SITE INFORMATION AND CORRESPONDENCE

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a L 6425 Pacific Avenue Page 2 F PHS/EHD concurs that carbon absorption is a more cost effective treatment option than thermal oxidation when influent concentrations are reduced. On March 6, 1996, the change from thermal oxidation to carbon absorption was completed under a permit change by the San Joaquin Valley Unified Air Pollution Control District. Monitoring wells that continue to evidence petroleum hydrocarbons including: MWI, MW2, MW3, MW8, MW10, and MW12, will be sampled quarterly and all other monitoring wells on a yearly basis unless there is evidence to suggest increased sampling frequency of perimeter well's is warranted. PHS/EHD in discussion with WEGE granted approval for the use of Regenesis "Oxygen Releasing Compound" (ORC) socks to enhance bioremediation through increased oxygenation in the area of MW12. Since groundwater extraction was discontinued, due to the possibility of influencing the Lincoln Center chlorinated hydrocarbon plume, the petroleum hydrocarbon plume associated with this site has continued to migrate off site, despite limited bioventing of MW8. WeeklY'`� ventingof MW8 commenced on January 25, 1995 and continues to remove : carbon dioxid '; to enhance oxygen transfer and to attempt to control plume migration. PHS/EHD agrees that a six month evaluation period should be sufficient to demonstrate the effectiveness of the addition of ORC socks in MW12 versus bioventing of MW8 to retard plume migration. In order to monitor the effect of ORC, dissolved oxygen measurements r will be collected from MW5, MW8, MW11, and MW12 prior to the introduction and subsequently on a monthly basis. The ORC socks will be removed one week prior to obtaining groundwater samples for analysis and the ORC socks will be replaced following sample collection. PHS/EHD requested additional information with regard to the disposal of the spent/partial spent ORC socks, since the Regenesis Disposal Fact Sheet indicated that the socks be drummed and disposed. PHS/EHD reviewed the Morton International Materials Safety Data Sheet for Versamag Magnesium Hydroxide that indicated that the material is not a RCRA hazardous waste, but it should be managed at an authorized facility, in compliance with all applicable federal, state and local requirements. Magnesium hydroxide is the end product from the reaction with magnesium peroxide with water. PHS/EHD also reviewed the De1Mar Analytical lab data sheets which were included and that indicated that petroleum hydrocarbons ilwere not detected in samples ORC1 and ORC2. Also, the lab data sheets i indicated that ORC1 had a pH of 8.2 and TCLP magnesium concentration of 180 ppm and ORC2 had a pH of 10.8 and a TCLP magnesium concentration of 1,500 ppm. Please submit a description of how the ORC socks which will be used will be subsequently disposed. I