SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

r Mr. Carl Navarra Page 2 of 2 7500 W. Eleventh Street 15 February 2008 Tracy, CA Rounding off, TSJCI estimated the mass of LNAPL at 3,180 kilograms and the mass of sorbed fuel hydrocarbons at 2,105 kilograms; of these quantities, TSJCI estimated that the proposed remedial method could remove 1,590 to 3,180 kilograms of LNAPL and 138 kilograms of sorbed fuel hydrocarbons, for a total removed contaminant mass of 1,728 kilograms. By EHD calculation, this would represent a removal of approximately 32.7% of the contaminant mass, ignoring the dissolved phase which comprises a `very small portion of the total contaminant mass. In response to the EHD inquiry regarding the optimal contaminant mass to be removed to enable natural attenuation to complete the remediation process, TSJCI considered aerobic and anaerobic processes for the breakdown of fuel hydrocarbons and its relationship to contaminant concentration and the reduction oxidation potential (Redox potential). TSJCI concluded that high contaminant concentrations suppress the Redox potential, thereby favoring -anaerobic processes, the slower contaminant reduction mechanisms. TSJCI noted that LNAPL is the dominant contaminant phase for maintaining high dissolved contaminant concentrations, and by removing LNAPL, the time required for reestablishment of aerobic conditions in the core of the plume, and a more rapid degradation rate of hydrocarbons, would be proportionately reduced. The EHD tentatively approves the CAP and CAP addendum, but does not approve the initially proposed 10,000-gallon cap for removal of impacted groundwater and LNAPL. EHD approval must be obtained to cease removal of impacted., groundwater and/or LNAPL. During each extraction event, water samples must be collected for laboratory analysis to adequately estimate the fuel hydrocarbon mass removed and LNAPL, if present'in the trench, measured to estimate its volume. Before the EHD can give final approval of the CAP and CAP Addendum there 'are several practical issues that must-be addressed. The first issue is acquisition of an access agreement with and permission of the property owner(s) of the 7501 W. Eleventh Street site to implement the recommended remediation plan and submittal of these agreements to the EHD. The EHD is also concerned with safety and security issues presented by an open trench with a 15-foot depth, and with accumulation of potentially explosive vapor and flammable hydrocarbons in the trench. A safety plan for securing the trench during the time it is-open and-for minimizing-the risks posed by the accumulation of fuel hydrocarbons as LNAPL and/or vapor in the trench must be submitted to the EHD. Submit this plan to the EHD by 01 April 2008. Finally, once these issues have been adequately addressed, the EHD must conduct a 30-day public notification and participation period. If you have any questions or comments you may contact Nuel Henderson, Engineering Geologist at (209)468-3436. Sincerely, Nuel C. Henderson, Jr., PG Margaret agorio, R 115 Engineering Geologist Program Coordinator c: Mr. James Barton, CVRWQCB, 11020 Sun Center Dr. #200, Rancho Cordova, CA 95670 Dr. Dai Watkins, TSJCI, 1120 Hollywood Ave., Ste 3, Oakland, CA 94602 WP Continent Letter 0208