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<br /> Raymond Investment Corporation Page 2
<br /> 730 Channel Street October 8, 2009
<br /> Stockton, California 95202
<br /> The EHD approves, the installation of MW-6 located adjacent to soil boring SB-9 and down
<br /> gradient of the former underground storage'tank (UST)': Based on the boring log for soil boring
<br /> SB-9 that describes a silty sand layer between appeoximately twenty-four and thirty-six feet bsg,
<br /> and high concentrations of volatile organic compounds detected by a phbtoionization detector at
<br /> approximately twenty-five to thirty-two feet�bsg,`the-EHD believes MW-6-should be screened
<br /> between approximately twenty-five to forty-five feet bsg.
<br /> The EHD does not approve the installation of MW-7 at this time, as proposed by Condor. If
<br /> analytical data for groundwater collected from MW-6 demonstrates high concentrations of
<br /> petroleum hydrocarbon contamination, the EHD may reconsider installation of MW-7.
<br /> Instead of installingMW-7 at this time the EHD recommends the;advancement of a boring
<br /> g
<br /> south of the former UST- on an-adjacent parcel based on soil.data collected at approximately
<br /> eight feet bsg during the UST removal. High concentrations of total extractable petroleum
<br /> hydrocarbons-(TEPH) quantified as motor oil (TEPH-MO) and TEPH quantified as diesel
<br /> (TEPH-D), as well as other chemicals of concern, were detected in soil collected from the south
<br /> side of the former UST. Due to physical limitations (a tree and fence), soil boring SB-5 was
<br /> advanced as' near the source of contamination as 'vi as possible; however,`the EHD believes
<br /> additional investigation is needed to delineate the vertical and lateral extent of soil and
<br /> groundwater contamination south of the source area.
<br /> The EHD concurs with Condor's recommendation to install up to three additional monitoring
<br /> wells (MW-8, MW-9, and MW-10) in the sidewalk or parking lane on the west side of Grant
<br /> Street based on detection of contaminants of concern in groundwater collected from MW-5.
<br /> Condor proposes to install the wells with screens between approximately thirty, and forty-five
<br /> feet bsg, but as noted above, the EHD recommends shallow wells to be screened between
<br /> approximately twenty-five to forty-five feet bsg.
<br /> Condor proposes to analyze soil and groundwater samples collected during the well installations
<br /> and initial quarterly groundwater monitoring events for total petroleum hydrocarbons (TPH)
<br /> quantified as gasoline (TPH-G), TEPH-D, TEPH-MO, TEPH quantified as kerosene (TEPH-K);
<br /> benzene, toluene, ethyl benzene, and total xylenes (BTEX); methanol, ethanol, tertiary-butyl
<br /> alcohol (TBA), methyl tertiary-butyl ether (MTBE), ethyl tertiary-butyl ether (ETRE), di-isopropyl
<br /> ether (DIPE), 'tertiary-amyl methyl ether (TAME), 1,2-dichloroethane (1,2-DCA) and 1,2-
<br /> dibromoethane (EDB). Based on historical soil and groundwater data, the EHD believes the
<br /> following may be omitted from the analytical list: TEPH-K, methanol, ethanol, TBA, MTBE,
<br /> ETBE, DIPE, TAME, 1,2-DCA, and EDB.
<br /> Condor proposes to install three soil .vapor wells using a hand auger to advance the boreholes
<br /> to approximately five feet bsg while collecting soil samples for lithologic evaluation. Soil gas
<br /> samples will be collected in six-liter Summa canisters after the wells have been installed for a
<br /> minimum of forty-eight hours to allow time for subsurface conditions to equilibrate. Condor
<br /> proposes to analyze the soil vapor samples for BTEX, 1,1-difluoroethane (the leak detector
<br /> compound), total petroleum hydrocarbon-vapor (TPH-V), naphthalene, TBA, MTBE, ETBE,
<br /> DIPE, and TAME by Environmental Protection Agency method TO-15. In addition to the above
<br /> analyses, the EHD recommends that soil gas samples be analyzed for TPH quantified as diesel
<br /> (TPH-D) using analytical method TO-17.
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