Changes in SAR (sodium adsorption ratio), pH, and EC (electrical conductivity) of shallow groundwaters as a result of disposal of septic tank effluents into wet-tile-drained soils (Typic and Aeric Ochraquults) were studied during 1974, 1975, and 1976. Changes in these constituents in groundwaters were monitored at selected distances from the drainfield (by placement of sampling wells in the direction of groundwater flow), in waters intercepted by the agricultural tile, and control wells. Sodium adsorption ratio, pH, and EC generally decreased with increasing distance from the disposal area. The SAR decreased from 20 to 25 in samples adjacent to the drainfield to <2 in the control wells. The SAR in the drinking water supply was 40.
Soil samples were collected to the 160–cm depth at distances corresponding to the location of water-table wells. Changes in ESP (exchangeable sodium percentage), BS (base saturation), and pH occurred in both the Typic and Aeric Ochraquults and reflected changes detected in groundwater samples. Increased ESP, BS, and pH were observed adjacent to the disposal area in the argillic horizons when compared to the surface horizons. Values for these constituents in the argillic horizon decreased with increased sampling distance from the disposal area. In the control profile, their distribution was reversed, the surface horizon normally having increased ESP, BS, and pH compared to the subsurface horizons. The magnitude of the differences between the drainfield and the control areas was exemplified by the 350 ±/ml extractable Na in the argillic horizon adjacent to the drainfield, as compared to less than 10 ±/ml present in the control profile for the Typic Ochraquult.