Laserfiche WebLink
Ms. Debra Hamlin f <br /> Bridgestone/Firestone <br /> 5 March 2001 <br /> Page 2 <br /> w <br /> F <br /> Because of the shallow, damp setting, it is very likely that natural attenuation is occurring . <br /> at this site. The Lawrence Livermore National Laboratory (LLNL) and Texas Natural <br /> Resource Conservation Commission (TNRCC) have strongly suggested that hydrocarbon <br /> plumes diminish with time. In Geological Circular 97-1, "Extent, Mass, and Duration of <br /> Hydrocarbon Plumes from Leaking Underground Storage Tanks in Texas", the median <br /> time to lower site concentrations by a factor of 10 is 500 days. However, there is less <br /> published data available for natural attenuation rates for TPH in vadose zone soils. If one <br /> assumes a 5 percent per year rate for mass reduction, the remaining mass after 4 years of <br /> natural degradation would be estimated at 207 pounds or 30 gallons of weathered I <br /> gasoline. <br /> In addition, the site meets the low risk classification as developed by the California Water <br /> Resources Control Board guidance document, Guidelines for Investigation and Cleanup of <br /> MTBE and Other Ether-based Oxygenates, dated 27 March 2000. The potential for <br /> gasoline constituents to migrate from the vadose zone is minimized since the site is hard= <br /> scaped with sidewalks, pavement, and structures'. There are no sensitive environmental <br /> receptors or drinking water wells within a 2000-foot radius of this site. The groundwater <br /> is not used as a drinking water source. In summary, there is minimal risk to human health <br /> and the environment from a 30-year old release of petroleum hydrocarbons at this site. <br /> I <br /> { <br /> [S:8FS\Stockton\Memo\MEM00021 3/5/01 <br />