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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-1 

1 Chapter 6. Individual and ClusterClustered (Decentralized) 

2 Wastewater Treatment Systems 

6. 

3 Contents 

4 1 Nitrogen-Reduction Implementation Measures.......................Error! Bookmark not defined.

5 2 Introduction and Background ..................................................Error! Bookmark not defined.

6 3 Nutrient-Reduction Processes for the Decentralized Wastewater Sector .....Error! Bookmark 

7 not defined.

8 3.1 Nitrogen ..........................................................................Error! Bookmark not defined.

9 3.2 Nitrogen Pretreatment.....................................................Error! Bookmark not defined.

10 3.3 Permeable Reactive Barriers...........................................Error! Bookmark not defined.

11 3.4 System Configuration ...................................................................................configuration Error! 

12 3.5 Phosphorus......................................................................Error! Bookmark not defined.

13 4 Treatment Technologies and Costs..........................................Error! Bookmark not defined.

14 4.1 Conventional Systems.....................................................Error! Bookmark not defined.

15 4.2 Suspended Growth Systems............................................Error! Bookmark not defined.

16 4.3 Attached Growth Aerobic Systems.................................Error! Bookmark not defined.

17 4.4 Single-Pass and Recirculating Media Filters ..................Error! Bookmark not defined.

18 4.5 Add-On Anoxic Filters with a Carbon Source................Error! Bookmark not defined.

19 4.6 Composting Toilet Systems ............................................Error! Bookmark not defined.

20 4.7 Cluster Treatment Systems .............................................Error! Bookmark not defined.

21 4.8 Soil Dispersal Systems....................................................Error! Bookmark not defined.

22 5 Wastewater Planning and Treatment System Management.....Error! Bookmark not defined.

23 5.1 Public Education and Involvement .................................Error! Bookmark not defined.

24 5.2 Planning ..........................................................................Error! Bookmark not defined.

25 5.3 Performance Requirements.............................................Error! Bookmark not defined.

26 5.4 Recordkeeping, Inventories, and Reporting....................Error! Bookmark not defined.

27 5.5 Financial Assistance and Funding ..................................Error! Bookmark not defined.

28 5.6 Site Evaluation................................................................Error! Bookmark not defined.

29 5.7 System Design ................................................................Error! Bookmark not defined.

30 5.8 Construction/Installation.................................................Error! Bookmark not defined.

31 5.9 Operation and Maintenance ............................................Error! Bookmark not defined.
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-2 

1 5.10 Residuals Management ...................................................Error! Bookmark not defined.

2 5.11 Training and Certification/Licensing..............................Error! Bookmark not defined.

3 5.12 Inspections and Monitoring ............................................Error! Bookmark not defined.

4 5.13 Corrective Actions and Enforcement..............................Error! Bookmark not defined.

5 6 References................................................................................Error! Bookmark not defined.

6 

7 
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-3 

1 1 Nitrogen-Reduction Implementation Measures 

2 EPA recommends protecting surface waters in the Chesapeake Bay watershed from nitrogen (N)

3 discharged by decentralized wastewater treatment systems by using N-reduction technologies 

4 and enhanced system management.

Implementation Measures:

a) Specify the following risk-based, N-removal performance levels for all new and 

replacement individual and cluster systems:

− 20 milligrams per liter (mg/L) total nitrogen (TN) standard* for all new subdivisions 

and commercial and institutional developments and all system replacements 

throughout the Chesapeake Bay watershed.

− 10 mg/L TN standard* for all new developments and all system replacements in 

sensitive areas—i.e., between 200 and 1,000 feet of the ordinary high water mark of 

all surface waters, or between 200 and 500 feet of an open-channel municipal 

separate storm sewer system (MS4).

− 5 mg/L TN standard* for all new developments and system replacements in more 

sensitive areas—i.e., between 100 and 200 feet of the ordinary high water mark of all 

surface waters, or between 100 and 200 feet of an open-channel MS4.

− 100-foot setback from surface waters and open channel MS4s for all effluent 

dispersal system components.

* Effluent standards may be met by either system design or performance. A 

5 mg/L N reduction credit is given when using time-dosed, pressure-drip 

dispersal within 1 foot of the ground surface.

b) Ensure wastewater treatment performance effectiveness and cost efficiency by using 

cluster systems with advanced N-removal technology sufficient to meet the standards 

specified above for all newly developed communities and densely populated areas.

c) Sustain treatment system performance in perpetuity through management contracts with 

trained and certified operators for all advanced N-removal systems, and responsible 

management entity (RME) operation and maintenance (O&M) for all cluster systems.

d) Preserve long-term treatment system performance with management practices designed 

to protect system investments, by doing the following:

− Conducting GIS-based inventories of all individual and cluster (i.e., decentralized) 

wastewater systems in all areas that drain into the Chesapeake Bay or its tributaries. 

Inventory information includes system location (i.e., latitude/longitude), type, 

capacity, installation date, owner, and relevant information on complaints, service 

(including tank pump-out), repairs, inspections, and dates. Inventory data is stored 

electronically in a format amenable for use in watershed studies, system impacts 

analyses, and supporting general management tasks. EPA offers The Wastewater 

Information System Tool (TWIST) as a free resource for managing that information in 
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-4 

a user-friendly database. Health departments, state agencies, RMEs and others can 

adapt, amend, or otherwise modify TWIST without restriction or obligation.

− Requiring inspections for all systems at least once every 5 years; existing systems 

within sensitive areas are inspected at least once every 3 years; advanced treatment 

systems and those serving commercial, institutional, or industrial facilities are 

inspected at least semiannually. A qualified inspector inspects all systems on a 

schedule according to wastewater type, system size, complexity, location, and relative 

environmental risk. Inspections are consistent with EPA management guidelines for 

individual and cluster systems. A service professional or other trained person 

conducts routine monitoring on the basis of the system type, operating history, 

manufacturer’s recommendations, and other factors.

− Repairing or replacing all malfunctioning systems when discovered, with new or 

replacement technologies capable of meeting the N-removal standards specified 

above.

− Requiring reserve areas for installing a replacement soil dispersal system that is equal 

to at least 100 percent of the size of the original effluent dispersal area. Treatment 

systems using effluent time-dosing (i.e., not demand-dosing) to the soil can have 

reserve areas equal to at least 75 percent of the total required drainfield area. Systems 

with pressurized drip effluent dosing and those with dual drainfields operated on 

active/rest cycles (i.e., alternating drainfields) can have reserve areas equal to at least 

50 percent of the original required dispersal area.

e) Restore groundwater quality in areas where high-nitrate effluent plumes are near the 

surface and close to receiving surface waters by using effective, low-cost technologies 

such as permeable reactive barriers (PRBs). PRBs are low-cost, pH-controlled trenches 

filled with sand and a degradable carbon source, such as sawdust, shredded newspaper, or 

wood chips, designed to intercept groundwater plumes and reduce the TN concentration.

1 

2 EPA recommends protecting surface waters in the Chesapeake Bay watershed from nitrogen 

3 discharged by decentralized wastewater treatment systems by using nitrogen-reduction 

4 technologies and enhanced system management. Implementation measures supporting this 

5 recommendation are as follows:

6 Specify the following risk-based, nitrogen-removal performance levels for all new and 

7 replacement individual and clustered systems:

8 − 20 milligrams per liter (mg/L) total nitrogen standard* for all new subdivisions and 

9 commercial and institutional developments and all system replacements throughout 

10 the Chesapeake Bay watershed.

