EPA841-R-10-002 

May 12, 2010 

Guidance for 

Federal Land Management

in the Chesapeake Bay Watershed

Chapter 6. Decentralized Wastewater Treatment Systems 

Nonpoint Source Pollution 

Office of Wetlands, Oceans, and Watersheds 

U.S. Environmental Protection Agency 
Guidance for Federal Land Management in the Chesapeake Bay Watershed

Chapter 6. Decentralized Wastewater Treatment Systems 6‐1

Chapter 6.

Decentralized Wastewater Treatment

Systems 6. 

Contents 

1 Nitrogen-Reduction Implementation Measures....................................................................6-3

2 Introduction and Background ...............................................................................................6-6

3 Nutrient-Reduction Processes for the Decentralized Wastewater Sector............................6-9

3.1 Nitrogen.......................................................................................................................6-9

3.2 Nitrogen Pretreatment.................................................................................................6-9

3.3 Phosphorus ...............................................................................................................6-10

3.4 Permeable Reactive Barriers ....................................................................................6-11

3.5 System Configuration................................................................................................6-12

4 Treatment Technologies and Costs ...................................................................................6-13

4.1 Conventional Systems...............................................................................................6-15

4.2 Land/Vegetative Treatment Systems ........................................................................6-15

4.3 Suspended Growth Systems.....................................................................................6-15

4.4 Attached Growth Aerobic Systems............................................................................6-16

4.5 Add-On Anoxic Filters with a Carbon Source............................................................6-17

4.6 Composting Toilet Systems.......................................................................................6-18

4.7 Cluster Treatment Systems.......................................................................................6-19

4.8 Soil Dispersal Systems..............................................................................................6-19

4.9 Effluent Reuse...........................................................................................................6-20

5 Wastewater Planning and Treatment System Management..............................................6-23

5.1 Public Education and Involvement ............................................................................6-23

5.2 Planning ....................................................................................................................6-24

5.3 Performance Requirements ......................................................................................6-24

5.4 Recordkeeping, Inventories, and Reporting..............................................................6-25
Guidance for Federal Land Management in the Chesapeake Bay Watershed

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5.5 Financial Assistance and Funding.............................................................................6-25

5.6 Site Evaluation ..........................................................................................................6-25

5.7 System Design ..........................................................................................................6-26

5.8 Construction/Installation............................................................................................6-26

5.9 Operation and Maintenance......................................................................................6-27

5.10 Residuals Management.............................................................................................6-27

5.11 Training and Certification/Licensing ..........................................................................6-27

5.12 Inspections and Monitoring .......................................................................................6-28

5.13 Corrective Actions and Enforcement.........................................................................6-28

6 References.........................................................................................................................6-30
Guidance for Federal Land Management in the Chesapeake Bay Watershed

1 Nitrogen-Reduction Implementation Measures 

The U.S. Environmental Protection Agency (EPA) recommends protecting surface waters in the 

Chesapeake Bay watershed from nitrogen (N) discharged by decentralized wastewater 

treatment systems by using N-reduction technologies and enhanced system management. 

Implementation Measures: 

D‐1. 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 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 can be met by either system design or

performance, as verified by third‐party design review or field

verification. Except in sandy or loamy sand soils, a 5 mg/L N

reduction credit is given when using time‐dosed, pressurized

effluent dispersal within 1 foot of the ground surface and

more than 1.5 feet above a limiting soil/bedrock condition.

D‐2. 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.

D‐3. Sustain treatment system performance in perpetuity through management

contracts with trained and certified operators for all advanced N‐removal

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systems, and responsible management entity (RME) operation and

maintenance (O&M) for all cluster and nonresidential systems. RMEs

include sanitation districts, special districts, and other public or private

entities with the technical, managerial, and financial capacity to assure long‐

term system performance.

D‐4. 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) (USEPA 2006) as a free

resource for managing that information in 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 on a schedule according to

wastewater type, system size, complexity, location, and relative

environmental risk. At a minimum, qualified inspectors inspect all

systems at least once every 5 years and inspect existing systems within

sensitive areas at least once every 3 years. Inspect advanced treatment

systems, cluster systems, and those serving commercial, institutional, or

industrial facilities at least semiannually and manage such systems under

an O&M agreement or by an RME. Inspections are consistent with EPA

management guidelines for individual and cluster systems. A service

professional or other trained personnel conducts routine monitoring of

all systems, and periodic effluent sampling for cluster and nonresidential

systems, on the basis of system type, operating history, manufacturer’s

recommendations, and other relevant 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

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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 or shallow pressurized effluent dispersal 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.

D‐5. Remove nitrate in subsurface effluent plumes that enter 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 via denitrification.

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2 Introduction and Background 

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

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

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

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

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

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

(USEPA 2009). 

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

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

(USEPA 2004), although release of P into the environment is a concern in sandy soils under 

certain conditions, especially with poor vertical separation distance with groundwater (Bussey 

1996). However, N in wastewater is ultimately converted to nitrate upon infiltration into aerobic 

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

groundwater and surface water quality. For those reasons, in this guidance EPA focuses on 

implementation measures to reduce N. 

Decentralized wastewater systems contribute approximately 12.5 million pounds of N to the 

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

Chesapeake Bay nutrient loading models, most of the N load from such systems—about 

60 percent—comes from the Potomac and Susquehanna river drainage areas within 

Pennsylvania, Virginia, and Maryland. With 800,000 new systems predicted over the next 

15 years, significant reductions in N loads from new and existing systems are needed. 

