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Atlantic Richfield Company Page 12 <br /> . ARCO Station No 4932 Stockton California August 29,2002 <br /> in on-site wells MW-4, MW-6, EW-1, and SVE-1 Fluctuating concentrations are observed <br /> in the four wells since late 2000 and 2001 Since the third quarter 2001, groundwater <br /> monitoring event (July 20, 2001), concentrations of TPHg, benzene, and MtBE have been <br /> reported up to 140,000 ug/L(MW-4), 9,900 ug/L (EW-1), and 520,000 ug/L(EW-1), <br /> respectively (Table 2) LPH has also been present in wells MW-4 and SVE-1 A <br /> groundwater concentration map showing TPHg, BTEX, and MtBE analytical results for the <br /> third quarter 2002 monitoring event on July 12, 2002, is presented as Figure 6 Third quarter <br /> 2002 TPHg, benzene, and MtBE isoconcentration maps for both the shallow and deep water <br /> bearing zones are presented as Figures 7 through 12, respectively A report documenting the <br /> results of the third quarter 2002 groundwater monitoring event will be submitted in a separate <br /> document <br /> The total mass of hydrocarbons dissolved in groundwater below the site was calculated using <br /> the formula <br /> AxHxNxX = P <br /> Where <br /> A = impacted area <br /> H =height of impacted area <br /> . N= porosity <br /> X= contaminate concentration <br /> P =mass of contamination <br /> The soil density was determined by averaging clay and sand soil density—The volume was <br /> --------------------------------- <br /> calculated according to the extent of hydrocarbons reported in samples collected from <br /> monitoring wells and soil borings The total hydrocarbon mass dissolved in the groundwater <br /> is approximately 10,050 pounds or 1,432 gallons Tables and figures showing the mass <br /> calculations are included in Appendix K <br /> 5.0 REMEDIAL FEASIBILITY TESTING AND INTERIM <br /> REMEDIATION <br /> 5.1 Results of DPE Feasibility Testing <br /> Dual-phase extraction (DPE) was performed at the site by SECOR on February 12 through <br /> 16, 2001 The results are summarized from the SECOR report titled Interim <br /> RemediationlMulti-Phase Extraction Feasibility Test Report dated May 4, 2001 The results <br /> of this test are summarized in this section <br /> I 1ARCOIA9321PAR\PAR doc <br />