To Sewer or Not to Sewer?
When evaluating its wastewater options, each community should take a methodical approach that considers all types and sizes of wastewater infrastructure — public and private. Individual on-site septic systems can be a very reliable, low-cost means of wastewater treatment and disposal. State sanitary codes have evolved to provide a sound basis for design and installation of these systems. Since the treatment and disposal occurs on the same property where the wastewater is created, individual systems avoid the cost of a collection system. Given that cost advantage, it is instructive to consider septic systems as the “baseline” and to try to use them unless there is a documented reason not to.
Why on-lot disposal may not be adequate
It has been Wright-Pierce’s experience that if individual on-lot systems need to be enhanced or replaced, it is for one or more of the following five reasons:
- Ensuring sanitary conditions — correction or avoidance of unsanitary conditions (that is, public health problems) such as effluent surfacing over a leaching field, inadequate set-back from a private well, or direct discharge of sanitary wastewater to a watercourse.
- Protecting the water supply — preventing contaminants (such as bacteria, viruses or nitrates) from reaching private or public drinking water sources.
- Protecting surface waters from nutrient enrichment — reducing nutrients that can cause accelerated degradation of freshwater ponds (typically phosphorus) or estuarine waters (typically nitrogen).
- Addressing convenience and aesthetic issues — avoiding unsightly mounded septic systems or individual treatment systems that may be the only way to achieve compliance with the sanitary code if off-site options do not exist, or avoiding frequent septage pumping that creates odor and disruption.
- Enabling sustainable economic development — providing off-site wastewater treatment and disposal so that on-site conditions (such as impermeable soils or shallow groundwater) are not the limiting factors to community growth and development.
If one or more of these problems exist,there are two fundamental approaches:
- Repair or enhance the on-site system to address its limitations.
- Eliminate the on-site system and convey the wastewater to another location where it can be better treated or disposed of.
Improving on-lot systems
Enhancements to on-lot systems may take many forms. To optimize the effectiveness of any septic-tank-and-leaching-field system, the owner should perform periodic inspections and regular pumping of septage. On large parcels, there may be room for an expanded/relocated leaching field to minimize break-out potential, increase the depth to groundwater or increase the setback from private wells. In areas where cumulative loading of nutrients from septic systems is causing surface water impacts, there are many proprietary treatment systems that can be installed to supplement the septic tank to remove more of the nitrogen and phosphorus. The Massachusetts Alternative Septic System Test Center (www.masstc.org) is a good source of information on available technologies and their performance.
Implementing off-site solutions Providing supplemental on-lot treatment systems to enhance a septic system is often a viable solution, particularly in neighborhoods of large lots where collection systems would be expensive. However, the homeowner is then burdened with both the capital cost of the treatment system and its ongoing operational costs. Where these costs are excessive, communities should look into off-site solutions to include:
- Cluster systems, serving less than 30 properties where the treatment and disposal system is near the lots with on-site problems, thus avoiding large wastewater transport costs.
- Satellite systems, serving a school, shopping center or neighborhood remote from existing sewer systems.
- Centralized systems, large enough to serve all or a large fraction of a community’s wastewater needs.
In general, as the size of the treatment system increases, “economies of scale” provide a lower cost per gallon created. Countering those cost savings is the cost of transport facilities to bring collected wastewater to the treatment site. In some areas, suitable sites large enough for centralized treatment facilities are scarce, and the costs of transport and land purchase can erase some or all of the economies of scale. Documenting needs for improved wastewater disposal, and evaluating the costs of small and large-scale options, is the essence of comprehensive wastewater management planning. Wright-Pierce has developed interdisciplinary planning tools that consider the inter-related nature of our water resources, and we have a depth of experience in the technologies and regulatory
programs that can support both centralized and decentralized approaches.
What’s the best solution?
In municipal wastewater management, does “one size fit all?” The clear answer is “no”. Each community must look at all systems, ranging from on-site to decentralized to centralized, to find the most cost-effective and sustainable solution or combination of solutions for its particular circumstances.