Progressive Packer/Zone Sampling Method for VOC Plume Delineation in Consolidated Aquifers

Abstract

AbstractThe progressive packer/zone sampling method was used to identify the bottom of a plume of volatile organic compounds (VOCs) in the parts‐per‐million (ppm) range using one well in each of three separate locations. The method involves progressively drilling a 20‐foot length of borehole through casing, setting an inflatable packer at the top of the drilled zone, purging the zone of three volumes of water using the airlift method, sampling the zone in situ through the packer string using a bailer, then repeating the procedure.A plume consisting of chlorinated VOCs, alcohols, and vinyl chloride occurs in a low‐yielding fractured bedrock aquifer located in the Passaic Formation at a site in central New Jersey. The thickness of the plume in total VOC concentrations exceeding 1 ppm was determined using the progressive packer/zone sampling method to a depth of 200 feet. The first borehole was completed as a monitoring well in the “hottest” zone encountered during testing. Additional wells were then clustered with this exploratory well to delineate the plume in the parts‐per‐billion (ppb) range. Cross contamination from previously sampled zones was not a problem as long as total VOCs in the ppm range were targeted and the sample interval was properly purged.Instead of using a multiple well cluster consisting of an indefinite number of wells to determine the bulk thickness of a plume at a specific location, information from one borehole may suffice during the exploratory phase. Costs to the client and cross contamination potential to the aquifer can be minimized by limiting the number of boreholes needed for vertical delineation.