11 − 10 mg/L total nitrogen standard* for all new developments and all system 

12 replacements in sensitive areas—i.e., within 1,000 feet of the ordinary high water 

13 mark of all surface waters, or within 500 feet of an open-channel municipal separate 

14 storm sewer system (MS4).
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-5 

1 − 5 mg/L total nitrogen standard* for all new developments and system replacements 

2 within 200 feet of the ordinary high water mark of all surface waters, or within 200 

3 feet of an open-channel MS4.

4 − 100-foot setback from surface waters and open channel MS4s for all effluent 

5 dispersal system components.

6 * Effluent standards may be met by either system design or performance. A 5 mg/L 

7 nitrogen reduction credit is given when using time-dosed pressure drip dispersal within 

8 1 foot of the ground surface.

9 Ensure wastewater treatment performance effectiveness and cost efficiency by using cluster 

10 systems with advanced nitrogen-removal technology sufficient to meet the standards specified

11 above for all newly developed communities and densely populated areas.

12 Sustain treatment system performance in perpetuity through management contracts with trained 

13 and certified operators for all advanced nitrogen-removal systems, and responsible management 

14 entity (RME) operation and maintenance (O&M) for all clustered systems.

15 Preserve long-term treatment system performance with management practices designed to 

16 protect system investments, by doing the following:

17 − Conducting GIS-based inventories of all individual and clustered (i.e., decentralized) 

18 wastewater systems in all areas that drain into the Chesapeake Bay or its tributaries. 

19 Inventory information includes system location (i.e., latitude/longitude), type, 

20 capacity, installation date, owner, and relevant information on complaints, service 

21 (including tank pump-out), repairs, inspections, and dates. Inventory data is stored 

22 electronically in a format amenable for use in watershed studies, system impacts 

23 analyses, and supporting general management tasks. EPA offers The Wastewater 

24 Information System Tool (TWIST) as a free resource for managing that information in 

25 a user-friendly database.Health departments, RMEs and others can adapt, amend, or 

26 otherwise modify TWIST without restriction or obligation.

27 − Requiring inspections for all systems at least once every 5 years; existing systems 

28 within sensitive areas are inspected at least once every 3 years; advanced treatment 

29 systems and those serving commercial, institutional, or industrial facilities are 

30 inspected at least semiannually. A qualified inspector inspects all systems on a 

31 schedule according to wastewater type, system size, complexity, location, and relative 

32 environmental risk. Inspections are consistent with EPA management guidelines for 

33 individual and clustered systems. A service professional or other trained person 

34 conducts routine monitoring on the basis of the system type, operating history, 

35 manufacturer’s recommendations, and other factors.

36 − Repairing or replacing all malfunctioning systems when discovered, with new or 

37 replacement technologies capable of meeting the nitrogen-removal standards 

38 specified above.

39 − Requiring reserve areas for installing a replacement soil dispersal system that is equal 

40 to at least 100 percent of the size of the original effluent dispersal area. Treatment 

41 systems using effluent time-dosing (i.e., not demand-dosing) to the soil can have 

42 reserve areas equal to at least 75 percent of the total required drainfield area. Systems 

43 with pressurized drip effluent dosing and those with dual drainfields operated on 
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-6 

1 active/rest cycles (i.e., alternating drainfields) can have reserve areas equal to at least 

2 50 percent of the original required dispersal area.

3 Restore groundwater quality in areas where high-nitrate effluent plumes are near the surface and 

4 close to receiving surface waters by using effective, low-cost technologies such as permeable 

5 reactive barriers (PRBs). PRBs are low-cost, pH-controlled trenches filled with sand and a 

6 degradable carbon source, such as sawdust, shredded newspaper, or wood chips, designed to 

7 intercept groundwater plumes and reduce the total nitrogen concentration.

8 2 Introduction and Background 

9 Individual on-site and clusterclustered (decentralized) wastewater systems treat household and 

10 commercial wastes in suburban, exurban, and rural areas throughout the Chesapeake Bay 

11 watershed. The Chesapeake Bay Program (USEPA 2009) estimates that about 25 percent of the 

12 homes in the watershed—2.3 million total—rely on these systems, which disperse treated 

13 effluent to the soil. EPA predicts that decentralized system installations will increase over the 

14 next 20 years by about 35 percent (i.e., 800,000 new systems), eventually reaching 3.1 million

15 (USEPA 2009). 

16 Nearly all the solids and phosphorus (P) discharged from decentralized wastewater systems are 

17 retained by the soil, through physical filtration, adsorption, and precipitation processes (USEPA 

18 2004). However, Nnitrogen in wastewater is ultimately converted to nitrate upon infiltration into 

19 aerobic soils, a stable, soluble, and highly mobile form of this nutrient that negatively affects 

20 groundwater and surface water quality. 

21 Decentralized wastewater systems contribute approximately 12.5 million pounds of Nnitrogen to 

22 the Chesapeake Bay annually, or about 4.5 percent of the total. According to current Chesapeake 

23 Bay nutrient loading models, most of the Nnitrogen load from such systems—about 60 percent—

24 comes from the Potomac and Susquehanna river drainage areas, specifically Pennsylvania, 

25 Virginia, and Maryland. The Chesapeake Bay Nnitrogen-reduction goal for the decentralized 

26 wastewater sector calls for a reduction to 9.4 million pounds per year from the current load of 

27 12.5 million pounds annually. With 800,000 new systems predicted over the next 15 years, 

28 significant reductions in Nnitrogen loads from new and existing systems are needed. 

29 The Chesapeake Bay nutrient and sediment reduction goals include decreases in current and 

30 future pollutant loads from decentralized treatment systems. A new generation of “hardware and 

31 software”—treatment technologies and management practices—are needed to achieve the 

32 reductions. This section describes those technologies, management practices, and associated 

33 implementation measures. Implementation measures for achieving the reductions include 

34 installing treatment units with optimal Nnitrogen-removal capabilities in sensitive areas near 

35 surface waters; using standard Nnitrogen removal systems in other areas; and ensuring that all 

36 treatment systems are appropriately operated, maintained, and managed. The measures 

37 encompass a range of treatment technologies, planning and performance considerations, and 

38 management actions needed to address Nnitrogen export from decentralized systems. The 

39 implementation measures described in this chapter support two primary goals for addressing 

40 Nnitrogen inputs to the Chesapeake Bay from these systems: 
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-7 

1 • Prevent further impairment of the Chesapeake Bay by significantly reducing Nnitrogen

2 levels in wastewater from new residential, commercial, and institutional developments 

3 using decentralized systems 

4 • Reduce Nnitrogen inputs to the Chesapeake Bay from existing individual and 

5 clusterclustered wastewater systems by replacing malfunctioning systems with better6 performing technologies and by managing all systems to ensure long term performance 

7 Implementation measures to achieve those goals include repairing or replacing malfunctioning 

8 systems, targeting high-risk systems in sensitive areas for replacement with advanced treatment 

9 units, clustering replacement systems where possible to implement better-performing and more 

10 efficient community treatment facilities, inspecting all systems throughout the Chesapeake Bay 

11 watershed, and installing PRBs where technically and economically feasible to reduce Nnitrogen

12 concentrations in targeted effluent plumes. Those approaches are based on more than 2 decades 

13 of research and field studies on decentralized system applications. 

14 Key findings on the systems’ performance, their effects on groundwater, and the opportunities 

15 presented by next-generation treatment technologies are summed up in the Final Report for the 

16 La Pine National Decentralized Wastewater Treatment Demonstration Project (2005), a joint 

17 effort of EPA and other federal, state, and local agencies: 

18 The groundwater investigations have found significant existing nitrogen pollution 

19 and the 3-D model has predicted extensive future contamination of the aquifer. 

