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App/ied GeoSystems 43255 Mission Blvd. Suite B Fremont, CA 94539 (415)651-1906 <br /> July 14 , 1987 <br /> AGS Job 87031-2 <br /> 0714RNIB <br /> Mr. Robert Niblack <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> 3443 Routier Road <br /> Sacramento, CA 95827-3098 <br /> Subject: Work plan for contaminant distribution delineation, <br /> USA Station #110, 2132 East Mariposa Road, Stockton, <br /> California. <br /> Mr. Niblack: <br /> In response to the concerns you expressed regarding our work plan <br /> for delineation work at the above-referenced site (AGS Work Plan <br /> #87031-2 , dated May 13 , 1987 ) , Applied GeoSystems would like to <br /> make the following clarifications, as requested in your letter of <br /> 17 June, 1987 . <br /> 1 . Ground water gradient will be calculated by measuring the <br /> elevation of the top of casing in each well relative to an <br /> arbitrary reference point with an accuracy of less than 0 . 01 <br /> feet. These values will be combined with depth to water <br /> measurements, generally accurate to within 0 .01 feet, to <br /> calculate relative elevation values for each well and thus <br /> derive a calculated ground water gradient. <br /> 2. Auger flights will be steam-cleaned prior to use and between <br /> borings. This was the intent expressed in the original work <br /> plan. <br /> 3 . Cuttings from drilling and water from purge and sampling <br /> operations will be placed in drums and left on site until <br /> they are characterized and a suitable disposal mechanism <br /> selected. Disposal alternatives will include transport to <br /> licensed hazardous waste facilities or on site treatment if <br /> the levels of contamination warrant such measures. <br /> 4. Soil samples will be evaluated using a field photoionization <br /> hydrocarbon detector (Photovac TIP) . At least one sample <br /> from each boring, and each sample which registers a reading <br /> greater than background levels for total hydrocarbons on <br /> the TIP, will be analyzed for TPH (EPA Method 8015 or <br /> 8020 - see attached) . All water samples will be analyzed <br /> for benzene, toluene, ethylbenzene, total xylenes (BTEX) , <br /> and total volatile hydrocarbons (EPA Method 602) . Soil <br />