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<br />Chevron Products Company 9
<br />Former Chevron Service Station #9-5775,301 West Kcttleman Lane, Lodi, California June 5, 2001
<br />Analytical data from soil samples collected at the site Indicate that typically, the maximum
<br />concentration of hydrocarbons Is found at approximately 15 feet bgs, and that these concentrations
<br />decrease exponentially to below detection linuts at 35 feet In order to conservatively estimate the
<br />mass of hydrocarbons In soil, concentrations of petroleum hydrocarbons were assumed to be
<br />distributed linearly with respect to depth Concentration isocontours used to calculate the mass
<br />remaining in soil are presented in Attachment I as Figures I-1, I-2, and I-3 The equation used Is
<br />included as Attachment J The results of this calculation Indicated that the amount of TPHg,
<br />benzene, and MtBE remaining in soil were 1,450 lbs, 370 lbs, and 67 lbs, respectively.
<br />The amount of TPHg, benzene and MtBE removed from the subsurface was calculated by using
<br />SVE mass removal estimates from I" quarter 2001. According to the SVE records, the amount of
<br />TPHg, benzene, and MtBE removed to date are 3,769 5 lobs, 85 1, 440 3 lbs, respectively This
<br />information Is summarized in the following table -
<br />CONSTITUENT ESTIMATED MASS REMOVED TO MASS REMAINING" 4 PERCENTAGE
<br />HYDROCARBON , DATE (lbs) -1$ IN,SOIL-"(lbs)'=1 _r "~ REMOVED,
<br />MASS (lbs) ' QUARTER'2001 QUARTER{2001' ° r
<br />-. s iv _. s , au
<br />Gasoline 1,450 3,769.5 -2,319.5 260
<br />Hydrocarbons
<br />Benzene 370 851 284.9 23
<br />MtBE 67 4403 -372.7 657
<br />The difference between the estimated hydrocarbon mass and amount removed is most likely
<br />attributable to Isolated areas within the assessment area that contain higher contaminant
<br />concentrations than previously identified
<br />3.3 Petroleum Hydrocarbon Dissolved in Groundwater
<br />In A -Zone monitoring wells, the maximum concentrations of TPHg, benzene, and MtBE during
<br />the March 21-23, 2001 sampling event were found to be 980 ug/1 (MW -3), 380 ugll (MW -3), and
<br />2,000 ug/l (EX -3), respectively The lateral extent of the A -Zone groundwater hydrocarbon plume
<br />is defined by wells MW -7A, MW -8A, MW -10A, MW -12A, MWA 3, and MW -20A
<br />Concentrations of TPHg, benzene, and MtBE in the A -Zone are illustrated on Figures 8, 9, and 10.
<br />Historical groundwater analytical data Is included as Attachment D
<br />In B -Zone monitoring wells, the maximum concentrations of benzene and MtBE reported during
<br />the March 21-23, 2001 sampling event were found to be 0 59 ug/1 and 7 2 ug/l, respectively, in
<br />well MW -5B The lateral extent of MtBE is defined to 1 ug/1 by B -Zone wells MW -7B, MW -11B,
<br />and MW -12B MtBE concentrations in B -Zone wells from March 21 to 23, 2001 are Illustrated on
<br />Figure 11
<br />I IChevron1957751ParFrpl9-5775PARFRP2 doc
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