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CLOSURE REQUEST REPORT Section No 3 0
<br /> Former Amencan Forest Products Company 07/31/0l
<br /> 2801 West Lane Page 3-4
<br /> Stockton,Cahfomm
<br /> was confirmed at several soil borings, including SBA, SB-4, SB-5, SB-13, SB-15, DMW-5, SB-20, and
<br /> DMW-6 (Table 3) For reference, groundwater levels have ranged between 69 and 35 feet bgs, which is
<br /> consistently below the zone of impacted soil
<br /> The most recent soil data is for samples collected in December 1998 Results indicated that TPHd is still
<br /> present in the subsurface at a maximum reported concentration of 18,000 mg/kg (DMW-6) Results also
<br /> confirm the vertical distribution previously discussed, with impacts limited to depths shallower than 30
<br /> feet bgs
<br /> Review of analytical data for parameters other than TPHd indicate that TPHd is the only contaminant of
<br /> concern at the site All other analyzed parameters were either non-detect, or below concentration limits
<br /> specified for PRGs, as suggested by the EPA (2000) for residential soil
<br /> 34 MASS BALANCE OF HYDROCARBON IN SOILS FOLLOWING EXCAVATION
<br /> Soil analytical results of samples collected from soil borings by Bechtel National, J H Kleinfelder, and
<br /> Dames & Moore are compiled in Table 3 Prior to remedial action, the highest concentrations of TPHd
<br /> were at the east and west ends of the former maintenance shop building at depths of 15 to 20 feet TPHd
<br /> concentrations decrease horizontally and vertically away from these two apparent source areas
<br /> Figures 9 through 14 present the areas of the excavated soils in relation to the impacted areas of soils
<br /> prior to excavation at depths of 10, 15, 20, 25, 30 and 35 feet bgs A mass-balance calculation was
<br /> completed based on the areas of impacted soils by using soil concentration contour maps of TPHd in 5-
<br /> foot increments from 10 to 35 feet bgs (Dames & Moore, 1988)
<br /> The method used to complete the mass balance calculation was performed as described in Appendix C
<br /> The mass of hydrocarbon in soils prior to excavation was estimated by calculating the cross-sectional
<br /> areas of impacted soils for concentrations exceeding 100, 1,000, 5,000, and 10,000 mg/kg After the area
<br /> of each soil layer was computed, areas within each concentration range were converted to concentration
<br /> and mass of TPHd as described in Appendix C The results of the mass balance calculation are
<br /> summarized below
<br /> MASS BALANCE O TPHdI SOIL
<br /> TPHd Concentration Initial TPHd Mass Mass Re oved Percent Removed Mass Remaining
<br /> Range(mg/kg) (k ) (!%) %) (kg)
<br /> > 10,000 3,738 3,738 100 0
<br /> 5,000-- 10,000 6,310 4,814 76 1,496
<br /> 1,000—5,000 11,385 2,385 21 9,000
<br /> 100- 1,000 2,071 74 4 1,997
<br /> Total 23,5 11,011 47 12,493
<br /> kg = kilogram
<br /> mg/kg = milligrams per kilogram
<br /> TPHd = total petroleum hydrocarbon as diesel
<br /> As summarized in this table, approximately 11,000 kilogram(kg) of TPHd was removed from the vicinity
<br /> .� of the two former underground tanks This mass of TPHd in soil accounted for roughly 47% of the
<br /> estimated initial mass In addition, approximately 88% of the remaining impacted soil has concentrations
<br /> of TPHd below 5,000 mg/kg TPHd
<br /> K 1840191afp1afp_closure_rpl doc
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