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t j GRANITE CONSTRUCTION, FRENCH CAMP WKA No 2088 03 April 29, 1993 i Page 7 iCONCLUSIONS AND RECOMMENDATIONS The laboratory results of soil samples obtained from the two angle borings (B1 and B2) indicate ithat the sods beneath the 2,000-gallon waste oil tank located adjacent to the easterly side of the shop building do not contain significant concentrations of petroleum hydrocarbons, nor do they icontain elevated concentrate ns of the waste oil metals ca mium, chromium lead, zinc, and nickel �� Analysis of the samples obtained from soils beneath the former dispenser island reveal relatively i high concentrations of diesel Laboratory test results indicate that the contamination does not extend laterally to adjacent borings Field observations during the construction of boring B4 revealed that diesel contamination likely extends from the surface to a depth of approximately 12 ifeet below site grade Based on these data, we recommend that the contaminated soil in the area of the former dispenser island (estimated at 250 to 300 cubic yards) be excavated, stockpiled on- site, and characterized for subsequent treatment or disposal iThe soils adjacent to the four underground fuel storage tanks contain moderate to moderately high concentrations of gasoline at depths ranging from approximately 15 feet to 25 feet below site i grade The area of contamination encompasses approximately 9,500 square feet and remediation would require removal of approximately ten feet of "clean" overburden soil (estimated at 4,000 i to 4,500 cubic yards) to access the contamination Based on the large volume of soil requiring remediation (estimated at 6,000 to 6,500 cubic yards), we believe that a vapor extraction system will be the most cost-effective method of treatment i Laboratory results of the ground water sample obtained from monitoring well MW-3 reveal that igasoline contamination is present in the ground water beneath the site Because the lateral extent of contamination has not been-defined in the down-gradient direction, we recommend the iinstallation of three additional wells 'at the locations shown on Plate 3 Following installation and sampling of the additional wells, an appropriate remedial option for the ground water, if necessary, can be implemented io `dW WALLACE KUHL Recycled paper Fr ASSOCIATES INC.