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<br /> Mr. Michael T. Goldstein
<br /> October 18 , 1985
<br /> Page 4
<br /> The calibrated model indicates that initially 14 pounds of chloroform
<br /> leaked from the storm water basin into the shallow groundwater
<br /> zones . The leak occurred between July 28 and July 29 , 1984 , during
<br /> the hyperchlorination of the basin. Chloroform concentrations in
<br /> monitoring wells BC2, BC3 , BC4 , and BC5 measured on October 9 , 1984 ;
<br /> BC10 on April 28 , 1985, and concentrations in BC12 and BC14
<br /> September 9 , 1985 , were used to fix the amount of the initial leak.
<br /> The low concentration in BC2 , BC3 , BC4 , and BC5 on December 7 , 1984 ,
<br /> and the low concentration in BC6 and BC7 on December 27 , 1984 ,
<br /> indicate there was no significant leakage in the period from the
<br /> initial leak to the start of sludge removal .
<br /> Excavation of sludge from the basin, which began in early 1985 ,
<br /> caused intermittant infiltration of water through chloroform
<br /> containing soils. This allowed another 15 pounds of chloroform to
<br /> enter the shallow aquifer before April 20 , 1985; 13 pounds of this
<br /> chloroform entered on January 12 , 1985. Chloroform concentrations in
<br /> BC2 , BC3 , BC4 , BC5 , and BC7 on January 31 , 1985 , in conjunction with
<br /> field observations fix the time. Concentration in BC-10 on February
<br /> 28 , 1985 , and March 11 , 1985 ; and BC-12 on September 9 , 1985 ,
<br /> September 16 , 1985 , September 23 , 1985 , and October 7 , 1985 fix the
<br /> amount. Another pound of chloroform was introduced into the aquifer
<br /> on February 15 , 1985 , and the other pound infiltrated over the entire
<br /> 3 month period. Concentrations in BC7 and BC11 on February 28 , 1985 ,
<br /> RWl on May 2 , 1985 , and RW1 and BC7 on June 24 , 1985 , fix the time
<br /> and the amount.
<br /> Simulation
<br /> Analysis of simulations demonstrated chloroform that leaked into the
<br /> aquifer after April 20 , 1985, was recovered by the recovery system
<br /> initiated on July 1 , 1985 . The simulations showed 96 pounds of
<br /> chloroform entered the aquifer between April 20 , 1985, and October
<br /> 15 , 1985 . The simulations also demonstrated the recovery well system
<br /> has removed approximately 95 pounds of chloroform as of October 15 ,
<br /> 1985. The water pumped from R111 has been intermittantly discharged
<br /> into the excavated basin introducing variable amounts of chloroform
<br /> into the aquifer. This has also leached chloroform out of sediments
<br /> under the basin and the aquifer. The effectiveness of the recovery
<br /> system has been confirmed by the decreasing chloroform concentrations
<br /> in the wells around the basin after September 20 , 1985.
<br /> Extent of Plume
<br /> The extent of the chlorform plume on September 3 , 1985 , is shown on
<br /> Figure 1 ; and the predicted extent of the plume on January 2 , 1985 ,
<br /> is shown on Figure 2. The furthest extent of the 50 ppb
<br /> concentration contour was within 700 feet of the basin on September
<br /> 3 , 1985 , and will only be 900 feet away from the basin on January 12 ,
<br /> 1985. The high chloroform concentratons in the vicinity of the basin
<br /> and RW1 , shown on Figure 1 , are the result of discharging water from
<br /> RW1 to the basin. The concentrations in this vicinity are
<br /> BROWN AND CALDWELL
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