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R604 UPDATE 14 12-28-1992 readings to evaluate the effects of vapor recovery 4 Sample for fecal coliform from MW3 , MW4, MW5 and MW6 on a quarterly basis during the quarterly sampling. 5 Perform monthly monitoring and sampling of the vapor stream using the WEGE portable lab FID--GC & confirmation for benzene and toluene with the PID 10 S 50 chromatograph and include the results in a monthly update status report LOCATION Regal Station 604 (parcel ## 139-020-08) is located at 1448 N. El Dorado and Harding Way, Stockton, San Joaquin County, California The site is in projected section 2 , T1N, R6E, MDB&M at approximately 14 feet above mean sea level Initial drilling (November, 1989) encountered ground water at approximately 32 feet below sea level (47 ' below the surface) and flowing an an east to southeasterly direction, see figures 1, 2 , and 3 UPDATE STATUS REPORT 414 WELL SAMPLING AND ANALYTICAL TECHNIQUES Depth to ground water and vacuum measurements were obtained from all of the ground water monitoring wells on December 7, 1992 Depth to top of fluid and ground water measurements were obtained using a clean product water interface probe The probe, lowered into the well attached to a tape calibrated in 0 02 foot intervals, signals at the contact of floating product and at the top of ground water. The measurement is obtained from the calibrated tape reading adjacent to a reference point on the casing The probe is cleaned with trisodium phosphate soapy water, with a distilled water rinse, before measuring the next well Measurements are started at the historically cleanest wells and progressed to the dirtiest wells All depth to ground water measurements were obtained before purging the wells for sampling The depth to water is then subtracted from the elevation of the casings reference point for a corrected ground water elevation A computer generated gradient program was not utilized The more interpretive gradient map was developed by calculating the gradient from each well to all surrounding wells (difference in ground water elevations/distance between wells) , "Z e « MW1 to MW2, MW to MW3 , MW1 to MW4 , and MW1 to MW6 Depth to ground water data from MW5 is not used, this well was installed in a slant boring and produces an anomalous high when used From these gradient lines, data points representing the contact for the proposed contours are plotted along each individual line . Once the data points have been plotted between all the wells, the data points representing a given gradient elevation (-45 foot contour, for example) are connected with site specific factors, "z e 11incorporating conditions caused by local geology, hydrogeology, utility trenches, etc . These are used to page 2