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Mr. Michael T. Goldstein October 14 , 1985 Page 2 Monitoring Well Installation As recommended in our letter of August 14 and agreed upon by Georgia- Pacific and the RWQCB, two additional monitoring wells (BC12 and BC13 ) were installed north of the Georgia-Pacific plant to further define the downgradient extent of chloroform in the shallow groundwater. One of the wells ( BC12 ) was constructed to monitor the "shallow" and "deep" saturated zones monitored by . the existing wells (BC2 through BC11 ) . The other well (BC13 ) was installed in the next deeper sandy to gravelly zone beneath a depth of 80 feet (below the "deep" zone ) . Both wells were sampled to determine if chloroform was present in the groundwater and if its concentration was above 50 micrograms per liter (ug/1) . Water samples from the wells contained chloroform concentrations of approximately 150 and less than 2 ug/l from BC12 and BC13 , respectively. These results indicated that an additional downgradient well, screened above the 80-fcoot depth, would be required to define the downgradient extent of chloroform migration. This well, BC14 , was subsequently installed and its chloroform concentration wsas less than 10 ug/1. Because of the low chloroform concentration in BC14 , we believe that the downgradient extent of the chloroform plume has ben established. Monitoring wells BC12, BC13 , and BC14 were installed in Units 2 and 3 of the Sycamore Village subdivision north of the Georgia-Pacific ' s plant on August 28 , August 29 , and September 4 , 1985, respectively. The wells were installed under the direction of Brown and Caldwell geohydrologists by PC Exploration of Roseville, California. A truck- mounted Mobile B-53 drilling rig equipped with nominal 6-inch diameter hollow-stem augers was used to advance the boreholes. Soil samples were obtained through the augers for classification purposes using a 5-foot continuous tube soil sampler and a standard penetration test (SPT) sampler. All down-hole equipment was steam- cleaned or washed with laboratory-grade detergent and rinsed with distilled water prior to drilling each borehole or obtaining each soil sample. Monitoring wells were subsequently installed in each borehole. Wells were constructed of 2-inch diameter flush-threaded Schedule 40 PVC blank pipe and 0. 020-inch machine-slotted pipe. Bottom caps and top plugs were installed on each well. The screened section of each well was sand packed with Number 2 or 3 Lapis Luster sand produced by Lone Star Sand of Monterey, California. Well BC12 was completed with two screened intervals to monitor the groundwater zones which are monitored by Wells BC2 through BC11 . During completion of the well , an attempt was made to separate the upper and lower screened intervals of the well, using a bentonite pellet seal. Seal placement was not successful, as a thin bentonite layer was placed in the upper screened interval. This layer does not interfere with the proper functioning of the well . Concrete or a neat cement grout was placed BROWN AND CALDWELL 110 BOX 604S WA(NUT CHL FK.CA 94596-Q. O•(415)937-9010 TELEX 33-6490•OFFICE AT 3480 BUSKIRK AVENUE PLEASANT HILL 94523