Use of Decentralized Wastewater Treatment Systems in the Uni

Jinming Chen, PhD, PE
Office of Groundwater andDrinking Water, USEPA, Washington, DC, 20460

AbstractAdecentralized system is an onsite or cluster wastewater system that is used totreat and dispose of relatively small volumes of wastewater, generally fromindividual or groups of dwellings and businesses that are located relativelyclose together. Decentralized systems are usually installed in less densely populated areas such as rural communities. In the U.S.,decentralized systems serve approximately 25 percent of the populationnationwide and about one-third of new construction employs this type oftreatment today. In comparison,the rural population in China is about 15 times more than that in the U.S. Thus, it can be expected that theamount of wastewater generated from the rural communities in China will beseveral folds (if not ten or more folds) greater than that in the U.S.. Subsequently, decentralized systemswill probably be a vital technology for water pollution control in China’srural areas in the future due to their cost-effective and simplicity. This paper reviews management practicesand related policies for the use of decentralized systems in the U.S. so thatthis technology can better be understood and promoted for the wastewatertreatment to protect public health and the environment in small and ruralcommunities in China.Introduction

Adecentralized system is an onsite or cluster wastewater system that is used totreat and dispose of relatively small volumes of wastewater, generally fromindividual or groups of dwellings and businesses that are located relativelyclose together. Onsite wastewatersystems have been used since the mid-1800s, with technological advancesimproving the systems from simple outhouses to cesspools, to septic tanks, tosome of the more advanced treatment units available today for additionalnutrient removal and disinfection requirement. Since centralized systems require collection of wastewaterfor an entire community at substantial cost, adequately managed decentralizedsystems can achieve significant cost savings while recharging local aquifersand providing other water reuse opportunities close to points of wastewatergeneration. Also, these systemscan help to promote better watershed management by avoiding the potentiallylarge transfers of water from one watershed to another that can occur withcentralized treatment.

In the U.S.,decentralized systems have been recognized as a viable wastewater managementalternative for rural and suburban communities to preserve environmentalquality at a reasonable cost.According to the U.S. Census Bureau, 61 percent of housing units insmall communities (<10,000 people) that represent about 10 percent of thetotal wastewater need in the U.S. use decentralized systems for wastewaterdisposal (Figure 1). Aboutone-fourth of all homes in America (about 26 million) are currently served bydecentralized wastewater treatment systems. About one-third of new construction employs this type oftreatment today. It has also beenestimated that about 4 billion gallons of wastewater are treated and releaseddaily by these systems.

Therural population in the U.S. is about 64 millions, contributing to 24 percentof the total population (www.census.gov).For comparison, there are about 850 millions people living the ruralareas, approximately representing 67 percent of the China’s total population(www.iiasa.ac.at/Research/LUC/ChinaFood/data/urban). Taking account of both ongoing urbanization and growth ofthe rural population, it can be expected that the wastewater generated from therural communities in China will sustain several folds (if not ten folds)greater than that in the U.S. Aseconomic reform and development continue and the environmental awareness isbeing raised in China, the wastewater pollution control is getting anincreasing attention in both urban and rural areas. Consequently, decentralized systems will be widely installedand used in the rural communities across China. Adequate management practices are the key to the success ofapplying such a traditional and vital technology for the wastewater treatmentto protect public health and the environment.

The objectiveof this paper is to review management practices and related policies for theuse of decentralized systems in the U.S. so that the technology can better beunderstood and practiced in China where a large need of this technology can beanticipated in the future.

In 1972, The U.S.Congress enacted the first comprehensive national clean water legislation(i.e., the Clean Water Act - CWA) in response to growing public concern forserious and widespread water pollution.　The fundamental national goals of the CWA are:

· To eliminate the discharge ofpollutant into the nation’s waters, and

· To achieve water quality levels that fishable and swimmable.

