Raw waste

Septic tank

Effluent

On-site wastewater treatment systems

Alternative collection systemsBruce Lesikar

Extension Agricultural Engineering SpecialistThe Texas A&M University System

B-60988-00

Figure 1: A small-diameter gravity sewer system.

There’s great news for rural Texas communities needing to developwastewater management infrastructure. Today, rural Texans havemore options than ever before to manage wastewater. These op-

tions offer:

✓ Protection for the environment,

✓ Flexibility for communities toplan for future economic growth,and

✓ Lower installation costs thantraditional centralized wastewatermanagement systems.

Wastewater in rural areas isusually treated at first by on-site

treatment systems—often septicsystems—at each home. These workwell in areas where the population islow and the environment can accom-modate the amount of waste produced.

But if the population grows or ifthe land cannot handle the wastewater,the community as a whole must takesteps to address its wastewaterproblems. Before, communities whose

septic systems were failing had onlyone choice in managing wastewateradequately: to install an extensivepipe network to collect wastewater toa centralized, highly maintainedwastewater treatment plant.

Now rural communities have anew option: They can use a combina-tion of conventional septic systems,advanced on-site systems, and clusteror other land-based treatment systemsto manage wastewater (Fig. 1). Thisnew approach is called decentralizedwastewater treatment.

According to the EnvironmentalProtection Agency (EPA), decentral-ized systems:

✓ Protect public health and theenvironment,

✓ Are appropriate for low-densitycommunities,

✓ Can be used in varying siteconditions,

✓ Provide additional benefits forecologically sensitive areas, and

✓ Can save significant amounts ofmoney while recharging localaquifers and providing otherwater reuse opportunities close towhere the wastewater is gener-ated.

In fact, in a 1997 report to theU.S. Congress, the EPA found that thedecentralized approach to wastewatermanagement favors rural communitiesand frequently is less expensive thancentralized sewage systems.

Because Texas has no compre-hensive, statewide strategy thatprovides for the cost-effectivetreatment of municipal wastewater inrural areas, many rural Texas commu-nities need to devise wastewatermanagement systems to effectivelyprotect public health and environmen-tal quality, accommodate futurehousing needs and facilitate growth.

Centralized approachfavored previously

Thanks to major federal fundingduring the 1970s and ’80s, most urbancommunities across Texas installedcentralized wastewater systems tomeet their citizens’ needs. The CleanWater Act of 1972 provided federalmoney to plan, design and buildpublic wastewater infrastructure.Usually, larger communities werefavored over smaller ones to receivemost of the federal funds.

The federal money, combinedwith the communities’ failure toadequately maintain traditional septicsystems, justified the construction ofsewers and wastewater treatmentplants.

These centralized systems havebeen termed the “big pipe” or “sewerthe country” approach. They involveinstalling an extensive network oflarge sewer pipes throughout acommunity to collect wastewater andbring it to a central treatment plant.After being treated, the wastewater isdischarged into a stream or body ofwater.

Today, however, major federalfunding for wastewater managementprojects has been reduced, and Texascommunities must bear the cost ofinstallation, operation and mainte-nance. Sewer systems cannot beexpanded throughout rural areasbecause they cost too much andbecause increasingly strict environ-mental requirements make it difficultand costly to discharge treatedwastewater into rivers, streams andcoastal waters.

Decentralized optionsToday there are many alternatives

to centralized sewers, including:

✓ Conventional septic systems,which are dependable optionswhere soil conditions are favor-able and the systems are properlymaintained.

✓ Advanced on-site systems (sandfilters, aerobic treatment units,trickling filters, constructedwetlands, pressure distributionsystems, drip distributionsystems, spray distributionsystems and disinfection systems)and community facultativelagoons/spray irrigation systems.These can be used over a muchbroader range of site and soilconditions than can conventionalseptic systems.

✓ Cluster systems, which use smallcollection networks to bringwastewater from a limitednumber of houses (usually five to100) to a common treatment anddisposal area. Cluster systems usesmall-diameter gravity sewersand pressure sewer systems thatare less expensive to install thanthe large pipes used in thecentralized approach (Fig. 2).

Communities frequently use acombination of systems: clustersystems in areas that are more denselypopulated or that have poor soilconditions; and on-site systems wheresoil conditions are favorable.

