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September 2, 1992 <br /> 10433 382 <br /> Mr. Chuck Kolesar Harding Lawson Associates <br /> Page 2 <br /> Some of the petroleum molecules dissolved in groundwater can adsorb to the aquifer media beneath <br /> the water table; however, this chemical partitioning is commonly considered a part of the groundwater <br /> system, and is not soil contanunation. Moreover, the amount of chemical adsorbed to the aquifer <br /> material can be directly calculated if the dissolved-phase concentrations and chemical partitioning <br /> (distribution)coefficients are known. <br /> Determination of the vertical distribution of the dissolved hydrocarbons can be accomplished using <br /> deep monitoring wells. Groundwater samples obtained from the wells and published partitioning <br /> coefficients for petroleum hydrocarbon constituents can be used to determine the total mass of <br /> contaminants present in the groundwater system. The RWQCB is interested in determining the total <br /> hydrocarbon mass in the groundwater system. If Shell agrees to the installation of a deep monitoring <br /> well(s)to characterize the vertical distribution of hydrocarbons in groundwater, the total hydrocarbon <br /> mass present in the groundwater system can also be determined using the method described above. <br /> Chemical analysis of saturated soil beneath the water table can also provide this information; however <br /> these data are not reproducible, and the RWQCB will probably require installation of deep wells in any <br /> case. Accordingly, we do not recommend conducting chemical analysis of saturated soil samples as <br /> requested by the RWQCB. <br /> We trust this is the information you require. If you have any questions, feel free to contact either of the <br /> undersigned at (415) 892-0821. <br /> Yours Very Truly, <br /> '4x" r`'^'6 <br /> Daniel J. Craig, R.G <br /> Senior Hydrogeologist <br /> v <br /> cholas C. Pogoncheff <br /> Associate Hydrogeologist <br /> djc/vertchar <br /> References: Haley, J.L., Hanson, B., Enfield, C., and Glass, J., 1991. Evaluating the Effectiveness of <br /> Ground Water Extraction Systems. Ground Water Monitoring Review, Winter 1991. <br /> HLA, 1991. Preliminary Hydrogcologic Assessment, Shell Oil Distribution Facility, Stockton, California. <br /> May 3. <br /> cc: Rick Schroeder, Shell Oil Company <br />