US EPA Wastewater Treatment Manual Background and Use of Onsite Wastewater Treatment Systems
     

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US EPA Wastewater Treatment Manual - Online

- EPA600/R-00/008 - Chapter1: 
Background and Use of Onsite Wastewater Treatment Systems

1.1 Introduction
1.2 History of onsite wastewater treatment systems
1.3 Regulation of onsite wastewater treatment systems
1.4 Onsite wastewater treatment system use, distribution, and failure rate
1.5 Problems with existing onsite wastewater management programs
1.6 Performance-based management of onsite wastewater treatment systems
1.7 Coordinating onsite system management with watershed protection efforts
1.8 USEPA initiatives to improve onsite system treatment and management
1.9 Other initiatives to assist and improve onsite management efforts


1.1 Introduction

Onsite wastewater treatment systems (OWTSs) have evolved from the pit privies used widely throughout history to installations capable of producing a disinfected effluent that is fit for human consumption. Although achieving such a level of effluent quality is seldom necessary, the ability of onsite systems to remove settleable solids, floatable grease and scum, nutrients, and pathogens from wastewater discharges defines their importance in protecting human health and environmental resources. In the modern era, the typical onsite system has consisted primarily of a septic tank and a soil absorption field, also known as a subsurface wastewater infiltration system, or SWIS (figure 1-1).

In this manual, such systems are referred to as conventional systems. Septic tanks remove most settleable and floatable material and function as an anaerobic bioreactor that promotes partial digestion of retained organic matter. Septic tank effluent, which contains significant concentrations of pathogens and nutrients, has traditionally been discharged to soil, sand, or other media absorption fields (SWISs) for further treatment through biological processes, adsorption, filtration, and infiltration into underlying soils.

Conventional systems work well if they are installed in areas with appropriate soils and hydraulic capacities; designed to treat the incoming waste load to meet public health, ground water, and surface water performance standards; installed properly; and maintained to ensure long-term performance.

Figure 1-1. Conventional onsite wastewater treatment system


Source: NSFC, 2000.

These criteria, however, are often not met. Only about one-third of the land area in the United States has soils suited for conventional subsurface soil absorption fields. System densities in some areas exceed the capacity of even suitable soils to assimilate wastewater flows and retain and transform their contaminants. In addition, many systems are located too close to ground water or surface waters and others, particularly in rural areas with newly installed public water lines, are not designed to handle increasing wastewater flows.

Conventional onsite system installations might not be adequate for minimizing nitrate contamination of ground water, removing phosphorus compounds, and attenuating pathogenic organisms (e.g., bacteria, viruses).

Nitrates that leach into ground water used as a drinking water source can cause methemoglobinemia, or blue baby syndrome, and other health problems for pregnant women. Nitrates and phosphorus discharged into surface waters directly or through subsurface flows can spur algal growth and lead to eutrophication and low dissolved oxygen in lakes, rivers, and coastal areas. In addition, pathogens reaching ground water or surface waters can cause human disease through direct consumption, recreational contact, or ingestion of contaminated shellfish.

Sewage might also affect public health as it backs up into residences or commercial establishments because of OWTS failure.

Nationally, states and tribes have reported in their 1998 Clean Water Act section 303(d) reports that designated uses (e.g., drinking water, aquatic habitat) are not being met for 5,281 waterbodies because of pathogens and that 4,773 waterbodies are impaired by nutrients. Onsite systems are one of many known contributors of pathogens and nutrients to surface and ground waters. Onsite wastewater systems have also contributed to an overabundance of nutrients in ponds, lakes, and coastal estuaries, leading to overgrowth of algae and other nuisance aquatic plants.

Threats to public health and water resources (table 1-1) underscore the importance of instituting management programs with the authority and resources to oversee the full range of onsite system activities--planning, siting, design, installation, operation, monitoring, and maintenance. EPA has issued draft Guidelines for Management of Onsite/ Decentralized Wastewater Systems (USEPA, 2000) to improve overall management of OWTSs. These guidelines are discussed in more detail in chapter 2.

Table 1-1. Typical pollutants of concern in effluent from onsite wastewater treatment systems

Pollutant Public health or water resource impacts
Pathogens Parasites, bacteria, and viruses can cause communicable diseases through direct or indirect body contact or ingestion of contaminated water or shellfish. Pathogens can be transported for significant distances in ground water or surface waters.
Nitrogen Nitrogen is an aquatic plant nutrient that can contribute to eutrophication and dissolved oxygen loss in surface waters, especially in nitrogen-limited lakes, estuaries, and coastal embayments. Algae and aquatic weeds can contribute trihalomethane (THM) precursors to the water column that might generate carcinogenic THMs in chlorinated drinking water. Excessive nitrate-nitrogen in drinking water can cause methemoglobinemia in infants and pregnancy complications.
Phosphorus Phosphorus is an aquatic plant nutrient that can contribute to eutrophication of phosphorus-limited inland surface waters. High algal and aquatic plant production during eutrophication is often accompanied by increases in populations of decomposer bacteria and reduced dissolved oxygen levels for fish and other organisms.

1.2 History of onsite wastewater treatment systems

King Minos installed the first known water closet with a flushing device in the Knossos Palace in Crete in 1700 BC. In the intervening 3,700 years, societies and the governments that serve them have sought to improve both the removal of human wastes from indoor areas and the treatment of that waste to reduce threats to public health and ecological resources. The Greeks, Romans, British, and French achieved considerable progress in waste removal during the period from 800 BC to AD 1850, but removal often meant discharge to surface waters; severe contamination of lakes, rivers, streams, and coastal areas; and frequent outbreaks of diseases like cholera and typhoid fever.

By the late 1800s, the Massachusetts State Board of Health and other state health agencies had documented links between disease and poorly treated sewage and recommended treatment of wastewater through intermittent sand filtration and land application of the resulting sludge.

The past century has witnessed an explosion in sewage treatment technology and widespread adoption of centralized wastewater collection and treatment services in the United States and throughout the world. Although broad uses of these systems have vastly improved public health and water quality in urban areas, homes and businesses without centralized collection and treatment systems often continue to depend on technologies developed more than 100 years ago.

Septic tanks for primary treatment of wastewater appeared in the late 1800s, and discharge of tank effluent into gravel-lined subsurface drains became commonpractice during the middle of the 20th century (Kreissl, 2000).

