/once only

Pumps (15 HP pond and 35 HP fi lter electric submersible with fl oat level 

controllers)

$4,200/ Mo. (combined cost)

Secondary metering pump for pretreatment $1,000/once only

Controller module (brain box) $3,500/ Mo.

Mobilization/demobilization $500/once only

100 KVA generator (diesel powered) $3,000/Mo.

System assembly (40 hours) Varies with site location and complexity 

(estimated $10,000/once only) System disassembly (20 hours)

System operator $85/hr ?

System performance data monitoring and reporting costs2

 (20 hrs/Mo. @ $75) $1,500

1. Absolute worst case ultra-high infl uent turbidity (>3,000 NTU).

2. Data management, validation, and production of the monthly discharge monitoring report to ecology.
16

Once Only Costs – Does Not Include Physical Site Preparation

Sand Filter

Mobilization cost and sand fi lling $1,000/once only

Demobilization cost $500/once only

Pretreatment Tank

Mobilization cost $500/once only

Demobilization cost $500/once only

Secondary metering pump for pretreatment $1,500/once only

Controller Module (Brain Box)

Mobilization/demobilization $500/once only

System assembly (40 hours) Varies with site location and complexity 

(estimated $10,000/once only) System disassembly (20 hours)

 $14,500

Hard Recurring Monthly Costs

Sand fi lter (48" diameter, 4-pod system auto backwash 400 gpm output) $3,500/Mo.

20,000-gal pretreatment tank $1,500/Mo.

Pumps (15 HP pond and 35 HP fi lter electric submersible with fl oat level controllers) $4,300/ Mo. (combined cost)

100 KVA generator (diesel powered) $3,000/Mo.

Controller module (brain box) $3,500/ Mo.

System performance data monitoring and reporting costs3

 (20 hrs/Mo. @ $75) $1,500

$17,300

Variable Monthly Costs

System operator $85/hr ?

Diesel cost @ $3.00 per gal with an average consumption of 6 gph ?

Chitosan (normal dose rate @ $9.00/10,000 gallons treated at 1 ppm) ?

Chitosan (high dose rate @ $27.00/10,000 gallons treated at 3 ppm4

) ?

3. Data management, validation, and production of the monthly discharge monitoring report to ecology. 

4. Absolute worst case ultra-high infl uent turbidity (3,000 to 10,000 NTU).
17

Pretreatment Using a Mobile Tank and the Additional Pump Adds Considerable Cost to the Treatment System.

If a Detention Basin Exists Onsite, It May Be Used for Pretreatment; Th us Saving the Cost of the Pretreatment Tank and the Extra Pump.

 Backwash Discharge Flow Control Valve

Front Pressure Gauge Sand Filter Input Flow Control Valve

Chemical 

Pump Chemical 

Tote

Chemical Pretreatment Transfer Pipe

Auto Backwash Sand Filter

Sand Filter Output Flowmeter/Totalizer

Submersible Electric Pump

Settling Tank

Recycle Line

Backwash 

Detention Cell

Dirty Water from 

Construction Site

Clean Water to Discharge

Chemical Treatment System Schematic 

Using Mobile Tank for Pretreatment

Back Pressure Gauge

Stormwater Detention/Pretreatment Basin

Pump

Construction Site Stormwater Conveyed to 

Detention Basin

Chemical Storage/Metered Pumping 

Chemical

Backwash Water

Treated Stormwater Discharged to 

Receiving Water Chemical Treatment System 

Sand Filter System Chemical Treatment System 

Schematic Using a Detention 

Basin for Pretreatment
18

Estimating Total Monthly System Costs Based on Th ree Reasonable Scenarios

Th e cost to treat sediment-contaminated stormwater or dewatering water is directly related to the quantity of 

water treated. It is easy to see that if there was no precipitation or dewatering requiring treatment the total cost 

of this system would simply be $17,300 per month. Th ere would be no labor or fuel costs and minimal reporting 

costs. But since this is not a practical expectation, three hypothetical use levels and calculated costs based on these 

assumptions are presented. Assume that on average the chitosan dose rate is 2 mg/L (1 mg/L for pretreatment and 1 

mg/L for sand fi ltration). Th e use levels are:

• Light use defi ned as operating the system for 4 hours per day, 10 days out of the month (totaling 

960,000 gallons treated per month).

• Moderate use defi ned as operating the system 6 hours per day, 15 days out of the month (totaling 

2,160,000 gallons treated per month).

• Heavy use defi ned as operating the system 10 hours per day, 20 days out of the month (totaling 

4,800,000 gallons treated per month).5

Scenario One

Light use defi ned as operating the system for 4 hours per day, 10 days out of the month (totaling 960,000 gallons treated per month).

