The overall objectives of a study initiated in 1972 by the Water Resources Research Center (Univ. of Arizona), in cooperation with the Pima County Dept. of Sanitation, are to examine the possibility of interactions between recharged river water and deposits in adjoining landfills, and if such interactions occur to evaluate the effect on native groundwater quality. Corresponding to these objectives, the principal function of a monitoring program initiated during the project was to characterize background water levels and native groundwater quality during normal low flows (i.e., sewage flows) in the river, and to monitor changes, if such occur, during flood flows. As it turns out, data from the project should also be applicable to the anticipated irrigation of farmland near Marana, using effluent from the Impending Ina Rd Treatment Facility. In particular, clues will be provided on transformations in sewage effluent quality during infiltration and deep percolation. The first phase of the project was conducted at the Ina Rd landfill and the second involved both the Ina Rd and Ruthrauff Rd fills. Results of the first phase were reported in a paper by Wilson and Small. This report will review the results of the second study phase. Specific objectives of the studies during the second phase included (1) obtaining river water and well water samples for chemical and microbiological analysis, (2) monitoring water level changes in available wells and (3) characterizing general features of the geohydrology in the vicinity of the landfills.

A series of bench-scale experiments was carried out to determine the rate and efficiency with which benzene and p-xylene, components of gasoline, could be removed from an unsaturated soil by air stripping. Glass columns, 30 cm in length, were packed with soil and wetted to volumetric moisture contents of 10 and 18 percent. Air saturated with one of the volatile organic compounds (VOCs) was used to load the column. Clean air was used to strip the contaminant from the soil. Benzene and p-xylene concentrations in the soil water and air were reduced four orders of magnitude after a few hours (2-8) of stripping. Benzene was removed faster than p-xylene. Air flow was the rate-limiting step early in the stripping, however slow desorption from the soil became rate-limiting as the stripping progressed. As moisture content increased the rate of removal of both contaminants decreased.