As an initialstep toward the goals, the CWA contained a national policy to provide fundingfor publicly owned treatment works.Such a policy focused primarily on large, centralized collection andtreatment systems. This effort didnot recognize the benefits of properly managed decentralized wastewater systemsin achieving the goals of the CWA.

The 1977amendments to the CWA required communities to examine or consider alternativesto conventional centralized systems, and provided a financial set-aside forsuch treatment systems to be built.The amendments encouraged a number of state and local governments, withthe support of the Research and Development programs in the U.S. EnvironmentalProtection Administration (USEPA), to experiment with different types of decentralizedsystems that could accommodate a variety of site and community conditions andmeet environmental protection goals if properly operated and maintained. The efforts led to construction ofseveral thousand facilities utilizing innovative and/or alternativedecentralized technologies by the year 1990.　

In 1990,incentive set-aside funding was replaced by the Clean Water State RevolvingFund (CWSRF) program, which provides communities with low interest loans. Nationally, the CWARF has in excess of $27billion in assets and has issue $23 billion in loans. Since 1993 small communities have received from 18 to 29percent of the total on an annual basis.Clearly, the CWSRF has helped supplement the limited financial resourcesavailable for decentralized treatment systems. However, this program has only been able to meet a portionof the total needs. Currently,other federal funding sources can also be accessible for decentralized systems,including the USEPA’s Nonpoint Source Program, Rural Utilities Services in theU.S. Department of Agriculture, and the Community Development Block Grant fromthe U.S. Department of Housing and Urban Development. Furthermore, state-funded programs supporting decentralizedsystems are also ongoing in several states.

At present, there is not anymandatory guideline or standard at the federal level for practices ofdecentralized wastewater systems.In most states, local health departments issue construction andoperating permits to install onsite/decentralized systems under state lawsgoverning public health protection and abatement of public nuisances. Some states are beginning to add waterresource protection provisions to their onsite/decentralized system regulationsbecause of the possible impacts from nitrogen and phosphorus.

Under most regulatoryprograms, the local permitting agency conducts a site assessment to determinewhether the soils present can provide adequate treatment, to ensure that groundwater resources will not be threatened, and to stipulate appropriate setbackdistances from buildings, driveways, property lines, and surface waters. Some states will permit alternativesystems if conventional soil-based systems are not allowable. Very few permitting agencies conductregular inspections of onsite/decentralized systems after they are installed.

Types of Decentralized Systems

Decentralizedsystems include conventional onsite systems, cluster systems, and alternativewastewater treatment technologies like constructed wetlands, composting toilets,recalculating sand filters, anaerobic upflow filters, sequencing batchreactors, evapotranspiration systems, and small wastewater treatment"package" plants that serve single or multiple buildings.

Mostonsite/decentralized treatment systems include a septic tank, which digestsorganic matter and separates floatable matter (e.g., oils and grease) andsettleable solids from the wastewater.Usually, a septic tank is followed by a soil absorption field wheretrenches are dug wide enough to accommodate open-jointed drain title laiddirectly on the exposed trench bottom.Soil-based systems discharge septic tank effluent into a series ofperforated pipes buried in a leach field, leaching chambers, or other specialunits designed to slowly release effluent into the soil or surface water. Alternative systems are wastewatertreatment systems installed at sites where conventional soil-based systems(with a leach or drain field) are not appropriate due to inadequate soils,excessive slopes, high seasonal ground water tables, or other factors. Alternative systems may use pumps orgravity to trickle septic tank effluent through sand, organic matter (e.g.,peat, sawdust), constructed wetlands, or other media to remove or neutralizepollutants like disease-causing pathogens, nitrogen, phosphorus, and othercontaminants. Some alternative systems are designed to evaporate wastewater ordisinfect it before it is discharged to the soil or surface waters. More information on thesetechnologies can be found from the USEPA’s Design Manual described later inthis paper.

Problems and Federal RemedyActions in the U.S.

