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• CURRENT SOURCE (BEFORE DILUTION) INFLUENT SUMMARY(LAB) Total Petroleum Hydrocarbons as Gasoline (TPHG) Conc This Period SVE system down since 11/24/97 due to low TPHG concentrations in soil vapor TPHG Conc Last Period NA Initial TPHG Conc 9,900 mg/m3 (November 9, 1994 [following system upgrade]) Benzene Conc This Period NA Benzene Conc Last Period NA Initial Benzene Concentration 290 mg/m3 (November 9, 1994[followings stem upgrade]) DISCUSSION Results of this monitoring event indicate that concentrations of dissolved gasoline hydrocarbons in wells MW-1 through MW-7, and MW-10 are consistent with levels detected in previous sampling events Wells MW-1 and MW-10 contained MTBE concentrations of 12 7 and 19 5 micrograms per liter (µg/L), respectively, using USEPA Method 8020 However, MTBE concentrations for wells MW-1 and MW-10 were below method detection limits using USEPA Method 8260 Additionally, MTBE was detected in well MW-4 at a concentration of 3 80 Ixg/L using USEPA Method 8260 The groundwater gradient and direction of groundwater flow (southeast) were generally consistent with previous data Groundwater elevation increased approximately 2 73 feet from the previous sampling event (September 1998) . The oxygenates, tertiary butanol, MTBE, di-isopropyl ether (DIPS), ethyl tertiary butyl ether (ETBE), and tertiary amyl methyl ether (TAME) were analyzed in samples collected from groundwater monitoring wells MW-1 through MW-7, and MW-10 using USEPA Method 8260 Due to non-detect analytical results for oxygenates (other than MTBE,) using USEPA 8260 for all wells, Pinnacle, on behalf of ARCO, requests no further analysts for oxygenates with the exception of MTBE using only USEPA Method 8020 Pinnacle shut down the SVE system on November 24, 1997, due to low soil vapor concentrations and is currently pulsing the system on a periodic basis The SVE system remained shut down during the fourth quarter 1998 The air sparge system was shut down on November 24, 1997, along with the SVE system to evaluate feasible remediation alternatives Based on data and remediation techniques evaluation, the air sparge system was restarted on January 20, 1998, and operated at a low flow rate for bubbling and oxygen addition to the groundwater The addition of oxygen into the groundwater will help to promote biodegradation of petroleum hydrocarbons in impacted groundwater at the site As a result of air bubbling in air sparge wells AS-1, AS-2, and AS-3, since January 1998, dissolved oxygen levels to monitoring wells MS-1(s), MS-2(s), MS-3(s), and MW-2 have increased significantly as shown in Table 5 Pinnacle will continue to monitor the effects of SVE system pulsing and air bubbling during the first quarter 1999 ME 1ARCM21301QTRLY\2130Q498 DOC-9811sg 1 ��