ARCHIVED REPORTS_GROUNDWATER MONITORING AND PROGRESS REPORT 4TH QUARTER 2011

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' In a letter dated September 21, 2009, the CVRWQCB concurred with our recommendations and directed submission of a well destruction workplan to be followed by a corrective action plan (CAP) detailing ' the ozone-injection system. We submitted the Well Destruction Workplan on October 5, 2009, which the CVRWQCB approved on October 12, 2009. Well destruction activities occurred from November 9 to 18, 2009, and we submitted our Well Destruction Report to the CVRWQCB on December 11, 2009. ' We submitted the CAP on November 16, 2009, and the CVRWQCB conditionally approved the CAP on November 25, 2009, pending submittal of a Notice of Intent (NOI) permit application for ozone ' injection. We submitted the NOI and subsequent Addendum to the CVRWQCB on January 11 and March 18, 2010, respectively. In an email dated February 2, 2010, the CVRWQCB authorized us to proceed with startup and operation of the ozone-injection system. ' In January 2010 we installed seventeen 2-inch-diameter sparge wells (AS-6 through AS-22) at the approximate locations depicted on Figure 3. The well construction details are summarized on Table 4. We began full-time operation of the ozone-sparge system (ozone system)on June 29, 2010. ' In a letter dated June 27, 2011, the CVRWQC13 provided comment on our June 6, 2011, Second Quarter—2011 Groundwater Monitoring and Progress Report, directed a September shut-down of the ' ozone system to be followed by two months of groundwater rebound monitoring of wells MW-1, MW-3 and GWX-1, and (if appropriate) submittal of a Closure Request Report. We ceased operating the ozone system on September 21, 2011. The results of the October and November 2011 groundwater ' rebound monitoring for wells MW-1, GWX-1 and MW-3 are presented in the following sections. FOURTH QUARTER— 2011 —OCTOBER REBOUND MONITORING ' Groundwater Level Measurements On October 24, 2011, we measured the depth to groundwater in wells MW-1, MW-3 and GWX-1 using ' an electronic water level indicator. Groundwater was encountered at 27.01, 25.62 and 26.86 feet below the top of casing (TOC) in the three wells, respectively. A summary of the TOC elevations, depth to groundwater measurements and groundwater elevations is presented in Table 1. Well Purging and Sampling ' We used a portable 12-volt submersible pump to extract approximately three casing volumes of groundwater (69 to 97 gallons) from wells MW-1, MW-3 and GWX-1. We decontaminated the pump before and after each use by washing in an AlconoxTm solution followed by sequential rinses with ' potable and distilled water. During the well purging activities, we monitored the extracted water for pH, electrical conductivity and temperature and recorded this information on Monitoring Well Sampling Data sheets copies of which are in Appendix A. We placed the extracted groundwater in five Department of Transportation (DOT)-approved, 17-H, 55-gallon drums temporarily stored onsite ' pending subsequent disposal following regulatory protocol. Following well purging, we collected a groundwater sample from the well with a dedicated disposable ' polyethylene bailer. We decanted each sample from the bailer through a low-flow, sample release tube into six laboratory-provided, hydrochloric acid-preserved, 40-milliliter (ml) volatile organic analysis vials, and for the samples undergoing hexavalent chromium (CrVI) analyses, one 250-m1 plastic container. We sealed and labeled each sample, placed the samples in chilled coolers and subsequently transported the samples to their respective laboratories using standard chain-of-custody documentation. 1 ' Project No.S9183-06-03 -3 - January 30,2012