ARCHIVED REPORTS_ANNUAL 2009 GROUNDWATER MONITORING AND SAMPLING REPORT

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Mr.M.Scott Mansholt—CEMC Annual 2009 Groundwater Monitoring and Sampling Report April 9 Page 3 ofril 15,200 9 Alden Park ' identified. The former oil-storage reservoir concrete lining was found to be relatively intact at approximately 6 feet bgs. • Monitoring wells were installed during the investigations in 1986 (MW-1/KJC), 1987 (MW-1 through MW-17), and 1996 (MW-18 through MW-21). MW-19 was properly destroyed in March 2000, and MW-1/KJC, MW-2, MW-13, and MW-17 were ' properly destroyed in April 2006. • A municipal water supply-well survey was conducted in 1986. It was concluded that local municipal wells do not withdraw water from the upper water-bearing zone. • A dual-technology strategy of soil venting and oil-trap collection was initiated in 1989 and terminated in 1995. In 1996, it was reported that approximately 3,000 gallons of oil had been remediated through a combination of biodegradation, volatilization, and ' extraction. The bio-vent building was demolished, and an associated vacuum well was properly destroyed in 2006. • During an alley reconstruction project in April/May 2007, approximately 173 tons (119 cubic yards) of hydrocarbon-affected soil were excavated and removed. Five oil- seep vaults that collected SPO, and associated petroleum hydrocarbon-affected soil were ' removed in May 2007. • The results of a health risk assessment reported that residual petroleum hydrocarbons in soil should not result in health risks greater than those considered acceptable by regulatory agencies. Acceptable excess cancer risk levels used in the evaluation were 1x10-6 for residential exposure and 1x10-5 for non-residential exposure (for park Imaintenance workers). A reference list of environmental investigation reports for the site is included as Attachment A. ' GROUNDWATER MONITORING AND SAMPLING MONITORING ' Monitoring and sampling has been conducted quarterly and/or semi-annually at the site since 1995 under MRP-R5-2003-0801. The RWQCB issued MRP Order No. R5-2006-0812 in December 2006 to replace the previous MRP2. The new MRP stipulated that groundwater ' sampling would be performed annually, and SPO recovery would continue to be performed quarterly. Depth to groundwater was measured in MW-4, MW-7 through MW-12, and MW-14 on January 15, 2009. Cumulative depth-to-groundwater measurements and groundwater elevations are provided in Table 1. A potentiometric map showing groundwater elevation contours and flow direction is shown on Figure 3. Field data sheets are provided as Attachment B. 2. RWQCB,2006. Monitoring and Reporting Program Order No.R5-2006-0812,Alden Park,Tracy,San Joaquin County. December 15.