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San Joaquin County DIRECTOR <br /> Environmental Health Department Donna Heran,REHS <br /> P •• <br /> .c0 ASSISTANT DIRECTOR <br /> z 600 East Main Street Laurie Cotulla,REHS <br /> U): �' :{ Stockton, California 95202-3029 PROGRAM COORDINATORS <br /> •• Carl Borgman, REHS <br /> s C4 <br /> Website: wwwS OV.Or /ehd Mike Huggins,REHS,RDI 15 9 Margaret Lagorio,REHS <br /> Phone: (209)468-3420 Robert McClellon, REHS <br /> Fax: (209)464-0138 ,teff Carruesco,REHS,RDI <br /> Kasey Foley,REHS <br /> Terrence Fox JUL 0 9 2008 <br /> Cal Trans District 6 <br /> 2015 East Shields Avenue, Suite 100 <br /> Fresno CA 93726 <br /> Subject: Stockton Yard Maintenance Station Site Code: 10193 <br /> 1604 B Street <br /> Stockton CA 95201 <br /> San Joaquin County Environmental Health Department(EHD) has reviewed Well Installation and Well <br /> Destruction Work Plan (Work Plan) dated June 26, 2008 submitted on your behalf by Geocon <br /> Consultants, Inc. (Geocon)and has the following comments. <br /> The Work Plan proposes the destruction of groundwater monitoring wells MW-7, MW-8 and MW-9, <br /> and the installation of groundwater monitoring wells, MW-13, MW-14 and MW-15. <br /> Destruction of the three wells is proposed because groundwater analytical results from them have <br /> been reported non-detect for approximately five years, and due to the rising groundwater elevation the <br /> screened intervals of the wells have been submerged for approximately 12 years. Geocon proposes to <br /> destroy the wells by pressure grouting. Following installation by tremmie pipe of neat cement grout to <br /> fill the well casing, the casing must then be pressurized to force the grout through the casing <br /> perforations and into the filter pack. A hole must be excavated around the well casing 12 inches larger <br /> in diameter than the original borehole to a depth of three feet, the well casing must then be cut to six <br /> inches above the bottom of the excavation and additional grout added to fill the casing and spill over <br /> into the excavation to create a 'mushroom cap' that is a minimum of one foot thick. <br /> The three wells proposed for installation will have screen intervals to intercept the shallow <br /> groundwater interface. The proposed new wells will not, however, replace the wells proposed for <br /> destruction. The new wells will be located to surround well VW-2, which is the well reporting the <br /> highest concentrations of contaminants in the groundwater. <br /> The EHD has previously directed submittal of a Site Conceptual Model (SCM). Geocon has requested <br /> an extension to the August 1, 2008 deadline for submittal of the SCM in order to incorporate additional <br /> data obtained from the proposed well installations into the model. The EHD approves the proposed <br /> well destructions and installations. A Report of Findings documenting the work and the SCM are due <br /> for submittal to the EHD within 60 days following the completion of field activities. If you have any <br /> questions please call Lori Duncan at(209)468-0337. <br /> Sincerely, <br /> Lori Duncan, Senior REHS Margareagorio, RENS <br /> Registered Environmental Health Specialist Program Coordinator <br /> c: James Barton, CVRWQCB, 11020 Sun Center Drive#200, Rancho Cordova 95670 <br /> Rebecca Silva, Geocon, 3160 Gold Valley Drive#800, Rancho Cordova CA 95742 <br />