Groundwater recharge and quality transformations during the initiation and management of a new stabilization lagoon.

Abstract

The objectives of an investigation at a new stabilization lagoon near Tucson, Arizona were 1) to estimate seepage losses; 2) to monitor the subsurface movement of seepage water and associated quality transformations; and 3) to compare the field data on nitrogen transformations with parallel data from a predictive computer model. Raw sewage was metered into the newly constructed lagoon. Seepage losses were calculated from data on inflow, evaporation, and change in storage of the lagoon. Water samples were obtained from depths of 40, 60 and 100 ft below the surface of the lagoon. The native groundwater table is 70 ft below the land surface in this area. Surface and subsurface water samples were examined for coliform organisms, plus various physical and chemical constituents. Estimated seepage rates from the lagoon ranged from 0.40 ft/day to 0.03 ft/day. A computer model was tested using the nitrate values obtained from the collected water samples. The model assumed that flow was entirely in the vertical direction and that the flow environment was aerobic. The actual nitrate values at 60 ft and values computed from the model were compared at the beginning of the inundation and after 69 days, with the results closely corresponding. No apparent undesirable effects occurred from seepage on the groundwater quality.