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GeofogicatTechn Wks Inc. �. 2741 River7Zoad a ' 7vfadesto CaI furnin 9535I (209)538-6424& #538-5852 Addendum To January 8, 1999 WorkYlan Marci's.Diesel Service 2969 Loomis Road Stockton, CA L.� March 2, 2000 ` Project No. 770.2 1.0 INTRODUCTION On January 9, 1999, Wm. J. Hunter & Associates prepared a revised work plan for the Marci's Diesel Service site. This work plan called for the installation of two monitoring wells, MW-5 an MW-6. These wells were to be completed as nested wells if contamination was noted by field methods below a depth of 80 feet bgs. 2.0 PROPOSED CHANGES Installation of nested wells often results in the wells becoming filled with grout during the installation of the grout between the two sand packs. To properly install nested wells it requires the use of 10.25 inch a.d. augers which are slower to use and reduce the fuel efficiency of the rig, hence a higher expense per foot of drilling. Due to the difficulty and expense of constructing nested wells, GTI proposes to install two borings at the MVi -5 location and one boring at the MW-6 location. r The first boring will be drilled 15 feet past the last contamination noted by field methods. If this boring extends past 80 feet bgs it will be completed as a deep, discretely screened monitoring well and named MW-105. Soil samples will be collected at five-foot intervals. The drill rig will Then be moved over 3 feet and a boring will be free drilled to 75 feet and a L� monitoring well (MW-5) will be installed according to the construction details provided in Mr: Hunter's Jandary 8, 1999 work plan. If the contamination does not extend past 80 feet bgs then only the ''water table well`(MW-5) will be installed. At the location for:MW-6, only one well will be installed. This well will be drilled to a depth of 75 feet and constructed as planned in Mr. Hunter's January 8, 1999 work plan. 3 f