Issue 17
Septic Solutions
by Marian Wineman
Some facts about septic systems may surprise you. In "Saving Our Estuarine Playgrounds" (Issue #16), I discussed the fact that the largest source of pollution for most estuaries is the nitrogen and pathogens that come from septic systems. Most areas that are not served by sewage-treatment plants rely on individual septic systems for wastewater disposal. Many of these septic systems are either poorly located or inadequately maintained.
Of course, sewage-treatment plants aren't perfect either — they are costly, require sewage to be transported long distances and can leak during collection and storms. But effluent discharged from sewage-treatment plants usually contains about a quarter of the nitrogen concentration per household of effluent discharged from properly functioning septic systems. Also, when wastewater is discharged from treatment plants, it is usually discharged well away from shore, into bodies of water with currents that further dilute the remaining contaminants.
Most of us don't really want to know the story of where refuse goes when it leaves the house. It's easier not to know. We can simply pay the sewer bill and wipe our hands clean. But maybe where it goes and what happens to it after it leaves our houses is important. We want to have healthy water to drink, clean beaches to play on and to know that our kids will be able to enjoy a salmon dinner when they grow up. To understand more about solutions to the problems created by traditional septic systems, let's look at some alternatives that can help protect our estuaries and our larger environment.
The septic system is generally an inexpensive and convenient way to manage and dispose of household wastewater. Typically, it consists of a 1,000-gallon concrete tank connected to a drainfield (a series of foot-wide trenches, each containing a perforated distribution pipe surrounded by gravel or stone). The tank is installed in a sizeable area of the front or back yard that has been cleared of trees and other vegetation. Wastewater liquids flow through the tank, into the perforated pipes in the trenches and then out through the holes in the pipes and into the surrounding gravel and soil. The tank retains the solids. As the liquid effluent flows through the soil, pathogens (bacteria and viruses) are filtered out or naturally destroyed. An appropriate soil type also retains some phosphorus and some forms of nitrogen from the effluent. In the right conditions, this soil-filtration process eliminates most pathogens before they reach the groundwater or nearby surface waters such as wetlands, rivers, lakes and estuaries. However, septic systems only treat nitrogen and phosphorus to a limited extent and are only effective for treating pathogens when the septic system is situated in the right spot and is well maintained.
Septic System Location & Maintenance
A septic system works best in soils that adequately purify and absorb the wastewater. Gently sloping, organic/humus-rich, permeable soils with deep water tables make the best sites. Some sites can be approved for a drip line drainfield system that discharges to surface soils (only six inches below ground). This minimizes the amount of tree-clearing required for the drainfield. The trees and plants help take up the water and filter it instead of allowing it to flow into the groundwater. Conventional systems continue to work only if they are properly maintained, including regular inspection and tank pump-out. The pumped-out waste still needs to be hauled from your home to a special septic-treatment facility — many of these plants have additional problems such as odor and excess nitrogen discharges.
As mentioned in the previous article, be careful what you put down the drain. The tank and drainfield should be located away from surface water sources such as foundation drains, roof water, gutter water and surface water on driveways and other paved areas. Do not compact the drainfield or drive vehicles over it. Most septic-tank cleaners don't work, and many of these products contain chemicals that damage the drainfield by disrupting the soil-filtration and retention processes. When the drainfield function is disrupted, nitrogen can contaminate the groundwater, nearby drinking-water wells and waterways.
Some soils and some locations are just not suitable for either conventional or alternative septic systems because not all soils can absorb wastewater or purify it. Septic systems that are installed in poor locations and/or in unsuitable soils usually leak raw, untreated or minimally treated sewage to the soil surface, nearby waterways, wetlands or groundwater. Soil types in which septic systems don't work well include those with too much moisture or sand (water flows downward too fast) or clay (restricts the downward flow of water). The drainfield location also can't have rock too close to the surface, be too small or too steep
Alternatives with Drainfields
Fortunately, many innovative systems exist that can be used for problem sites, where the amount of available space or the soil conditions make conventional drainfields ineffective or where an existing septic system has failed. Alternative systems are also used to reduce nitrogen when discharging to nitrogen-sensitive areas such as estuaries. These systems include additional or different parts than a traditional septic system. Here are several alternatives that provide equivalent or substantially better pollution-reduction capability than ordinary systems:
Septic Mound or Raised Bed Systems are a common alternative. These are very similar to standard septic systems but usually involve bringing in special soil or fill to treat effluent. A typical raised-bed design is made by mounding sand about four feet above the normal ground surface.
Advanced Material Media Filtration Systems typically include a concrete box with a filter inside (e.g. natural filters such as sand, gravel or peat or synthetic filters such as foam or glass).
Rotating Biological Contactor Systems work differently from other types of filtration systems because they add the advantage of rotation (or multiple passes of the effluent over a filtration media, such as the ones described above). A pipe network pumps the wastewater through the filter two or more times before it is discharged to the soil or to a regular drainfield.
Aerobic Septic Systems add oxygen to and circulate air inside the treatment tank, which speeds up the treatment process and produces a cleaner effluent. This mechanism costs more to operate and maintain than most septic systems. A disinfection system may be added to provide additional treatment. Disinfection treats the effluent by using chemicals such as chlorine, calcium hypochlorite, ozone or UV light. Adding a disinfection stage to the aerobic system may eliminate the need for a drainfield.
Alternatives without Drainfields
These systems without drainfields are a great benefit to homeowners who want to retain their wooded lots:
Waterless and Low-Water Systems use chemical, composting or incinerating toilets.
Graywater-Separation Systems (see "Graywater in the Garden", Issue #15) use another alternative design that doesn't require a traditional tank and drainfield. These are often used where there is a limited water supply or when land-use restrictions don't permit a conventional system. They don't really treat the effluent but discharge limited pollutants to the environment.
An Alternative Community Treatment System — in Action
The residents in a neighborhood near where my folks live voluntarily converted all their homes from individual septic systems to a community treatment system. One of the houses within the community was converted to a treatment facility that handles 21,000 gallons of wastewater per day (the equivalent of waste from about 80 homes) by using rotating biological contactors. A resident of the community is a licensed plant operator. The benefit to the adjacent waterway, Rock Harbor, which flow into Cape Cod Bay, is a 7 - 18-fold decrease in nitrogen discharge — as well as a reduction in other contaminants — compared to the potential discharge from conventional septic systems for each home.
Using alternative single-family or community treatment systems will help protect our beloved estuaries
Marian Wineman lives with her husband and seven-year-old daughter a few blocks east of Puget Sound and enjoys paddling on Pleasant Bay during the summer.
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