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19 July 1995 <br /> AGE-NC-95-0109 <br /> Page 8 of 8 <br /> decrease of nearly 90% from baseline concentrations <br /> The most recent soil samples indicate that petroleum hydrocarbon impacted soil is present at the <br /> northern end of the site m a zone 10 to 15 feet thick at depths between 33 and 45 feet Only verylow <br /> concentrations of hydrocarbons remain at the southern end of the impacted soil plume <br /> The microbiological and soil vapor data collected at the site and the analysis of soil samples from <br /> borings. P 10 through P 13 continue to indicate that the addition of hydrocarbon-degrading bacteria <br /> has had a positive influence on the reduction of hydrocarbon concentrations in the soil <br /> 53 RECONDAENDATIONS <br /> Both soil and groundwater data collected during the first quarter of 1995 continue to indicate that <br /> overall hydrocarbon concentrations at the site are decreasing and the impacted ground water plume <br /> has not nugrated beyond known boundaries <br /> We recommend deletion of the vapor monitoring requirement at the site Although a trend in the <br />• vapor data can be interpreted, the overall importance of the data for completion of the project is <br /> questionable Soil samples continue to provide the most definitive data concerning the progress of <br /> the remediation Ground water monitoring will continue according to the RMRP Additional soil <br /> sampling is scheduled for September 1995 <br /> An analysis of the remaining hydrocarbon impacted soil at the site will be performed using a computer <br /> modeling program for risk assessment (American Petroleum Institute's SESOII.) to evaluate the <br /> feasibility of facilitating site closure The risk assessment will be completed and presented to the <br /> CVRWQCB in a separate report Upon completion, we suggest a meeting with the CVRWQCB to <br /> discuss results of the risk assessment model <br /> 6.0. LIMITATIONS <br /> Our professional services were performed using that degree of care and skill ordinarily exercised by <br /> environmental consultants practicing in this or similar localities The findings were based upon field <br /> measurements and analytical results provided by an independent laboratory Evaluations of the <br /> geologic/hydrogeologic conditions at the site for the purpose of this investigation are made from a <br /> limited number of available data points(i a monitoring wells, soil borings) and subsurface conditions <br /> may vary away from these data points No other warranty, expressed or implied, is made as to the <br /> professional recommendations contained in this report <br />