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R604 :UPDATE 23 10-20-1993 <br /> System Operation: <br /> Currently a flow rate of 63 cubic feet per minute is being <br /> maintained (as of October 6, 1993) through the two blowers that <br /> are placed in series, prior to exhausting through 2 (in series) <br /> 110 gallon and one 85 gallon activated carbon vapor scrub units . <br /> These are serviced by Exceltran and Cameron Yakima for change- <br /> out and rejuvenation. From August 20, through October 6, 1993 <br /> the system has operated 676 hours and recovered 149 pounds of <br /> gasoline range hydrocarbons or approximately 5 . 3 pounds per day, <br /> which is approximately a half of the production during the June, <br /> 1993 update status report of 9 8 pounds per day. <br /> METHODS AND QA/QC <br /> WELL SAMPLING AND ANALYTICAL TECHNIQUES <br /> Depth to ground water and ground water samples were obtained from <br /> all of the ground water monitoring wells on September 15, 1993 . <br /> Vacuum measurements were obtained from all of the wells on <br /> October 6, 1993 . Depth to top of fluid and ground water <br /> measurements were obtained using a clean product water interface <br /> probe . The probe, lowered into the well attached to a tape <br /> calibrated an 0 . 02 foot intervals, signals at the contact of <br /> floating product and at the top of ground water. The measurement <br /> is obtained from the calibrated tape reading adjacent to a <br /> reference point on the casing. The probe is cleaned with <br /> trisodium phosphate water followed by a distilled water rinse <br /> before measuring the next well Measurements are started at the <br /> historically cleanest wells and progress to the dirtiest wells <br /> All depth to ground water measurements were obtained before <br /> purging the wells for sampling. The depth to water is then <br /> subtracted from the elevation of the casing' s reference point for <br /> a corrected ground water elevation. A computer generated <br /> gradient program was not utilized. The more interpretive <br /> gradient map was developed by calculating the gradient from each <br /> well to all surrounding wells (difference in ground water <br /> elevations/distance between wells) , "i .e . " . MW1 to MW2 , MW to <br /> MW3 , MW1 to MW4, and MW1 to MW6 Depth to ground water data from <br /> MW5 is not used; this well was installed in a slant boring and <br /> produced an anomalous high when used. From these gradient lines, <br /> data points representing the contact for the proposed contours <br /> are plotted along each individual line . Once the data points <br /> have been plotted between all the wells, the data paints <br /> representing a given gradient elevation (-45 foot contour, for <br /> example) are connected with site specific factors, n1 e 11 <br /> incorporating conditions caused by local geology, hydrogeology, <br /> utility trenches, etc. These are used to control the contour <br /> between data points. This site is presently being influenced by <br /> vapor extraction at MW5, VSB3, VSB5, VSB9 and VSB11 . A vacuum at <br /> these wells and surrounding wells will influence the shape of the <br /> ground water surface and subsequent flow directions of the ground <br /> water. To obtain representative measurements that show the <br /> influence by the vacuum extraction at this site, a vacuum <br /> measurement is obtained at the well head before removing the cap <br /> and the subsequent depth to water measurement is corrected for <br /> the negative vacuum head (potentiometric head) . <br /> page 4 <br />