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

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

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

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

implementation measures. Implementation measures for achieving the reductions include 

installing treatment units with optimal N-removal capabilities in sensitive areas near surface 

waters; using standard N-removal systems in other areas; and ensuring that all treatment 

systems are appropriately operated, maintained, and managed. The measures encompass a 

range of treatment technologies, planning and performance considerations, and management 

actions needed to address N export from decentralized systems. 

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The implementation measures described in this chapter support two primary goals for 

addressing N inputs to the Chesapeake Bay from these systems: 

 Prevent further impairment of the Chesapeake Bay by significantly reducing N levels in 

wastewater from new residential, commercial, and institutional developments using 

decentralized systems 

 Reduce N inputs to the Chesapeake Bay from existing individual and cluster wastewater 

systems by replacing malfunctioning systems with better-performing technologies and by 

managing all systems to ensure long term performance 

Implementation measures to achieve those goals include repairing or replacing malfunctioning 

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

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

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

watershed, and installing PRBs where technically and economically feasible to reduce N 

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

2 decades of research and field studies on decentralized system applications. 

Key findings on system performance, effects on groundwater, and the opportunities presented 

by next-generation treatment technologies are summarized in the Final Report for the La Pine 

National Decentralized Wastewater Treatment Demonstration Project (Rich 2005), a joint effort 

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

The groundwater investigations have found significant existing nitrogen pollution 

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

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

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

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

denitrifying technologies, the existing contamination would be flushed from the 

groundwater system via existing natural discharge points. 

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

proportion of the nitrogen in residential wastewater, found that conventional 

systems are not protecting the aquifer from nitrate contamination. Conventional 

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

discharged from septic tanks were found to achieve significantly less 

denitrification when process and environmental variables were accounted for. 

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

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

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identified and tested a number of denitrifying wastewater systems and found that performance 

varies considerably. However, some systems do perform optimally in removing TN from the 

effluent—e.g., to concentrations lower than 5 mg/L—and others are capable of N effluent levels 

in the 10 and 20 mg/L range. 

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

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

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

(Walker et al. 1972; Robertson and Cherry 1992). N concentrations in effluent plumes are 

affected by soil oxygen levels, soil composition, plant uptake, labile carbon content, travel 

distance, rate of movement, mixing, and other factors. The measures specified in this chapter 

include descriptions of treatment and dispersal systems that can meet the performance 

standards needed to protect the Chesapeake Bay and its tributaries and include more stringent 

treatment levels in sensitive areas near waterbodies. Such measures are consistent with efforts 

in the states that have already been adopting treatment zone setbacks and treatment standards 

to address N and other pollutants in coastal areas (Joubert et al. 2003). 

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3 Nutrient-Reduction Processes for the 

Decentralized Wastewater Sector 

Nutrients—primarily P and N—are usually present in significant levels in domestic and 

commercial wastewater. Nutrient treatment and removal involve processes that occur either in 

treatment system components or in the receiving environment, as summarized below. 

3.1 Nitrogen 

N is the primary pollutant of concern along the coastal areas of the eastern United States, 

including the Chesapeake Bay. N discharges are a concern both as a drinking water 

contaminant (nitrate) and as an aquatic plant nutrient, particularly in N-sensitive surface waters 

and nearshore marine waters. N is not readily or consistently removed in conventional individual 

and cluster soil-based systems because conventional soil-discharging systems are not designed 

to remove N, and most soils have a limited capacity to retain or remove N. Organic N in 

wastewater is generally converted to ammonium N in the septic tank. Ammonium N is quickly 

nitrified as the wastewater infiltrates the aerobic soil. Nitrate-N is stable, soluble, and highly 

mobile in the subsurface environment. Biological denitrification of the nitrate is usually limited 

because the soil is often aerobic near the ground surface and usually has very little organic 

carbon, which is required by heterotrophic denitrifying microorganisms. Therefore, where N 

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

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

3.2 Nitrogen Pretreatment 

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

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

is the recirculating media filter, with timed pressure-dosing effluent dispersal. The filter media is 

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

septic tank (or pump/recirculating tank) and filter several times before discharge. Denitrification 

is supported by the low-oxygen, high-carbon environment that exists in the recirculating tank. 

The systems are able to consistently remove an average of 50 percent or more of the TN in the 

septic tank effluent—reducing the TN from a typical influent range of 40–50 mg/L for single 

family homes to 15–20 mg/L (Otis 2007; USEPA 2002a; Jenssen and Siegrist 1990; Higgins et 

al. 2002; Smith et al. 2008; Rich et al. 2003). 

To achieve TN levels of 3–5 mg/L and lower, an additional denitrifying unit process is usually 

installed to augment the pretreatment system. To sustain a denitrification process capable of 

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high levels of N removal, the nitrified effluent from the pretreatment process must be exposed to 

a reactive carbon source in a low-oxygen environment before discharge. For larger installations, 

methanol, acetic acid, molasses, or other organic chemicals are added to the anaerobic reactor. 

However, the cost of building, operating, and maintaining an external chemical feeding system, 

coupled with the cost of chemicals, power for a feed pump, controls, and chemical storage 

increase N-removal expenses substantially. 

Carbon sources are not equal in terms of O&M requirements. For example, methanol is very 

sensitive to under- or over-dosing, and thus requires special attention to ensure that the system 

is monitored enough to control dosing for optimal N-removal and biochemical oxygen demand 

control. By contrast, sawdust and newspapers need to be replaced only when effluent N breaks 

through (i.e., the denitrification capacity of the sawdust or newspaper has been exhausted). 