Variable Cost Element Duration Cost

Operating labor @ $85/hr Reasonably expect 50 hours $4,250

Fuel consumption (diesel) 40 hours @ 6 gph $720

Chitosan consumption 2 mg/L based on previous assumption $1,760

System performance data monitoring and reporting 10 hrs/Mo. @ $75 $750

Senior operator project oversight Assume 2 site visits (1 hour each) @ $120/hr $240

Meeting with regulatory personnel 2 hours @ $120/hr $240

Total Variable Costs $7,960

Hard Cost Elements $17,300

Total Hard & Variable Costs $25,260

Considering the total cost of $25,260 divided by the total amount of water treated (960,000 gallons), the cost per 

gallon of water treated is $0.026 or $260 per 10,000 gallons of water treated to meet state discharge standards.

5. Heavy use is most often associated with continuous dewatering activities, dredging, and unusually heavy or prolonged precipitation events.
19

Example of Sand Filter System with Chemical Enhancement and Batch Tanks for Settling.

Example Schematic for Dosing Flocculants at the Dewatering Pump Intake.

Example of a Simple Chemical Treatment 

System Using a Stilling Basin

Single-Wall, 

Corrugated

Pipe on

Slope

Stable Inlet (Rock and Geotextile)

Baffle (Rock or Geotextile)

Surface Outlet

Outlet to Stream

Stilling

Basin

Flocculant Pump

Water Pump

Flocculant Tank

Hose to Intake

Floating Intake

Turbid Water Source
20

Scenario Two

Moderate use defi ned as operating the system 6 hours per day, 15 days out of the month (totaling 2,160,000 gallons treated per month).

Variable Cost Element Duration Cost

Operating labor @ $85/hr Reasonably expect 105 hours $8,925

Fuel consumption (diesel) 90 hours @ 6 gph $1,620

Chitosan consumption 2 mg/L based on previous assumption $3,956

System performance data monitoring and reporting 15 hrs/mo @ $75 $1,125

Senior operator project oversight Assume 2 site visits (1 hour each) @ $120/hr $240

Meeting with regulatory personnel 2 hours @ $120/hr $240

Total Variable Costs $16,106

Hard Cost Elements $17,300

Total Hard & Variable Costs $33,406

Considering the total cost of $33,406 divided by the total amount of water treated (2,160,000 gallons), the cost per 

gallon of water treated is $0.015 or $150 per 10,000 gallons of water treated to meet state discharge standards.

Scenario Th ree

Heavy use defi ned as operating the system 10 hours per day, 20 days out of the month (totaling 4,800,000 gallons treated per month).6

Variable Cost Element Duration Cost

Operating labor @ $85/hr Reasonably expect 240 hours $20,400

Fuel consumption (diesel) 200 hours @ 6 gph $3,600

Chitosan consumption 2 mg/L based on previous assumption $8,800

System performance data monitoring and reporting 20 hrs/mo @ $75 $1,500

Senior operator project oversight Assume 4 site visits (2 hour each) @ $120/hr $960

Meeting with regulatory personnel 2 hours @ $120/hr $240

Total Variable Costs $35,500

Hard Cost Elements $17,300

Total Hard & Variable Costs $52,800

Considering the total cost of $52,800 divided by the total amount of water treated (4,800,000 gallons), the cost per 

gallon of water treated is $0.011 or $110 per 10,000 gallons of water treated to meet state discharge standards.

6. Heavy use is most often associated with continuous dewatering activities, dredging, and unusually heavy or prolonged precipitation events.
21

Example of Chemically Treated Discharge Water Being Mixed in a Corrugated Pipe Before Discharge into a Stilling Basin. 

Example of Passive Dosing System by Pumping Turbid Water Th rough Corrugated Pipe Containing Solid Flocculants. 
22

Typical Layout of a Chemical Treatment System on a Construction Site.

Construction Perimeter

Example Layout of a Chemical Treatment 

System on a Construction Site

Construction Entrance

Flow from Disturbed Area

Sediment Basin

Chemical Treatment System

Outlet

Emergency Outlet (Rock and Geotextile)

Stream
23
Technical Report published by

Technology Deployment Program

Western Federal Lands Highway Division

Federal Highway Administration

610 East 5th St.

Vancouver, WA 98661

For more information or additional copies 

contact:

Amit Armstrong, Ph.D., P.E. 

Phone: 360.619.7668

Fax: 360.619.7846

Amit.Armstrong@fhwa.dot.gov