Effect of Tile Drainage on Disposal of Septic Tank Effluent in Wet Soils

Abstract

AbstractA field‐performance study was conducted to determine the feasibility of artificially draining wet soils to permit satisfactory operation of septic tank effluent disposal fields. Tile drains placed 1.2 and 1.8 m deep with 3‐ and 6‐m horizontal separations, respectively, around disposal fields were monitored during wet winter months. Ground‐water drawdown beneath septic tank disposal fields was measured and tile drainage water was analyzed for NO3‐N, total coliform, and fecal coliform.Tile placed at either depth lowered ground water sufficiently to prevent saturated soil conditions in disposal fields. Vertical mean groundwater separation distances of as little as 23 cm below disposal trench bottoms with a horizontal setback of 3 m between the tile drain and disposal field resulted in acceptable quality for drainage water discharges based on Oregon Department of Environmental Quality standards. Results indicated that design specifications were a practical means of overcoming wetness limitations for onsite sewage disposal on drainable soils in western Oregon.