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RPR. 8.2005 8:13AN PdWNV. SERVICES 0 N0.234 P.3 <br /> Department of Toxic Substances Control <br /> Alan C.Lloyd,Ph.[). 8800 Cal Center Drive <br /> Age GalIFPicy rotary Sacramento, California 95826-3200 Arnold overnonagger <br /> CaVRPp <br /> MEMORANDUM <br /> TO: Duane White <br /> Hazardous Substance Engineer <br /> Northem California Cleanup Operations Unit <br /> FROM: James Rohrer, RGc _ 11crpl 2 <br /> Engineering Geolp st <br /> Northern California Geologic Services Unit <br /> REVIEWED 1�' <br /> 6Y; � Mi e Finch, R� <br /> Senior Engineering Geologist <br /> Northern California Geologic Services Unit <br /> DATE: March 18, 2005 <br /> SUBJECT: REVIEW OF WORK PLAN TO ADDRESS GROUNDWATER <br /> CONDITIONS IN THE VICINTITY OF MW-26R AND TO DECOMMISSION EIGHT <br /> MONITORING WELLS, FORMER MANUFACTURED GAS PLANT, STOCKTON, <br /> CALIFORNIA, DATED FEBRUARY 2005, <br /> The Geologic Services Unit(GSU) of the Department of Toxic Substances Control <br /> (DTSC) was requested to review geologic aspects of the subject document and provide <br /> comments and recommendations. Following are the GSU's comments and <br /> recommendations, <br /> COMMENTS AND RECOMMENDATIONS <br /> 1) Page 9, last paragraph: It is indicated that a drilling method similar to the other <br /> method used to install B zone monitoring wells will be used to install the new B-zone <br /> well (MW-27). During drilling activities aquitard material will likely be penetrated. As <br /> such, the drilling method used must allow for sealing off aquitards to prevent a conduit <br /> between groundwater zones. <br /> RECOMMENDATION <br /> Provide an explanation of the drilling method to the GSU and how that method <br /> will not compromise aquitards during drilling. A mud rotary or air rotary casing <br /> hammer drilling method would allow for preventing the formation of a conduit <br /> between the A zone and B zone and between flow zones within the B zone. <br /> ® Printed on Recycled Paper <br />