Field-measured and simulated water flow beneath a surface line source in a fragipan soil
Nearly one-third of the soils in Pennsylvania contain fragipans. On-site sewage disposal systems on these soils have historically been failure prone. These failures lead to contamination of surface and ground waters. A field study was conducted to determine in situ, two-dimensional, steady-state soil water pressure and hydraulic head distributions beneath a surface line source in a fragipan soil. Field-saturated hydraulic conductivity (K[sub fs]) was measured in situ for each layer with the Guelph permeameter. Tensiometers were used to determine the soil water pressure distribution for five application rates ranging from 125 mm day [sup [minus]1] to 625 mm day[sup [minus]1] in 125 mm day[sup [minus]1] increments. Steady-state groundwater mounds formed beneath the line source for all application rates. With exception of the largest application rate, these mounds extended laterally 3 m downslope and 2 m upslope from the source. The mound associated with the largest rate extended 3.5 m downslope. The main effect of increasing application rate was to increase pressure beneath the free water surface instead of increasing lateral spreading of the mound. Hydraulic head distributions indicated that lateral gradients for all application rates were smaller than vertically downward gradients. An effort was made to validate a finite difference model that solves the two-dimensional, steady-state, saturated-unsaturated form of Richards' equation. Calculated soil water pressure was plotted against measured values to facilitate comparison by linear regression to test for unit slope and zero intercept. Model acceptance was based on linear regression results and achievement of a mean absolute difference that was [le] to the corresponding mean field spatial standard deviation. Comparison results indicated that the model yielded acceptable results at comparison locations up to 1 m laterally on either side of the source for the 3 largest application rates only.
- Research Organization:
- Pennsylvania State Univ., University Park, PA (United States)
- OSTI ID:
- 5509129
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SEWAGE
LEAKS
WASTE DISPOSAL
SOILS
HYDRAULIC CONDUCTIVITY
PRESSURE GRADIENTS
WATER
CONTAMINATION
FAILURES
MATHEMATICAL MODELS
PENNSYLVANIA
TENSIOMETERS
DEVELOPED COUNTRIES
HYDROGEN COMPOUNDS
MANAGEMENT
MEASURING INSTRUMENTS
NORTH AMERICA
OXYGEN COMPOUNDS
USA
WASTE MANAGEMENT
WASTES
540220* - Environment
Terrestrial- Chemicals Monitoring & Transport- (1990-)