The Use of a Specialized Drilling and Ground‐Water Sampling Technique for Delineation of Hexavalent Chromium Contamination in an Unconfined Aquifer, Southern New Jersey Coastal Plaina

Abstract

ABSTRACTWoodward‐Clyde Consultants was retained to investigate a ground‐water contamination problem caused by disposal of chromium‐laden process water into an unlined lagoon in the Coastal Plain sediments of southern New Jersey. During the course of the investigation, a technique for sampling of formation water at specific horizons during drilling was developed. This technique consists of the following procedure: (1) drilling a borehole to the base of a sampling horizon; (2) lowering a wire‐wound well screen and riser pipe to the bottom of the borehole and gravel‐packing the screen; (3) pumping the borehole well until the discharge is clear of drilling fluid; and (4) pumping at least 100 gallons of formation water before collecting the sample and performing field water quality tests.Analysis of water samples withdrawn from a cluster of five wells, drilled to and screened at specific depths of 20 to 100 feet, verified that the special drilling and sampling technique developed was a valid method to obtain representative, in‐situ water samples from specific horizons. This sampling procedure was then used to substantiate surface earth‐resistivity survey data and provide important information on the vertical distribution of the contaminant within the aquifer. The delineation of the contaminant within the aquifer was an important part of Woodward‐Clyde Consultants'responsibility to evaluate the extent and magnitude of ground‐water contamination at the plant site and design an economically and technically feasible system for the removal and treatment of the contaminated ground water and eventual recovery of the chromium.