Scientists, engineers, and manufacturers in the wastewater treatment industry have developed a wide range of alternative technologies designed to address increasing hydraulic loads and water contamination by nutrients and pathogens. These technologies can achieve significant pollutant removal rates. With proper management oversight, alternative systems (e.g., recirculating sand filters, peat-based systems, package aeration units) can be installed in areas where soils, bedrock, fluctuating ground water levels, or lot sizes limit the use of conventional systems.

Alternative technologies typically are applied to the treatment train beyond the septic tank (figure 1-2). The tank is designed to equalize hydraulic flows; retain oils, grease, and settled solids; and provide some minimal anaerobic digestion of settleable organic matter. Alternative treatment technologies often provide environments (e.g., sand, peat, artificial media) that promote additional biological treatment and r emove pollutants through filtration, absorption, and adsorption. All of the alternative treatment technologies in current use require more intensive management and monitoring than conventional OWTSs because of mechanical components, additional residuals generated, and process sensitivities (e.g., to wastewater strength or hydraulic loading).

Figure 1-2. Typical single-compartment septic tank with at-grade inspection ports and effluent screen

Please contact Lynnann Hitchens at 513-569-7672 for details.

Source: NSFC, 2000

Replacing gravity-flow subsurface soil infiltration beds with better-performing alternative distribution technologies can require float-switched pumps and/ or valves.

As noted in chapter 4, specialized excavation or structures might be required to house some treatment system components, including the disinfection devices (e.g., chlorinators, ultraviolet lamps) used by some systems.

In addition, it is often both efficient and effective to collect and treat septic tank effluent from clusters of individual sources through a community or cluster system driven by gravity, pressure, or vacuum. These devices also require specialized design, operation, and maintenance and enhanced management oversight.

1.3 Regulation of onsite wastewater treatment systems

Public health departments were charged with enforcing the first onsite wastewater "disposal" laws, which were mostly based on soil percolation tests, local practices, and past experience. Early codes did not consider the complex interrelationships among soil conditions, wastewater characteristics, biological mechanisms, and climate and prescribed standard designs sometimes copied from jurisdictions in vastly different geoclimatic regions. In addition, these laws often depended on minimally trained personnel to oversee design, permitting, and installation and mostly untrained, uninformed homeowners to operate and maintain the systems.

During the 1950s states began to adopt laws upgrading onsite system design and installation practices to ensure proper functioning and eliminate the threats posed by waterborne pathogens (Kreissl, 1982). Despite these improvements, many regulations have not considered cumulative ground water and surface water impacts, especially in areas with high system densities and significant wastewater discharges.

Kreissl (1982) and Plews (1977) examined changes in state onsite wastewater treatment regulations prompted by the publication of the first U.S. Public Health Service Manual of Septic-Tank Practice in 1959. Plews found significant code revisions under way by the late 1970s, mostly because of local experience, new research information, and the need to accommodate housing in areas not suited for conventional soil infiltration systems.

Kreissl found that states were gradually increasing required septic tank and drainfield sizes but also noted that 32 states were still specifying use of the percolation test in system sizing in 1980, despite its proven shortcomings. Other differences noted among state codes included separation distances between the infiltration trench bottom and seasonal ground water tables, minimum trench widths, horizontal setbacks to potable water supplies, and maximum allowable land slopes (Kreissl, 1982).

Although state lawmakers have continued to revise onsite system codes, most revisions have failed to address the fundamental issue of system performance in the context of risk management for both a site and the region in which it is located. Prescribed system designs require that site conditions fit system capabilities rather than the reverse and are sometimes incorrectly based on the assumption that centralized wastewater collection and treatment services will be available in the future.

Codes that emphasize prescriptive standards based on empirical relationships and hydraulic performance do not necessarily protect ground water and surface water resources from public health threats. Devising a new regime for protecting public health and the environment in a cost-effective manner will require increased focus on system performance, pollutant transport and fate and resulting environmental impacts, and integration of the planning, design, siting, installation, maintenance, and management functions to achieve public health and environmental objectives.

1.4 Onsite wastewater treatment system use, distribution, and failure rate

According to the U.S. Census Bureau (1999), approximately 23 percent of the estimated 115 million occupied homes in the United States are served by onsite systems, a proportion that has changed little since 1970. As shown in figure 1-3 and table 1-2, the distribution and density of homes with OWTSs vary widely by state, with a high of about 55 percent in Vermont and a low of around 10 percent in California (U.S. Census Bureau, 1990).

New England states have the highest proportion of homes served by onsite systems: New Hampshire and Maine both report that about half of all homes are served by individual wastewater treatment systems. More than a third of the homes in the southeastern states depend on these systems, including approximately 48 percent in North Carolina and about 40 percent in both Kentucky and South Carolina. More than 60 million people depend on decentralized systems, including the residents of about one-third of new homes and more than half of all mobile homes nationwide (U.S. Census Bureau, 1999). Some communities rely completely on OWTSs.

Figure 1-3. Onsite treatment system distribution in the United States

Please contact Lynnann Hitchens at 513-569-7672 for details.

Source: U.S. Census Bureau, 1990.