20 The model also predicted, based on the field performance of denitrifying systems 

21 in the project, that contamination could be slowed or stopped using onsite 

22 wastewater treatment technologies, and that, as the region is retrofitted with 

23 denitrifying technologies, the existing contamination would be flushed from the 

24 groundwater system via existing natural discharge points. 

25 The field test program, in addition to identifying systems that can remove a large 

26 proportion of the nitrogen in residential wastewater, found that conventional 

27 systems are not protecting the aquifer from nitrate contamination. Conventional 

28 systems that were previously thought to denitrify up to 50% of the nitrate 

29 discharged from septic tanks were found to achieve significantly less 

30 denitrification when process and environmental variables were accounted for. 

31 The La Pine Project, EPA’s Environmental Technology Verification (ETV) program, the 

32 National Sanitation Foundation standards program, and other research efforts across the country 

33 have identified and tested a number of denitrifying wastewater systems and found that 

34 performance varies considerably. However, some systems do perform optimally in removing 

35 TNtotal nitrogen from the effluent—e.g., to concentrations as low as 5 mg/L—and others are 

36 capable of Nnitrogen effluent levels in the 10 and 20 mg/L range. 

37 Higher treatment performance levels are needed in sensitive areas to protect or restore surface 

38 water quality. Research and field studies confirm that effluent plumes with elevated nitrate levels 

39 move laterally over long distances—i.e., greater than 300 feet in unconfined, sandy aquifers 

40 (Walker et al. 1972; Robertson et al. 1989; Robertson and Cherry 1992). NNitrogen

41 concentrations in effluent plumes are affected by soil oxygen levels, soil composition, plant 

42 uptake, labile carbon content, travel distance, rate of movement, mixing, and other factors. The 
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-8 

1 measures listed in this chapter incorporate the general availability of treatment and dispersal 

2 systems that can meet the performance standards needed to protect the Chesapeake Bay and its 

3 tributaries with more stringent treatment levels in sensitive areas near waterbodies. States have 

4 been adopting treatment zone setbacks and standards to address Nnitrogen and other pollutants in 

5 coastal areas (Joubert et al. 2003). 

6 3 Nutrient-Reduction Processes for the Decentralized 

7 Wastewater Sector 

8 Nutrients—primarily Pphosphorus and Nnitrogen—are present in somewhat significant levels in 

9 domestic and commercial wastewater. Nutrient treatment and removal involve processes that 

10 occur either in treatment system components or in the receiving environment, as summarized 

11 below. 

12 3.1 Nitrogen 

13 NNitrogen is the primary pollutant of concern along the coastal areas of the United States, 

14 including the Chesapeake Bay. NNitrogen discharges are a concern for both nitrate 

15 contamination of drinking water wells and as an aquatic plant nutrient, particularly in Nnitrogen16 sensitive surface waters and nearshore marine waters. NNitrogen is not readily or consistently 

17 removed in conventional individual and cluster soil-based systems because most soils have a 

18 limited capacity to retain or remove Nnitrogen. Conventional soil-discharging systems are not 

19 designed to remove Nnitrogen. Organic Nnitrogen in wastewater generally is converted to 

20 ammonium Nnitrogen in the septic tank. Ammonium Nnitrogen is quickly nitrified as the 

21 wastewater infiltrates the aerobic soil. Nitrate-Nnitrogen is stable, soluble, and highly mobile in 

22 the subsurface environment. Biological denitrification of the nitrate is usually limited because 

23 the soil is often aerobic near the ground surface and usually has very little organic carbon, which 

24 is required by the heterotrophic denitrifying microorganisms. Therefore, where Nnitrogen

25 removal is required for dispersal, pretreatment that achieves both nitrification and denitrification 

26 usually is necessary before the wastewater is dispersed to the soil. 

27 3.2 Nitrogen Pretreatment 

28 Many reasonably priced natural and mechanical pretreatment systems, specifically designed for 

29 individual and cluster systems, are available today. The most popular example of such systems is 

30 the recirculating media filter, with timed dosing and drip or pumped effluent dispersal. The filter 

31 media is typically sand, gravel, textile or peat. A portion of the filtered effluent is recycled 

32 several times back to the septic tank (or pump/recirculating tank) before further filtration and 

33 discharge. Denitrification is supported by the low-oxygen, high-carbon environment that exists 

34 in the recirculating or septic tanks. Those systems are able to consistently remove an average of 

35 50 percent of the TNtotal nitrogen in the septic tank effluent—reducing the TNtotal nitrogen

36 from a typical influent range of 40–50 mg/L for single family homes to 15–20 mg/L (Otis 2007; 

37 USEPA 2002ETV 2009; Jenssen and Siegrist 1990; Higgins et al. 2002; Smith et al. 2008; Rich 

38 et al. 2003). 
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-9 

1 To achieve TNtotal nitrogen levels of 3–5 mg/L and lower, a denitrifying process unit is usually 

2 installed after the nitrification stage (e.g., aerobic attached or suspended growth media filter) in 

3 the pretreatment system. To sustain a denitrification process, a reactive carbon source must be 

4 added to complete the nitrate removal. For larger installations methanol, acetic acid, molasses, or 

5 other organic chemicals are added to the anaerobic reactor. However, the costs of constructing 

6 and O&M of an external chemical feeding system and the cost of chemicals, power for a feed 

7 pump, controls, and chemical storage increase removal expenses substantially. 

8 Proprietary denitrifying units, which avoid the need for feed pumps, controls, and chemicals are 

9 now available. Such units include a slowly degradable organic material in the reactor tank that 

10 can last several years. Field testing has documented TNtotal nitrogen effluent concentrations of 

11 3–5 mg/L and even lower (Smith et al. 2008; Lombardo et al. 2005). 

12 Further Nnitrogen removal occurs after pretreated effluent is uniformly dosed and rested during 

13 discharge into the soil, where soil oxygen levels, carbon sources, temperature, and residence time 

14 are key factors. That removal is quoted to be about 50 percent (Long 1995; Otis 2007). 

15 Additionally, someSome soils do contain sufficient labile carbon to denitrify effluents regardless 

16 of the method of dispersal (Anderson 1998; Gold et al. 2002; Starr and Gillham 1986; Bushman 

17 1996; Hiscock et al. 1991). Other variables include seasonal use (Postma 1992), in-stream 

18 processes, including the matrix through which the groundwater enters nearby surface waters 

19 (Birgand 2000; Stewart and Reneau 1984Hoover 2003), and the distance from the source to the 

20 receiving surface waters (Stacey 2002). One British study (Hiscock et al. 1991) estimates that the 

21 average groundwater carbon content would account for removal of 3 mg/L of nitrate. 

