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'r . <br /> R604 :UPDATE 18 5-12-1993 <br /> METHODS AND QA/QC � <br /> WELL SAMPLING AND ANALYTICAL TECHNIQUES <br /> Depth to ground water and vacuum measurements were obtained from <br /> all of the ground water monitoring wells on March 30, and April ( ' <br /> 15, 1993 . Depth to top of fluid and ground water measurements t <br /> were obtained using a clean product water interface probe. The r <br /> probe, lowered into the well attached to a tape calibrated in <br /> 0 . 02 foot intervals, signals at the contact of floating product <br /> and at the top of ground water The measurement is obtained from <br /> the calibrated tape reading adjacent to a reference point on the <br /> casing. The probe is cleaned with trisodium phosphate soapy <br /> water followed by a distilled water rinse before measuring the <br /> next well . Measurements are started at the historically <br /> cleannest wells and progress to the dirtiest wells All depth to <br /> ground water measurements were obtained before purging the wells <br /> for sampling The depth to water is then subtracted from the <br /> elevation of the casing' s reference point for a corrected ground <br /> water elevation A computer generated gradient program was not <br /> utilized The more interpretive gradient map was developed by <br /> calculating the gradient from each well to all surrounding wells <br /> (difference in ground water elevations/distance between wells) , <br /> "i .e . " MW1 to MW2 , MW to MW3 , MW1 to MW4 , and MW1 to MW6 . Depth <br /> to ground water data from MW5 is not used, this well was <br /> installed in a slant boring and produces an anomalous high when <br /> used. From these gradient lines, data points representing the € <br /> contact for the proposed contours are plotted along each <br /> individual line Once the data points have been plotted between <br /> all the wells, the data points representing a given gradient <br /> elevation (-45 foot contour, for example) are connected with site <br /> specific factors, Ili e. 11 incorporating conditions caused by local <br /> geology, hydrogeology, utility trenches, etc ; These are used to <br /> control the contour between data points . This site is presently <br /> being influenced by vapor extraction at MW5 , VSB3 , VSB5, VS29 and <br /> VSB11 A vacuum at these wells and surrounding wells will <br /> influence the shape of the ground water surface and subsequent <br /> flow directions of the ground water To obtain representative <br /> measurements that show the influence by the vacuum extraction at <br /> this site, a vacuum measurement is obtained at the well head <br /> before removing the cap and the subsequent depth to water <br /> measurement is corrected for the negative vacuum head <br /> (potenti.ometric head) . <br /> Vapor Recovery System and Monitoring: <br /> As stated in the Update Status Report #11, SB3 , SB5, SB9 and SB11 i <br /> were converted into vapor extraction wells on July 22 , 1992 <br /> (VSB3 , VSB5, VSB9 and VSB11) Along with MWS, these wells are <br /> manlfolded to a vapor extraction system with individual valved <br /> orifices for flow control and measurement from the individual <br /> wells The individual wells are fitted with a PVC tee head with <br /> a locking air tight cap, for well access The tee lateral (2 <br /> inch) is fitted with a 1/4 inch pipe to tubing fitting for <br /> obtaining vacuum/pressure and temperature readings A pipe to <br /> hose 2 inch union is placed between the tee and the 2 inch PVC <br /> page 4 <br />