Table 1-2. Census of housing tables: sewage disposal, 1990
 

Public sewer

Septic tank or cesspool

Other means

Number

Percent

Number

Percent

Number

Percent

United States 76,455,211 74.8 24,670.877 24.1 1,137,590 1.1
Alabama 910.782 54.5 728,690 43.6 30,907 1.9
Alaska 144,905 62.3 59,886 25.7 27,817 12.0
Arizona 1,348,836 81.3 282,897 17.0 27,697 1.7
Arkansas 601,188 60.1 382,467 38.2 17,012 1.7
California 10,022,843 89.6 1,092,174 9.8 67,865 0.6
Colorado 1,283,186 86.9 183,817 12.4 10,346 0.7
Connecticut 935,541 70.8 378,382 28.6 6,927 0.5
Delaware 212,793 73.4 74,541 25.7 2,585 0.9
District of Columbia 276,481 99.3 575 0.2 1,433 0.5
Florida 4,499,793 73.8 1,559,113 25.6 41,356 0.7
Georgia 1,638,979 62.1 970,686 36.8 28,753 1.1
Hawaii 312,812 80.2 72,940 18.7 4,058 1.0
Idaho 264,618 64.0 142.879 34.6 5,830 1.4
Illinois 3,885,689 86.2 598,125 13.3 22,461 0.5
Indiana 1,525,810 67.9 703.032 31.3 17,204 0.8
Iowa 869,056 76.0 264,889 23.2 9,724 0.9
Kansas 847,767 81.2 187,398 17.9 8,947 0.9
Kentucky 849,491 56.4 600,182 39.8 57,172 3.8
Louisiana 1,246,678 72.6 442,758 25.8 26,805 1.6
Maine 266,344 45.4 301,373 51.3 19,328 3.3
Maryland 1,533,799 81.1 342,523 18.1 15,595 0.8
Massachusetts 1,803,176 72.9 659,120 26.7 10,415 0.4
Michigan 2,724,408 70.8 1,090,481 28.3 33,037 0.9
Minnesota 1,356,520 73.4 467,936 25.3 23,989 1.3
Mississippi 585,185 57.9 387,406 38.3 37,832 3.7
Missouri 1,617,996 73.6 532,844 24.2 48,289 2.2
Nebraska 218,372 60.5 135,371 37.5 7,412 2.1
Nevada 534,692 80.9 117,460 17.8 8,469 1.3
New Hampshire 456,107 87.9 60,508 11.7 2,243 0.4
New Jersey 250,060 49.6 246,692 49.0 7,152 1.4
New Mexico 2,703,489 87.9 357,890 11.6 13,931 0.5
New York 452,934 71.7 161,068 25.5 18,056 2.9
North Carolina 1,403,033 49.8 1,365,632 48.5 49,528 1.8
North Dakota 204,328 73.9 66,479 24.1 5,533 2.0
Ohio 3,392,785 77.6 940,943 21.5 38,217 0.9
Oklahoma 1,028,594 73.1 367,197 26.1 10,708 0.8
Oregon 835,545 70.0 349,122 29.3 8,900 0.7
Pennsylvania 3,670,338 74.3 1,210,054 24.5 57,748 1.2
Rhode Island 293,901 70.9 118,410 28.6 2,261 0.5
South Carolina 825,754 58.0 578,129 40.6 20,272 1.4
South Dakota 207,996 71.1 78,435 26.8 6,005 2.1
Tennessee 1,213,934 59.9 781,616 38.6 30,517 1.5
Texas 5,690,550 81.2 1,266,713 18.1 51,736 0.7
Utah 528,864 88.4 65,403 10.9 4,121 0.7
Vermont 115,201 42.5 149,125 55.0 6,888 2.5
Virginia 1,740,787 69.7 707,409 28.3 48,138 1.9
Washington 1,387,396 68.3 630,646 31.0 14,336 0.7
West Virginia 427,930 54.8 318,697 40.8 34,668 4.4
Wisconsin 1,440,024 70.0 580,836 28.3 34,914 1.7
Wyoming 151,004 74.2 49,055 24.1 3,352 1.6

Source: U.S. Census Bureau, 1990.

A number of systems relying on outdated and under performing technologies (e.g., cesspools, drywells) still exist, and many of them are listed among failed systems. Moreover, about half of the occupied homes with onsite treatment systems are more than 30 years old (U.S. Census Bureau, 1997), and a significant number report system problems.

A survey conducted by the U.S. Census Bureau (1997) estimated that 403,000 homes experienced septic system breakdowns within a 3-month period during 1997; 31,000 reported four or more breakdowns at the same home. Studies reviewed by USEPA cite failure rates ranging from 10 to 20 percent (USEPA, 2000). System failure surveys typically do not include systems that might be contaminating surface or ground water, a situation that often is detectable only through site-level monitoring. Figure 1-4 demonstrates ways that effluent water from a septic system can reach ground water or surface waters.

Figure 1-4. Fate of water discharged to onsite wastewater treatment systems.

Please contact Lynnann Hitchens at 513-569-7672 for details.

Source: Adapted from Venhuizen, 1995.

Comprehensive data to measure the true extent of septic system failure are not currently collected by any single organization. Although estimates of system failure rates have been collected from 28 states (table 1-3), no state had directly measured its own failure rate and definitions of failure vary (Nelson et al., 1999). Most available data are the result of incidents that directly affect public health or are obtained from homeowners' applications for permits to replace or repair failing systems.

The 20 percent failure rate from the Massachusetts time-of transfer inspection program is based on an inspection of each septic system prior to home sale, which is a comprehensive data collection effort. However, the Massachusetts program only identifies failures according to code and does not track ground water contamination that may result from onsite system failures. In addition to failures due to age and hydraulic overloading, OWTSs can fail because of design, installation, and maintenance problems.

Hydraulically functioning systems can create health and ecological risks when multiple treatment units are installed at densities that exceed the capacity of local soils to assimilate pollutant loads. System owners are not likely to repair or replace aging or otherwise failing systems unless sewage backup, septage pooling on lawns, or targeted monitoring that identifies health risks occurs.

Because ground and surface water contamination by onsite systems has rarely been confirmed through targeted monitoring, total failure rates and onsite system impacts over time are likely to be significantly higher than historical statistics indicate.

For example, the Chesapeake Bay Program found that 55 to 85 percent of the nitrogen entering an onsite system can be discharged into ground water (USEPA, 1993). A 1991 study concluded that conventional systems accounted for 74 percent of the nitrogen entering Buttermilk Bay in Massachusetts (USEPA, 1993).

Table 1-3. Estimated onsite treatment system failure rates in surveyed states.

State Estimated system failure
rate (percentage)
Failure definition
Alabama 20 Not given
Arizona 0.5 Surfacing, backup, surface or ground water contamination
California 1-4 Surfacing backup, surface or ground water contamination
Florida 1-2 Surfacing backup, surface or ground water contamination
Georgia 1.7 Public hazard
Hawaii 15-35 Improper construction, overflow
Idaho 20 Backup, surface or ground water contamination
Kansas 10-15 Surfacing, nuisance conditions (for installations after 1980)
Louisiana 50 Not given
Maryland 1 Surfacing, surface or ground water contamination
Massachusetts 25 Public health
Minnesota 50-70 Cesspool, surfacing, inadequate soil layer, leaking
Missouri 30-50 Backup, surface or ground water contamination
Nebraska 40 Nonconforming system, water quality
New Hampshire <5 Surfacing, backup
New Mexico 20 Surfacing
New York 4 Backup, surface or ground water contamination
North Carolina 15-20 Not given
North Dakota 28 Backup, surfacing
Ohio 25-30 Backup, surfacing
Oklahoma 5-10 Backup, surfacing, discharge off property
Rhode Island 25 Not given
South Carolina 6-7 Backup, surface or ground water contamination
Texas 0-15 Surfacing, surface or ground water contamination
Utah 0.5 Surfacing, backup, exceed discharge standards
Washington 33 Public health hazard
West Virginia 60 Backup, surface or ground water contamination
Wyoming 0.4 Backup, surfacing, ground water contamination
a Failure rates are estimated and vary with the definition of failure.
Source: Nelson et al., 1999.

