ARCHIVED REPORTS_ANNUAL 2014 GRAOUNDWATER MONITORING AND SAMPLING REPORT

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Mr.C.Dean Hubbard—Central Valley RWQCB Annual 2014 Groundwater Monitoring and Sampling Report April 29,2014 Alden Park Page 3 of 7 ' and extent of SPO and dissolved hydrocarbons has shown little variation since monitoring began in 1995. The plume of affected groundwater is stable. ' PREVIOUS ENVIRONMENTAL ACTIVITIES Several environmental investigations have been conducted at the Site since 1971, and are briefly discussed as follows: • Site assessments were conducted to determine the extent of hydrocarbon-affected soil and groundwater in May 1971, October 1986, September 1987, and April 1996. An area of hydrocarbon-affected soil and groundwater centered at the ' former reservoir location was 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. The survey concluded that local municipal wells do not withdraw water from the upper water- bearing zone. • Soil venting and oil-trap collection were 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 maintenance workers). A reference list of environmental investigation reports for the Site is included as Attachment A. ' GROUNDWATER MONITORING AND SAMPLING MONITORING ' Groundwater monitoring and sampling have been conducted at the Site since 1997 and started with quarterly sampling under MRP 97-801. In 2003, sampling frequency changed to semi-annual under MRP R5-2003-0801. The current MRP (R5-2006-0812), ' which has been in place since 2006, stipulates that groundwater sampling be performed annually. Though not stipulated in the MRP, SPO recovery has been performed on a