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<br /> Mr James L Barton
<br /> January 26, 2005
<br /> Page 7
<br />' not detected at or above laboratory reporting limits The California Department of Health
<br /> Services (DHS) has not established a maximum contaminant level (MCL) for motor oil
<br /> On behalf of Stone Bros , GHH submitted a Workplan To Redevelop and Assess Well MW-1
<br /> dated September 1, 2004 and Addendum to Workplan to Redevelop and Assess Well MW-1
<br /> dated September 10, 2004 The RWQCB approved the GHH Workplan and Addendum to
<br />' Workplan, with conditions, as stated in the RWQCB letter dated September 10, 2004
<br /> On September 22, 2004 ENSR witnessed GHH conducting the field activities included in the
<br />' GHH Workplan to Redevelop and Assess Well MW-1 dated September 1, 2004 and Addendum
<br /> to Workplan to Redevelop and Assess Well MW-1 dated September 10, 2004 Following the
<br /> completion of the field activities ENSR collected a "split" groundwater grab sample from MW-1
<br /> and submitted the sample to CLS for analysis of TPHg, TPHd and motor oil by EPA Method
<br /> 8015 Modified, VOCs by EPA Method 82608, CAM 17 Metals by EPA Methods 200 7, 200 8
<br /> and 245 1, and polynuclear aromatic compounds by EPA Method 8310 Except for motor oil
<br /> and CAM 17 metals (arsenic, barium and zinc) detected at 5 5 pg/L, 21 pg/L, 350pg/L, and
<br /> 190 pg/L, respectively, analytes were not detected at or above laboratory reporting limits The
<br /> MCLS for arsenic and barium are 50 pg/L and 1000 dig/L, respectively
<br /> Groundwater sample analytical results for groundwater samples collected from well MW-1 on
<br /> August 31, 2004 and September 22, 2004 are summarized in ENSR's Updated Site Conceptual
<br /> Model, Quarterly Monitonng and Remediation Status, Well Installation, and Well Destruction
<br /> Report, Third Quarter 2004, dated October 29, 2004
<br /> Discussion
<br /> Groundwater analytical results for monitoring wells MW-9R, MW-10, MW-12, MW-14, MW-16,
<br /> MW-17, MW-18D, MW-24S, MW-24D, and MW-25D indicate that the AS/SVE system appears
<br /> to be effective at decreasing concentrations of dissolved TPHg and benzene in Unit B, Unit C
<br /> and Unit D beneath the site
<br /> Monitoring wells MW-1 through MW-6, and AS-26 screened in Unit B showed increases in
<br /> benzene concentrations since the third quarter 2004 sampling event There is a general
<br /> downward concentration trend for benzene in wells MW-1 through MW-6, and AS-26 since the
<br /> fourth quarter 2003 sampling event Wells MW-1 through MW-4, MW-6, and MW-11, screened
<br /> in Unit B and MW-8D screened in Unit D showed increases in TPHg concentrations since the
<br /> third quarter 2004 sampling event There is a general downward concentration trend for TPHg
<br /> in wells MW-1 through MW-4, MW-6, and MW-11 since the fourth quarter 2003 sampling event
<br /> Based on the concentrations of the redox parameters it appears that natural attenuation is
<br /> occurring within the boundaries of and at the outer edges of the plume An increase in D O in
<br /> the aquifer to above 3 to 4 ppm should trigger much more aerobic degradation This can be
<br /> accomplished through aggressive sparging with air
<br /> J Trojects10B94015098-2931Workrng%Reports%5098 4th Qtr 04-QMR doc
<br /> Celebrating 35 Years of Excellence in Environmental Services
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