22 3.3 Permeable Reactive Barriers 

23 One recent development that can be applied to remove groundwater nitrate from plumes that 

24 have adverselyalready aversely affected the quality of nearby receiving water is the PRB 

25 concept. Those barriers, which consist of a trench filled with a degradable carbon source (e.g., 

26 sawdust, newspaper), are sited to intercept high-nitrate groundwater plumes (WE&T 2009). As 

27 the plumes pass through the low-oxygen, carbon-rich barrier, bacteria break down nitrate 

28 molecules to use the oxygen for cell respiration. In areas where receiving waters are already 

29 eutrophied, the trenches can provide immediate relief by removing nitrate from the incoming 

30 groundwater. Addressing the source of the high-nitrate plume—densely sited septic systems—

31 would also produce results, but any measureable effects would likely take several years. 
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-10 

1 PRBs are installed as long, 

2 narrow trenches perpendicular 

3 to the incoming plume and 

4 parallel to shoreline. A calcium5 based source of alkalinity is 

6 usually included with the 

7 carbon media to assure high 

8 rates of denitrification. Such 

9 systems have been successfully 

10 demonstrated in North America 

11 and Europe (Robertson and 

12 Cherry 1995; Lombardo et al. 

13 2005; USEPA 1998). PRB costs 

14 range from about $5,000 to 

15 $15,000 per equivalent dwelling 

16 unit (i.e., in the plume sourcing 

17 area), depending on soils, 

18 geology, depth to groundwater, 

19 subsurface hydrology, 

20 construction access, existing infrastructure, and other factors. 

21 3.4 System Configurationconfiguration

22 As noted above, a certain level of treatment process unit sophistication and soil discharge 

23 technique (e.g., pressure dosing, drip tube dispersal) are required for optimum Nnitrogen

24 removal. Their cost in terms of both hardware and management needs can be significantly 

25 mitigated through the use of cluster systems that treat wastewater from multiple homes or 

26 businesses. ClusterClustered systems, also called community or distributed systems, have 

27 become extremely popular in areas where high levels of wastewater treatment are required, 

28 where space is too limited for on-site conventional soil-discharging systems, and local funding 

29 capacity precludes conventional sewage collection and treatment. 

30 3.5 Phosphorus 

31 In general, most regions of the Chesapeake Bay watershed have soils that retain Pphosphorus

32 from decentralized systems. The process involves chemical adsorption to soil particles and 

33 precipitation reactions with soil minerals, including iron, calcium, and aluminum (Tyler et al. 

34 2003; Stone Environmental 2005). The soil’s capacity to remove Pphosphorus is significant both 

35 spatially and temporally. Saturation fronts of Pphosphorus move only inches or less per year 

36 through all but coarse sandy or gravelly soils. 

37 Wastewater system designers maximize Pphosphorus removal rates by locating the infiltration 

38 system in medium- to fine-textured soils that are as far from surface waters as possible, and 

39 extending the infiltration system along the contour of the installation site. Also, uniform dosing 

40 and resting dispersal by pressure or drip distribution will maximize Pphosphorus removal by the 

Source: USEPA 1998 

Figure 6-1. Permeable reactive barrier conceptual approach.
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-11 

1 soil through maximizing the contact time between the effluent and the soil. System age reduces 

2 the capacity of the soil to remove Pphosphorus. 

3 If native soils are not amenable to adsorption removal, other adsorption methods also are 

4 available (Stone Environmental 2005; Dimick et al. 2006; USEPA 2002; Robertson et al. 1989). 

5 Although some Pphosphorus can be removed by pretreatment systems that contain high 

6 concentrations of adsorptive elements or by biological Pphosphorus removal, soil adsorption is 

7 by far the most common, and least expensive, means of removal. 

8 4 Treatment Technologies and Costs 

9 Key considerations in treatment system selection are wastewater flow, strength (i.e., biochemical 

10 oxygen demand), the presence of nonconventional organic or inorganic constituents, the 

11 sensitivity of the receiving environment, and the capacity of system managers to operate and 

12 maintain it over the long term. Given those factors, note that both the selection and ongoing use

13 of a specific technology is driven by management considerations. For example, wastewater 

14 characterization and assessment of the receiving environment are planning-level activities that 

15 result in establishing performance standards, which begin to identify the narrow range of 

16 treatment technology options and related design considerations. Once a specific system is 

17 selected, construction oversight, operation, inspection, maintenance, and residuals removal—all 

18 management program elements—become paramount in ensuring perpetual performance. 

19 The subsections that follow discuss the primary treatment system technology classes. The final 

20 section of this chapter summarizes management program elements that support the 

21 implementation measures provided at the beginning of this chapterrecommendations listed 

22 above. 

23 4.1 Conventional Systems 

24 Conventional treatment systems featuring septic tanks and soil infiltration systems are the most 

25 commonly used wastewater treatment technologies. The soil dispersalabsorption system 

26 facilitates aerobic treatment, degradation, filtration, and adsorption of contaminants not treated or 

27 retained by the septic tank. However, Nnitrogen removal is somewhat limited, with TNtotal 

28 nitrogen concentrations before soil application typically in the 40–50 mg/L range. In sandy soils 

29 with little organic content, high oxygen levels, and poor downgradient mixing Nnitrogen

30 concentrations can remain high even after several hundred feet of effluent plume movement 

31 (Walker et al. 1973; Robertson and Cherry 1992; Robertson et al. 1989; Cogger 1988; Joubert et 

32 al. 2004). Given the low Nnitrogen removal rates of conventional systems (i.e., averaging 20 

33 percent TNtotal nitrogen removal; Otis 2007; Smith et al. 2008; Jenssen and Siegrist 19901989), 

34 they are no longer appropriate for use in new communities or densely developed areas in the 

35 Chesapeake Bay watershed. 

36 4.2 Suspended Growth Systems 

37 Suspended growth systems, such as activated sludge-based aerobic treatment units, are generally 

38 effective in nitrifying septic tank effluent. Denitrification, however, is limited. Aerobic units that
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-12 

1 feature with aeration thatstopped and started periodically stops and starts show improvedimprove

2 denitrification. Sequencing batch reactors, which first fills and then draws, in with fill/draw

3 alternating aerobic/anoxic cycles in a single tank may also meet the 20 mg/L recommended 

4 effluent limit for areas more than 1,000 feet of surface waters in the Chesapeake Bay watershed, 

5 when effluent is dispersed to the soil via time-dosed, pressure- drip lines (Washington State 

6 Department of Health 2005). Capital costs for on-site suspended growth systems range from 

7 $7,500 to $15,000, with O&M expenses of $400 to $800 per year when all suggested O&M tasks 

8 are performed (Tetra Tech 2007). 

9 4.3 Attached Growth Aerobic Systems 

10 These systems (sometimes called trickling filters) use natural aeration instead of mechanical, 

11 produce less sludge for disposal, and require less power and O&M than the suspended growth 

12 units in performing the same tasks. They also require a recirculation step to meet more stringent 

13 TNtotal nitrogen removal objectives. Commercially available systems come in lightweight 

14 packages and employ lightweight media for easy installation. They also require about 20 percent 

15 less physical footprint than typical trickling filters. When properly loaded and operated, they can 

16 produce very high nitrification levels that must be followed by a denitrification step to exceed 

17 the typical 50 percent Nnitrogen-removal rate. On-site capital costs are slightly higher in general 

18 than the suspended growth ATUs ($10,000 to $16,000), but O&M costs are significantly less, 

19 e.g., about $200–300 per year (USEPA 2010; Tetra Tech 2007). 

20 4.4 Single-Pass and Recirculating Media Filters 

21 Single-pass media filters—sand filters, textile filters, peat systems, mounds, and other packed 

22 media bed units—achieve excellent nitrification levels but generally do a poor job with 

23 denitrification unless some, or all, of the effluent passes through a carbon-rich, low-oxygen 

24 environment after the nitrification stage. That can be accomplished by recirculating a portion of 

25 the effluent back to the septic tank or a pump tank, or by adding a denitrification unit to the 

26 system (see below), or both. Media filters have a long record of excellent performance, with 

27 nitrification rates as high as 95 percent (Otis 2007; Smith et al. 2008; USEPA 2002). The 

28 treatment process is stable year-round and can be employed through either custom-built, 

29 nonproprietary engineered systems or commercial units that can be installed in a single day. 