Although these land-based,alternative wastewater systems areviable options, many rural areas havenot considered implementing them.The treatment strategies are relativelynew and seldom recommended bysome consultants. In the past, thesetreatment techniques were notconsidered to be mainstream optionsthat communities could depend on.

But land-based systems are themost cost-effective and environmen-tally sound wastewater treatmentoptions for rural communities, nowand in the future. Because thesesystems affect streams and rivers onlyminimally, communities need toconsider developing land-basedsystems to protect their streams andother water resources.

Management,maintenance andinspections are key

The decentralized approach canbe successful only if a managementprogram is established to ensure thatthe systems are inspected and main-tained regularly. Although ruralcommunities are best served bywastewater technologies that aredecentralized, they require a central-ized management network to overseethem.

Figure 2: A septic tank effluent pump (STEP) system.

Raw waste

Septic tankEffluent

Pump tank

Trained, certified system opera-tors can ensure that the systemsfunction effectively. Centralizedmanagement can be used for acommunity, a county or a multiple-county area.

New long-termstrategy needed

Many rural communities need tocreate wastewater managementinfrastructure, not only to effectivelyprotect public health and the environ-ment, but also to provide for futurehousing needs and to facilitate soundgrowth.

Many rural communities have noreliable wastewater managementinfrastructure, while nearby cities andtowns have public sewers andwastewater treatment plants. So therural areas miss out on economicbenefits even when industries movein, because the population leapfrogsinto nearby urban centers. Eventually,the additional wastewater loadexceeds the municipal treatmentplant’s capacity, a developmentmoratorium is imposed, and theeconomic vitality of the area isthreatened.

Rural communities need todevelop comprehensive, long-termstrategies for the timely and cost-effective treatment of wastewater.They cannot meet current and futuredischarge requirements quickly withjust one project. Although land-basedsystems are the most cost-effectiveand environmentally sound system forrural communities under present andanticipated future conditions, theyrequire extensive planning andimplementation in phases, dependingon the area to be served.

Needs assessmentTo develop a comprehensive

wastewater management plan, acommunity should begin by assessinglocal needs. The first step is to define

the problem clearly. The communityshould compile information oncurrent wastewater problems, docu-ment obvious signs of system failure,compile water use data, and define theservice area.

Planning processOnce the needs have been

assessed, the planning process shouldbegin. A community needs to:

✓ Organize. This requires identify-ing local leaders and availabletalent.

✓ Establish planning goals andidentify issues relevant towastewater management. Oftenthese address public health andenvironmental quality, but alsoshould include economic devel-opment and growth issues.

✓ Gather data. Study environmentalfactors such as soil resources,groundwater quantity and quality,surface water quality and theability of these waters to acceptand treat additional wastewaterloads and site conditions forindividual or community systems.

✓ Examine the financial ability ofresidents to pay for design,construction and operation ofwastewater infrastructure options.

Treatment optionsWastewater can be treated and

disposed of using either land-basedtechnologies or surface-water dis-charge systems. Community leadersmust consider the many optionsbetween conventional septic systemsand traditional surface water dis-charge systems. Often the soils in acommunity may be suited for a land-based system, but because of docu-mented septic system failure, theleaders assume that the soils cannotsupport this approach.

However, government regulatorsprefer the land-based alternativesbecause they have minimal environ-mental impacts on streams and rivers.

Land-based systems include landapplication systems that discharge ontop of the ground (called surfaceapplication systems) and those thatdischarge underground into the soil(called subsurface disposal systems).

Land-based systems are consid-ered nondischarge because thewastewater does not dischargedirectly into our water resources.Typically, surface-water dischargesystems use mechanical devices toaerate the wastewater before discharg-ing it into a stream or river.

Ultimately, community leadersmust select a consultant to help designthe program. However, some consult-ants who conduct community needsassessments are unfamiliar with land-based options. As a result, their firstrecommendation often is to develop atreatment facility that discharges tosurface water.

When using land-based technolo-gies, communities must determine themost cost-effective balance betweenon-site and cluster or communitysystems. To generate and analyzealternatives:

✓ Determine if individual lots couldbe improved by using advancedon-site systems on problem siteswhere septic systems are failing.