Proprietary denitrifying units, which avoid the need for additional feed pumps, controls, and 

chemicals, are now available. Such units include a slowly degradable organic material in the 

reactor tank that can last several years. Field testing has documented TN effluent 

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

Further N removal occurs in the soil, particularly when pretreated effluent is dispersed uniformly 

via alternating dose/rest cycles. Plant uptake of N, soil oxygen levels, carbon sources, 

temperature, and residence time are key factors in N-removal levels during this final stage of 

treatment, which are estimated in the 50 percent reduction range (Long 1995; Otis 2007). 

Additionally, some soils contain sufficient labile carbon to denitrify effluents regardless of the 

method of dispersal (Anderson 1998; Gold et al. 2002; Starr and Gillham 1986; Bushman 1996; 

Hiscock et al. 1991). Other important variables could include seasonal use (Postma 1992), 

in-stream processes, including the matrix through which the groundwater enters nearby surface 

waters (Birgand 2000; Stewart and Reneau 1984), and the distance from the source to the 

receiving surface waters (Stacey 2002). One study from the U.K. (Hiscock et al. 1991) estimates 

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

3.3 Phosphorus 

Approximately 20 to 30 percent of the P in wastewater is removed in septic tanks (Lombardo 

2006). P removal in soil effluent dispersal systems is achieved primarily by mineral precipitation. 

The process involves sorption and complex biogeochemical mechanisms that rely on dissolved 

P mineralization with iron, calcium, and aluminum (Tyler et al. 2003; Stone Environmental 2005; 

Lombardo 2006). The stability of those processes is influenced by pH, redoximorphic conditions, 

and the chemistry of aluminum and iron. The soil’s capacity to remove P is significant both 

spatially and temporally. Sorption can be reversible—as with sands, or relatively permanent, as 

in soils high in iron oxides. 

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In general, most regions of the Chesapeake Bay watershed have soils that retain high levels of 

P from decentralized systems. Areas where soil-based, P-removal rates are low include highly 

permeable soils, such as sands, loamy sands, and soils very high in gravel. In areas with 

sufficient soil P-removal capacity, saturation fronts of P move only inches or less per year. 

Wastewater system designers maximize P-removal rates by locating the infiltration system in 

medium- to fine-textured soils that are as far from surface waters as possible, and extending the 

infiltration system along the topographic contour of the installation site. Also, uniform dosing and 

resting dispersal by pressure or drip distribution will optimize P removal in the soil by increasing 

the contact time between the effluent and the soil. 

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

(Stone Environmental 2005; Dimick et al. 2006; USEPA 2002a). Although some P can be 

removed by pretreatment systems that contain high concentrations of adsorptive elements or by 

biological P removal, soil adsorption is by far the most common and least expensive means of 

removal. Where soils are inadequate for P removal, mound systems that use more appropriate 

soil (possibly imported) might be required. System use over time slowly reduces the capacity of 

the soil to remove P. 

3.4 Permeable Reactive Barriers 

Specific types of PRBs have been developed to remove nitrate from groundwater plumes that 

would otherwise adversely affect surface water quality. PRBs consist of a trench filled with a 

degradable carbon source (e.g., sawdust, newspaper) and are sited to intercept high-nitrate 

groundwater plumes (WE&T 2009) before they enter surface waters (Figure 6-1). As the plumes 

pass through the low-oxygen, 

carbon-rich barrier, bacteria 

break down nitrate molecules to 

use the oxygen for cell 

respiration. In areas where 

receiving waters are already 

eutrophied, the trenches 

provide immediate relief by 

removing nitrate from the 

incoming groundwater. 

Addressing the source of the 

high-nitrate plume (i.e., densely 

sited septic systems) would 

also produce results, but any 

measureable effects would 

likely take several years 

Source: USEPA 1998 

Figure 6-1. PRB conceptual approach. 

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because of slow effluent plume movement in most soils and could be more expensive and 

require more maintenance than installing PRBs. 

PRBs are typically installed as long, narrow trenches perpendicular to the incoming plume and 

parallel to the shoreline. The most effective ones for removing nitrate from plumes are filled with 

a carbon-based media mix that controls for changes in pH. Such systems have been 

successfully demonstrated in North America and Europe (Vallino and Foreman 2008; Robertson 

and Cherry 1995; Lombardo et al. 2005; USEPA 1998). Costs range from about $5,000 to 

$15,000 per equivalent dwelling unit (i.e., in the plume sourcing area), depending on soils, 

geology, depth to groundwater, subsurface hydrology, construction access, existing 

infrastructure, and other factors. Zero valent iron, now used for some industrial wastewater 

treatment applications, has been studied as a nutrient-removal media in PRBs and other system 

components. Obstacles with this technology include reduction of nitrate to ammonia rather than 

N gas and relatively high costs (Cheng 1997). New variations of this technology hold promise 

for removing some of these obstacles (Lee et al. 2007). 

3.5 System Configuration 

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

(e.g., pressure dosing, drip dispersal) are required for optimum N removal. Their cost in terms of 

both hardware and management needs can be significantly mitigated through the use of cluster 

systems that treat wastewater from multiple homes or businesses. Cluster systems, also called 

community or distributed systems, have become extremely popular in areas where high levels 

of wastewater treatment are required, where space is too limited for on-site conventional soildischarging systems, and local funding capacity precludes conventional sewage collection and 

treatment (see Section 4.6). 

It should be noted that soil-discharging wastewater systems that have the capacity to serve 20 

or more people per day are defined by EPA as Class 5 underground injection wells and are 

therefore subject to permitting and other requirements for large-capacity septic systems under 

the federal Safe Drinking Water Act. Further, any decentralized system that accepts waste other 

than sanitary wastewater (such as industrial waste) is an Underground Injection Control (UIC) 

Class 5 Injection Well. UIC regulatory information for large-capacity septic systems is posted at 

http://www.epa.gov/safewater/uic/class5/types_lg_capacity_septic.html. 

