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C.�" 'ri-i.'.�'.-.: -�„ m.. .�,._ en `'�r.'-,' _".ta'?:�t-�: ,f-`.�. ltd_. ry Yet.�Y� .. �'Y.� at'� s�r"re� �yi` � �`�d+e�' �.e7� �;yJ r,�'- `�'��� � a "r';. ':7:✓ � 4�' <br />�z <br /> f <br /> PRELIMMARY REPORT <br /> Moreland C-oart Shett <br /> f Staktoa,California <br /> Dena Project Na 4o_^a-146 <br /> Page 7 <br /> 1 ; 2.5 Reetonal GPoIo2v and FIy_droa_ eoIoQv <br /> Stockton lies within the Great Valley geomorphic province. The regional geology consists of <br /> unconsolidated deposits of sand,silt,and clay which were deposited in fluvial and deltaic environments. <br /> S <br /> A regional map showing the ground water elevation contours for the unconfined aquifer for the fall of <br /> 1986 indicates ground water is at a depth of 30 feet below ground surface and generally flows toward the <br /> a' southwest <br /> (DWR, 19$6). <br /> f`j 2�;-6 Slte <br /> �., Subsurface geology at the site lt:ts been inferred from drilling eight soil borings at the site. Soil borings <br /> SB-1 through SB-6 were drilled during the pretank closure assessment,while soil borings SB-7 and SB-8 <br /> were advanced during the Phase I investigation, <br /> i r <br /> . Figure 3 shows the surface trace of cross-section AA'. Cross-section AW presents the inferred <br /> distribution of soils beneath the site and is shovru in Figure 4. Silt and clay predominate from ground <br /> level to a depth of approximately 25 feet. A water-bearing silty sand unit underlies the silt and clay and " <br /> appears to be continuous across the site. This silty sand unit was€first encountered in soil boring SB-7 j <br /> r at a depth of 29 feet below ground surface and in soil boring SB-8 at a depth of 7A feet. <br /> Ljs <br /> In the vicinity of the former tank excavation,n clay layer is present and extends from ground surfarx to <br /> approximately 24 feet below grade. This clay layer is approximately 11 feet thick beneath the backfill of ; <br /> 7 the former tank excavation(Figure 4). <br /> i, 2.7 Resuils o MousSite ssessments <br /> On December 27 and 29, 1988,during the tank closure activities,a Delta geologist collected seven soil <br /> samples from the bottom of the former tank excavation. On January 3, 1989, six soil samples were <br /> �+ collected from the product line trenches. The samples were submitted to a Cahiornia-certified laboratory <br /> ---for-chemical anal --:- ---- - - ------ - — - --- - - <br /> yses. -'l 6 analytical data are presented in Tables 3 and 4. A Tank Clasrere Repan <br /> '{ documenting ttaese activities was submitted to the County on April 6, 1989. <br /> 3 <br /> K 1 <br /> 11 IMF mid <br /> F <br />