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1 <br /> ENM <br /> 123970MM <br /> Mr James L Barton <br />' January 26, 2005 <br /> Page 8 <br />' Concentrations of TPHg and benzene reported in soil vapor samples collected on <br /> November 12, 2004 showed an overall decrease in TPHg and benzene The highest reported <br /> concentrations of TPHg and benzene in soil vapor were detected in well VEW-2 at 570 pg/L and <br /> 1 3 pg/L, respectively Additionally, wells MW-2 and MW-19S had detectable concentrations of <br /> MTBE to soil vapor above the laboratory reporting limit <br />' The groundwater gradients appear similar to previous quarters Groundwater elevation <br /> deceased approximately 3 feet since December 2004 <br />' MTBE was not detected at or above the laboratory reporting limit in any of the monitoring wells <br /> during the fourth quarter 2004 groundwater monitoring and sampling event <br />' Consistent with the CAO No 5-00-707, and in response to the RWQCB letter dated <br /> October 4, 2004, ENSR installed two additional monitoring wells (MW-31 and MW-32) on <br /> November 16 and 17, 2004 These wells were requested to define groundwater flow direction in <br />' the water bearing Unit C and D, respectively In addition, the downgradient and cross gradient <br /> extent of petroleum hydrocarbon constituents in groundwater in Unit C and Unit D were defined <br /> A well installation report for newly installed wells MW-31 and MW-32 will be submitted during <br /> January 2005 A copy of the RWQCB letter dated October 4, 2004 is included as <br />' Attachment G <br /> Recommendations <br /> Since the fourth quarter 2003, ENSR has observed stable to deceasing trends of dissolved <br /> TPHg and benzene concentrations in groundwater samples collected from monitoring wells <br /> located within the site boundaries, with the exception of B-zone monitoring well MW-11 Based <br /> on the stable to deceasing trends in wells located onsite except for B-zone monitoring well <br /> MW-11, ENSR recommends the following <br /> The AS system should continue to be operated in a pulse operations mode <br /> • Future analyses of groundwater parameters related to intrinsic biodegradation should <br /> not include ethene and ethane as they do not relate to hydrocarbon/BTEX monitored <br /> natural attenuation <br /> • Move forward permitting the SVE system and proposed emission modifications <br /> • Cease tasks required to implement an in-situ chemical oxidation (ISCO) technology at <br /> this site <br /> Move forward with modifications to AS system to include the installation of one additional <br /> sparge well to the vicinity of MW-3 and modify MW-23S into a sparge well Both <br /> modifications are proposed to increase dissolved oxygen concentrations in the C-zone <br /> • Continue the monitoring and reporting program (MRP) of CAO No 5-00-707 with <br /> modifications that include reductions to groundwater analysts and frequency <br /> • <br /> J IProfects10694015098-2931WorkinglRepvrts15098 4th Qtr 04-QMR doc <br /> Celebrating 35 Years of Excellence to Environmental Services <br />