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4 Treatment Technologies and Costs 

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

biochemical oxygen demand), the presence of nonconventional organic or inorganic 

constituents, the sensitivity of the receiving environment, and the capacity of system managers 

to operate and maintain it over the long term. Given those factors, both the selection and 

ongoing use of a specific technology is driven by management considerations. For example, 

wastewater characterization and assessment of the receiving environment are planning-level 

activities that result in establishing performance standards, which begin to identify the narrow 

range of treatment technology options and related design considerations. Once a specific 

system is selected, construction oversight, operation, inspection, maintenance, and residuals 

removal—all management program elements—become paramount in ensuring perpetual 

performance. 

The La Pine Decentralized Wastewater Demonstration Project (Rich 2005) has provided some 

of the most comprehensive field data on the performance of various system types. The 

project—funded by EPA and supported by the Deschutes County, Oregon, Environmental 

Health Division; Oregon Department of Environmental Quality; and the U.S. Geological 

Survey—monitored system performance between 1999 and 2005 (see Figure 6-2 and 

Table 6-1). System performance was found to be affected by a number of variables, but in 

general the level of analysis provides insight on the range of pollutant removal that can be 

expected from the various system types. The figure and table that follow summarize key data 

from the project; detailed performance results, system descriptions, and other information are 

available in the final project report (Rich 2005). 

The subsections that follow discuss the main classes of treatment system technologies. The 

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

implementation measures provided at the beginning of this chapter. Table 6-2 provides 

examples of biological N-removal performance from the literature for a variety of technologies. 

Table 6-3 contains details on specific treatment systems described in the subsections below. 

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Source: Rich 2005. 

Figure 6-2. Effluent TN concentrations for systems tested in the La Pine Project. 

Table 6-1. System components and type classifications for Figure 6-2 

System component/type General classification 

Septic Tank Primary treatment vessel 

Lined Sand Filter Attached growth, sand media 

Bottomless Sand Filter Attached growth, sand media 

AdvanTex AX-20 Attached growth, textile media 

AdvanTex RX-30 Attached growth, textile media 

Puraflo Attached growth, peat media 

Dyno2 Attached growth, gravel media, wetland polishing 

Amphidrome Attached growth/suspended growth hybrid 

Biokreisel Attached growth/suspended growth hybrid 

EnviroServer Attached growth/suspended growth hybrid 

FAST Bio-Microbics Attached growth/suspended growth hybrid 

IDEA Suspended growth 

Nayadic Suspended growth 

NiteLess Suspended growth with add-on anoxic filter 

NITREX Add-on anoxic filter 

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4.1 Conventional Systems 

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

commonly used wastewater treatment technologies. The soil dispersal system facilitates aerobic 

treatment, degradation, filtration, and adsorption of contaminants not treated or retained by the 

septic tank. However, N removal is somewhat limited, with TN concentrations before soil 

application typically in the 40–50 mg/L range. In sandy soils with little organic content, high 

oxygen levels, and poor downgradient mixing, N concentrations can remain high even after 

several hundred feet of effluent plume movement (Walker et al. 1973; Robertson and Cherry 

1992; Cogger 1988; Joubert et al. 2003). Given the low N-removal rates of conventional 

systems (i.e., averaging 20 percent TN removal; Otis 2007; Smith et al. 2008; Jenssen and 

Siegrist 1990), they are no longer appropriate for use in new communities or densely developed 

areas in the Chesapeake Bay watershed. 

4.2 Land/Vegetative Treatment Systems 

Land treatment systems, such as spray irrigation systems, are permitted in some places but 

have not been widely used because of their large land area requirements (USEPA 2000). In 

general, such vegetative treatment systems have shown poor performance with regard to N 

removal. However, in recent years, significant advances have been made. The Living Machine, 

a proprietary decentralized wastewater treatment system has been used successfully for largecapacity applications, such as schools. While the system delivers advanced N removal, it relies 

on multiple treatment processes including anaerobic and aerobic reactors, a clarifier, and an 

ecological fluidizer bed (USEPA 2002b), which drive up the cost. Eco-machines are similar in 

concept to The Living Machine and are capable of advanced N removal. Costs for both of these 

technologies make sense for only fairly large-capacity applications. They are not practical for 

individual residential systems but could be useful for cluster and large system applications. 

4.3 Suspended Growth Systems 

Suspended growth systems, such as activated sludge-based aerobic treatment units (ATUs), 

are generally effective in nitrifying septic tank effluent. Denitrification is somewhat limited but 

can be aided by process controls (e.g., recirculation) and effluent dispersal via time-dosing into 

the upper soil horizon (Stewart 1988). Aerobic units that feature aeration that periodically stops 

and starts show improved denitrification. Sequencing batch reactors, which first fill and then 

draw, in alternating aerobic/anoxic cycles in a single tank might also meet the 20 mg/L 

recommended effluent limit for areas more than 1,000 feet from surface waters in the 

Chesapeake Bay watershed, when effluent is dispersed to the soil via time-dosed pressure 

application (Washington State Department of Health 2005). Capital costs for conventional 

on-site suspended growth systems range from $7,500 to $15,000 per equivalent dwelling unit 

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(EDU), with O&M expenses of $400 to $800 per EDU per year when all suggested O&M tasks 

are performed (Tetra Tech 2007). 

N removal in larger cluster applications of suspended growth systems (i.e., > 200 homes) can 

be enhanced by incorporating a membrane bioreactor process (MBR) unit, which screens 

wastewater through very small pore-size filters. MBRs are more common to centralized 

treatment facilities because of operating costs and economy of scale issues. However, 

individual home-sized and small cluster units are beginning to be developed for the U.S. market 

(e.g., BioBarrier, ZeeWeed; WERF 2006). The high-quality effluent provides opportunities for 

treated water reuse. Cost and performance data for individual and small cluster applications of 

MBRs are not widely available and are likely to vary greatly. Energy costs, particularly to 

operate the pumping components, are often significant, especially in smaller system 

applications (USEPA 2007). 

