Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: 5/1/2004
Publication Date: 7/1/2004
Citation: Owens, P.R., Rutledge, E.M., Osier, S.C., Gross, M.A. 2004. Response of effluent absorption rates to resting trenches of a serially loaded septic filter field. Proceedings of 10th National Symposium on Individual and Small Community Sewage System. p. 223-230.
Interpretive Summary: Septic systems are used in 38% of the homes in the United States. They are used by rural homeowners but they also allow for urban expansion by providing wastewater treatment while awaiting public sewerage. The serially loaded septic tank filter field is one of the most popular designs. In the serially loaded filter field, the first trench continuously absorbs effluent until the effluent load exceeds the absorption capacity; then, effluent flows into the second and subsequent trenches where the process of absorption and overflow continues. If the filter field is not able to absorb all the effluent, it fails by surfacing of effluent. Continuous application of effluent causes a crust or clogging mat to form at the gravel-soil interface. This study found that placing an alternating valve and re-routing the wastewater around the upper trenches during the summer months in the filter field would allow for aeration and microbial breakdown of the clogging mat. This resting of upper trenches management technique will substantially improve the long-term performance of a serially loaded septic system.
Technical Abstract: The objective of this research is to test the hypothesis that summer resting of septic trenches can increase both spring and fall effluent absorption rates (EAR). Earlier studies have assumed that the crust at the soil-trench interface has been degraded by aerobic microbial activity and thereby increase EAR. This study was initiated on an 11-year-old serially loaded septic system. The filter field consists of eight 9-to 17-m long, 60-cm wide, and 46-cm deep trenches on 3-to 4-m centers in a Hapludult. Effluent absorption rates (EAR) were calculated by dividing the effluent load by the trench bottom area used. The filter field was rested during the summers of years 10 through 14. During years 7 through 10, the mean EAR had been near stable at about 2.8 cm d-1. This mean rate increased to 11 cm d-1 in the fall of year 11, and 12 cm d-1 in the fall of year 13. Spring EAR increased to 6.2 cm d-1 in year 14. These data indicate that resting increased EAR in all cases, approximately 280 percent in the fall and 70 percent in the spring.