Strategies for Rural Development in Areas with Limited Public Infrastructure: Alternative Septic Systems
Precautions on Small Lots
Maine’s geology is highly variable. Certain situations call for particular caution. Maine’s Subsurface Wastewater Disposal Rules are fairly comprehensive in describing most of the likely site challenges. Challenging topography, sensitive environmental conditions, and environmental best practices can sometimes dictate requirements for individual lot sizes that will need to be larger larger than the 20,000 square foot minimum size considered optimal for compact development. Situations that require careful engineering analysis and planning include:
- Locations near wellheads of public water supplies. These wellheads are often located in overburden (sand-and-gravel) aquifers. Septic systems should never be located near or in the drawdown zones surrounding the wellheads; particularly in the case of high-flow wells located near one or more high-flow septic systems, the actual footprint of the drawdown area may be larger than the standard minimum offset distances as specified in the wastewater rules. For public supply wells in overburden aquifers, assuming a heavy daily demand, the most sensitive wellhead protection zone is measured by a travel time of 200 days, which is also the expected lifespan of viruses in groundwater. In general, designated growth areas should not encompass wellhead protection zones. See, for example, ”Best Management Practice for Groundwater Protection: A Guide for Public Water Suppliers and Local Officials,” Maine State Drinking Water Program, Sept. 30, 2003.
Shallow (less than 3 feet) to bedrock, or coarse sand-and-gravel soils without a hydrologic barrier between the septic system and either the bedrock or the water table. This does not necessarily affect lot size, but it does require careful attention to the design, installation, and maintenance of septic systems under these conditions. Wells in these soil conditions should be drilled to depths of more than 100 feet and installed with long casings set and grouted into the bedrock.
Development on significant slopes.When multiple septic systems are placed on slopes, and there are drinking water sources located farther down the slope, there is a greater risk that the wells will become contaminated with nitrates. Regulators should carefully review the placement of septic systems and wells in hilly terrain, and pre-treatment technology for nitrates should be strongly considered as a mitigation technique for first-time systems if an alternative site (or offsite location) for a disposal field will not work. As a general practice, dense development using septic systems should be limited on slopes above wellheads.
Development in the sub-watersheds of nutrient-sensitive lakes and estuaries, especially where land uses are underlain by coarse, unconsolidated sediments. For example, a series of studies of nitrogen loading in the sub-watersheds draining to Waquoit Bay on Cape Cod increased with density of septic systems, with effects on crucial sea grasses and eutrophication. There was not a one-to-one translation of land use to nutrient loading, but the relationship was statistically significant. The tested sub-watersheds ranged in area from about 150 acres to about 6,700 acres, and the density of development ranged up to just under 2 units per acre. Sensitive sub-watersheds should not, as a general rule, be included in designated growth areas. Rather, these areas are best served by very low densities (less than one unit per 2 to 5 acres) with regulations that preserve healthy natural buffers in place between development and surface waters.
System design engineer Joan Brooks, PhD, a.k.a. "The Peat Lady" explains why Peat Filtering Systems are an ideal solution for small, water-front lots:
( 6 min. 3 sec. Video)
 Valiela, Ivan, et.al. December 1992. “Couplings of Watersheds and Coastal Waters: Sources and Consequences of Nutrient Enrichment in Waquoit Bay, Massachusetts.” Estuaries, vol. 15, no. 4.
Related Work Plan Components
- Climate Change and Infrastructure Resilience
- Modernizing Communications/Electric Utility Infrastructure
In Washington County: Judy East