4.4 Attached Growth Aerobic Systems 

These systems (sometimes called trickling filters or media filters) use natural aeration instead of 

mechanical, produce less sludge for disposal, and require less power and O&M than the 

suspended growth units in performing the same tasks. All the systems listed in Table 6-3 are 

varieties of attached growth system types. Like suspended growth systems, attached growth 

treatment units also require a recirculation step to meet more stringent TN-removal objectives. 

Commercially available systems come in lightweight packages and employ lightweight media for 

easy installation. They also require about 20 percent less physical footprint than typical trickling 

filters. When properly loaded and operated, they can produce very high nitrification levels that 

must be followed by a denitrification step to exceed the typical 50 percent N-removal rate. 

Attached growth systems are also often quite stable compared with suspended growth 

processes, which might be important, particularly for decentralized systems serving periodically 

or seasonally used facilities. On-site capital costs are slightly higher in general than the 

suspended growth ATUs ($10,000–$16,000 per EDU), but O&M costs are significantly less, 

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

N removal in attached growth media filters can be optimized through internal treatment system 

process controls. Single-pass media filters—sand filters, textile filters, peat systems, mounds, 

and other packed media bed units—achieve excellent nitrification levels but generally do a poor 

job with denitrification unless some, or all, of the effluent passes through a carbon-rich, lowoxygen environment after the nitrification stage. That can be accomplished by recirculating a 

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

to the system, or both. Media filters have a long record of excellent performance, with 

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

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

6‐16 Chapter 6. Decentralized Wastewater Treatment Systems
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nonproprietary engineered systems or commercial units that can be installed in a single day. 

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

of $200 to $400 per EDU per year (USEPA 2010; Tetra Tech 2007). 

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

with about 50–70 percent TN reduction. The systems recycle part of the effluent back to the 

septic tank or the recirculating tank, where the anoxic environment and available carbon 

facilitate denitrification processes. Design considerations include the ratio of effluent recirculated 

and the configuration of the recycle plumbing, i.e., ensuring that the recycled effluent is 

discharged to a tank location with low oxygen and some carbon. TN effluent concentrations can 

be as low as 10 mg/L, which can be further reduced in the soil by using time-dosed, pressuredrip effluent dispersal. Engineered systems and proprietary units are widely available and can 

serve single homes or large subdivisions. Capital costs for recirculating systems range from 

$9,500 to $20,000 per EDU, with O&M expenses of $350 to $600 per EDU per year (USEPA 

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

4.5 Add-On Anoxic Filters with a Carbon Source 

Optimal denitrification can be achieved by passing nitrified effluent through a low-oxygen, 

carbon-rich environment before soil dispersal. Engineered and proprietary systems featuring 

add-on anoxic filters with an external carbon source (e.g., methanol, sawdust, newspapers) 

have performed successfully in single-home and cluster applications. For example, at least one 

commercially available product (NITREX) regularly produces effluent with N concentrations of 

less than 5 mg/L (Heufelder et al. 2007, see also Figure 6-2 and Table 6-2). Others claim to 

have similar systems with comparable performance, although, to date, independent field 

verification is lacking. NITREX relies on a passive nitrate remediation biofilter unit that uses a 

processed wood by-product as the filter medium. Other system designs discussed above can 

approach that level when paired with time-dosed, shallow pressurized dispersal. Capital costs 

for add-on denitrification systems range from $3,500 to $7,000 and more per EDU, with O&M 

expenses of less than $100 per year (Washington State Department of Health 2005). Note that 

those are added costs and do not include costs for the septic tank, nitrification process unit, or 

soil dispersal system—just the add-on component. 

Chapter 6. Decentralized Wastewater Treatment Systems 6‐17
Guidance for Federal Land Management in the Chesapeake Bay Watershed

Table 6-2. Examples of biological N removal performance from the literature 

Technology examples 

TN removal efficiency 

(%) 

Effluent TN 

(mg/L) 

Suspended growth 

Aerobic units w/ pulse aeration 25%–61%a 37–60a

Sequencing batch reactor 60%b 15.5b

Attached growth 

Single-Pass Sand Filters (SPSF) 8%–50%c 30–60c

Recirculating Sand/Gravel Filters (RSF) 15%–84%d 10–47d

Multi-Pass Textile Filters (AdvanTex AX20) 64%–70%e 3–55e

RSF w/ Anoxic Filter 40%–90%f 7–23f

RSF w/ Anoxic Filter & external carbon source 74%–80%g 10–13g

RUCK system 29%–54%h 18–53h

NITREX 96%i 2.2i

Source: Adapted from Washington Department of Health 2005 

Notes: Overall performance can vary, depending on system configuration and other factors. For detailed descriptions of 

treatment processes and technologies, see 

http://www.psparchives.com/publications/our_work/hood_canal/hood_canal/n_reducing_technologies.pdf. 

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 

e. NSF International 2009 

f. Ayres Associates 1998; Sandy et al. 1988 

g. Gold et al. 1989 

h. Brooks 1996; Gold et al. 1989 

j. Rich et al. 2003 

4.6 Composting Toilet Systems 

Composting toilet systems that contain and treat toilet wastes can reduce watershed N 

discharges significantly, because such wastes account for 70–80 percent of the TN load in 

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

public facility settings. Like all systems, they require appropriate design and ongoing 

maintenance. A graywater treatment system is needed if the facility generates sink, laundry, or 

other graywater, therefore adding to the cost. Capital costs for composting systems (and 

excluding the cost of graywater systems) range from $2,500 to $10,000, with O&M expenses of 

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

local codes and the owner’s attitude, though acceptance and use of composting systems is 

6‐18 Chapter 6. Decentralized Wastewater Treatment Systems
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increasing because of improved designs, performance, and lower maintenance requirements. 