1.5 Problems with existing onsite wastewater management programs

Under a typical conventional system management approach, untrained and often uninformed system owners assume responsibility for operating and maintaining their relatively simple, gravity-based systems. Performance results under this approach can vary significantly, with operation and maintenance functions driven mostly by complaints or failures. In fact, many conventional system failures have been linked to operation and maintenance failures.

Typical causes of failure include unpumped and sludge-filled tanks, which result in clogged absorption fields, and hydraulic overloading caused by increased occupancy and greater water use following the installation of new water lines to replace wells and cisterns. Full-time or high use of vacation homes served by systems installed under outdated practices or designed for part-time occupancy can cause water quality problems in lakes, coastal bays, and estuaries. Landscape modification, alteration of the infiltration field surface, or the use of outdated technologies like drywells and cesspools can also cause contamination problems.

Newer or "alternative" onsite treatment technologies are more complex than conventional systems and incorporate pumps, recirculation piping, aeration, and other features (e.g., greater generation of residuals) that require ongoing or periodic monitoring and maintenance. However, the current management programs of most jurisdictions do not typically oversee routine operation and maintenance activities or detect and respond to changes in wastewater loads that can overwhelm a system.

In addition, in many cases onsite system planning and siting functions are not linked to larger ground water and watershed protection programs. The challenge for onsite treatment regulators in the new millennium will be to improve traditional health based programs for ground water and surface water protection while embracing a vigorous role in protecting and restoring the nation's watersheds.

The challenge is significant. Shortcomings in many management programs have resulted in poor system performance, public health threats, degradation of surface and ground waters, property value declines, and negative public perceptions of onsite treatment as an effective wastewater management option. (See examples in section 1.1.) USEPA (1987) has identified a number of critical problems associated with programs that lack a comprehensive management program:

  • Failure to adequately consider site-specific environmental conditions.
  • Codes that thwart adaptation to difficult local site conditions and are unable to accommodate
  • effective innovative and alternative technologies.
  • Ineffective or nonexistent public education and training programs.
  • Failure to include conservation and potential reuse of water.
  • Ineffective controls on operation and maintenance of systems, including residuals (septage, sludge).
  • Failure to consider the special characteristics and requirements of commercial, industrial, and large residential systems.
  • Weak compliance and enforcement programs.
  • These problems can be grouped into three primary areas: (1) insufficient funding and public involvement; (2) inappropriate system design and selection processes; and (3) poor inspection, monitoring, and program evaluation components. Management programs that do not address these problems can directly and indirectly contribute to significant human health risks and environmental degradation.

1.5.1 Public involvement and education

Public involvement and education are critical to successful onsite wastewater management. Engaging the public in wastewater treatment issues helps build support for funding, regulatory initiatives, and other elements of a comprehensive program. Educational activities directed at increasing general awareness and knowledge of onsite management efforts can improve the probability that simple, routine operation and maintenance tasks (e.g., inspecting for pooled effluent, pumping the tank) are carried out by system owners.

Specialized training is required for system managers responsible for operating and maintaining systems with more complex components. Even conventional, gravity-based systems require routine pumping, monitoring, and periodic inspection of sludge and scum buildup in septic tanks. Failing systems can cause public health risks and environmental damage and are expensive to repair. System owners should be made aware of the need for periodically removing tank sludge, maintaining system components, and operating systems within their design limitations to help maximize treatment effectiveness and extend the life of the systems.

Information regarding regular inspections, pumping, ground water threats from chemicals, hydraulic overloading from roof runoff or other clear water sources, pollutant loads from garbage disposal units, drain field protection, and warning signs of failing systems can be easily communicated. Flyers, brochures, posters, news media articles, and other materials have proven effective in raising awareness and increasing public knowledge of onsite wastewater management issues (see Resources section).

Meetings with stakeholders and elected officials and face-to-face training programs for homeowners can produce better results when actions to strengthen programs are required (USEPA, 1994). Public involvement and education programs are often overlooked because they require resources, careful planning, and management and can be labor-intensive. However, these efforts can pay rich dividends in building support for the management agency and improving system performance. Public education and periodic public input are also needed to obtain support for developing and funding a wastewater utility or other comprehensive management program (see chapter 2).

1.5.2 Financial support

Funding is essential for successful management of onsite systems. Adequate staff is required to implement the components of the program and objectively enforce the regulations. Without money to pay for planning, inspection, and enforcement staff, these activities will not normally be properly implemented. Financial programs might be needed to provide loans or cost-share grants to retrofit or replace failing systems.

Statewide public financing programs for onsite systems like the PENNVEST initiative in Pennsylvania provide a powerful incentive for upgrading inadequate or failed systems (Pennsylvania Infrastructure Investment Authority, 1997). Regional cost-share programs like the Triplett Creek Project in Kentucky, which provided funding for new septic tanks and drain field repairs, are also effective approaches for addressing failed systems (USEPA, 1997). Chapter 2 and the Resources section provide more information on funding options for onsite systems and management programs.

Managing onsite systems is particularly challenging in small, unincorporated communities without paid staff. Programs staffed by trained volunteers and regional "circuit riders" can help deliver technical expertise at a low cost in these situations. Developing a program uniquely tailored to each community requires partnerships, ingenuity, commitment, and perseverance.

1.5.3 Support from elected officials

In most cases the absence of a viable oversight program that addresses the full range of planning, design, siting, permitting, installation, operation, maintenance, and monitoring activities is the main reason for inadequate onsite wastewater system management. This absence can be attributed to a number of factors, particularly a political climate in which the value of effective onsite wastewater management is dismissed as hindering economic development or being too restrictive on rural housing development. In addition, low population densities, low incomes, underdeveloped management entities, a history of neglect, or other unique factors can impede the development of comprehensive management programs.

Focusing on the public health and water resource impacts associated with onsite systems provides an important perspective for public policy discussions on these issues.

Sometimes state and local laws prevent siting or design options that could provide treatment and recycling of wastewater from onsite systems. For example, some state land use laws prohibit using lands designated as resource lands to aid in the development of urban uses. Small communities or rural developments located near state resource lands are unable to use those lands to address onsite problems related to space restrictions, soil limitations, or other factors (Fogarty, 2000).

The most arbitrary siting requirement, however, is the minimum lot size restriction incorporated into many state and local codes. Lot size limits prohibit onsite treatment system installations on nonconforming lots without regard to the performance capabilities of the proposed system. Lot size restrictions also serve as an inappropriate but de facto approach to land use planning in many localities because they are often seen as establishing the allowable number of housing units in a development without regard to other factors that might increase or decrease that number.

