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• • Ms. Lori Duncan Project 880-039.1A April 12, 2002 Page 2 Monitoring Well Pair Installation One groundwater monitoring well pair consisting of a shallow well (MW -4R -S) and one deep well (MW -4R -D) will be installed at the general location shown on Figure 1. To evaluate the vertical extent of impacted soil and appropriate screen intervals the deep well will be continuously sampled from 40 -feet bgs to approximately 80 -feet or until two consecutive soil samples show absence of petroleum impact. The wells will be drilled using 8 -inch hollow -stem auger drilling equipment. All down -hole drilling and sampling equipment will be steam -cleaned following the completion of the soil boring. The need for additional deep wells will be evaluated following sampling MW -4R -D for four quarters. All work will be done in accordance with stipulations of permits obtained from the SJCEHD. The shallow well will be completed to approximately 30 feet below ground surface (bgs) and will be screened from approximately 15 to 30 feet bgs. Screen intervals for the deep well will be chosen based on extent of impacted soil. It is proposed that the deep well will be screened with 5 -feet of factory -slotted screen at the vertical extent of impacted soil. Groundwater monitoring wells will be completed by installing 2 -inch diameter, flush -threaded, Schedule 40 PVC casing and 0.020 -inch factory -slotted screen. A number 3 sand pack, or equivalent, will be placed in the annular space across the entire screened interval, and will extend approximately 2 to 3 -feet above the top of the screen for the well. A 2 to 3 -foot bentonite transition seal will be placed atop the sand pack, and a Portland cement seal will extend from the bentonite transition seal to the ground surface. The Portland cement seal will be emplaced by tremie pipe or through the center of the hollow -stem augers in one continuous operation from the bottom of the interval to be filled to the top. Soil Sampling A minimum of three soil samples from the wells described in the March 13, 2002 work plan and this addendum will be submitted to the laboratory for the analysis of total IT CORPORATION SAC:\\\SACRFP 1 \COMMON\sacDP\2002\PRJ\PJ8\880\880039 I A.2ac.doc (01040000)