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Mr Mike lnfuma March 27,2006 C A M B R I A HYDROCARBONS IN GROUNDWATER Three depth discrete groundwater grab samples were collected in each boring in order to adequately assess the lateral and vertical extent of hydrocarbons in groundwater The table below presents laboratory results of groundwater analysis Sample ID Depth TPHg Benzene Toluene F'th}l- MTBE TAME benzene Concentrations reported in p L B-5 20 <50 <0 5 <0 5 <0 5 2 <0 5 30 <50 <0 5 2 <0 5 42 <0 5 40 <50 <0 5 0.7 <0 5 8 <0 5 B-6 24 <50 <0 5 <0 5 <0 5 <0 5 <0 5 31 <50 <0 5 <0 5 <0 5 26 <0 5 405 <50 <05 07 <05 <05 <05 B-7 20 <50 <0 5 0 5 <0 5 <0 5 <0 5 30 <50 <0 5 1 <0 5 <0 5 4 1 <0 5 40 <50 <0 5 <0 5 <0 5 7 <0 5 No TPHg or benzene was reported in any groundwater grab sample collected MTBE was reported in borings B-5 through B-7 at concentrations ranging from non-detect to 42 µg/L in B-5 at 30 fbg B-5 and B-6 groundwater samples collected at 30 fbg and 31 fbg, respectively, reported concentrations of 42 4g/L and 26 ftg/L These results are the only samples which exceed the California maximum contaminant levels (MCLS) of 13 pglL for MTBE Groundwater grab samples collected at approximately 30 fbg are from the lower portion of the groundwater bearing zone in which monitoring wells C-1 through C-3 are screened within Depth discrete sampling indicates that MTBE appears to be limited to the lower groundwater bearing zone at approximately 30 fbg, up-gradient and down-gradient of the former USTs at relatively low concentrations MTBE is generally defined both vertically and laterally by down-gradient water samples from soil boring B-7 A hydrogeologic cross-section with estimated MTBE concentration contours in groundwater is presented as Figures 8 Groundwater grab sample results are summarized in Table 3 • 5