The most common question when talking with a homeowner about options dealing with a failed soil treatment system is: Can you do anything to make the existing system work?
You need to approach the answer carefully and remember that it is very site-specific. The answer also depends on factors that are sometimes hard to determine. First, was the system well constructed to begin with? What are the flow characteristics in the house? How have they changed?
Has regular maintenance been performed? Does the system comply with current state and local codes? Often, the most cost-effective solution is to replace the system and use the occasion as time for homeowner education.
Changing usage
Before recommending the new system, it is always good to talk with the owners about their water use patterns and to evaluate where they can make changes for the benefit of the onsite treatment system.
This homeowner evaluation of water use starts the discussion of what the future system should look like and how big it needs to be. Here is an example. A frantic call came from a homeowner that sewage was surfacing in the backyard. It turned out that the system was on a beautiful lot with many mature evergreens. These trees were in the only place on the lot where a new system could be built to replace the failing trenches.
The homeowner said there were three teenagers in the house and that they all took long showers every day. When the owner asked if anything could be done to avoid cutting the trees to replace the system, an obvious suggestion was to put on a water meter to measure the daily flow and to take steps to reduce usage. This was also the time to point out that systems have a finite capacity and exceeding it creates problems.
In the first week, the water meter showed that while the system was designed for 450 gpd, it was receiving nearly 700 gpd. The home-owner set out on a water-conservation plan that included timing showers and cutting off the hot water after five minutes. Lo and behold, the surfacing stopped, and they did not have to replace the system.
This outcome isn’t possible in all cases. But the example illustrates that household water use can have a major impact on system performance and should be looked at as part of any potential system renovation. It also shows that a water meter can be very helpful in identifying potential problems and devising solutions.
Better effluent
Another area to look at in soil treatment area renovation is improving the quality of effluent coming from the house. If the septic tank was not maintained regularly or is too small for the house, or if use patterns are such that the effluent BOD exceeds 175 mg/l, the system can be potentially renovated by providing a cleaner effluent.
Since BOD is a measure of the organic loading to the system and contributes to development of a thicker and more resistant biomat, reducing the organic loading can increase system performance over time.
One way to renovate the system would be to rest it for a while to reduce the biomat and restore some infiltrative capacity. This, along with reducing the organic loading from the house and increasing septic tank capacity to reduce the BOD, can be effective. This is why having the ability to manage where effluent is delivered is an effective management strategy.
In recent years, to help clean up effluent, installers have moved to adding pretreatment devices to knock down the BOD and fats, oils and grease (FOG). One example was a failing set of trenches installed in fill and disturbed soil.
There was limited space on the lot, so the solution was to install a recirculating sand filter and as much additional linear footage of trenches as possible within the area available. The bottom line: The filter worked so well that the system recovered and the additional trenches never saw a drop of effluent. And this was on a very tough site.
Workings of filters
Recirculation means cycling the wastewater through a filter a number of times, improving waste removal and increasing bacterial decomposition. Wastewater moves from the house to the septic tank and then by gravity to a recirculation tank. From there, the water is pumped to the filter (sand media in the previous example, but peat and textile filters work too).
After passing through the filter, the water is pumped back to the recirculation tank, where it mixes with more septic tank effluent. Effluent is pumped repeatedly through the filter and then back to the recirculation tank. Ideally, the recirculation ratio is at least 5:1 before the effluent is released to the soil treatment area.
The filter is in a watertight liner or container. Although the liner can be made from a number of materials, 30 mil polyvinyl chloride (PVC) is the most common and reliable. The filter is composed of 12 inches of drainage media. Outflow is provided by a 4-inch pipe surrounded by drainfield rock. The depth of the outflow should be 12 to 18 inches below the bottom of the filter media. Effluent must drain freely out of the media, since saturation reduces filter effectiveness.
In future articles, we will explain installation of different media filters.