The systems are more frequently used in public settings, such as parks and campgrounds. 

4.7 Cluster Treatment Systems 

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

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

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

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

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

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

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

uniform application throughout the larger drainfield. Collection technologies include grinder 

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

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

vacuum systems. 

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

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

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

logistics, treatment facility design, land availability, materials, labor costs, and other factors. 

Cluster systems can achieve economies of scale to provide high levels of treatment at costs 

significantly less than individual systems and centralized sewer systems. New cluster systems 

generally range from $10,000 to $18,000 per EDU in non-urbanized areas of new development, 

with higher costs for retrofits in urban areas, depending on the treatment technology used 

(USEPA 2010; Tetra Tech 2007). Replacement and retrofit systems have similar costs, but 

collection system installation can drive costs higher. An RME with the technical, financial, and 

managerial capacity to ensure viable, long-term, cost-effective performance is essential for 

cluster system applications. Total system annual O&M costs range from $450 to $750 per EDU 

per year (Tetra Tech 2007). 

4.8 Soil Dispersal Systems 

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

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

netting; and gravelless, open-bottomed leaching chambers. N removal in the soil increases 

when effluent is dispersed in a time-dosed manner (i.e., dose/rest cycle) in the uppermost soil 

horizon (i.e., within one foot of the ground surface). Time-dosed, pressure-drip dispersal in the 

top 12 inches of soil has been credited with a 50 percent reduction in Tennessee (Long 1995), 

making the option an important feature for achieving the performance standards recommended 

Chapter 6. Decentralized Wastewater Treatment Systems 6‐19
Guidance for Federal Land Management in the Chesapeake Bay Watershed

6‐20 Chapter 6. Decentralized Wastewater Treatment Systems

in this chapter. As in all effluent dispersal systems, maximizing the separation distance between 

effluent application and restrictive soil boundaries (e.g., hardpan, bedrock, perched water 

tables, seasonal high water tables) improves performance. 

Another effluent-dispersal strategy that improves performance is the use of alternating soil 

dispersal fields. Most conventional systems continuously load drainfields with effluent, resulting 

in a gradual reduction of the soil’s capacity to treat effluent over time. Alternating drainfields that 

are used for 6 months then rested for 6 months improves the performance of the soil dispersal 

system and should be favored over conventional drainfields. Such systems require relatively low 

additional investment and can greatly extend the life of the soil dispersal system (Noah 2006). 

Maintenance programs for such systems should be designed and implemented in concert with 

the local health department or RME to ensure that flow-diversion devices are operated on 

schedule. Because this strategy applies to conventional septic drainfields, this recommendation 

applies primarily to areas of new development outside sensitive areas and subdivisions. 

4.9 Effluent Reuse 

Reusing treated wastewater system effluent can significantly reduce N discharge to the 

environment. Many of the technologies suggested for advanced decentralized wastewater 

treatment in the Chesapeake Bay watershed can, with adaptations, be used to produce 

reclaimed water for beneficial reuses, including aquifer recharge, landscape irrigation, toilet 

flushing, fire protection, cooling and other nonpotable indoor and outdoor purposes (USEPA 

2004). When reclaimed water is used for irrigation, reuse can offset potable water demand by 

augmenting supply while sequestering nutrients in vegetative matter and offsetting fertilizer use 

(WERF 2010). Reclaimed water technologies generally include recirculating filtration systems 

and membrane bioreactors, amended with disinfection systems (most commonly, chlorination or 

ultraviolet disinfection or both), online monitoring systems, on-site storage, and sometimes 

specific chemical feed systems for conditioning treated effluent to meet water quality demands 

for specific reuses (e.g., pH adjustment for cooling water). Nonreactive dye injection is 

sometimes required by building codes for reclaimed water to be used indoors. Costs for 

decentralized reclaimed water systems are highly context-specific and dependent on the 

intended reuse application, system size, and local or state regulatory requirements (WERF 

2010) but can be assumed to add 50 percent to the costs of a more traditional decentralized 

system. 
Chapter 6. Decentralized Wastewater Treatment Systems 6‐21 Table 6-3. Products that have completed the EPA ETV process for N reduction in domestic wastewater from individ

2005 System name Technology Description of process Performance 

Waterloo Biofilter® Model 4-Bedroom Waterloo Biofilter Systems, Inc. 143 Dennis St.: P.O. Box 100 Rockwood, Ontario Canada N0B 2K0 http://www.nsf.org/business/water_quality_ protection_center/pdf/Waterloo-VS- SIGNED.pdf Fixed film trickling filter. The biofilter unit uses 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 TN with an average TN 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. $13

systWatwou$7,0

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 switches between 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 TN effluent of 15 mg/L over the 13-month testing period at the Massachusetts Alternative Septic System Test Center (MASSTC). $7,5

manwou$15inst

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 TN with an average TN effluent of 14 mg/L over the 12-month testing period at MASSTC. $11

inclinstmana todistcos
6‐22 Chapter 6. Decentralized Wastewater Treatment Systems

Table 6-3. Products that have completed the EPA ETV process for N reduction in domestic wastewater from individ2005 (continued) System name Technology Description of process Performance 