    Note: This manual is not intended to be used to determine appropriate or inappropriate uses of land. The information the manual presents is intended to be used to select appropriate technologies and management strategies that minimize risks to human health and water resources in areas that are not connected to centralized wastewater collection and treatment systems.

When developing a program or regulation, the common tendency is to draw on experience from other areas and modify existing management plans or codes to meet local needs. However, programs that are successful in one area of the country might be inappropriate in other areas because of differences in economic conditions, environmental factors, and public agency structures and objectives. Transplanting programs or program components without considering local conditions can result in incompatibilities and a general lack of effectiveness. Although drawing on the experience of others can save time and money, local planners and health officials need to make sure that the programs and regulations are appropriately tailored to local conditions.

Successful programs have site evaluation, inspection, and monitoring processes to ensure that regulations are followed. Programs that have poor inspection and monitoring components usually experience low compliance rates, frequent complaints, and unacceptable performance results. For example, some states do not have minimum standards applicable to the various types of onsite systems being installed or do not require licensing of installers (Suhrer, 2000). Standards and enforcement practices vary widely among the states, and until recently there has been little training for local officials, designers, or installers.

USEPA has identified more effective management of onsite systems as a key challenge for efforts to improve system performance (USEPA, 1997). In its Response to Congress on Use of Decentralized Wastewater Treatment Systems, USEPA noted that "adequately managed decentralized wastewater treatment systems can be a cost-effective and long term option for meeting public health and water quality goals, particularly for small towns and rural areas."

In addition, the Agency found that properly managed onsite systems protect public health and water quality, lower capital and maintenance costs for low-density communities, are appropriate for varying site conditions, and are suitable for ecologically sensitive areas (USEPA, 1997). However, USEPA identified several barriers to the increased use of onsite systems, including the lack of adequate management programs. Although most communities have some form of management program in place, there is a critical lack of consistency. Many management programs are inadequate, underdeveloped, or too narrow in focus, and they might hinder widespread public acceptance of onsite systems as viable treatment options or fail to protect health and water resources.

1.6 Performance-based management of onsite wastewater treatment systems

Performance-based management approaches have been proposed as a substitute for prescriptive requirements for system design, siting, and operation. In theory, such approaches appear to be both irresistibly simple and inherently logical. In practice, however, it is often difficult to certify the performance of various treatment technologies under the wide range of climates, site conditions, hydraulic loads, and pollutant outputs they are subjected to and to predict the transport and fate of those pollutants in the environment.

Despite these difficulties, research and demonstration projects conducted by USEPA, the National Small Flows Clearinghouse, the National Capacity Development Project, private consultants and engineering firms, academic institutions, professional associations, and public agencies have collectively assembled a body of knowledge that can provide a framework for developing performance-based programs.

Performance ranges for many alternative systems operating under a given set of climatic, hydrological, site, and wastewater load conditions have been established. The site evaluation process is becoming more refined and comprehensive (see chapter 5) and has moved from simple percolation tests to a more comprehensive analysis of soils, restrictive horizons, seasonal water tables, and other factors. New technologies that incorporate lightweight media, recirculation of effluent, or disinfection processes have been developed based on performance.

A performance-based management program makes use of recent developments to select and size system technologies appropriate for the estimated flow and strength of the wastewater at the site where treatment is to occur. For sites with appropriate soils, ground water characteristics, slopes, and other features, systems with subsurface wastewater infiltration systems (SWISs) might be the best option.

Sites with inadequate soils, high seasonal water tables, or other restrictions require alternative approaches that can achieve performance objectives despite restrictive site features. Selecting proven system designs that are sized to treat the expected wastewater load is the key to this approach. Installing unproven technologies on provisional sites is risky even if performance monitoring is to be conducted because monitoring is often expensive and sometimes inconclusive.

1.6.1 Prescriptive management programs

Onsite system management has traditionally been based on prescriptive requirements for system design, siting, and installation. Installation of a system that "complies" with codes is a primary goal. Most jurisdictions specify the type of system that must be installed and the types and depth of soils that must be present. They also require mandatory setbacks from seasonally high water tables, property lines, wells, surface waters, and other landscape features. Some of these requirements (e.g., minimum setback distances from streams and reservoirs) are arbitrary and vary widely among the states (Curry, 1998).

The prescriptive approach has worked well in some localities but has severely restricted development options in many areas. For example, many regions do not have appropriate soils, ground water tables, slopes, or other attributes necessary for installation of conventional onsite systems. In Florida, 74 percent of the soils have severe or very severe limitations for conventional system designs, based on USDA Natural Resources Conservation Service criteria (Florida HRS, 1993).

1.6.2 Hybrid management programs

Some jurisdictions are experimenting with performance- based approaches while retaining prescriptive requirements for technologies that have proven effective under a known range of site conditions. These prescriptive/performance-based or "hybrid" programs represent a practical approach to onsite system management by prescribing specific sets of technologies or proprietary systems for sites where they have proven to be effective and appropriate.

Regulatory entities review and evaluate alternative systems to see if they are appropriate for the site and the wastewater to be treated. Performance based approaches depend heavily on data from research, wastewater characterization processes, site evaluations, installation practices, and expected operation and maintenance activities, and careful monitoring of system performance is strongly recommended. Programs that allow or encourage a performance-based approach must have a strong management program to ensure that preinstallation research and design and postinstallation operation, maintenance, and monitoring activities are conducted appropriately.

Representatives from government and industry are supporting further development of management programs that can adequately oversee the full range of OWTS activities, especially operation and maintenance. The National Onsite Wastewater Recycling Association (NOWRA) was founded in 1992 to promote policies that improve the market for onsite wastewater treatment and reuse products. NOWRA has developed a model framework for onsite system management that is based on performance rather than prescriptive regulations. The framework endorses the adoption and use of alternative technologies that achieve public health and environmental protection objectives through innovative technologies and comprehensive program management. (NOWRA, 1999)

1.7 Coordinating onsite system management with watershed protection efforts

During the past decade, public and private entities involved in protecting and restoring water resources have increasingly embraced a watershed approach to assessment, planning, and management. Under this approach, all the land uses and other activities and attributes of each drainage basin or ground water recharge zone are considered when conducting monitoring, assessment, problem targeting, and remediation activities (see figure 1-5). A watershed approach incorporates a geographic focus, scientific principles, and stakeholder partnerships.

Figure 1-5. The watershed approach planning and management cycle

Please contact Lynnann Hitchens at 513-569-7672 for details.

