Publication Summary

This technical report documents the results of the soil gas survey and ground water sampling at the Endicott School, located in Whitman County. The primary objective of the soil gas survey was to determine the configuration of the contaminant plume. Secondary objectives were to evaluate why free product was not being recovered and to assess the cause of the mounded water table in the central portion of the site.

This technical report documents the results of the soil gas survey and ground water sampling at the Endicott School, located in Whitman County. The primary objective of the soil gas survey was to determine the configuration of the contaminant plume. Secondary objectives were to evaluate why free product was not being recovered and to assess the cause of the mounded water table in the central portion of the site.

High concentrations of benzene were detected in wells west of a former tank area. These results coincide with analytical results from previous studies. Samples were collected for general chemistry parameters to assess the cause of the mounded water table in the central portion of the site. Elevated concentrations of some of the parameters were detected in a few of the wells. None of the results could confirm or dispute the idea that the mounded water table is the result of a leaking storm or sewer line beneath the bus barn. However, this sampling was conducted in August, which is a low use time of the school facilities.

The poor product recovery is probably due to one or a combination of three factors. First, the apparent product thickness in the monitoring wells is probably much greater than the actual product thickness on the aquifer. Second, ground water flow direction is highly variable, and during part of the year the recovery trench may not be located downgradient of the plume. And third, the effective radius of influence of the recovery trench is limited due to the clayey soils. All three of these factors are either the result of, or are exacerbated by, the fine-grained soil (silty clay) in the vadose zone and the aquifer and would make product recovery more difficult.