ARCHIVED REPORTS XR0001659 - Laserfiche WebLink

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Final Remedial Plan - Geweke 2 January 1992 Page 4 of 15 ' collected from greater depths, which could be interpreted as . contamination along the capillary fringe (former or current, depending on the water level fluctuation) . Barings GL2 and GL3 , which were drilled in the location of the former tanks, did not indicate the detection of elevated levels of hydrocarbon, ' contaminants. In addition, the contamination level in MW-4 has been consistently high. Therefore, we believe that the .source has to be located near MW-4 . It is our understanding that the dispenser was located in the general location of ' that well. Based upon these ' data, it appears that the contamination originated from the dispenser area. To confirm our interpretation, a limited soil gas survey is recommended (Section 3 . 7 . 1. ) . ' Typically, the lateral extent of hydrocarbon contamination that originates from a single point source, in a soil type such as that ' of the subject site, does not exceed 25 feet in diameter. The current depth to ground water is assumed to be 60 feet, which concurrently represents the maximum vertical extent of the plume. Approximately 1, 200 cubic yards of contaminated soil exists at the site. Based upon this volume and the typical concentration of total petroleum hydrocarbons (TPH) that had impacted ground water of 6, 000 mg/kg (ppm) , approximately 3 , 000 gallons of gasoline had been released to the soil, indicating a total mass of approximately 18 , 500 pounds. Based on the assumption that the radii of the dissolved contamination plume are 200 and 400 feet, the thickness of the impacted zone is 2 feet and the effective porosity of the sandy aquifer material is 200 , approximately 240, 000 gallons of ' contaminated ground water appear to be present at the site. Please note that the figures used here are liberally calculated. ' The actual volume of contaminated soils and water, the average level of contamination and subsequently the total volume of product released are likely to be less than presented here. ' 2 . OBJECTIVES ' Without a doubt, our most valuable resources are those that sustain life. The quality of the water we drink and of the air we breathe is critical to us all. We need to employ effective methods to mitigate contaminated sites without transferring the contaminants from one medium to another, while keeping costs to the responsible parties affordable. ' Since both the soil and ground water have been impacted by the unauthorized release, a concurrent mitigation for both media needs 1