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Groundwater Mounding below a Surface Line Source in a Typic Fragiudalf

Agricultural Research Department, Tennessee Valley Authority, P.O. Box 1010, Muscle Shoals, AL 35660

D. D. Fritton

Dep. of Agronomy, Pennsylvania State Univ., University Park, PA 16802

*Corresponding author.

ABSTRACT

Nearly one-third of the soils in Pennsylvania contain fragipans. Onsite sewage disposal systems on these soils historically have been failure prone. This leads to a public health hazard due to contamination of surface and groundwaters with unrenovated effluent. In order to gain a better understanding of water flow in a soil that contains a fragipan, a field study was conducted to determine in situ, two-dimensional, steady-state water flow patterns from a surface line source. Tensiometers were used to determine the soil water pressure head distribution for five application rates ranging from 125 to 625 mm d^–1 in 125 mm d^–1 increments. Field results indicated that steady-state groundwater mounds (mound-shaped regions of saturation) developed for all application rates because of the reduced permeability of the fragipan and the presence of small lateral hydraulic gradients on either side of the saturated region. Field results were simulated with a finite difference solution of the steady-state Richards' equation. Simulated results agreed well with field measurements within the region of saturation for the three highest application rates. However, the model underpredicted the height of the mounds for the two lowest application rates. The application rate both experimentally and theoretically seemed to have little influence on the hydraulic head beyond 2 m laterally in either direction from the source.

Received for publication February 4, 1993.