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Groundwater Sampling <br /> Upon approval from the County,Tosco will recommence weekly purging as indicated in the <br /> approved interim remediation plan. To assist in the calculation of mass removal, Tosco will <br /> collect groundwater samples on a monthly basis from the UST Cavity well and MW3 (both after <br /> purging) and from the vacuum truck. Groundwater samples will be submitted to a California- <br /> certified laboratory for analysis of oxygenated compounds ethanol, methyl tertiary butyl ether <br /> (MTBE) tertiary butyl alcohol (TBA), di-isopropyl ether(DIPE), ethyl tertiary butyl ether <br /> (ETBE), and tertiary amyl methyl ether(TAME)using EPA Method 8260. Monthly analysis will <br /> continue for a period of six (6) months to establish mass removal trends and interim remedial <br /> effectiveness. <br /> Tosco will continue to collect quarterly groundwater samples from wells MW 1 through <br /> MW l OS/UD during quarterly groundwater monitoring and sampling events. Groundwater <br /> samples collected from wells MW 1 through MW l OS/l/D will be analyzed for TEPHd, TPPHg, <br /> BTEX,MTBE, ethanol, TBA, DIPE, ETBE, and TAME using the EPA methods 8015/8020 and <br /> 8260 respectively. Additionally, monitoring wells MW-1, MW-2 and MW-3 will be sampled on <br /> a quarterly basis for a complete suite of petroleum constituents by EPA method 8260A. These <br /> analyses will be discontinued after two quarters if other petroleum compounds are not detected. <br /> The laboratory analytical results from the monthly and quarterly sampling events will be used to <br /> calculate the estimated mass removal of dissolved hydrocarbons from groundwater beneath the site. <br /> Data Reporting <br /> Hydrocarbon mass removal and purged groundwater volume will be reported quarterly in ERI's <br /> Quarterly Summary Report for Environmental Investigation submitted during the month following each <br /> reporting period. The effectiveness of interim remediation will also be evaluated and included in this <br /> report. Tosco will also review the previously collected data and provide calculated estimates of mass <br /> dissolved hydrocarbons removed to date. <br /> Tosco respectfully requests that the County provide authorization as soon as possible to <br /> recommence interim remedial activities as outlined above. Please do not hesitate to call me at <br /> (916) 774-2910 if you have any questions or require additional information. <br /> Sincerely, <br /> C <br /> Edward C. Ralston <br /> Environmental Project Manager <br /> cc. Mr. Warren Hartzell, California Regional Water Quality Control Board-Central Valley Region <br /> Mr. Glenn Matteucci, Environmental Resolutions, Inc. <br /> 2 <br />