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R604 :UPDATE 22 9-17-1993 Sys tem operation: . Currently a flow rate that fluctuates between 82 cubic feet per minute and 80 cubic feet per minute is being maintained through the two blowers that are placed in series, prior to exhausting through 2 (in series) 110 gallon and one 85 gallon activated carbon vapor scrub units . These are serviced by Exceltran and Cameron Yakima for change-out and rejuvenation. From July 19, to August 20, 1993 the system has operated 630 hours and recovered 118 pounds of gasoline range hydrocarbons or approximately 3 .7 pounds per day, which is approximately a third of the production during the June, 1993 update status report of 9 . 8 pounds per day. METHODS AND QA/QC WELL SAMPLING AND ANALYTICAL TECHNIQUES Depth to ground water and vacuum measurements were obtained from all of the ground water monitoring wells on August 20, 1993 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 water followed by a distilled water rinse before measuring the next well . Measurements are started at the historically cleanest wells and progress 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 casing' s 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) , "i .e If 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 produced 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, "i e " incorporating conditions caused by local geology, hydrogeology, utility trenches, etc. These are used to control the contour between data points This site is presently being influenced by vapor extraction at MW5, VSB3 , VSB5, VSB9 and VSB11 A vacuum at these wells and surrounding wells will influence the shape of the ground water surface and subsequent flow directions of the ground water To obtain representative measurements that show the influence by the vacuum extraction at this site, a vacuum measurement is obtained at the well head before removing the cap and the subsequent depth to water measurement is corrected for the negative vacuum head (potentiometric head) page 4