30 Capital costs for single-pass filters range from $5,500 to $13,000, with O&M expenses of $200 

31 to $400 per year (USEPA 2010; Tetra Tech 2007). 

32 Recirculating media filters have been in use for many years and feature high nitrification rates 

33 with about 50 percent denitrification. The systems recycle part of the effluent back to the septic 

34 tank or the recirculating tank, where the anoxic environment and available carbon facilitate 

35 denitrification processes. Design considerations include the ratio of effluent recirculated and the 

36 configuration of the recycle plumbing, i.e., ensuring that the recycled effluent is discharged to a 

37 tank location with low oxygen and some carbon. TNTotal nitrogen effluent concentrations can be 

38 as low as10 as10 mg/L, which can be further reduced in the soil by using time-dosed, 

39 pressurepressurized-drip effluent dispersal. Engineered systems and proprietary units are widely 

40 available and can serve single homes or large subdivisions. Capital costs for recirculating 
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-13 

1 systems range from $9,500 to $20,000, with O&M expenses of $350 to $600 per year (USEPA 

2 2010; Tetra Tech 2007; Washington State Department of Health 2005). 

3 4.5 Add-On Anoxic Filters with a Carbon Source 

4 As noted in the discussion on recirculating media filters above, optimal denitrification can be 

5 achieved by passing nitrified effluent through a low-oxygen, carbon-rich environment before soil 

6 discharge. Engineered and proprietary systems featuring add-on anoxic filters with an external 

7 carbon source (e.g., methanol, sawdust, newspapers, and such) have performed successfully in 

8 single-home or clusterclustered applications. For example, commercially available products 

9 regularly produce an effluent with Nnitrogen concentrations of less than 5 mg/L. Other system 

10 designs discussed above can also achieve this level when paired with time-dosed, pressure- or 

11 drip dispersal. Capital costs for add-on denitrification systems range from $3,500 to $57,000, 

12 with O&M expenses of less than $100 per year (Washington State Department of Health 2005). 

13 Note that this does not include the septic tank, nitrification step, or soil dispersal system—just 

14 the add-on component. 

15 4.6 Composting Toilet Systems 

16 Composting toilet systems that contain and treat toilet wastes can reduce watershed Nnitrogen

17 discharges significantly, because such wastes account for 70–80 percent of the TNtotal nitrogen

18 load in domestic wastewater. Composting systems have been successfully used in both private 

19 and public facility settings. Like all systems, they require appropriate design and ongoing O&M 

20 attention. A greywater treatment system will be needed if the facility generates sink, laundry, or 

21 other greywater. Capital costs for composting systems range from $2,500 to $10,000, with O&M 

22 expenses of $50 to $100 per year (USEPA 1999). The single-house viability of such systems 

23 depends on the owner’s attitude. The systems are more commonly used in public settings. 

24 4.7 Cluster Treatment Systems 

25 Generally, cluster systems collect wastewater from multiple houses through low-cost sewerage 

26 and treat and disperse the effluent to soil-based dispersal systems similar to on-site systems. 

27 Many homes and businesses can be served by a single treatment facility. Most cluster systems 

28 feature septic tanks on each building lot; collection piping that operates via gravity, vacuum, or 

29 pressure; a treatment facility with attached growth process units; and a soils-based dispersal field 

30 for the effluent. Add-on anoxic denitrification filters can be included. Effluent is typically 

31 dispersed to the soil under pressure (e.g., pressure, drip, time or demand dosing) to assure 

32 uniform application throughout the larger drainfield. Collection technologies include grinder 

33 pump systems, which macerate and transport all sewage; effluent sewers, such as the septic tank 

34 effluent pump (STEP); the septic tank effluent gravity (STEG) collection system; and vacuum 

35 systems. 

36 Advanced treatment systems can facilitate local reuse of the treated effluent for toilet flushing, 

37 irrigation, industrial purposes, or just be used to replenish aquifers. The cost of a cluster 

38 collection system varies significantly according to the number of users, collection system 

39 logistics, treatment facility design, land availability, materials/labor costs, and other factors but 
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-14 

1 averages around $10,000 per dwelling served. Cluster systems can achieve significant economies 

2 of scale to provide high levels of treatment at costs significantly less (25 percent to 50 percent) 

3 than centralized sewer systems. New cluster systems generally range from $8,000 to $18,000 per 

4 connection, depending on the treatment technology used (USEPA 2010; Tetra Tech 2007). 

5 Replacement and /retrofit systems have similar costs, but collection system installation can drive 

6 costs higher. An RME with the technical, financial, and managerial capacity to ensure viable, 

7 long-term, cost-effective performance is needed for cluster system applications. Total system 

8 annual O&M costs range from $450 to $750 (Tetra Tech 2007). 

9 Table 6-1. Examples of biological Nnitrogen removal performance from the literature 

Technology examples

TN removal efficiency

(%)

Effluent TN

(mg/L)

Suspended growth

Aerobic units w/ pulse aeration 25%–61% a37–60a

Sequencing batch reactor 60% b15.5b

Attached growth

Single-Pass Sand Filters (SPSF) 8%–50% c30–60c

Recirculating Sand/Gravel Filters (RSF) 15%–84% d10–47d

Multi-Pass Textile Filters 14%–38% e,i 9–83 e,i

RSF w/ Anoxic Filter 40%–90% f7–23 f

RSF w/ Anoxic Filter w/ external carbon source 74%–80% g10–13 g

RUCK system 29%–54% h18–53 h

Nitrex 96% j2.2 j
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-15 

1 

Source: Adapted from Washington Department of Health 2005.

Notes:

a. California Regional Water Quality Control Board 1997; Whitmeyer et al. 1991

b. Ayres Associates 1998

c. Converse 1999; Gold et al. 1992; Loomis et al 2001; Nolte & Associates 1992; Ronayne et al. 1982

d. California Regional Water Quality Control Board 1997; Gold et al. 1992; Loomis et al 2001; Nolte & Associates 

1992; Oakley et al. 1999; Piluk and Peters 1994; Ronayne et al. 1982
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-16 

e. Leverenz et al. 2001

f. Ayres Associates 1998; Sandy et al. 1988

g. Gold et al. 1989

h. Brooks 1996; Gold et al. 1989

i. Loomis et al 2001

j. Rich et al. 2003

1 4.8 Soil Dispersal Systems 

2 Gravity-based, soil dispersal systems generally include conventional perforated pipe; laid in 

3 stone-filled trenches or purchased with Styrofoam beads surrounding the pipe and wrapped in 

4 netting; and gravelless, open-bottomed leaching chambers. Soil dispersal increases its level of 

5 Nnitrogen removal when it occurs in a time-dosed manner and uses pressure-drip irrigation 

6 piping installed within one1 foot of the surface of the ground. Using time-dosed, pressure-drip 

7 dispersal in the top 12 inches of soil is credited with a 50 percent reduction in TNtotal nitrogen

8 (Long 1995), making this option an important feature for achieving the performance standards 

9 recommended in this chapter. 

10 Also, because most conventional systems continuously load drainfields resulting in reduction of 

11 the soil’s capacity to treat effluent over time, alternating dosing systems (active/rest cycles) that 

12 extend the useful life of the soil dispersal system should be favored over conventional gravity13 flow drainfields. These systems require relatively low additional investment and can greatly 

14 extend the life of the soil dispersal system (Noah 2006).for many years. Maintenance programs 

15 for such systems should be designed and implemented in concert with the local health 

16 department or RME to ensure that flow-diversion devices are operated on schedule. This 

17 recommendation applies primarily to areas of new development outside sensitive areas. 
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-17 

1 

Source: La Pine Demonstration Project 2005. 

