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GRANITE CONSTRUCTION—FRENCH CAMP Page 9 WKA No 2088 09 October 10, 2005 beneath the site is impacted with trace to moderate concentrations of petroleum hydrocarbons However, concentrations of gasoline and benzene have significantly decreased (percent change of ' approximately—93 1% and—99 7%, respectively) over the last I 1 years Gasoline and benzene were reported in the past (September 28, 1993) at concentrations as high as 3,200 µg/L and 510 µg/L, respectively However, the latest quarterly sampling (October 29, 2004) has shown that rgasoline and benzene concentrations have decreased to concentrations as low as 220 gg/L and 1 2 gg/L, respectively Similarly, diesel is present in groundwater at concentrations ranging from 87 to 180 µg/L but has shown little change over time MTBE was reported only in the October 2004 sampling event and only in well MW7 at a trace concentration of 0 56 µg/L Although MTBE was ' detected in well MW7, the reported concentration of 0 56 µg/L is well below the current primary maximum contaminant level (MCL) of 13 �tg/L(established in 2000 which was based upon cancer risk) and the secondary MCL of 5 µg/L (established in 1999 to protect consumers from taste and ' odor associated with MTBE in drinking water) Historical groundwater flow direction beneath the site has been generally to the northwest with an average estimated hydraulic gradient of 0 003 feet/foot Based on groundwater monitoring and sampling since 1993 the contaminant plume has significantly reduced in size, appears to be stable (not migrating) and on the decline and the chemical concentrations of concern in groundwater are at or below the water quality objects In our opinion, the remaining constituents in soil and ' groundwater will continue to degrade over time ' Furthermore, based on reported soil and groundwater petroleum hydrocarbon concentrations, the relatively flat groundwater gradient beneath the site, and the significant distance to sensitive receptors,the likelihood that sensitive receptors will be impacted appears minimal Based on data obtained during removal of the USTs, subsurface soil and groundwater ' investigations and quarterly monitoring and sampling events, it is our opinion that this site meets the criteria for designation as a "low risk groundwater site" as described in the March 1994 Appendix B Tri-Regional Staff Recommendations for Preliminary Investigation and Evaluation of Underground Storage Tank Site No Further Action Requests Therefore, on behalf of Granite Construction, we respectfully request that the site be considered for "No Further Action" We recommend the site be closed and the wells properly abandoned in accordance with the San • Joaquin County Public Environmental Health Department guidelines ' WALLACE KUHL Recycled paper Er ASSOCIATES INC