ARCHIVED REPORTS_XR0007688 - Laserfiche WebLink

Home Browse Search

URS . Mr Harlin Knoll Page 5 San Joaquin County Environmental Health Department ARCO 2093 February 24, 2005 through June 2001 and was shut down because of low influent concentrations The AS system was shut ut down in May 2004 Remediation system design drawings are included as Attachment I As of September 2004, active remediation has removed a cumulative mass of 3,617 pounds of TPHg and approximately 10 6 pounds of benzene from the vadose zone The SVE system performance evaluation and mass removal data are presented in Attachment J In addition, approximately 1,000 cubic yards of contaminated soil have been removed from the site and disposed Soil removal details are presented in Attachment F CONTAMINANT MASS REMAINING AND DISTRIBUTION Mass estimates for baseline soil and groundwater contamination are based on historic data collected between 1987 and 1993 Present day mass estimates are based on current groundwater monitoring results (Table 1) and the remediation system performance evaluation (Attachment J) Figures showing the plume dimensions used for the historic and present-day mass estimates, tabulated calculations, and a list of conditions and assumptions are present in Attachment K Historical soil data suggest initial soil masses of TPHg and benzene were approximately 4,144 pounds and 4 8 pounds, respectively Historic groundwater data suggest initial groundwater masses of TPHg and benzene were 149 pounds and 3 7 pounds,respectively (Attachment K) SVE system performance data indicate that approximately 3,617 pounds of TPHg were removed from the soil In addition, 1,000 yards of contaminated soil were removed during the UST replacement The average concentrations of TPHg and benzene in the 15 samples collected from the disposed soil is 230 Img/kg and 0 55 mg/kg, respectively, assuming a uniform distribution of TPHg and benzene, approximately 745 pounds of TPHg and 18 pounds of benzene were removed during UST replacement activities Assuming a total initial TPHg mass of approximately 4,293 pounds and a total initial benzene mass of approximately 8 5 pounds, and assuming that a total of 4,362 pounds of TPHg and 12 4 pounds of benzene were removed by the SVE system and soil excavation and disposal activities, there should be only minor soil contamination remaining beneath the site The mass estimate for TPHg remaining at the site is 0 25 pounds in groundwater Mass estimates for remaining benzene and methyl tert-butyl ether (MtBE) are less than one-one thousandth of a pound each, also in groundwater(Attachment K) 10 K 1WprocesslJ5 BP ARC01020931Closure Report\Draft of 2093 Closure Report doe