Limitations on infiltration and reinjection of treated groundwater to remove trace amounts of pesticides in groundwater and soil

Abstract

AbstractInfiltration and reinjection of treated groundwater have been used to increase the recovery of pesticide‐related constituents at a pesticide formulation plant that produces consumer pesticide products. The stratigraphy at the site consists of silty and sandy clay deposits overlying a shallow silt, sand, and gravel aquifer. The groundwater and soils in two areas in the northwest portion of the property have been identified as being significantly affected by pesticide and pesticide‐related compounds.An integrated system of soil removal, recovery wells, injection wells, an infiltration gallery, and a cut‐off wall was selected as the best remedial alternative. Groundwater modeling, column tests, biological jar tests, and a pilot test demonstrated the feasibility of the system. The affected groundwater is treated to drinking‐water quality by a system of filtering and carbon adsorption. Approximately 75 percent of the treated water is reinjected or allowed to infiltrate through the vadose zone, and the remainder is discharged to the local sewer system. Initially, the system was effective in removing the dissolved, suspended, and weakly adsorbed constituents. Subsequently, the recovery rate of the chemical constituents became dependent on chemical and physical processes related to the presence of residual amounts of dense, nonaqueous phase liquids and the clay content of the strata. The rate of pesticide recovery has decreased because of the retarding effect of the clay and the low solubility of the pesticides.