ARCHIVED REPORTS XR0008182 - Laserfiche WebLink

Home Browse Search

i CLOSURE REQUEST 5-31-94 silts and clays from the surface to the 24 to 29 foot depth along the northern and eastern boundaries of the site, with this sequence much deeper towards the southwest and center of the site (49 to 50 feet below the surface) . Moisture content and porosity tests were run on the 25 foot depth samples obtained from SB14, and the 30 foot depth sample from SB15 . These samples showed a moisture content ranging from 30k to 36t and a porosity of 40% to 46% respectively, see Appendix I . Beneath this silt/clay sequence is a three to seven foot thick clayey, silty sand. This sand is found in all of the borings with the exception of SBI, SB2, SB11, SB14 , P3D, MW1, MW3 , and MW7 which are located along the western and south central portion of the site. These wells showed a continuation of the surface to near surface silt/clay sequence. Beneath this sand is a sequence of clayey silts to silty clays that overlay the aquifer sand that contains interbedded silts and clays . This contact is found at a depth of approximately 50 feet below the surface at MW1, MW2, MW3, MW4, and SB2 (north and east portions of the site. A clay is found beneath this sand at approximately 53 feet below the surface at MW1, MW2, MW3, SB9, SB11 and SB15 . Ground water was initially encountered in soil boring SB2 and monitor wells MW1, MW2, MW3, and MW4 at approximately 47 feet below the surface . This water fluctuates between elevations of -31 and --46 feet below mean sea level (45 to 60 feet below the surface) , see Tables 1, 2 and Figure 6 . T e ground water depth was measured from the surface in the borings, and from the top of the casing in the monitor wells. Ground water flow directions were interpreted from the ground water gradient that was produced from measurements taken from the monitor wells . The local gradient follows what was described earlier in Regional Geology and Hydrogeology in that it flows to the southeast, towards downtown Stockton. But, vapor extraction, local recharge events and city well pumping influence the flow direction as measured monthly The ground water sampled from monitor wells at this site is in the uppermost (shallowest) aquifer of a flood basin and/or alluvium fan deposit and is most likely associated with the Victor formation Due to the limited thickness of this aquifer and the younger overlying formations, most wells an the area produce their water from deeper sources (Laguna and Mehrten formations) The quality of the different aquifers situated in the Stockton area is dependent upon several factors : A. The area of recharge. B Time, length, and route of water migration. C The quality of the overlying aquifer. D Man made obstructions, such as wells, drainages, etc. There are no true aquitards within the Stockton area that have shown the capabilty to block the downward movement of ground water pagel6