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r� <br /> Tina Berry page 2 <br /> UNOCAL#5098 <br /> Some points taken into consideration were; <br /> • the high levels of hydrocarbon contamination (TPH-G at 32,000 ppb and Benzene at 6,500 ppb on <br /> December 19, 1995 and as high as 100,000 ppb of TPH-G and 18,000 ppb of Benzene ) in MW-11, <br /> • the maximum possible dispersion expected from two (2) inch wells is only 6 to 8 feet laterally per year <br /> and the distance between these two wells exceeds optimal parameters for the ORC to effectively <br /> disperse, <br /> • the rise in dissolved oxygen in groundwater in this area resulting from the ORC placement is only <br /> expected to reach 2 to 6 ppm higher than non-ORC affected wells, (due to minimum well size, optimal <br /> well location, and too low of a number of wells and socks) and cannot effectively be expected to <br /> significantly reduce hydrocarbon contamination. <br /> PHS-EHD recommends that UNOCAL explore other remedial possibilities that will reduce continuing <br /> impact to the groundwater from soil contamination that may still exist as well as groundwater hydrocarbon <br /> contamination reduction. ORC is an option, but as technical experts of RBP have indicated, will require a <br /> better designed system of wells to effectively reduce contamination. It is the evaluation of PHS-EHD that <br /> the placement of ORC socks at this time in the two wells proposed is not the most feasible option and can <br /> not approve your proposal as submitted. <br /> In order to effectively "monitor"your site now and in the future and should policies and guidelines currently <br /> in proposal form be adopted, monitoring wells for this site must be constructed in such a way that the <br /> screened interval is both above and below the water table. Monitoring wells not meeting this requirement <br /> will be required to be replaced. In addition, UNOCAL should prepare a feasibility study that addresses the <br /> costs to actively remediate this site as required by PHS-EHD and submit the study for evaluation in a <br /> timely manner. <br /> Until further directed, this site will remain on a quarterly monitoring and sampling schedule. In addition to <br /> current constituents being sampled for at all wells for this site, and until further directed, please include <br /> MTBE groundwater analysis in the next and all future quarterly reports. As soon as it can be established <br /> that groundwater levels have stabilized and sampling events are representative of actual groundwater <br /> conditions, PHS-EHD will evaluate requests to modify the sampling frequency. <br /> Please direct your submittals or any questions you may have to Michael Infurna at(209)468-3454. <br /> Donna Heran, REHS, Director <br /> Environmental Health Division <br /> Michael Infurna, Senior REHS Margam REHS <br /> LOP/Site Mitigation Unit Lead Senior <br /> MI/ <br /> c: CVRWQCB- G.L. Boggs <br /> c: SWRCB -G. Lockwood <br />