Source: Ohio EPA, 1997.

Because onsite systems can have significant impacts on water resources, onsite/decentralized wastewater management agencies are becoming more involved in the watershed protection programs that have developed in their regions. Coordinating onsite wastewater management activities with programs and projects conducted under a watershed approach greatly enhances overall land use planning and development processes.

A cooperative, coordinated approach to protecting health and water resources can achieve results that are greater than the sum of the individual efforts of each partnering entity. Onsite wastewater management agencies are important components of watershed partnerships, and their involvement in these efforts provides mutual benefits, operating efficiencies, and public education opportunities that can be difficult for agencies to achieve individually.

1.8 USEPA initiatives to improve onsite system treatment and management 

In 1996 Congress requested USEPA to report on the potential benefits of onsite/decentralized wastewater treatment and management systems, the potential costs or savings associated with such systems, and the ability and plans of the Agency to implement additional alternative wastewater system measures within the current regulatory and statutory regime.

A year later USEPA reported that properly managed onsite/decentralized systems offer several advantages over centralized wastewater treatment facilities (USEPA, 1997; see http://www.epa.gov/owm/decent/response/index.htm). The construction and maintenance costs of onsite/decentralized systems can be significantly lower, especially in low-density residential areas, making them an attractive alternative for small towns, suburban developments, remote school and institutional facilities, and rural regions. Onsite/decentralized wastewater treatment systems also avoid potentially large transfers of water from one watershed to another via centralized collection and treatment (USEPA, 1997).

USEPA reported that both centralized and onsite/ decentralized systems need to be considered when upgrading failing systems. The report concluded that onsite/decentralized systems can protect public health and the environment and can lower capital and maintenance costs in low-density communities. They are also appropriate for a variety of site conditions and can be suitable for ecologically sensitive areas (USEPA, 1997). However, the Agency also cited several barriers to implementing more effective onsite wastewater management programs, including the following: 

  • Lack of knowledge and public misperceptions that centralized sewage treatment plants perform better, protect property values, and are more acceptable than decentralized treatment systems. 
  • Legislative and regulatory constraints and prescriptive requirements that discourage local jurisdictions from developing or implementing effective management and oversight functions. 
  • Splitting of regulatory authority, which limits the evaluation of alternatives, and a lack of management programs that consolidate planning, siting, design, installation, and maintenance activities under a single entity with the resources and authority to ensure that performance requirements are met and performance is maintained. 
  • Liability laws that discourage innovation, as well as cost-based engineering fees that discourage investment in designing innovative, effective, low-cost systems. 
  • Grant guidelines, loan priorities, and other financial or institutional barriers that prevent rural communities from accessing funds, considering alternative wastewater treatment approaches, or creating management entities that span the jurisdictions of multiple agencies. 

Model framework for onsite wastewater management

  • Performance requirements that protect human health and the environment.
  • System management to maintain performance within the established performance requirements.
  • Compliance monitoring and enforcement to ensure system performance is achieved and maintained.
  • Technical guidelines for site evaluation, design, construction, and operation and acceptable prescriptive designs for specific site conditions and use.
  • Education/training for all practitioners, planners, and owners.
  • Certification/licensing for all practitioners to maintain standards of competence and conduct.
  • Program reviews to identify knowledge gaps, implementation shortcomings, and necessary corrective actions.

Source: NOWRA, 1999.

USEPA is committed to elevating the standards of onsite wastewater management practice and removing barriers that preclude widespread acceptance of onsite treatment technologies. In addition, the Agency is responding to calls to reduce other barriers to onsite treatment by improving access to federal funding programs, providing performance information on alternative onsite wastewater treatment technologies through the Environmental Technology Verification program (see http://www.epa.gov/etv/) and other programs, partnering with other agencies to reduce funding barriers, and providing guidance through cooperation with other public agencies and private organizations.

USEPA supports a number of efforts to improve onsite treatment technology design, application, and funding nationwide. For example, the National Onsite Demonstration Project (NODP), funded by USEPA and managed by the National Small Flows Clearinghouse at West Virginia University, was established in 1993 to encourage the use of alternative, decentralized wastewater treatment technologies to protect public health and the environment in small and rural communities (see http://www.nesc.wvu.edu).

In addition, USEPA is studying ground water impacts caused by large-capacity septic systems, which might be regulated under the Class V Underground Injection Control (UIC) program. Large capacity septic systems serve multiple dwellings, business establishments, and other facilities and are used to dispose of sanitary and other wastes through subsurface application (figure 1-6).

Domestic and most commercial systems serving fewer than 20 persons are not included in the UIC program (see http://www.epa.gov/safewater/uic/classv.html for exceptions and limitations), but some commercial facilities serving fewer than 20 people may be regulated. States and tribes with delegated authority are studying possible guidance and other programs that reduce water resource impacts from these systems. USEPA estimates that there are more than 350,000 large-capacity septic systems nationwide. 

Figure 1-6. Large-capacity septic tanks and other subsurface discharges subject to regulation under the Underground Injection Control Program and other programs.


Please contact Lynnann Hitchens at 513-569-7672 for details.

USEPA also oversees the management and reuse or disposal of septic tank residuals and septage through the Part 503 Rule of the federal Clean Water Act. The Part 503 Rule (see http://www.epa.gov/owm/bio/503pe/) established requirements for the final use or disposal of sewage sludge when it is applied to land to condition the soil or fertilize crops or other vegetation, deposited at a surface disposal site for final disposal, or fired in a biosolids incinerator.

The rule also specifies other requirements for sludge that is placed in a municipal solid waste landfill under Title 40 of the Code of Federal Regulations (CFR), Part 258. The Part 503 Rule is designed to protect public health and the environment from any reasonably anticipated adverse effects of certain pollutants and contaminants that might be present in sewage sludge, and it is consistent with USEPA's policy of promoting the beneficial uses of biosolids.

USEPA has also issued guidance for protecting wellhead recharge areas and assessing threats to drinking water sources under the 1996 amendments to the Safe Drinking Water Act (see http://www.epa.gov/safewater/protect.html and http://www.epa.gov/safewater/whpnp.html). State source water assessment programs differ because they are tailored to each state's water resources and drinking water priorities. However, each assessment must include four major elements: 

  • Delineating (or mapping) the source water assessment area 
  • Conducting an inventory of potential sources of contamination in the delineated area 
  • Determining the susceptibility of the water supply to those contamination sources 
  • Releasing the results of the determinations to the public 

Local communities can use the information collected in the assessments to develop plans to protect wellhead recharge areas and surface waters used as drinking water sources. These plans can include local or regional actions to reduce risks associated with potential contaminant sources, prohibit certain high-risk contaminants or activities in the source water protection area, or specify other management measures to reduce the likelihood of source water contamination. Improving the performance and management of onsite treatment systems can be an important component of wellhead and source water protection plans in areas where nitrate contamination, nutrient inputs, or microbial contaminants are identified as potential risks to drinking water sources. 