✓ Evaluate the feasibility ofcombining individual on-sitesystems and small cluster land-based systems.

✓ Assess the merits of providing acommunitywide wastewatercollection and treatment system.All too often, land-based optionsare ignored and decision makersare guided to surface-waterdischarge options as the preferredchoice.

The more information thecommunity provides about localneeds and wants, the better theguidance they can give the consultant.Leaders must insist on a comprehen-sive review of alternatives thatincludes on-site treatment improve-ments, community cluster land-basedtreatment options and a community-wide collection system.

By insisting that the consultantprovide a system that will meet the

needs of the community, leaders canensure that the best interests of allresidents are served.

Community optionsCommunities may choose from

several collection, treatment anddisposal technologies.

Collection technologies

Most sewer systems in largecities have the traditional network oflarge-diameter pipes that collectwastewater from homes and take it bygravity to a wastewater treatmentplant. Gravity sewers, as the namesuggests, convey wastewater by usingthe natural slope of the land.

Gravity sewers have severaldisadvantages. They need lift stationswhen the slope of the land requiresthat the wastewater be carried to ahigher elevation. Because the linesmust be laid at a sharp enough angleto move solids through the line, theexcavation costs can be substantial toinstall sewers deep enough to functionvia gravity flow.

Large-diameter pipe must beused, drastically increasing construc-tion costs. Large sewers can also haveproblems with inflow and infiltrationof water through the pipe joints andconnections. Inflow and infiltrationincreases the total amount of waterthat the wastewater treatment system.must handle.

Yet many areas can use alterna-tive wastewater collection networks,including small-diameter gravitysewers, small-diameter pressuresewers and vacuum sewers.

✓ Small-diameter gravity sewers(Fig. 1), sometimes calledeffluent sewers, use a septic tankat each home to remove the largesolids. Because only liquids flowthrough the collection network,the wastewater collection pipescan be of a smaller diameter. Thesmaller pipes can be installed

nearly on grade, making con-struction costs much lower thanfor traditional gravity sewers.

✓ Small-diameter pressure sewersinclude septic tank effluent pumpsystems (STEP) and grinderpump systems. The STEP system(Fig. 2) uses gravity to conveywastewater from a house to aseptic tank. Then the effluentflows to the pump vault, where itis pumped under pressure to thetreatment system or to othergravity lines.

Like the STEP system, thegrinder pump system uses gravityto convey wastewater from ahouse to a holding tank. But apump inside the tank grinds andshreds solid particles in thewastewater as it pumps. Then thewastewater is pumped underpressure to the treatment systemor to a gravity line.

✓ Vacuum sewers include aholding tank with a vacuum valveat the home connected by acollection network to a vacuumpumping station at a centralwastewater treatment plant. Whenthe holding tank has a specificvolume of wastewater, thevacuum valve meters the waste-water into the collection linewhile maintaining the vacuum inthe line. Both water and solidsare transported to the wastewatertreatment plant.

The installation costs for small-diameter pressure systems andvacuum sewers are usually relativelylow for the same reasons as for small-diameter gravity sewers. Thesesystems follow contours, whichlowers costs. However, operation andmaintenance costs are potentiallyhigher because they use a pump tomove the water rather than gravity.

Pressure sewer collectionnetworks typically have fewerproblems with inflow and infiltrationthan traditional gravity sewers. One

potential problem, though, is that theycan be affected by grease buildup,other blockages in the pipes andelectrical outages. Also, the accumu-lated solids in the septic tanks must beremoved periodically as part ofoperation and maintenance.

Treatment and disposal

Mechanical treatment processesinclude preliminary treatment (whichprovides the least treatment andpollutant removal), primary treatment,secondary treatment and tertiarytreatment (which treats wastewaterthe most).

Some wastewater treatmentplants can meet their surface-waterdischarge permit limits by providing asecondary level of treatment. How-ever, in nutrient-sensitive watershedsand other environmentally sensitiveareas, the treatment plants mustinclude more advanced (and expen-sive) processes to meet surface-waterdischarge permit limits.

