Bacteriological groundwater quality characteristics on the Walnut Gulch Experimental Watershed

Abstract

Groundwater aquifers are generally considered to be free from surface water pollution sources. Aquifer recharge mechanisms in arid lands appear to differ radically from those in more temperate climates. The groundwater beneath the Walnut Gulch Experimental Watershed located in southeastern Arizona is bacteriologically contaminated from three predominate sources: 1) the natural background contamination occurring from normal runoff-erosion syndromes; 2) rangeland grazing pressure which increases the pollution entering groundwater via runoff events, and; 3) the practice in Tombstone, Arizona of disposing of raw sewage effluent into abandoned mine shafts which subsequently penetrates the groundwater table. It is apparent that arid lands permit vast volumes of water to infiltrate drainage channels as a form of transmission loss. The results of this study clearly indicate that surface runoff water is penetrating local well fields. It should be obvious that best management practices where they involve arid land agriculture must be more thoroughly understood. If the amounts of pollutants are controlled with more efficiency, then the amounts of pollutants entering groundwater will be lessened. Land management practices in the southwest such as using desert soils for solid wastes disposal, injection wells, sewage effluent dumping, or other such activities must be thoroughly evaluated before they are blindly implemented as panacea solutions.