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s <br /> Mr. Maurice Benson <br /> April 16, 2009 <br /> Page 2 <br /> Comment <br /> The proposed location for the new monitoring well (LM193AU) at Warehouse 10 <br /> appears to be located away from the persistent TCE source identified beneath <br /> Warehouse 10 in the unsaturated soil. The DDJC-Tracy Warehouse 10 <br /> Investigation Report (Figures 3-1, 3-2, and 3-3) identifies the highest TCE <br /> concentrations in soil vapor and soil at locations CPT-6, CPT-8, CPT-9, and <br /> CPT-10, all located in the north/ northeastern portion of Warehouse 10. The <br /> proposed monitoring well location, while located adjacent to the highest TCE <br /> concentration (CPT method) in groundwater (32.8 pg/L), is up-gradient from <br /> these higher TCE soil/soil vapor concentrations and would not account for the <br /> contaminant distributions/mass located down-gradient portion based on current <br /> data. DTSC recommends relocating LM193AU approximately 70'+ to the <br /> north/northeast, placed down-gradient of CPT-8, CPT-9, CPT-10, and located <br /> adjacent (preferably west) of CPT-6 location. DTSC considers the revised <br /> monitoring location more appropriate to determine if TCE is present at <br /> concentrations greater than the ACL of 5 pg/L, by better representing the <br /> locations of the highest TCE concentrations in soil gas and soil at Warehouse 10. <br /> If you have any questions or comments regarding this letter, please feel free to contact <br /> me at (916) 255-3713 or e-mail me at pmacnich(a)dtsc.ca.aov. <br /> Sincerely, <br /> r' %lwi'% �, % <br /> Peter MacNicholl, P.E. <br /> Remedial Project Manager <br /> Sacramento Office <br /> Brownfields and Environmental Restoration Program <br /> cc: Mr. Mike Thomas <br /> URS Corporation <br /> Crown Corporate Center <br /> 2870 Gateway Oaks Drive, Suite 300 <br /> Sacramento, California 95833 <br />