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1 <br /> f <br /> Ig <br /> PROBLEM ASSESSMENT REPORT <br /> Shell Servige Station <br /> ° 7910 Lower Se-ramento Road,Stockton,California <br /> Shell WIC No.204-7524.0808 <br /> Delta Project No.40.68.:47 <br /> ' Page 9 <br /> 3.3 Monitorin Welts <br /> The locations of three flinch-diameter monitoring wells (MW4,MW-2,and MW-3) installed on site on <br /> August 11 and 13,1989,are shown in Figure 2. The wells werE constructed with Schedule 40 PVC riser pipe, <br /> 0.010 slot size screen,and#3 Monterey sand filter pack,and were sealed with bentonite pellets and neat <br /> ' cement groat. Construction details are presented in Appendix A. Each monitoring well was screened from <br /> 48 to 68 feet below grade and was developed aftrr installation. On August 14,1989,monitoring wells MW-1 <br /> 4..; through MW-3 were surveyed for horizontal and vertical control. A temporary bench mark was used as the <br /> reference datum. This bench mark is located at the south-southwest comer of flue sidewalk along the <br /> f7i Southeast side of the station Fjullding. An elevation of 100 feet was assumed for the temporary bench mark <br /> 3: <br /> 3.4 Ground Wrtter• <br /> 4e: <br /> z Depths to ground water were measured and recorded in the monitoring wells on August 15 and <br /> September 2E, 1989,and May 11 and June 26, 1990(Table 5). Depth to ground water ranged from 57.13 <br /> to 5967 fest. Calculations of the direction of ground water flow fromwater levels collected on <br /> f �p August 15, 1989,and June 26,1990,indicate that flow was towards the northeast and east,respectively. The <br /> r <br /> - � b draulic , <br /> s" y gradient was estimated to be 0.001 on both dates. Ground water contour maps were generated <br /> from the water levels collected on August 15,1989,and June 26,1990,and are presented in Figures 6 and 7. <br /> a 3i <br /> d7 TABLE 5 <br /> Ground Water Elevations <br /> Reference Elevats~; Depth to Ground Water <br /> Monitoring Well from To of(,asin <br /> P B Ground.Water <br /> 'zLJ <br /> .� ocatian _ Dae lfeetL. Fat Elevation <br /> ��. MW-1 08/15/89 98.11 57.50 40.51 <br /> r i 09/26/89 98.11 5&.59 3932 <br /> 00651 98.11 58.bI 39-c,0 <br /> 98.11 57.00 41.11 <br /> � 9 -- --- 99.0s&s4- - <br /> 4--- -- <br /> -- <br /> 05/11/90 -99.09 59.67 39.42 <br /> 99.01 57.75 <br /> 99.01 58.03 <br /> 41.06 <br /> i - MW-3 M5189 98.93 <br /> 5835 <br /> y OS ]4 90 98 93 .. 59.44 <br /> 39-49 . <br /> r <br /> 57.43 41.50 <br /> Nf16190 <br /> r l 98.93 57.80 41.13 <br /> g <br /> ' NOTE. An amumed elevation of 100 feet was used as the bench mark elevation. <br /> a <br /> i6 t <br /> 5 <br /> - <br /> ,r <br />