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December 2, 1997 Page 3 The scope of work in this addendum is presented to comply with requests from PHS/EHD for submittal of a work plan addendum which addresses all of their concerns, as outlined above. SCOPE OF WORK Task I - Installation of Additional Groundwater Monitoring Wells On May 3, 1996, perimeter Monitoring Wells MW-3, MW-10, MW-l2, and MW-13 were abandoned at the request of the City of Stockton to accommodate widening of Pacific Avenue (Figure 1). The four wells will be replaced as described below, to comply with the PHS/EHD request. Task 1.1 - Prefield Activities. The four new wells will be placed as close as possible to their original locations. Discussions will be held with PHS/EHD, the City of Stockton, and private landowners to locate the wells in areas acceptable to all parties. All proper permits and access agreements will be obtained prior to well installations. Underground Service Alert (USA) will be notified 48 hours in advance of the scheduled work. Task 1.2 - Well Installations. The four wells will be installed using hollow-stem auger drilling equipment. The wells will be constructed of 2-inch diameter Schedule 40 polyvi- nyl chloride (PVC) well casing and 0.02-inch machine-slotted well screen. Each well will be installed to a depth of approximately 50 feet below ground surface (bus) with a screened interval from a depth of 30 to 50 feet bgs (depth to groundwater in nearby existing monitoring wells is 35 to 40 feet bgs). A sand pack, of 2/12 graded sand or its equivalent, will be placed from the bottom to approximately 1 foot above the screened interval. A minimum 2-foot bentonite seal will be placed above the sand pack, and a neat cement/bentonite slurry will be tremmied from the top of the bentonite seal to the surface. The wells will be completed using a surface vault and locking cap mechanism. All waste soils will be properly disposed of off site. Task 1.3 - Well Development. The newly installed wells will be developed by surging followed by bailing. During development„the clarity of the discharged water will be monitored.. When the groundwater becomes clear, the well will be considered developed and ready for sampling. Task 1.4 - Wellhead Survey. The elevation of each top of well casing will by surveyed to sea level datum by a California-licensed surveyor. The horizontal coordinates of the well will also be surveyed. Task 2 - Soil Investigation Original soil investigations by Resna Industries (Resna), found hydrocarbons concen- trated beneath the northern portion of the underground storage tank (UST) pit and'the 3111657A'•STOCK 1.DOC