Althoughonsite/decentralized wastewater systems are usually installed after a permit isreceived from a local health department or other agency, most are not managedafterward under a centralized management program. Untrained and uninformed system owners are often responsiblefor operating and maintaining their systems after they are installed. Someoversight agencies have developed programs that feature renewable operatingpermits, regular inspections, required maintenance (e.g., septic tank pumping),and periodic monitoring, but they are relatively few in number. In 1995, the U.S. Bureau of the Censusindicated that at least 10 percent of onsite/decentralized systems (about 2.2million systems) malfunctioned, and some communities reported failure rates ashigh as 70 percent. State agenciesreport that these failing systems are the third most common source of groundwater contamination.

Most system failures arerelated to inappropriate design and poor maintenance. It has been estimated that only 32% of the total land areain the United States has soils suitable for onsite systems, which utilize thesoil for final treatment and disposal of wastewater. Under pressures of development, however, soil-based systems(with a leach or drain field) have been installed at sites with inadequate orinappropriate soils, excessive slopes, and high ground water tables. These instances can result in hydraulicfailures and water resource contamination. Also, failure to perform routine maintenance (e.g., pumpingthe septic tank at least every 3-5 years) can cause solids in the tank tomigrate into the drain field and clog the system.

Clearly, the performance ofdecentralized wastewater systems has become a national issue of great concernfor sustainable environmental protection.To address this concern, the USEPA has taken the following actions:

1. Submitted its Response toCongress on Use of Decentralized Wastewater Treatment Systems in 1997

2. Proposed Guidelines for Management of Onsite/Decentralized Wastewater Systemsin 2000

3. Revising Onsite WastewaterTreatment and Disposal Systems Design Manual in 2001.

For better understanding these actions, the content of above threedocuments are briefly described below:

Response to Congress on Use of Decentralized WastewaterTreatment Systems:

In this report, the USEPAfirmly concluded that adequately managed decentralized wastewater systems canbe a cost-effective and long-term option for meeting public health and waterquality goals, particularly for small, suburban, and rural areas. Because of some barriers, however, the expanded use of decentralized wastewater systems was inhibited. The USEPA identified the following fivesuch major barriers:

A. Lack of knowledge andpublic misperception. Theperception of some homeowners, realtors, and developers that centralizedsystems are better for property values and are more acceptable thandecentralized systems, even if they are far more costly, makes it difficult todemonstrate that properly designed and managed decentralized systems canprovide equal or more cost-effective service. Also, many regulators and wastewater engineers are notcomfortable with decentralized systems due to a lack of knowledge.　 Decentralized systems, particularly thenon-conventional types, are not included in most college and technical instructionalprograms.

B. Legislative and regulatory constraints. State enabling legislation thatprovides the necessary legal powers for carrying out important managementfunctions may be absent, vague, or not clearly applicable to decentralizedsystems. Most importantly, inalmost all states, legislative authority for centralized and decentralizedwastewater systems is split between at least two state agencies. It is also common for legislativeauthority for decentralized systems to be split between state and localgovernments, resulting in further confusion regarding accountability andprogram coordination. Under theseconditions, decentralized wastewater systems have not gained equal statue withcentralized facilities for public health and environmental protection.

C. Lack of management programs. Few communities have developed thenecessary organizational structures to effectively manage decentralizedwastewater systems, although such management programs are consideredcommonplace for centralized wastewater facilities and for other services (e.g.,electric, telephone, water).Without such management, decentralized systems may not provide adequatetreatment of wastewater.

D. Liability and engineering fees.Homeowners and developers areoften unwilling to accept the responsibility and potential liability associatedwith unfamiliar systems such as those providing decentralized treatment. Also, engineers’ fees are often basedon a percentage of project cost and have little incentive for designing lowcost systems.

E. Financial limitations. USEPA’s Construction Grants program,and now the Clean Water SRF program, has been the major source of wastewatertreatment facility funding. Theseprograms are generally available only to public entities. Difficulties exist for privately-ownedsystems in obtaining public funds under current federal and state grant andloan programs.

