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Based on previous investigations, the aquifer beneath the site appears to be unconfined with both fine and coarse-grained layers separating the shallow and deep monitoring wells. The horizontal groundwater gradient is relatively flat ranging from 0.002 to 0.03. The groundwater flow direction is generally southwesterly. Upward and downward vertical gradients have been observed between shallow well MW- 26 and deep well DW-2. The depth to groundwater generally ranges from 10 to 15 fbg. Aquifer testing at well MW-20 indicates that hydraulic conductivities range from 1 to 3 feet per day within shallow groundwater,but this location contains more sandy strata than most other portions of the facility. Previous Work 1985 and 1986 Well Installations: Wells MW-1 through MW-12 were installed during July 1985 and wells MW-13 through MW-22 were installed during April 1986. Wells MW-1 through MW-19 were installed as part of Shell's internal program to monitor groundwater near plant facilities. Wells MW-20 through MW-22 were installed to monitor groundwater downgradient of a separate-phase plume identified as well MW-1. No information could be found regarding the installation of well MW-23. 1993 Plume Characterization Investigation: Three phases of hydropunch plume assessment activities were performed during February and September 1993 (Harding Lawson Associates, October 15, 1993). The scope of work included 54 hydropunch borings, the installation of four shallow zone groundwater monitoring wells (MW-24 through MW-27), and the installation of one deep zone well (DW-1). The groundwater analytical results were adequate to delineate the extent of the plume to the south and east. However, the extent to the west and southwest was not defined. Hydrocarbon-impacted groundwater on the former Navy property west and southwest of the Shell Terminal maybe a result of another potential source. The former Nary IR Site 4 was thought to be this source. 1994 Site Investigation: During July 1994, PEG investigated the horizontal extent of petroleum constituents in soil and groundwater near secondary source areas (SSAs) 1 through 3. Soil, vapor, and groundwater samples were collected from 19 sample points (GP-1 through GP-19) located on and offsite (PEG, August 1994). Based on the investigation results, well MW-28 was proposed downgradient of SSA-3 located approximately 300 feet southwest of well MW-27. Additionally, further investigation was proposed east of SSA-1. During December 1994, PEG investigated the horizontal extent of petroleum constituents in soil and groundwater near SSA-1 (PEG, August 1994). Soil, vapor, and groundwater samples were collected from 7 sample points (GP-20 through GP-26) located offsite. Based on the investigation results, well MW-29 was proposed east of SSA-1 located approximately 50 feet east-southeast of well MW-11. 1729 2