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i <br /> 1 <br /> ' 1444 MARIPOSA ROAD <br /> . WKA No 2938 06 <br /> September 6,2000 <br /> ' Page 16 <br /> revealed extremely high concentrations(several orders of magnitude above those of the vast <br /> majority),use of a straight mathematical average would have resulted in unrealistically higher <br /> average concentrations <br /> ' The data used was derived from the 50 soil samples obtained from soil borings drilled in the <br /> vicinity of the former UST excavation and 60 groundwater samples obtained during quarterly <br /> monitoring and sampling events performed from March 29, 1993 to April 18,2000 <br /> ' Based on the lognormal distribution calculations, the average weight/volume of petroleum <br /> hydrocarbons potentially present in the soil beneath the site was calculated to be approximately <br /> 17 pounds or 3 gallons <br /> Dissolved Groundwater Contamination <br /> Dissolved groundwater contamination was assumed to be limited to the area in the immediate <br /> vicinity north of well MW4 and approaching wells MW1 and MW2 (Plate No 3) <br /> For our calculations, we assumed that the samples were representative of the top 40 feet of the <br /> groundwater column and that the native sandy silt/clayey silt/silty clay/sandy clay material has a <br /> relative porosity of approximately 47% Based on these assumptions and the lognormal <br /> distribution calculations,the estimated volume of dissolved petroleum hydrocarbons potentially <br /> ' present in the groundwater beneath the site is approximately 48 gallons or 348 pounds <br /> 1 Results of laboratory analysis used, along with statistical calculations are provided on,Tables 1 <br /> through 6 Estimates of mass volume calculation for soil and groundwater are presented in <br /> 1 Appendix A A checklist of required data for no further action as outlined in Appendix B of the <br /> Tri-Regional Recommendations and the guidelines provided in the July 19, 1996 Revised Draft <br /> 1 Recommendation for Low Risk Site Classification in the Central Valley Region is presented in <br /> Appendix B <br /> ' Conclusions and Recommendations <br /> ' It is our opinion that the site has met the criteria for classification as a"low risk groundwater <br /> • case" as defined by the CVRWQCB,based on the following <br /> o00 <br /> WALLACE KUHL <br /> Rec ciedpapzr &ASSOCIATES INC <br />