BioclereTM Model 16/12 Aquapoint, Inc. 241 Duchanine Blvd. New Bedford, MA 02745 http://www.nsf.org/business/water_quality_ 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 TN with an average TN effluent of 16 mg/L over the 13-month testing period at MASSTC. $7,50

total sincludBiocleoptionof $12manufuse in home maintea 27-hcosts home

Retrofast 0.375 System Bio-Microbics 8450 Cole Parkway Shawnee, KS 66227 http://www.nsf.org/business/water_quality_ 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 denitrification. Intermittent use of the blower can also be programmed to reduce electricity use and to increase nitrification. Averaged 51% removal of TN with an average TN effluent of 19 mg/L over the 13-month testing period at MASSTC. Produ

for the Systebe $4on exiincludblowecontrorepresMicrobcould multip

Recip® RTS-500 System 

Bioconcepts, Inc. P.O. Box 885 

Oriental, NC 28571-0885 

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

Fixed film filter 

This is the newest product to complete 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 TN with an average TN effluent of 15 mg/L over the 12-month testing period at MASSTC. 

Very lthis sibuilt foprototby itse$8,00septic would would conditcost fobe $1

Source: Adapted from Washington Department of Health 2005 
Guidance for Federal Land Management in the Chesapeake Bay Watershed

5 Wastewater Planning and Treatment System 

Management 

The previous section describes N-removing individual or cluster wastewater system 

technologies, system configurations, and effluent dispersal options. This section describes 

management considerations that are essential for optimizing treatment system selection, sizing, 

performance, and long-term use, such as inventory systems, wastewater planning, performance 

standards, siting and installation guidelines, operation, inspection, maintenance, and residuals 

handling. The management tasks described in this section are paramount for reducing nutrient 

inputs to the Chesapeake Bay because they establish the framework for selecting and using 

specific treatment systems in particular locations. For example, advanced cluster systems are 

the best approach for protecting and restoring the Chesapeake Bay when considering 

wastewater facilities for new subdivisions and replacing significant numbers of malfunctioning 

systems in existing subdivisions. 

The following subsections summarize key management program elements viewed as important 

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

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

management program topics (USEPA 2005, 2010). Specific, detailed information on each topic 

below is provided in EPA’s (2005) Handbook for Managing Onsite and Clustered (Decentralized) 

Wastewater Treatment Systems, available online at 

http://cfpub.epa.gov/owm/septic/septic.cfm?page_id=289. 

5.1 Public Education and Involvement 

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

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

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

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

must keep the community engaged, involved, and informed. Managers should give special 

consideration to explaining the need for new requirements for system upgrades, inspections, or 

other performance measures. 

EPA has partnered with a variety of nonprofit organizations involved in decentralized 

wastewater management to improve public education, outreach, and involvement through 

development of informational materials, technical products, and training programs. Links to 

these partner organizations and the educational, technical, and other resources they provide are 

provided at http://cfpub.epa.gov/owm/septic/septic.cfm?page_id=260. EPA maintains a 

Chapter 6. Decentralized Wastewater Treatment Systems 6‐23
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repository of print, radio, and TV public service announcements and other materials specifically 

pertaining to septic system education in its Nonpoint Source Outreach Toolbox, online at 

http://www.epa.gov/nps/toolbox/. 

5.2 Planning 

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

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

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

and wastewater infrastructure investments. Integrating wastewater planning functions provides 

better long-term management of facilities and can help local officials deal with a number of 

needs such as sewer overflows, National Pollutant Discharge Elimination System effluent 

limitations, total maximum daily loads (TMDLs), and antidegradation requirements. For 

example, integrated planning can minimize problems associated with competition for infiltration 

areas between wastewater and stormwater management facilities in new developments, and is 

useful in anticipating and preventing adverse water quality effects. Variables to consider during 

the planning process include wastewater flows, proximity and uses of nearby water resources, 

landscape topography, hydrology, hydrogeology, soils, environmentally sensitive areas, 

infrastructure system options and locations, population densities, and need and potential for 

clustering treatment or reuse facilities. 

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

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

Clean Water Act 305(b) assessment reports, TMDLs, wellhead and source water protection 

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

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

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

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

supporting decentralized wastewater treatment would be integrated, or at least coordinated, with 

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

5.3 Performance Requirements 

Performance requirements for systems are necessary to minimize the risks they pose to health 

and water resources. Performance requirements specify objectives for each wastewater 

management system, which can include physical, chemical, and biological process 

components. Performance compliance is based on pollutant-removal estimates for the various 

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

wetlands, soil, disinfection), verified by periodic field inspections and sampling. Performance 

can be measured via numeric or narrative criteria. Numeric criteria reflect time-based, mass 

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loadings or pollutant-concentration limits designed to protect sensitive water resources. 

Pollutants commonly targeted in performance requirements include nutrients, bacteria, oxygen 

demand, and solids. 

5.4 Recordkeeping, Inventories, and Reporting 

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

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

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

electronic databases with field unit data entry (i.e., using a handheld personal digital assistant), 

save-to-file computer assisted design drawings, user-specified reporting formats, and GISbased spatial data management and user interface systems. 

5.5 Financial Assistance and Funding 

Financial assistance might be needed to (1) develop or enhance a management program; 

(2) provide support for constructing and modifying wastewater facilities; and (3) support 

operation of the program. Funding for program development and operation is often available 

from public and private loan or grant sources, supplemented by local matching funds. It can also 

be derived from some form of resource sharing among management program partner 

organizations such as planning departments or health and water resource agencies. Developing 

an RME and financing for constructing and operating facilities require larger investments that 

might come from grants and loans or public-private partnerships. Long-term operating costs are 

usually borne by system users through payment of fees and assessments. 

