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r ~ Ms. Lori Duncan January 11, 2005 Page 5 of 7 area would provide more conclusive evidence of vertical delineation of the plume". EHD also requested the installation of three additional shallow monitoring wells to further define the plume. Pursuant to this request, the following workplan is proposed: Investigation of the Lateral Extent of Groundwater Contamination Ground Zero proposes to install three additional shallow monitoring wells to further investigate the lateral extent of groundwater contamination. Ground Zero proposes to install one well to the west, one well to the northwest and one well to the south of impacted well MWS. The locations of proposed groundwater monitoring wells are presented on Figure 5. The three proposed wells will be installed to a depth of approximately 19 feet bgs. The borings will be advanced by a drilling contractor with a California C-57 license using a rig equipped with 8-inch diameter hollow stem augers. The borings will be completed as groundwater monitoring wells and will be constructed of 2-inch diameter, Schedule 40 FVC blank and slotted casing. The screened interval will consist of 0.010" machine-slotted casing. Since groundwater beneath the site is very shallow(approximately 5-7.5 feet bgs) The wells will be screened from approximately 4 feet bgs to approximately 19 feet bgs. The filter pack will consist of No. 2/12 Monterey sand from the bottoms of the wells to approximately 1.5 feet above the tops of the screens. The remaining annular space will be completed with 2 feet of hydrated bentonite overlain by concrete grout. Each well will be fitted at the surface with a locking cap and watertight,traffic rated well box. Drilling and well installation will be conducted under the supervision of California Registered Geologist. The borings will be sampled at 5-foot intervals for soil classification and possible analytical testing. All soil samples will be classified in accordance with ASTM Designation D2488-90, which is equivalent to the Unified Soil Classification System. We anticipate submitting soil samples collected from the capillary fringe and the bottom of the hole from each well for chemical analysis. Additional samples may be submitted for analysis, dependent upon field evidence of contamination. Soil samples selected for analysis will be immediately capped, labeled and placed in an ice chest for transport to the laboratory. Soil samples selected for analysis will be submitted to a State-certified laboratory under chain of custody protocol. The samples will be analyzed for total petroleum hydrocarbons as gasoline (TPHg) using EPA Method 801513; benzene, toluene, ethylbenzene, xylenes (BTEX) using EPA method 8021 B, and oxygenated gasoline additives and lead scavengers using EPA method 8260B. Investigation of Vertical Extent of Groundwater Contamination Ground Zero proposes to advance one soil boring (Figure 5)to a depth of approximately 40 feet bgs further downgradient of the former UST using a direct push drilling rig equipped with CPT probes. The CPT probes will be pushed to a depth of approximately 40 feet bgs, based upon the results of the previous vertical investigation, to characterize lithology beneath the site. After lithology has been characterized through CPT, the hole will be grouted to the ground surface. A second boring will be advanced, adjacent to the first, using 8-inch hollow stern augers to complete a groundwater monitoring well. G:\GROUNDZE\TuffBoy\Reports\Workplans\WP 1204.doc