Land-based treatment anddisposal technologies include:

✓ A variety of lagoons;

✓ Fixed media filters, includingsand filters, gravel filters, textilefilters, and other biofilters;

✓ Subsurface dispersal systems,such as a large variety of ad-vanced on-site systems, includingthe traditional gravity distributiontechnologies, pressure manifolddistribution and pressure distribu-tion, including low-pressure pipeand drip distribution technolo-gies; and

✓ Surface dispersal systems, whichare sometimes called spraydistribution systems.

One of the advanced pressuredistribution technologies is dripdistribution (Fig. 3), which can beinstalled at a home site or over amulti-acre site to treat and distributewastewater from a small community.

Surface dispersal systems includeslow-rate spray distribution and reusesystems. These disperse the wastewa-ter onto the ground.

The slow-rate spray distributionsystem is designed to have a very lowapplication rate; a reuse systemsupplies the water needs of the grassand vegetation growing at the site.Slow-rate spray distribution systemsrequire the greatest amount of landarea; the reuse system uses a smallerland area and generally requires 3months of storage for the monthswhen the plants use less water,especially during winter.

Both the subsurface and surfacedispersal land-based technologies usenatural physical, chemical and biolog-ical soil processes to treat the waste-water as it passes through the soil.

As with any mechanical waste-water treatment system, land-basedtreatment sites must have enough landto accommodate future expansion.

However, planning for these needs isimportant, because land-basedtreatment systems have a defined,finite capacity for growth withoutavailable additional land.

Cost-effectivenessWhen considering wastewater

management systems, rural communi-ties must consider two main compo-nents: the collection system, which isthe first and often most costly; and thewastewater treatment and disposalsystem.

The costs for wastewater infra-structure include the capital expendi-tures as well as the costs of operationand maintenance. Often costs aremeasured in dollars per thousandgallons for operation and mainte-nance, or in dollars per gallon forinitial capital.

Although the costs for wastewa-ter management vary dramaticallyfrom system to system, land-based

Figure 3: A drip distribution system for treatment and dispersal.

Flow meter

PVC manifold

PVC tees

Field flush line returnsfrom the high point of the manifold line

PVC manifold

Air vent and highest point

Treatment tank

Dosing tank

House Pump Filters

Valves

systems generally cost less than thosedischarging into streams.

Approaches comparedThe decentralized approach to

wastewater management has seldombeen compared evenly with thecentralized approach. However,Congress asked the EPA to evaluatethe capabilities and cost-effectivenessof the decentralized approach towastewater management, and toidentify barriers and solutions toimplementing this approach.

The agency’s report, EPAResponse to Congress (EPA, 1997),includes a detailed analysis of costs ina hypothetical rural community (Fig.4), comparing the decentralizedapproach with the traditional central-ized approach to establish a wastewa-ter management infrastructure.

The rural community wasassumed to have 450 people living in135 homes located on 1-acre lots orlarger than were serviced by conven-tional septic systems. It was assumedthat 50 percent of the septic systems(67 systems) were failing.

Three wastewater managementoptions were considered for the ruralcommunity’s installation and long-term operation and maintenance:

✓ A centralized system,

✓ Cluster systems, and

✓ Managed on-site systems.

Expenditures included the capitalcosts to install the systems and annualcosts to operate and maintain them.Capital costs were annualized over 30years (the life of the system) for eachtechnology using a discount rate of 7percent. Costs are presented in 1995dollars in Table 1.

This analysis revealed that thedecentralized approach (using eithermanaged on-site systems or clustersystems) frequently is more cost-effective than centralized sewers forsparsely developed rural communi-ties. The cost of estimates includedestablishing a management programto provide long-term maintenance ofeach technology.

The most cost-effective optionfor meeting performance goals is touse new on-site systems of advanceddesigns to replace failing conven-tional septic systems. Using clustersystems with alternative collectionsystems to replace failing septicsystems is not significantly moreexpensive. If soils were unsuitable foron-site systems, the cluster alternativewould be the best choice.

As the distance between homes inthe rural area increases, however,cluster system collection costsincrease. Compared to on-site orcluster system options, centralizedcollection and treatment is not cost-effective in this case.

More and more on-site systemsare being managed in the United

Table 1. Comparison of hypothetical EPA rural community technology costs for three types of wastewater managementsystems.

