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Mr. Robert Doss, P.E. 3 , �,.> <br /> September 17, 1991 SEP 19 1991 <br /> Page 3 <br /> iFO <br /> ENVNIVtN?r�L HEALTH <br /> Prc."! <br /> LI\IVII � IJP- \41i"J <br /> 10. Figure 4 . 4 - PG&E should evaluate a residential exposure <br /> scenario when developing the Risk Assessment. The most <br /> conservative scenario must be used when seeking a permanent <br /> remedial solution. <br /> 11. Chapter 5.3 - Because tar residuals exist in soils, PVC <br /> screens may not provide long term stability against chemical <br /> degradation. PVC has poor chemical resistance to aromatic <br /> hydrocarbons. The wells must be designed and constructed to <br /> resist chemical degradation from residuals found at the <br /> site. The Department recommends the use of stainless steel <br /> wire wrapped screens. Furthermore, this section should <br /> include a discussion of the mud management methods to be <br /> used during rotary drilling, keeping in mind that the <br /> Department only permits pure bentonite (non-beneficiated) <br /> drilling fluid additives to be used. Drilling fluids must <br /> be maintained at 9 1/2 lb/gal or less and must not contain <br /> more than 2% sand. <br /> 12 . Page 5-3, Paragraph 6 - Grout mixtures should not exceed 2% <br /> bentonite and 7 1/2 gallons of water for each 94 pound bag <br /> of cement. The only acceptable bentonite type is non- <br /> beneficiated. <br /> 13 . Chapter 7, Section II - The site description is not <br /> accurate. The site is much larger than one city block (see <br /> Chapter 1. 1. 1) . <br /> 14 . Chapter 8. 1 - Indicate what will be done with the drill <br /> cuttings if the analytical results do not indicate they are <br /> a "hazardous waste" . If results indicate otherwise, the <br /> cuttings must be disposed of within 90 days of generating <br /> the cuttings to a state approved class 1 disposal site or <br /> you must seek to obtain a hazardous waste facility storage <br /> permit. <br /> 15. Table 9. 1 - After analyzing the soil and groundwater <br /> samples, it may be necessary to conduct a second phase of <br /> the remedial investigation to fully characterize the site <br /> and/or the extent of contaminants. The proposed schedule <br /> should allow for such an investigation, if necessary, <br /> without impacting the remainder of the project schedule. <br />