SITE INFORMATION AND CORRESPONDENCE

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Mr. Michael T. Goldstein October 28 , 1985 Page 5 8 . Reactions which retard the movement of chloroform such as adsorption and organic fixation are negligible. 9 . Regional water flow will dilute chloroform concentrations. Extent of Plume The extent of the chlorform plume on September 3 , 1985 , is shown on Figure 1; and the predicted extent of the plume on January 12 , 1986 , is shown on Figures 2 and 3. Figure 2 represents the distribution of chloroform on January 12, 1986 , if RW1 stops pumping on November 15 , 1985 . Figure 3 shows the predicted distribution on January 12 , 1986 , if RWl continues pumping through January 1986 . The farthest extent of the 50 ppb concentration contour was within 700 feet of the basin on September 3 , 1985 , and will only be 900 feet away from the basin on January 12 , 1986 . The high chloroform concentrations in the vicinity of the basin and RW1 , shown on Figure 1 , are the result of discharging water from RW1 to the basin. The concentrations in this vicinity are decreasing and the chloroform is moving toward RW1 , confirmed by concentration in wells sampled on October 7 , 1985. . Both pumping scenarios predict chloroform concentrations to be below 350 ppb throughout the aquifer by January 12 , 1986 ; but Figures 2 and 3 show continued pumping of RW1 until January 1986, will purge the aquifer in the vicinity of the basin. The present number and location of monitor wells has been sufficient to calibrate the model and define the extent of the plume. Addi- tionally, these wells may be used to update the model as additional data becomes available. If you have any questions regarding the modeling, please call us. Very truly yours , BROWN AND • �C�AeL'D.WeE_�LLL Tho v"ee ' '�`` ThomaK. Wheeleryi� Project Manager �4&AMAA Karl J. Anania Geohydrologist TKW:KJA: lah Enclosure BROWN AND CALDWELL P.O.BOX 8045 WALNUT CREEK,CA 94596-1220• (415)937-9010 TELEX 33.6490•OFFICE AT 3480 BUSKIRK AVENUE PLEASANT HILL 94523