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` California Regional Water Quality Cc }rol Board = (\- ` Central Valley Region va ` Katherine Hart, Chair "y Arnold Linda S. Adams 11020 Sun Center Drive#200, Rancho Cordova,California 95670-6114 SChwarzenegger Secretary for Phone(916)464-3291 •FAX(916)464-4645 Environmental http://www.waterboards.ra.govicentralvalle Governor Protection ID)lu..,I! OV 18 August 2010 AUG 1 9 "10 Sergio Morescalchi ENVIKUNMtN I HEALTH Atlantic Richfield Company PERMIT/SERVICES P.O. Box 1257 San Ramon, CA 94583 DOCUMENTS REVIEW FOR COMMINGLED PLUME ACCOUNT CP0057 SITES AT 440 (TEXACO— SHELL, RB #390268)/441 (ARCO, RB #390657)/508 (CHEVRON, RB #390876) W. CHARTER WAY AND 1444 S. LINCOLN STREET, (COLUMBO/TOSCANA BAKERY, RB #390825) STOCKTON, SAN JOAQUIN COUNTY In a meeting with you on 22 June 2010, we discussed the distribution list for the above four sites. At that time you agreed that all written communications should be addressed to you as lead responsible party contact, and that the additional responsible parties be carbon copied (cc'd). The attached distribution list includes State Board, San Joaquin County, the three additional responsible parties (Chevron, Shell, and Sara Lee) and a list of interested parties (landowners, business operators, and consultants). Please provide corrections to the distribution list as necessary. Also, we have not been notified that a letter of commitment has been issued by the State Water Resources Control Board (SWRCB) Underground Storage Tanks (UST) Cleanup Fund, Commingled Plume Account (CPA). I reviewed Work Plan for Low Flow Sampling (Workplan) and Quarterly Groundwater Monitoring Report, Second Quarter 2008 (Report), received 30 July 2010 from your lead consultant Stantec. The documents were submitted in response to a larger list of recommendations agreed to during the above referenced meeting. The Workplan proposes a sample result comparison test conducted from 8 select wells (2 from each site) of the current conventional three casings purge volume groundwater sampling versus samples collected using the specified low flow sampling protocol. Low flow sampling has been proposed as a more cost effective and results comparable to conventional purging alternative. Dedicated sample tubing (stored in the well) and a new bladder for the bladder pump will be used first for each well. A flow through cell connected to the tubing will record pH, conductivity and temperature, with stability (end of low flow purge) defined as 0.1%, 3%, and 10% variance between two consecutive readings, respectively. Water levels will be periodically measured to determine if drawdown occurs. Care will be taken to not cause significant drawdown in the water column in the well, to avoid mixing of stagnant casing water with the sample taken from the middle of the screened interval and re-suspending solids from the bottom of the well, using a pump flow rate of less than 1 liter per minute. The Report states the specified low flow rate may be difficult to reach due to differences in individual well construction and geologic heterogeneity. A standard purge (typically 1 - 2 gallons per minute) with either a submersible or centrifugal pump, or with a bailer, will follow each low flow purge sampling, and samples for each method will be analyzed by one laboratory. A report of the data will demonstrate whether the two methods provide comparable data. The sampling and reporting will require six to eight weeks from start to finish. The Report states groundwater was sampled conventionally at all four sites on 24-25 May 2010. All wells are sampled semi-annually during the second and fourth quarters of each calendar year. Depth to California Environmental Protection Agenc ¢d Receded Paper