Estimation of Ground‐Water Mounding Beneath Septic Drain Fields

Localized ground‐water mounding beneath larger on‐site sewage disposal fields (septic drain fields) can reduce and even eliminate the waste‐water treatment that occurs in the unsaturated soil zone. Such mounding was previously predicted for longer times by a procedure of uncertain accuracy and having a number of limitations. In this paper, a new procedure is developed on a stronger theoretical basis. The governing equation may be solved by four different methods. The new procedure considerably extends the time range of applicability, and no longer restricts the proportions of the rectangular disposal field. Errors in the previous methods approached 20% in some cases. Comparisons of different methods to reduce mound heights where they are critical indicate that the most effective method is to subdivide the disposal field into separated subareas.