May 2007, Vol. 19, No.5

Small Communities

Alternative Wastewater Collection Systems

Jim Kreissl

In the late 1960s, it was found that installing conventional gravity collection systems in rural communities cost nearly four times more than the wastewater treatment facilities. Since increased lengths of pipe were needed to service these less densely populated areas, more lift stations were required. Therefore, operations and maintenance (O&M) costs often were higher for the collection systems than for the treatment facilities.

More recently, it has been discovered that local water tables have receded because the deeply laid conventional sewers, via infiltration and inflow, have drained much of the aquifers above the sewer inverts. In other sensitive areas, leaking sewers located above the water table have contaminated these aquifers. Situations such as these prompted the water quality industry to develop lower-cost sewers that are more watertight and laid at shallower depths. These alternative systems have seen hundreds of successful installations in the past 30 years.

None of the above problems with conventional sewerage should cause this technology to be abandoned. In fact, conventional sewers are still the most appropriate means of wastewater collection in densely populated urban areas because, unlike the alternative collection methods, they require no on-lot components.

What’s troubling to those familiar with the success of alternative systems is that many consulting engineers still don’t evaluate them fairly for their clients during facility planning. For conventional sewers, it is common to find cost estimates of $20,000 or more for each house served. With the limited resources available to fund these projects, smaller communities often balk at these estimates. Several successful managed decentralized solutions have been precipitated by community reactions to this “sticker shock,” causing them to seek less expensive solutions.

Alternative collection systems (ACSs) are subdivided into four distinct types: septic tank effluent gravity, septic tank effluent pumping, vacuum, and grinder-pump pressure. The first two are called effluent sewers because they convey septic tank effluent, while the latter two convey the entire wastewater flow. The tanks in the first two categories must be inspected or pumped periodically, with access guaranteed by an easement. The latter two types require an easement, but the on-lot tasks do not include tank pumping. For all ACS types, an annual preventive maintenance visit to each service location is recommended. Unplanned service calls to each on-lot system normally occur once every 6 or 7 years, based on decades of documented field data on properly installed systems. Vacuum systems require additional collector O&M for the vacuum station.

ACSs are best employed as part of the decentralized approach to attaining a distributed wastewater management solution, which may include several different wastewater management approaches. However, they also can be considered as merely alternatives to conventional collection systems. The same level of administrative management must be applied for both. Actual O&M demands generally are comparable to those of conventional systems (frequent O&M required by several lift stations versus annual O&M visits to each serviced lot). With the lower capital costs, the present worth comparison usually will favor the ACS.

A major reason for the increasing popularity of managed decentralized and distributed systems using ACSs is the lower cost per lineal foot due to the shallow, smaller collection lines. When nonmonetary benefits are considered, such as the reduced duration and degree of community disruption during the construction phase, less infiltration and inflow, and reduced water transfer from the originating basin, the reasons for not considering alternative systems become even less understandable.

In 1997, the U.S. Environmental Protection Agency (EPA) issued its Response to Congress on Use of Decentralized Wastewater Treatment Systems, which endorsed these and other decentralized technologies, when properly managed, as acceptable alternatives to conventional wastewater management systems. This report and several other EPA publications that followed stress the need for responsible management entities (RMEs) to ensure sustainable performance of these technologies. These RMEs, which vary in makeup (for example, rural electric cooperatives, municipal sewer districts, regional or local governments, and private utilities), now exist in several states. In all cases, RMEs are empowered to make and enforce rules, assess and collect user fees, and provide O&M for the systems. EPA’s Voluntary National Guidelines for Management of Onsite and Clustered(Decentralized) Wastewater Treatment Systems describes such management programs.

In essence, if a community can properly manage a conventional collection system, it also can manage an ACS. The real issue is why these systems are not routinely considered and evaluated as viable alternatives when performing facility planning for client communities. Engineering schools should incorporate these technologies into their undergraduate courses. Course modules are available from the National Environmental Services Center (Morgantown, W.V.) and the Consortium of Institutes for Decentralized Wastewater Treatment. Small communities should be made aware of the potential advantages of these technologies by regulators and community assistance agencies.

Probably the most effective way to facilitate more comprehensive facility planning would be through state legislation that requires it and ties it to funding eligibility. As long as unconventional solutions trigger additional variances, reviews, and time delays, there is not much incentive for innovation.

Jim Kreissl is an environmental consultant in Villa Hills, Ky.

Jim Kreissl is an environmental consultant in Villa Hills, Ky.