Integrating public and private entities with watershed management

In 1991 the Keuka Lake Association established a watershed project to address nutrient, pathogen, and other pollutant loadings to the upstate New York lake, which provides drinking water for more than 20,000 people and borders eight municipalities and two counties. The project sought to assess watershed conditions, educate the public on the need for action, and foster inter-jurisdictional cooperation to address identified problems. The project team established the Keuka Watershed Improvement Cooperative as an oversight committee composed of elected officials from the municipalities and counties. The group developed an 8-page inter-municipal agreement under the state home rule provisions (which allow municipalities to do anything collectively that they may do individually) to formalize the cooperative and recommend new laws and policies for onsite systems and other pollutant sources.

1.9 Other initiatives to assist and improve onsite management efforts 

Financing the installation and management of onsite systems can present a significant barrier for homeowners and small communities. USEPA and other agencies have developed loan, cost-share, and other programs to help homeowners pay for new systems, repairs, or upgrades (see chapter 2). Some of the major initiatives are the Clean Water State Revolving Fund (CWSRF), the Hardship Grant Program, the Nonpoint Source Pollution Program, USDA Rural Development programs, and the Community Development Block Grant (CDBG) program.

The CWSRF is a low-interest or no-interest loan program that has traditionally financed centralized, publicly owned treatment works across the nation (see http://www.epa.gov/owm/finan.htm). The program guidance, issued in 1997, emphasizes that the fund can be used as a source of support for the installation, repair, or upgrading of OWTSs in small-town, rural, and suburban areas. The CWSRF programs are administered by states and the territory of Puerto Rico and operate like banks.

Federal and state contributions are used to capitalize the fund, which makes low- or no-interest loans for important water quality projects. Funds are then repaid to the CWSRFs over terms as long as 20 years. Repaid funds are recycled to support other water quality projects. Projects that might be eligible for CWSRF funding include new system installations and replacement or modification of existing systems. Also covered are costs associated with establishing a management entity to oversee onsite systems in a region, including capital outlays (e.g., for pumper trucks or storage buildings). Approved management entities include city and county governments, special districts, public or private utilities, and private for-profit or nonprofit corporations.

The Hardship Grant Program of the CWSRF was developed in 1997 to provide additional resources for improving onsite treatment in low-income regions experiencing persistent problems with onsite treatment because of financial barriers. The new guidance and the grant program responded to priorities outlined in the Safe Drinking Water Act Amendments of 1996 and the Clean Water Action Plan, which was issued in 1998. 

The Nonpoint Source Pollution Program provides funding and technical support to address a wide range of polluted runoff problems, including contamination from onsite systems. Authorized under section 319 of the federal Clean Water Act and financed by federal, state, and local contributions, the program provides cost-share funding for individual and community systems and supports broader watershed assessment, planning, and management activities. Demonstration projects funded in the past have included direct cost-share for onsite system repairs and upgrades, assessment of watershed-scale onsite wastewater contributions to polluted runoff, regional remediation strategy development, and a wide range of other projects dealing with onsite wastewater issues. (See http://www.epa.gov/OWOW/NPS for more information.) 

The USEPA Office of Wastewater Management supports several programs and initiatives related to onsite treatment systems, including development of guidelines for managing onsite and cluster systems (see http://www.epa.gov/own/bio.htm). The disposition of biosolids and septage pumped from septic tanks is also subject to regulation by state and local governments (see chapter 4). 

The U.S. Department of Agriculture provides grant and loan funding for onsite system installations through USDA Rural Development programs. The Rural Housing Service program (see http://www.rurdev.usda.gov/rhs/Individual/ind_splash.htm) provides direct loans, loan guarantees, and grants to low or moderate-income individuals to finance improvements needed to make their homes safe and sanitary. The Rural Utilities Service (http://www.usda.gov/rus/water/programs.htm) provides loans or grants to public agencies, tribes, and nonprofit corporations seeking to develop water and waste disposal services or decrease their cost. 

The U.S. Department of Housing and Urban Development (HUD) operates the Community Development Block Grant Program, which provides annual grants to 48 states and Puerto Rico. The states and Puerto Rico use the funds to award grants for community development to small cities and counties. CDBG grants can be used for numerous activities, including rehabilitation of residential and nonresidential structures, construction of public facilities, and improvements to water and sewer facilities, including onsite systems. USEPA is working with HUD to improve system owners' access to CDBG funds by raising program awareness, reducing paperwork burdens, and increasing promotional activities in eligible areas. (More information is available at http://www.hud.gov/cpd/cdbg.html.) 

The Centers for Disease Control and Prevention (CDC) of the U.S. Public Health Service (see http://www.cdc.gov) conduct research and publish studies on waterborne infectious disease outbreaks and illness linked to nitrate contamination of ground water, both of which have been linked to OWTSs, among other causes. Disease outbreaks associated with contaminated, untreated ground water and recreational contact with water contaminated by pathogenic organisms are routinely reported to the CDC through state and tribal infectious disease surveillance programs. 

Individual Tribal Governments and the Indian Health Service (IHS) handle Indian wastewater management programs. The IHS Sanitation Facilities Construction Program, within the Division of Facilities and Environmental Engineering of the Office of Public Health, is supported by engineers, sanitarians, technicians, clerical staff, and skilled construction workers. Projects are coordinated through the headquarters office in Rockville, Maryland, and implemented through 12 area offices across the nation. The program works cooperatively with tribes and tribal organizations, USEPA, HUD, the USDA's Rural Utilities Service, and other agencies to fund sanitation and other services throughout Indian Country (see http://www.ihs.gov/nonmedicalprograms/dfee/reports/rpt1998.pdf).  

References  

Curry, D. 1998. National Inventory of Key Activities Supporting the Implementation of Decentralized Wastewater Treatment. Fact Sheet No. 3-2. Research conducted by the U.S. Environmental Protection Agency, Office of Wastewater Management. Available from Tetra Tech, Inc., Fairfax, VA.

Florida Department of Health and Rehabilitative Services (Florida DHRS).1993. Onsite Sewage Disposal System Research in Florida: An Evaluation of Current OSDS Practices in Florida. Report prepared for the Florida Department of Health and Rehabilitative Services, Environmental Health Program, by Ayres Associates, Tallahassee, FL.

