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Y' <br /> October 9, 2014 J <br /> Jy <br /> Carl Knowles 7 y <br /> PO Box 640 �✓ x- -t- <br /> Woodbridge, CA 95258 AC <br /> LOP Site: Knowles Station <br /> 1140 Hammer Lane <br /> V� <br /> Stockton, CA 95209 <br /> Subject: Proper Sampling Protocols <br /> The San Joaquin County Environmental Health Department (EHD) would like to address a <br /> concern regarding proper sampling protocols. <br /> EHD conducted a groundwater sampling event inspection on September 25, 2014. During the <br /> inspection, EHD observed the field technician measuring depth to water after taking a <br /> groundwater sample. EHD has established groundwater sampling guidelines in order to assure <br /> that groundwater sample results are as representative of aquifer conditions as possible. Before <br /> sampling, please discuss the importance of measuring the depth to water in the well after <br /> purging the appropriate volume and confirm that the well has recovered 80% of the original <br /> depth to your field technicians. A San Joaquin County Environmental Health Department <br /> Recommended Groundwater Sampling Guidelines and portions of Chapter 15: Site Assessment <br /> Pre-Field Work Considerations, California LOFT Manual: September 2012, are included for <br /> your reference. These documents in their entirety establish a standard of practice that <br /> minimizes variations in data caused by changes of workers, laboratories, etc. and should be <br /> followed to maximize data reliability. <br /> If you have any questions or concerns, please contact Angelica Sandoval Marin at (209) 468- <br /> 2807 or by e-mail at amarin@sjcehd.com. <br /> Sincerely, <br /> Angelica S. Marin, REHS Nuel C. Henderson, Jr., PG <br /> Senior Registered Environmental Health Specialist Engineering Geologist <br /> c: Scott G. Bittinger, P.G., Stratus Environmental, Inc., 3330 Cameron Park Drive, Ste 550, <br /> Cameron Park, CA 95682 <br /> Cori Condon. California Regional Water Quality Control Board Central Valley Region, <br /> 11020 Sun Center Drive, Suite 200, Rancho Cordova, California 95670 <br />