2 Figure 6-2. Effluent TNTotal Nitrogen concentrations for systems tested in the La Pine Project.
Chapter 6. Individual and Clustered (Decentralized) Wastewater Treatment Systems 6-18Chapter 6. Individual and Cluster (Decentralized) Wastewater Treatment Systems 6-18 Table 6-2. Products that have completed the EPA ETV process for 

Nnitrogen reduction in domestic wastewater fro

as of May 2005.System name Technology Description of process Performance Waterloo Biofilter® Model 4-Bedroom

Waterloo Biofilter Systems, Inc.143 Dennis St.: PO Box 100,Rockwood, Ontario

Canada N0B 2kO

http://www.nsf.org/business/water_quality_protection_center/pdf/Waterloo-VSSIGNED.pdf

Fixed film trickling filter.

The biofilter unit uses a patented lightweight open-cell foam that provides a large surface area. Settled wastewater from a primary septic tank is applied to the surface of the biofilter with a spray distribution system. The system can be set up using a single pass process (without any recirculation of biofilter treated effluent) or can use multi-pass configurations. The ETV testing results were generated by returning 50% of the biofilter effluent back to the primary compartment of the septic tank. 

It averaged 62% removal of total nitrogen with an average total nitrogen effluent of 14 mg/L over the 13-month testing period. Earlier testing of this product in a single pass mode demonstrated that it could produce a 20–40% TN reduction.

$1syWw$7

AmphidromeTM Model Single Family System:

F.R. Mahony & Associates, Inc.273 Weymouth St.

Rockland, MA 02370

http://www.nsf.org/business/water_quality_protection_center/pdf/Amphidrome_VS.pdf

Submerged growth sequencing batch reactor (SBR) in conjunction with an anoxic/equalization tank and a clear well tank for wastewater treatment

The bioreactor consists of a deep bed sand filter, which alternates between aerobic and anoxic treatment. The reactor operates similar to a biological aerated filter, except that the reactor changes from aerobic to anoxic conditions during sequential cycling of the unit. Air, supplied by a blower, is introduced at the bottom of the filter to enhance oxygen transfer.

It averaged 59% removal of total nitrogen effluent of 15 mg/L over the 13-month testing period at the Massachusetts Alternative Septic System Test Center (MASSTC).

$7mcoin

Septitech® Model 400 System

Septitech, Inc.220 Lewiston Road

Gray, ME 04039

http://www.nsf.org/business/water_quality_protection_center/pdf/SeptiTech_VS.pdf

Two-stage fixed film trickling filter using a patented highly permeable hydrophobic media

Clarified septic tank effluent flows by gravity into the recirculation chamber of the SeptiTech unit. A submerged pump periodically sprays wastewater onto the attached growth process and the wastewater percolates through the patented packing material. Treated wastewater flows back into the recirculation chamber to mix with the contents. Treated water flows into a clarification chamber and is periodically discharged to disposal unit (drainfield, drip irrigation, etc.)

Averaged 64% removal of total nitrogen with an average total nitrogen effluent of 14 mg/L over the 12-month testing period at MASSTC.

$1inineswdrap
Chapter 6. Individual and Clustered (Decentralized) Wastewater Treatment Systems 6-19Chapter 6. Individual and Cluster (Decentralized) Wastewater Treatment Systems 6-19
Chapter 6. Individual and Clustered (Decentralized) Wastewater Treatment Systems 6-20Chapter 6. Individual and Cluster (Decentralized) Wastewater Treatment Systems 6-20 Table 6-2. Products that have completed the EPA ETV process for nitrogen reduction in domestic wastewater from 

of May 2005. (continued) System name Technology Description of process Performance Bioclere TM Model 16/12 Aquapoint, Inc. 241 Duchanine Blvd. New Bedford, MA 02745 http://www.nsf.org/business/water_quali ty_protection_center/pdf/Bioclere-VS- SIGNED.pdf Fixed film trickling filter. Septic tank effluent flows by gravity to the Bioclere clarifier unit from which it is sprayed or splashed onto the fixed film media. Treated effluent and sloughed biomass are returned to the clarifier unit. A recirculation pump in the clarifier periodically returns biomass to the primary tank. Oxygen is provided to the fixed film by a fan located on the top of the unit. Averaged 57% removal of total nitrogen with an average total nitrogen effluent of 16 mg/L over the 13- month testing period at MASSTC. $7

toinBop$1min com27 coho

Retrofast 0.375 System: Bio-Microbics 8450 Cole Parkway Shawnee, KS 66227 http://www.nsf.org/business/water_quali ty_protection_center/pdf/Biomicrobics- FinalVerificationStatement.pdf Submerged attached-growth treatment system, which is inserted as a retrofit device into the outlet side of new or existing septic tanks. The RetroFAST 0.375 System is inserted into the second compartment of the septic tank. Air is supplied to the fixed film honeycombed media of the unit by a remote blower. Alternate modes of operation include recirculation of nitrified wastewater to the primary settling chamber for nitrification. Intermittent use of the blower can also be programmed to reduce electricity use and to increase nitrification. Averaged 51% removal of total nitrogen with an average total nitrogen effluent of 19 mg/L over the 13- month testing period at MASSTC. P

thra$4exinblpareunlo

Recip® RTS-500 System: Bioconcepts, Inc. P.O. Box 885 Oriental, NC 28571-0885 http://www.nsf.org/business/water_quali ty_protection_center/pdf/Bioconcepts_ Verification_Statement.pdf Fixed film filter This is the newest product to complete Environmental Technology Verification (ETV) Program testing. It is a patented process developed by the Tennessee Valley Authority (TVA) and uses a fixed film filter medium contained in two adjacent, equally dimensioned cells. Timers on each of the two reciprocating pumps control the process. Averaged 58% removal of total nitrogen with an average total nitrogen effluent of 15 mg/L over the 12- month testing period at MASSTC. Ve

sifoThes$1anansico$1
Chapter 6. Individual and Clustered (Decentralized) Wastewater Treatment Systems 6-21Chapter 6. Individual and Cluster (Decentralized) Wastewater Treatment Systems 6-21
Chapter 6. Individual and Clustered (Decentralized) Wastewater Treatment Systems 6-22Chapter 6. Individual and Cluster (Decentralized) Wastewater Treatment Systems 6-22 Table 6-2. Products that have completed the EPA ETV process for nitrogen reduction in domestic wastewater from 

of May 2005. (continued) Source: Adapted from Washington Department of Health 2005.
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-23 

1 5 Wastewater Planning and Treatment System Management 

2 The implementation measures in this section are Nnitrogen-removing individual or 

3 clusterclustered wastewater systems in sensitive areas coupled with management considerations 

4 such as inventory systems, wastewater planning, performance standards, siting and installation 

5 guidelines, operation, inspection, maintenance, and residuals handling. Management tasks are 

6 paramount for reducing nutrient inputs to the Chesapeake Bay because they establish the 

7 framework for selecting and using specific treatment systems in particular locations. For 

8 example, advanced cluster systems are the best approach for protecting and restoring the 

9 Chesapeake Bay when considering wastewater facilities for new subdivisions and replacing 

10 significant numbers of malfunctioning systems in existing subdivisions. 