Guidelines for Management of Onsite/DecentralizedWastewater Systems

Amongthe five major barriers in the USEPA’s response to the congress for usingdecentralized systems, the lack of adequate management is the most profoundfactor leading to failure of the existing decentralized systems. Consequently, the USEPA developed theguidelines to assist communities in establishing comprehensive managementprograms for onsite/decentralized wastewater systems to improve water qualityand protect public health. The Guidelineswill also help states, tribes, and communities develop, modify, and implementlaws and regulations in areas of onsite/decentralized wastewater systemmanagement planning. TheGuidelines focus on the following areas where better management can achievesignificant improvements in overall system performance:

· Planning to ensure that system densities do not exceed the ability ofregional soils and water resources to treat and assimilate pollutants.

· Site evaluations that characterize and help to protect soil, groundwater, and surface water resources.

· System designs that provide predictable performance levels of treatmentthat are appropriate for protecting public health and the environment.

· Operation and maintenance procedures ensure that systems are operatedproperly and that maintenance tasks (e.g., septic tank pumping, and inspectionof treatment units) are performed regularly.

· Monitoring and reporting to provide usable and easily accessible recordson system inventories, capacity, and performance.

· Follow-up and corrective actions to ensure that failing systems arerepaired, upgraded, or replaced before public health or water resources areadversely affected.

Onsite Wastewater Treatment and Disposal Systems Design Manual

The USEPA iscurrently revising the Design Manual initially developed in 1980 to provide newinformation on alternative treatment technologies and to promote aperformance-based approach to onsite/decentralized wastewater system management. The Design Manual will serve as thetechnical complement to the Management Guidelines and will be useful as areference to identify the environmental, technological, and administrative andpublic health factors to consider when developing an improved managementprogram. The Design Manual willalso contain information for program managers in assessing the environmentalimpacts of specific onsite/decentralized wastewater system technologies on boththe watershed and individual site levels and in the selection of appropriatetechnologies and management strategies.The revised Design Manual is expected to be available by the end of2001.

Summary

In contrast tocentralized sewage collection and treatment with high costs, decentralizedwastewater systems have been approved to be cost-effective in protecting humanhealth and environment in the rural areas. However, due to the lack of clear regulatory policies,authorities, and guidelines at both federal and state levels, the management ofdecentralized systems was not properly practiced and failure of such systemswas common in the U.S. Thisfailure caused significant contamination of groundwater that was considered amajor drinking water source in the rural community. The USEPA is partneringwith other federal agencies, states, tribes, local governments, andnongovernmental organizations to improve the management of decentralizedsystems. Although individuals usually own decentralized systems, a communitycan take a variety of steps to maintain effective systems, including:

· Periodicallyinspecting the system and requiring pumping when necessary.

· Requiringan operating permit that must be renewed periodically to ensure maintenance.

· Keepingfiles of all system locations and maintenance performed.

· Requiringprior approval by the local health officer of all repairs and replacements.

· Setting upa fund to help homeowners with needed repairs or replacements.

Nevertheless, with the refocused effortsfrom the governments and communities, decentralized systems are now gainingdesired recognition as a viable wastewater management alternative tocost-effectively preserve environmental quality in rural areas. The American experience could behelpful for the ongoing or upcoming efforts in China in this aspect.

References

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U.S. Environmental ProtectionAgency. 1999. Funding Decentralized WastewaterSystems Using the Clean Water State Revolving Fund. Office Water.EPA 832-F-99-001.

U.S. Environmental ProtectionAgency. 1999. Funding of Small Community Needs ０Through the Clean Water State Revolving Fund. Office of Water.EPA 832-F-99-057.

U.S. Environmental ProtectionAgency. 1999. U.S. Census Data on Small CommunityHousing and Wastewater Disposal and Plumbing Practices. Office of Water. EPA 832-F-99-060.

U.S. Environmental ProtectionAgency. 1997. Response to Congress on Use of DecentralizedWastewater Treatment Systems.Office of Water. EPA832-R-97-001b.

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