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HYDROCARBON-IMPACTED SOIL MASS ASSUMPTIONS AND CALCULATIONS MID VALLEY TRAILER SALES 2461 North Wilson Way, Stockton, CA Assumptions: An estimate of the vertical and areal extent of impacted soil surrounding the former UST and dispenser areas was made from samples collected from borings Bi through Ba. The radius of the area of impacted soil is approximated by the distance between Bi and B3 at 9 feet. The vertical distribution is limited to the soil between,7 feet bsg(base of excavation) and 20 feet bsg as determined by soil samples collected in December, 1999. The hydrocarbon plume below boring Bi is modeled to have the shape of two cones with a common base.- The average concentration of Vi is based on the following assumptions: The concentrations detected in samples from boring Bi are the maximum concentrations in the plume as Bi penetrated the soil directly underlying the former UST dispenser. The samples collected at-15 feet bsg in borings B3 and Ba have essentially non-detectable concentrations of TPH-g,and therefore define the shape and maximum extent of impacted soilThe average-concentration in the Bi samples_c2llected between 13 feet and s feet bsg is 6,620 mwkg.The average concentration for the whole plume in this —deptli interval is assumed tome sligl�iti—more than the average"core"concentration(6,620 mpg)and P outer plume margin concentration,(ND<_1.0).and is.assum-edato-be-approximately 4,000 mg/kg The average concentration of V2 was approximated using these assumptions(380.5 mg/kg)as the average "core" concentration, and (ND< 1.0) as the outer plume margin concentration. The average concentration wa tl�p,rgluce tgara io by dividing the�o�ta Ii�igntass per unit weight by the unit weight; i.e. 4,0mg/kg= ,0(�0 mg/kg/ 1,000,000 mg/kg'--'0.004 These assumptions of the hydrocarbon plume were calculated from soil sample data collected in,September 1997 and December 1999. Figure 1 shows the modeled plume dimensions, and concentrations: Volume of Impacted Soil In Each Cone:4 V, = 1/3-n(ri)2(h2)- 1/3Tn(r2)2(h,) 5 V2 = 1/3•n(rl)2 (hs) 9 711. V, = 1/3•r(9ft) (13 ft) - 1/3Tc(4ft) (5 ft) — 1018.92 ft x L � V2 = 1/37r(9ft)2 (5 ft) =424.12 ft3 V Mass of Impacted Soil:4 M,=V(125 lb M5, = 1018.92 ft3 x 125 lb/ft3= 127,365.00 lbs Ms2=424.12 ft3 x 125 lb/ft3= 53,015.00 lbs ✓ ,_- _ } " Mass of Gasoline:-+ Mg=(lbs soil)x avg concentration Mg, = 127,365.00 lbs (.004) = 509.5 lbs gas Mgt =53,015 lbs/(._0004),.�21.21 lbs gas Total Mass of Gasoline 530.71 pounds of gasoline no) S n„o,L-jjs jtD,,y-e4 Advanced GeoEnvironmental,Inc.