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BROWN AND CALDWELL OCT 31 1985 <br /> CONSULTING ENGINEERS <br /> ENVIROMENTAL HEALTH <br /> FERMIT/SERVICES <br /> October 28 , 1985 <br /> Mr. Michael T. Goldstein <br /> Georgia-Pacific Corporation <br /> 760 South Vail Avenue <br /> Montebello, California 90640 11-39-2092-05/1 <br /> Subject: Revised Summary of Computer Modeling of <br /> Groundwater in the Vicinity of the <br /> Tracy Plant <br /> Dear Mr. Goldstein: <br /> This letter is a revised summary of the results of our computer <br /> modeling of the chloroform plume in the shallow groundwater in the <br /> vicinity of the Tracy Chemical Packaging Plant. Revisions to the <br /> letter report of October 18 , 1985, include an additional simulation, <br /> pumping RW1 through January 1986 , and correction of dates in the <br /> original summary. The purpose of this modeling is to estimate the <br /> present position of the 50 parts per billion (ppb) concentration in <br /> the plume and to better define the shape and extent of the plume. <br /> The model can also be used to predict the future movement of the <br /> plume. <br /> The remainder of this letter describes the model , assumptions , <br /> calibration, and results. The estimated extent of the plume as of <br /> the beginning of September 1985 , is shown on Figure 1 . The predicted <br /> extent of the plume, assuming RW1 stops pumping on November 15 , 1985 , <br /> is shown on Figure 2. The plume extent , assuming RW1 continues <br /> pumping until January 1986 , is shown on Figure 3. <br /> Emphasis was placed on determining quantities of chloroform <br /> introduced into the shallow aquifer and the distribution of this <br /> chloroform with time. The simulations indicate that 155 pounds of <br /> chloroform entered the shallow groundwater and RW1 removed more than <br /> 95 pounds of this chloroform, as of October 15 , 1985 . This simula- <br /> tion-determined quantity closely matched the total concentration of <br /> chloroform discharged from RW1 , calculated using operating records <br /> and laboratory analyses from the recovery well. Further, the model <br /> indicated concentrations at BC-12 will not exceed 300 ppb, as shown <br /> on Figures 2 and 3 . <br /> Random-Walk <br /> The National Water Well Association interactive version of the <br /> Random-Walk solute transport model was utilized to evaluate <br /> PO.00X6045 WALNUT CREEK,CA94596-1220•(415)937-9010 TELEX33-6490. OFFICE AT 3480 BUSKIRK AVENUE PLEASANT HILL 94523 <br />