Strategies for Rural Development in Areas with Limited Public Infrastructure: Alternative Septic Systems

Failing and Substandard Systems

The primary causes of septic system failure are hydraulic and organic overloading of the leaching system.  Hydraulic overloading can cause wastewater to “pond” on top of the disposal field, or even back up into the building.  Organic overloading occurs when a septic tank is not pumped regularly, allowing solids to escape from the tank and settle in the disposal field. Eventually the solids clog all of the spaces at the stone-soil interface, and the entire system is rendered unusable.

Substandard wastewater treatment can occur if the leaching system receives and discharges effluent at a higher rate than the surrounding soils can assimilate it.  This causes contaminants to be transported through the soil before they have received adequate treatment in the disposal field and at the stone-soil interface, with the potential to escape to shallow groundwater and nearby surface waters.

On-site septic systems are among the many non-point sources of pollution for surface waters, and they are considered nationally to be the third most common source of groundwater contamination. Many older systems were installed before scientists fully understood how septic systems treat the effluent, and what soil and site conditions produce the best system performance.  These older systems may “function” in the sense that they are not backing up into the plumbing or creating odors and ponding in the yard, but they still do not always function properly in terms of treating the wastewater before it contaminates the groundwater table or surface water. Many existing rural villages do not have adequate soils, space, or site conditions to upgrade older systems to modern standards.  Many of Maine’s village communities were first developed during in the 18th and 19th centuries, when sanitary sewage disposal as we understand it today was rarely even considered; most homes and businesses on waterways used “straight pipe” plumbing to dispose of their household sewage, and also swam and fished in those same waterways.  The Town of Brownville was able to solve this problem by creating 12 clustered offsite septic systems to replace straight-pipe plumbing in its two village areas, greatly improving the water quality in the Pleasant River while providing modern septic treatment to properties on extremely small lots.

Many newer Maine communities wish to replicate the look and feel of these early American compact villages within their growth areas.  The use of clustered and onsite septic systems can help communities achieve this goal.  However, systems in more densely populated areas must be managed especially carefully to avoid the potential for failures that can lead to unhealthy nutrient and bacterial loading in the soil, particularly near or over important water resources, aquifers, and recreational or shellfish waters.

Maine Drinking Water Program Assistant Director Andy Tolman and Project Manager James Jacobsen discuss the common causes of septic system failure and the importance of good management:

( 8 min. 8 sec. Video)

Impacts of Septic Contamination on Surface Waters

Surface waters used for bathing and recreation are typically monitored for potential contamination, and swimming areas can be closed if pathogens, such as E. coli, are reported in high numbers. New methods for monitoring recreation areas have been developed in recent years, including microbial source typing to determine the likely source of any identified bacteria, and monitoring for surfactants and optical brighteners that are commonly found in laundry wastewater. 

An overabundance of nutrients from human sources in surface waters can lead to the excessive growth of algae and other nuisance aquatic plants, a process known as cultural eutrophication. Freshwater lakes and ponds can be significantly degraded by phosphorus from septic system effluent.  Coastal  bays and estuaries can also be degraded by high nutrient loads, and shorelines may need to be closed to shellfish harvesting if there are high pathogen counts in the waters.

One study of potential impacts from wastewater treatment practices sampled 14 small stream sites in Anchorage, Alaska, in medium and high-density neighborhoods.   Some of the adjacent properties were served by municipal sewers and storm sewers, while others used on-site septic systems with no storm sewers. The most highly urbanized sewered area also contained the highest concentrations of fecal coliform, E. coli and enterrococci bacteria in the water, indicating that the sewer pipes are probably leaking and leaching these pathogens into the soil (and eventually into the surface water).  Another study near Detroit, Michigan found traces of contamination from nearby conventional septic systems in the shallow groundwater table (less than 25 feet deep), but water from all of the deeper domestic water supply wells either met or exceeded all health-related drinking water standards.

 

Impacts of Septic Contamination on Drinking Water Sources

Pathogens from septic systems can enter drinking water sources when there is an inadequate vertical separation in the soils between the bottom of the disposal field and the seasonal high groundwater table. Nitrogen (in the form of nitrate and nitrite in drinking water supplies) can cause illness, particularly in infants. A properly functioning conventional septic system may not remove all of the nitrogen, so the cumulative impacts of nitrogen concentrations need to be assessed and mitigated if necessary through design and construction requirements.

In 1999, DEP and the Maine Geological Society conducted a study to determine the potential impacts on domestic wells from septic systems in 18 subdivisions. A total of 470 drilled wells were sampled for nitrate-nitrogen (NO -N) concentrations. Only two of the wells showed nitrate levels above the national drinking water standard of 10 mg/L. However, wells drilled to depths of less than 100 feet did show a higher average nitrate concentration than the deeper wells. The report concluded that the current regulations for locating onsite wells appeared to be adequate for water supply protection.

The cumulative impacts of multiple onsite systems can be evaluated and modeled by engineers and hydrogeologists, using risk assessment processes with mass loading equations of nutrients such as nitrates, their ability to move through soil, and their ultimate fate in groundwater or surface waters. A nitrate concentration assessment process is provided in the Maine wastewater rules to evaluate proper siting and separation from disposal fields when multiple wells or very large community wells are proposed for a subdivision that will use onsite or clustered septic systems.

 

Related Work Plan Components

Workgroup Contacts

In Aroostook County: Jay Kamm, Ken Murchison, Joella Theriault

In Washington County: Judy East