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R604 UPDATE 17 4-27-1993 On July 21, 22 , and 23 , 1992 , four new vadose zone vapor recovery • wells were installed and manifolded to the recovery system As of February 23 , 1993 the new wells along with MWS have produced 3851 . 4 pounds of gasoline range hydrocarbons, for a total recovery of 16967 4 pounds . From February 23 , to March 15, 1993 202 pounds of gasoline range hydrocarbons have been produced, as compared to the previous reported 506 9 pounds of gasoline range hydrocarbons from January 13 , to February 23 , 1993 , see Table 3 and Charts, Figures 6A through 6E of vapor recovery Vacuum Influence: As was stated earlier, vapor recovery has removed the lighter fractions of gasoline range petroleum hydrocarbons from the soil (through ethylbenzene) and has greatly reduced the petroleum hydrocarbons dissolved in the ground water beneath this site Figure 5 represents the vacuum influence generated from the vapor recovery system as measured before obtaining depth to ground water measurements on March 30 , 3993 System Operation Currently a flow rate that fluctuates between 70 cubic feet per minute and 94 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 two 85 gallon activated carbon vapor scrub units These are serviced by Exceltran and Cameron Yakima for change out and rejuvenation. From February 23 , to March 15 , 1993 the system has operated 478 hours and recovered 202 pounds of gasoline range hydrocarbons (10 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 March 30 , 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 soapy water followed by a distilled water rinse before measuring the next well Measurements are started at the historically cleannest 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 . " MW1 to MW2, MW to MW3 , MW1 to MW4 , and MW1 to MW6 Depth page 3