Fogarty, S. 2000. Land Use and Zoning Laws. Small Flows Quarterly 1(1):13.

Hoover, M.T., A.R. Rubin, and F. Humenik. 1998. Choices for Communities: Wastewater Management Options for Rural Areas. AG-585. North Carolina State University, College of Agriculture and Life Sciences, Raleigh, NC.

Kreissl, J.F. 1982. Evaluation of State Codes and Their Implications. In Proceedings of the Fourth Northwest On-Site Wastewater Disposal Short Course, September, University of Washington, Seattle, WA.

Kreissl, J.F. 2000. Onsite Wastewater Management at the Start of the New Millenium. Small Flows Quarterly 1(1):10-11.

National Onsite Wastewater Recycling Associations (NOWRA). 1999. Model Framework for Unsewered Wastewater Infrastructure. National Onsite Wastewater Recycling Association. July 1999. <http://www.nowra.org/Sept99/article_frame. html>. Accessed March 29, 2000.

Nelson, V.I., S.P. Dix, and F. Shepard. 1999. Advanced On-Site Wastewater Treatment and Management Scoping Study: Assessment of Short-Term Opportunities and Long-Run Potential. Prepared for the Electric Power Research Institute, the National Rural Electric Cooperative Association, and the Water Environment Research Federation.

Ohio Environmental Protection Agency (Ohio EPA). 1997. A Guide to Developing Local Watershed Action Plans in Ohio. Ohio Environmental Protection Agency, Division of Surface Water, Columbus, OH. 

Otis, J. 2000. Performance management. Small Flows Quarterly 1(1):12. 

Parsons Engineering Science. 2000. Septic System Failure Summary. Prepared for U.S. Environmental Protection Agency, Office of Water, under Contract 68-C6-0001. June 13, 2000.

Pennsylvania Infrastructure Investment Authority (PENNVEST). 1997. A Water, Sewer, and Stormwater Utility's Guide to Financial and Technical Assistance Programs. Pennsylvania Infrastructure Investment Authority, Harrisburg, PA.

Plews, G.D. 1977. The Adequacy and Uniformity of Regulations for Onsite Wastewater Disposal-- A State Viewpoint. In Proceedings of the National Conference on Less Costly Treatment Systems for Small Communities. U.S. Environmental Protection Agency, Cincinnati, OH.

Shephard, F.C. 1996, April. Managing Wastewater: Prospects in Massachusetts for a Decentralized Approach. Prepared for the ad hoc Task Force for Decentralized Wastewater Management. Marine Studies Consortium and Waquoit Bay National Estuarine Research Reserve.

Suhrer, T. 2000. NODP II at Work in the Green Mountain State. Small Flows Quarterly 1(1):12. Published by the National Small Flows Clearinghouse, Morgantown, WV.

Tchobanoglous, G. 2000. Decentralized Wastewater Management: Challenges and Opportunities for the Twenty-First Century. In Proceedings of the Southwest On-Site Wastewater Management Conference and Exhibit, sponsored by the Arizona County Directors of Environmental Health Services Association and the Arizona Environmental Health Association, Laughlin, Nevada, February 2000.

U.S. Census Bureau. 1990. Historical Census of Housing Tables: Sewage Disposal. <http:// www.census.gov/hhes/www/housing/census/ historic/sewage.html>.

U.S. Census Bureau. 1999. 1997 National Data Chart for Total Occupied Housing Units. http://www.census.gov/hhes/www/housing/ ahs/97dtchrt/tab2-6.html.

U.S. Environmental Protection Agency (USEPA). 1980b. Planning Wastewater Management Facilities for Small Communities. EPA-600/8- 80-030. U.S. Environmental Protection Agency, Office of Research and Development, Wastewater Research Division, Municipal Environmental Research Laboratory, Cincinnati, OH.

U.S. Environmental Protection Agency (USEPA).1980a. Design Manual: Onsite Wastewater Treatment and Disposal Systems. EPA 625/1-80/012. U.S. Environmental Protection Agency, Washington, DC.

U.S. Environmental Protection Agency (USEPA). 1987. It's Your Choice: A Guidebook for Local Officials on Small Community Wastewater Management Options. USEPA Office of Municipal Pollution Control (WH-595).

U.S. Environmental Protection Agency (USEPA). 1993. Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters. EPA840-B-92-002. U.S. Environmental Protection Agency, Office of Water, Washington, DC.

U.S. Environmental Protection Agency (USEPA). 1994. Environmental Planning for Small Communities: A Guide for Local Decision- Makers. EPA/625/R-94/009, U.S. Environmental Protection Agency, Office of Research and Development, Office of Regional Operations and State/Local Relations, Washington, DC.

U.S. Environmental Protection Agency (USEPA). 1996a. National Water Quality Inventory Report to Congress. [305b Report.] EPA 841-R- 97-008. U.S. Environmental Protection Agency, Washington, DC.

U.S. Environmental Protection Agency (USEPA). 1996b. Clean Water Needs Survey Report to Congress. http://www.epa.gov/owm/toc.htm 

U.S. Environmental Protection Agency (USEPA). 1997. Response to Congress on Use of Decentralized Wastewater Treatment Systems. EPA 832-R-97-001b.

U.S. Environmental Protection Agency, Washington, DC. U.S. Environmental Protection Agency (USEPA). 1998. Guidelines for Ecological Risk Assessment. EPA 630-R-95-002F. U.S. Environmental Protection Agency, Office of Research and Development, Risk Assessment Forum, Washington, DC. 

U.S. Environmental Protection Agency (USEPA). 2000. Draft EPA Guidelines for Management of Onsite/Decentralized Wastewater Systems. U.S. Environmental Protection Agency, Office of Wastewater Management, Washington, DC. Federal Register, October 6, 2000, 65(195): 59840-59841.

U.S. Public Health Service (USPHS). 1967. (Updated from 1959 version.) Manual of Septic Tank Practice. U.S. Public Health Service Publication No. 526. U.S. Department of Health, Education and Welfare.

Venhuizen, D. 1995. An Analysis of the Potential Impacts on Ground Water Quality of On-Site Watershed Management Using Alternative Management Practices. <http://www.venhuizen-ww.com>.

Water Environment Research Foundation (WEF). 1998. Watershed-Scale Ecological Risk Assessment--Watersheds. Final report, Project 93-IRM-4(A). Water Environment Research Foundation, Alexandria, VA.

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