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T. a I ;
<br /> YX
<br /> PRELIMTNARY REPORT SND TANK C-OSMF RFPORT
<br /> Tracy Boulevard Sheil
<br /> 3725 Tracy Boulevard,Tracy,California
<br /> Delta Project No.40-89-012
<br /> Page 5
<br /> 3.0 RESULTS OF MVESTIGATION ACTIVITIES
<br /> Subsurface geology,hydrogeology,soil chemistry,and water chemistry at the site have been inferred from
<br /> drilling and sampling 12 soil borings in which 3 were converted to monitoring wells (MW-1, MW-2, and
<br /> MW-3). The monitoring wells were abandoned on July 5,1994,and replaced on August 16,1990. The new
<br /> monitoring well locations are shown in Figure 2. Soil boring and former monitoring well locatio-,ts are shown
<br /> in Figure 3.
<br /> 3.1 Site Geoloey
<br /> Soil borings SB-I,SB-2,SB-3,and SB4 were drilled near the former underground storagr,tanks to depths
<br /> P--
<br /> of 21,16,16,and 16 feet,respectively. Soil borings SB-7,SB-8,SB-9,and SB-10 were drill(A within the area
<br /> of the new underground storage tanks to depths of 20,I6, 16,and 16 feet, respectively. Monitoring:veils
<br /> MW-1,MW-2,and MW-3 were drilled and installed around the perimeter of the site to a depth of 22 feet.
<br /> These wells were abandoned and replaced with monitoring wells MW-1A,MW-2A,and MW-3A on August
<br /> 16,1990. The new wells were installed adjacent to the abandoned well:ovations. Soil boring SB-11 was
<br /> drilled in front of the former service station building to a depth of 10 feet. Sail samples were collected at
<br /> 5-foot intervals for classification by the Unified Soil Classification System (USCS). Selected soil samples
<br /> were submitted to a California-certified laboratory for chemical analyses. Soil boring logs are presented in
<br /> Appendix C.
<br /> Cross-section AW traverses from the northwest to the southeast corner of the site through monitoring well
<br /> MW-3,soil borings S13-4 and SB-3,and monitoring well MW-2(Figure 4). Cross-section A-A'is shown in
<br /> Figure 5. The site is underlain by sandy to silty clay and clayey silt to a depth of 12 to 15 feet. Underlying
<br /> the finer-grained soils are silty sands which were observed to a depth of 21 feet below the ground surface.
<br /> 3.2 Ground Water
<br /> Depths to ground water were measured and recorded in the former monitoring wells on September 26 and
<br /> October 13, 1989, and April 'S7, 1990. Ground water was observed between 9 and 11 feet below ground
<br /> surface. All field measurements and observations are presented in Table 2. The direction of ground water
<br /> flow was calculated using the ground water elevations on September 26 and October 13, 1989,and April 27,
<br /> 1990. The direction of ground water flow on September 26, 1989, before ground water samples were
<br /> _.._.____collected,_was from..the.south_to_the.north.at_a.gradient.of_0.001._The_direction_of.ground_water flow on
<br /> October 13, 1989,was from the southwest to the northeast at a gradient of 0.001,and on April 27, 1990,was
<br /> from the southwest to northeast at a grtdient of 0.02. A ground water table contour map for September 26,
<br /> 1989,was generated and is presented in Figure 6.
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