Total annual costTotal capital cost Annual O&M* cost (annualized capital

Technology option (1995 $) (1995 $) plus O&M* - 1995 $)

Centralized systems $2,321,840 - $3,750,530 $29,740 - $40,260 $216,850 - $342,500

Alternative SDGS** collectionand small cluster systems $598,100 $3,720 $55,500

On-site systems $510,000 $13,400 $54,500

Note: The rural community consists of 450 people in 135 homes. (Adapted from EPA, 1997)* O&M: Operation and maintenance.

** SDGS: Small-diameter gravity sewers.

States. People in the northwest regionare leading the country in usingalternative collection systems tomanage their wastewater. They arecollecting data on the effectiveness ofthe technologies and the associatedcost for management of the technolo-gies.

SummaryThe viability of waste treatment

technologies varies substantially,depending on a community’s develop-ment density, financial resources, siteconditions and surface-water dis-charge requirements throughout thewatershed.

Infrastructure limitations,however, are rapidly changingbecause many communities arerealizing that land-based treatmenttechnologies are often the most cost-effective and environmentallyprotective way to handle municipalwastewater in rural and small commu-nities.

Today, many infrastructurechoices—ranging from centralized todecentralized and all options inbetween—are available to servecommunities’ needs (Table 2). Theseinclude a variety of on-site treatmentsystems, small-scale communitycollection and treatment systems, andlarge-scale municipal wastewatercollection and treatment systems.These options provide effectivemanagement of a community’s

Table 2. Advantages and requirements of small-scale alternative, on-site and cluster systems over the two extremes of conven-tional septic systems and centralized treatment plants.

Requirements

Regular operation and maintenance review and adjustment

Assessment of environmental impacts

System technology upgrades to meet emerging community andenvironmental needs

Advantages

Can be used in areas with low to very high development density

Appropriate for rural to urban landscapes

Moderate costs

Moderately complex technology

Figure 4: Base map of EPA hypothetical rural community (adapted from EPA, 1997).

Represents 10 rural homeswith properly functioningon-site systems

Represents 10 rural homeswith failing on-site systemsRiver

Direction of groundwater flow

(All homes are on one-acre lots or larger.)

wastewater regardless of the densityof development in the area.

In fact, frequently the bestapproach in a given community is acombination of centralized and decen-tralized systems. The location of eachdepends not only on the density ofdevelopment, but also on plans forlocating future growth, cost issues andwater quality and quantity concernsregarding nutrient-sensitive water-sheds.

Land-based options, such as on-site systems, cluster systems and landapplication systems, are often a moreenvironmentally friendly approachwhere surface waters are particularlyvaluable or vulnerable to contamina-tion.

New funding initiatives are beingdeveloped in Texas to establish adependable wastewater infrastructurein rural communities that will sustaingrowth and protect the environment.

As these initiatives come to fruition,the available funding should be usedto provide economically sound,dependable solutions to the largestnumber of communities possible.

More rural communities willbenefit if they embrace land-basedwastewater treatment options to meetfuture community needs.

This publication was adapted from Choices for Communities: Wastewater Management Options for Rural Areas, by the NorthCarolina Cooperative Extension Service. It was developed in cooperation with the Houston-Galveston Area Council of

Government’s On-Site Wastewater Project.

Produced by Agricultural Communications, The Texas A&M University System

All publications in the On-site Wastewater Treatment Systems series can be downloaded free from the World Wide Web at:

http://agpublications.tamu.edu/pubs/ewaste

Educational programs of the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disabilit y, religion, age or national origin.

Issued in fur therance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30, 1914, in cooperation with the United StatesDepar tment of Agriculture. Chester P. Fehlis, Deputy Director, The Texas Agricultural Exension Service, The Texas A&M Universit y System.30,000 copies, New For sale only: $1

The On-Site Wastewater Treatment Systems series of publications is a result of collaborative efforts of various agencies,organizations and funding sources. We would like to acknowledge the following collaborators:

Texas State Soil and Water Conservation Board USEPA 319(h) ProgramTexas On-Site Wastewater Treatment Research Council Texas Agricultural Extension ServiceTexas Natural Resource Conservation Commission Texas Agricultural Experiment StationUSDA Water Quality Demonstration Projects Texas On-Site Wastewater AssociationConsortium of Institutes for Decentralized Wastewater Treatment USDA Natural Resources Conservation Service