11 The following subsections summarize key management program elements viewed as important 

12 for controlling the input of nutrients and other pollutants to the Chesapeake Bay. EPA has 

13 provided extensive guidance, case studies, resources, references, and links on these management 

14 program topics (USEPA 2005, 2010). 

15 5.1 Public Education and Involvement 

16 Decentralized wastewater management programs require public support. The success of such 

17 programs will depend on how well homeowners, system service providers, and other 

18 stakeholders are involved in the development process. Unless people understand the need for a 

19 management program, there is little chance it will be adopted. Once in operation, the program 

20 must keep the community involved and informed. Managers should give special consideration to 

21 explaining the need for new requirements for system upgrades, inspections, or other performance 

22 measures. 

23 5.2 Planning 

24 Planning can be used to integrate management strategies for areas served by both centralized and 

25 decentralized wastewater treatment facilities, serve as the basis for ordinances and subdivision 

26 regulations, and synchronize the community growth plan in harmony with the water and 

27 wastewater infrastructure investments. Integrating wastewater planning functions provides better 

28 long-term management of facilities and can help local officials deal with a number of needs such 

29 as sewer overflows, National Pollutant Discharge Elimination System (NPDES) effluent 

30 limitations, Total Maximum Daily Loads (TMDLs), and antidegradation requirements. 

31 Integrated planning, which can minimize stormwater management problems created by new 

32 developments, is useful in anticipating and preventing adverse water quality effects, often by 

33 using LID and green infrastructure approaches. Variables to consider during the planning process 

34 include wastewater flows, proximity and uses of nearby water resources, landscape topography, 

35 hydrology, hydrogeology, soils, environmentally sensitive areas, infrastructure system options 

36 and locations, population densities, and need/potential for clustering treatment/reuse facilities. 

37 EPA supports a wide range of water resource planning and management functions through 

38 programs such as the Clean Water Act section 319 nonpoint source management program, the 

39 Clean Water Act 305(b) assessment reports, TMDLs, wellhead and source water protection 
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-24 

1 programs, watershed planning initiatives, coastal management, National Estuary Program, 

2 wetlands protection programs, water quality standards, continuous planning processes under 

3 section 303(e), water quality management processes under section 205(j) and 604(b), the Clean 

4 Water State Revolving Fund, and so on. Ideally, the planning and management activities 

5 supporting decentralized wastewater treatment would be integrated—or at least coordinated—

6 with these and other water resource programs, many of which the states operate. 

7 5.3 Performance Requirements 

8 Performance requirements for systems are derived by characterizing the risks they pose to health 

9 and water resources and by setting pollutant loading limits on the basis of limiting those risks to 

10 specific levels. Performance requirements specify objectives for each wastewater management 

11 system, which can include physical, chemical, and biological process components. Performance 

12 compliance is based on cumulative, extrapolated pollutant removals for the various system 

13 components (e.g., septic tank, suspended-growth or fixed-film reactors, lagoons, wetlands, soil, 

14 disinfection). Performance can be measured via numeric or narrative criteria. Numeric criteria 

15 reflect time-based, mass loadings or pollutant-concentration limits designed to protect sensitive 

16 water resources. Pollutants commonly targeted in performance requirements include nutrients, 

17 bacteria, oxygen demand, and solids. 

18 5.4 Recordkeeping, Inventories, and Reporting 

19 System inventories provide the nuts and bolts for on-site management. Basic system 

20 information—GIS location, type, design capacity, owner, installation, and servicing dates—is 

21 essential to an effective program. The best record-keeping programs feature integrated electronic 

22 databases with field unit data entry (i.e., using a handheld personal digital assistant), save-to-file

23 computer assisted design drawings, and user-specified reporting formats. 

24 5.5 Financial Assistance and Funding 

25 Financial assistance is needed to: (1) develop or enhance a management program; (2) provide 

26 support for constructing and modifying wastewater facilities; and (3) support operation of the 

27 program. Funding for program development and operation is often available from public and 

28 private loan or grant sources, supplemented by local matching funds. It can also be derived from 

29 some form of resource sharing among management program partner organizations such as 

30 planning departments or health and water resource agencies. Developing an RME and financing 

31 for constructing and operating facilities require larger investments that might come from grants 

32 and loans or public-private partnerships. Long-term operating costs are usually borne by system 

33 users through payment of fees and tax assessments. 

34 5.6 Site Evaluation 

35 Evaluating a proposed site in terms of its environmental conditions, physical features, and 

36 characteristics provides the information needed to size, select, and locate the appropriate 

37 wastewater treatment system. Regulatory authorities issue installation permits on the basis of the 

38 information collected and analyses performed during the site evaluation. Prescriptive site 
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-25 

1 evaluation, design, and construction requirements are based on experience with conventional 

2 septic tank/soil dispersalabsorption systems and empirical relationships that have evolved over 

3 the years. A soil analysis using core sampling to a depth of 4–6 feet or a backhoe pit, rather than 

4 a simple percolation test, provides the best approach for assessing soils, seasonal water table 

5 fluctuations, and other subsurface site features. Performance-based approaches require a more 

6 comprehensive site evaluation. Site evaluation protocols can include some presently employed 

7 empirical tests, specific soil properties tests and soil pits to characterize soil horizons, mottling,

8 and a variety of other properties. 

9 5.7 System Design 

10 Decentralized wastewater treatment system design requirements focus on protecting public 

11 health and water resources. However, systems should also be affordable and aesthetically 

12 acceptable. Prescriptive codes that specify standard designs for sites meeting minimum criteria 

13 simplify design reviews but limit development options and the potential for meeting performance 

14 requirements. Where management programs rely on the state code for design, there might not be 

15 any need for special design protocols. However, in sensitive environments where performance 

16 codes are employed, there is a need to include a design protocol even if it only expands the 

17 number of prescriptive system choices and site parameters for sites that do not meet the 

18 conditions for conventional systems. Design protocols should address the potential implications 

19 of water conservation fixtures, effects of different pretreatment levels on hydraulic and treatment 

20 performance of soil-based systems, and the O&M requirements of different pretreatment and soil 

21 dispersal technologies. 

22 5.8 Construction/Installation 

23 Poor installation can adversely affect performance of both conventional and advanced systems 

24 that rely on soil dispersion and treatment. Most jurisdictions allow installation or construction to 

25 begin after issuance of a construction permit, which occurs after the design and site evaluation 

26 reports have been reviewed and approved. Performance problems linked to installation/ 

27 construction are typically related to soil moisture conditions during construction, operation of 

28 heavy equipment on soil infiltration areas, use of unapproved construction materials (e.g., 

29 unwashed aggregate containing clay or other fines), and overall construction practices (e.g., 

30 altering trench depth, slope, length, location). The effects of improperly installed soil-based 

31 systems generally occur within the first year of operation in the form of wastewater backups. 

32 Some improper construction practices might not be as evident, and could take years to manifest 

33 themselves in the form of degraded groundwater or surface water. The regulatory authority or 

34 other approved professionals should conduct inspections at several stages during the system 

35 installation process to ensure compliance with design and regulatory requirements. 

36 5.9 Operation and Maintenance 

37 O&M for most systems includes some user awareness of inputs that might affect treatment 

38 processes, such as strong cleaners, lye, acids, biocides, paint wastes, oil and grease, and the like. 