5.6 Site Evaluation 

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

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

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

the information collected and analyses performed during the site evaluation. Prescriptive site 

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

septic tank/soil dispersal systems and empirical relationships that have evolved over the years. 

A soil analysis to a depth of 4 to 6 feet using a hand auger, drill rig, or a backhoe pit, rather than 

a simple percolation test, provides a better approach for assessing soils, seasonal water table 

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

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

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

and a variety of other properties. Modeling groundwater and surface water impacts of multiple 

Chapter 6. Decentralized Wastewater Treatment Systems 6‐25
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systems in defined areas (e.g., stream subwatershed) can help to further refine performance 

requirements and related system site and design considerations. 

5.7 System Design 

Decentralized wastewater treatment system design requirements focus on protecting public 

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

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

simplify design reviews, but they limit development options and the potential for efficiently 

meeting performance requirements. Where management programs rely on the state code for 

design, there might not be any need for special review procedures for alternative system 

designs. However, in sensitive environments where performance codes are employed, there is 

a need to include allowances for alternative designs even if they only expand the number of 

prescriptive system choices and site parameters for sites that do not meet the conditions for 

conventional systems. Design considerations should address the potential implications of water 

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

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

soil dispersal technologies. 

5.8 Construction/Installation 

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

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

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

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

construction are typically related to soil wetness during construction, operation of heavy 

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

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

depth, slope, length, location). The effects of improperly installed soil-based systems generally 

occur within the first year of operation in the form of wastewater backups. Some improper 

construction practices might not be as evident and could take years to manifest themselves in 

the form of degraded groundwater or surface water. The regulatory authority or other approved 

professionals should conduct inspections at several stages during the system installation 

process to ensure compliance with design and regulatory requirements. 

6‐26 Chapter 6. Decentralized Wastewater Treatment Systems
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5.9 Operation and Maintenance 

O&M is important for all wastewater treatment systems, especially those that rely on 

components that are difficult to remedy if damaged—such as a soil dispersal system. Most 

system user information includes building awareness of inputs that might affect treatment 

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

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

residential wastes, cleaning effluent screens/filters, and periodic tank pumping (e.g., every 3 to 

7 years). Systems employing advanced treatment technologies and electromechanical 

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

measuring and managing sludge levels (important for all systems), monitoring and adjusting 

treatment process and system timers, checking effluent filters, monitoring effluent quality, and 

maintaining disinfection equipment. Operators and service technicians should be trained and 

certified for the types of systems they will be servicing; services should be logged and reported 

into a management tracking system, such as EPA’s TWIST (USEPA 2006), so that long-term 

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

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

systems are involved. 

5.10 Residuals Management 

Septic tanks contain settleable solids, fats, oils, grease, and other residuals that require periodic 

removal. The primary objective for septage management is to establish procedures for handling 

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

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

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

other facilities for treatment, while the remaining 33 percent is applied to land. Federal 

regulations (under Title 40 of the Code of Federal Regulations Part 503) and state/local codes 

strive to minimize exposure of humans, animals, and the environment to chemical contaminants 

and pathogens that are often present in septage. Residuals management programs should 

include tracking or manifest systems that identify sources, pumpers, transport equipment, final 

destination, and treatment or management techniques. 

5.11 Training and Certification/Licensing 

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

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

wastewater management program. Training, along with certification or registration, provides 

system owners and users with competent service providers and promotes professionalism 

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

Chapter 6. Decentralized Wastewater Treatment Systems 6‐27
Guidance for Federal Land Management in the Chesapeake Bay Watershed

processes, system components, performance options, O&M requirements, and 

laws/regulations. Universities, colleges, technical schools, agency-sponsored training programs, 

regional/local workshops, or formal/informal apprenticeship programs can provide such training. 

Service providers should have extensive and detailed knowledge of their own service areas and 

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

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

training resources wherever possible. 

5.12 Inspections and Monitoring 

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

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

groundwater and surface waters for indicators of substandard treatment, such as the presence 

of human fecal bacteria and excess nutrients. All systems need to be inspected, at an interval 

defined by the technological complexity of system components, the receiving environment, and 

the relative risk posed to public health and valued water resources. The best approach is to 

establish an inspection regime and schedule on the basis of the system’s relative reliance on 

electromechanical components combined with health and environmental risk. Less effective 

surrogate approaches include, in order of descending effectiveness (1) requiring comprehensive 

inspections at regular intervals; (2) third-party inspections at the time of property transfer; 

(3) inspections only as part of complaint investigations. 

5.13 Corrective Actions and Enforcement 

A decentralized wastewater management program should be enforceable to assure compliance 

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

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

by requiring service providers to respond to system malfunctions. Program administrators 

should emphasize those tools that encourage compliance, rather than punishment. It also helps 

to have the support of the courts to implement an effective enforcement program. To assure 

compliance, management agencies typically need authority to do the following: 

 Respond promptly to complaints 

 Issue civil and criminal actions or injunctions 

 Provide meaningful performance inspections 

 Condemn systems or property 

 Issue notices of violation (NOVs) 

 Correct system malfunctions 

6‐28 Chapter 6. Decentralized Wastewater Treatment Systems
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 Implement consent orders and court orders 

 Restrict real estate transactions 

 Hold formal and informal hearings 

 Issue fines and penalties 

Chapter 6. Decentralized Wastewater Treatment Systems 6‐29
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6 References 

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

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

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

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

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

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

Behrends, L.L., L. Houke, P. Jansen, K. Rylant, and C. Shea. 2007. Recip Water Treatment 

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

Quality Dynamics. In Proceedings of the National Onsite Wastewater Recycling 

Association Annual Meeting, Baltimore, MD, March, 2007. 

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