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R604 :UPDATE 9-MARCH, 1992 • contour maps, Figures 4A and 4B, were then developed from these corrected reading, a computer generated gradient program was not utilized. More interpretive gradient maps were developed by calculating the gradient from each well to all surrounding wells (difference in ground water elevations/distance between wells) , ie. MWI 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 anomalous highs 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, ie. incorporating conditions caused by local' geology, hydrogeology, utility trenches, etc . , being utilized to controlled the contour between data points. After the depth to water measurements had been performed the well is purged for sampling. Water samples are obtained after purging the well of enough water so` that pH, conductivity and temperature stabilize. The wells are purged using a dedicated, sterile disposable bailer (dedicated to each well) , removing the water until the well has been depleted or pH, Temperature and Conductivity measurements have stabilized, (2 to 3 . 5 gallons) . During the March 5 , 1992, the wells were depleted prior to sampling (approximately 0 . 5 to 2 gallons purged) . The wells were then sampled using the same dedicated, sterile disposable bailer; once enough recharge had occurred to fill the necessary sample containers. The water sample is slowly drained from the bailer into the sample containers . The "purged" water is "contained" on site, in a 55 gallon 17H drum, see Appendix A. Enough water was sampled from each well to fill 4-40cc VOA vials (MW1 , MW2, MW3 , MW4, MWS and MW6 ) , with no air space . All containers are fitted with a teflon lined air tight cap. These vials and bottles are then labeled with the sample location, date sampled, time sampled, analyses to be run, initials of the sampler, and preservative if used (no preservatives were used) , placed in a zip lock baggie and then placed in a cooler with enough ice to maintain the sample at 40C. Prior to leaving the site, a chain of custody is filled out and the samples are then hand delivered to the laboratory for analysis. The samples are then chain-of-custody hand delivered the following day to MATRIX Analytical Laboratories (DHS#359 ) for Total Fuel Hydrocarbons and BTEX using EPA method 5030 and 602 . If samples are obtained for Fecal Coliform, they are hand delivered the same day to FGI Environmental, see Appendix A - Field Notes and Chemical Results . page 3