39 Gravity-flow, soil-infiltration systems require little O&M beyond limiting inputs to normal 

40 residential wastes, cleaning effluent screens/filters, and periodic tank pumping (e.g., every 3 to 7 
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-26 

1 years). Systems employing advanced treatment technologies and electromechanical components 

2 require more intensive O&M attention, e.g., checking switches and pumps, measuring and 

3 managing sludge levels, monitoring and adjusting treatment process and system timers, checking 

4 effluent filters, monitoring effluent quality, and maintaining disinfection equipment. Operators 

5 and service technicians should be trained and certified for the types of systems they will be 

6 servicing; services should be logged and reported to the management program so that long-term 

7 performance can be tracked. The use of a dial-up modem or Internet-based monitoring 

8 equipment can improve operator efficiency and performance tracking when large numbers of 

9 systems are involved. 

10 5.10 Residuals Management 

11 The primary objective for septage management is to establish procedures for handling and 

12 dispersing the material in a manner that protects public health and water resources and complies 

13 with applicable laws. Approximately 67 percent of the estimated 12.4 billion gallons of septage 

14 produced annually in the United States is hauled to publicly owned treatment works or other 

15 facilities for treatment, while the remaining 33 percent is land applied. Federal regulations (under 

16 40 CFR Part 503) and state/local codes strive to minimize exposure of humans, animals, and the 

17 environment to chemical contaminants and pathogens that are often present in septage. Residuals 

18 management programs include tracking or manifest systems that identify sources, pumpers, 

19 transport equipment, final destination, and treatment or management techniques. 

20 5.11 Training and Certification/Licensing 

21 A variety of professionals and technicians including planners, regulators, designers, installers, 

22 operators, pumpers, and inspectors, are all involved in some aspect of a decentralized wastewater 

23 management program. Training, along with certification or registration, provides system owners 

24 and users with competent service providers and raises the bar in promoting professionalism 

25 among the industry. Service providers need to have a solid working knowledge of treatment 

26 processes, system components, performance options, O&M requirements, and laws/regulations. 

27 Universities, colleges, technical schools, agency-sponsored training programs, regional/local 

28 workshops, or formal/informal apprenticeship programs can provide such training. Service 

29 providers should have extensive and detailed knowledge of their own service areas and a general 

30 grasp of other related activities (e.g., planning or site evaluation). Service providers should 

31 pursue opportunities for cross-training, joint accreditation/certification, and sharing of training 

32 resources wherever possible. 

33 5.12 Inspections and Monitoring 

34 Perhaps the most significant shortcoming in existing management programs is the lack of regular 

35 inspections and performance monitoring. Area-wide monitoring regimes include testing 

36 groundwater and surface waters for indicators of poor treatment, such as the presence of human 

37 fecal bacteria and excess nutrients. All systems need to be inspected, at an interval defined by the 

38 technological complexity of system components, the receiving environment, and the relative risk 

39 posed to public health and valued water resources. The best approach is to establish an inspection 

40 regime and schedule on the basis of the system’s relative reliance on electromechanical 
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Chapter 6. Individual and ClusterClustered (Decentralized) Wastewater Treatment Systems 6-27 

1 components combined with health and environmental risk. Less effective surrogate approaches 

2 include, in order of descending effectiveness (1) requiring comprehensive inspections at regular 

3 intervals; (2) third-party inspections at the time of property transfer; (3) inspections only as part 

4 of complaint investigations. 

5 5.13 Corrective Actions and Enforcement 

6 A decentralized wastewater management program should be enforceable to assure compliance 

7 with laws and to protect public health and the environment. Management agencies should have 

8 the legal authority to adopt rules and assure compliance by levying fines, fees, assessments, or by 

9 requiring service providers to respond to system malfunctions. Program administrators should 

10 emphasize those tools that encourage compliance, rather than punishment. It also helps to have 

11 the support of the courts to implement an effective enforcement program. To assure compliance, 

12 management agencies typically need authority to do the following: 

13 • Respond promptly to complaints 

14 • Issue civil and criminal actions or injunctions 

15 • Provide meaningful performance inspections 

16 • Condemn systems or property 

17 • Issue notices of violation (NOVs) 

18 • Correct system malfunctions 

19 • Implement consent orders and court orders 

20 • Restrict real estate transactions 

21 • Hold formal and informal hearings 

22 • Issue fines and penalties 

23 6 References 

24 Anderson, D.L. 1998. Natural denitrification in ground water impacted by onsite wastewater 

25 treatment systems. In Proceedings of the 8th National Symposium on Individual and Small 

26 Community Sewage Systems, American Society of Agricultural and Biological Engineers, 

27 Orlando, Florida, March 8–10, 1998, pp. 336–-345. 

28 Bedessem, M.E. 2005. Nitrogen removal in laboratory model leachfields with organic-rich 

29 layers. Journal of Environmental Quality 34:936–942.

30 Anderson, D.L. 2002. Pollutant attenuation below onsite wastewater treatment systems in 

31 Florida. In Proceedings of Northeast Onsite Wastewater Treatment Short Course, Newport, 

32 Rhode Island, March 24–26, 2002.

33 Barnard, et al. 2003. Biological Phosphorus Removal. publisher/journal details.
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1 Behrends, L.L., L. Houke, P. Jansen, K. Rylant, and C. Shea. 2007. Recip Water Treatment 

2 System with U.V. Disinfection for Decentralized Wastewater Treatment: Part II: Water 

3 Quality Dynamics. In Proceedings of the National Onsite Wastewater Recycling 

4 Association Annual Meeting, Baltimore, MD, March,dates?

5 Benisch, et al. 2006. How Low Can You Go? publisher/journal details.

6 Blankenship, K. 2007. Terms and trends. Bay Journal, Alliance for the Chesapeake Bay, January 

7 2007. Vol (no):pp–pp

8 Birgand, Francois. 2000. Quantification and Modeling of In-stream Processes in Agricultural 

9 Canals of the Lower Coastal Plain. North Carolina State University, Biological and 

10 Agricultural Engineering Department, Raleigh, NC.

11 Blankenship, K. 2009. New research finds nitrogen loads to the bay underestimated by 20%. Bay 

12 Journal, Alliance for the Chesapeake Bay. Vol (no):pp–pp

13 Boivin, M., R. Lacosse, and M.C. Belanger. 2007. An innovative wastewater treatment approach 

14 for commercial and community applications. In Proceedings of the National Onsite 

15 Wastewater Recycling Association Annual Meeting, Baltimore, MD, dates?.

16 Brown, W.E., W D. Hankins, and E.J. Leonard. 2009. Nitrogen pollution solutions. Water & 

17 Wastes Digest.49(9):pp–pp.

18 Bushman, J.L. 1996. Transport and Transformations of Nitrogen Compounds in Effluent from 

19 Sand Filter-Septic Systemsystem Draintile Fields. MS Thesis, Oregon State University. 

20 Cogger, C. 1988. On-Site Septic Systems: The Risk of Groundwater Contamination. Journal of 

21 Envir. Health, 51(1):12–16. Sept/Oct, 1988.

22 California State Water Resources Control Board. 2008. Draft EIR: AB885 Onsite Wastewater 

23 treatment Systems. <http://www.swrcb.ca.gov/water_issues/programs/septic_tanks/>.

24 Accessed date?

25 Chesapeake Bay Program. 2009. [Insert reference citation for Bay model & assumptions here]

26 Corr, S.H., and A. Blodig. 2006. Installation and Operational Problems with Innovative 

27 Alternative Wastewater treatment Systems. National Onsite Wastewater Recycling 

28 Association Annual Meeting; Denver, CO, dates?.

29 Corr, S.H. and N. Brown, 2002. Field performance of innovative/alternative technologies in the 

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