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°' '' �.�� f"� 3 »:� .L' -V 'Ri Z�w�-•� 'ax��.� .. .n �� M' .� Jr fin! '4.., � y. .;»a IY W1: STE•:R N GE 01, 0 G IC RE SSU RC1: S, � \ C , J.Ran4a11/14 November 1969 4 TPPH and benzene distribution in groundwater maps are shown on Figures 3 and 4. Both figures show the highest concentrations of hydrocarbon in the vicinity of well MW-1,at the south cud of the site,decreasing to the north-northwest. TPPH, reported as gasoline,were detected in groandwatcr samples from wells MW-1,Mw- 2, MW-4 and MW-5 at 20,000 ppb, 14,000 ppb, 170 ppb and 410 ppb,respectively. TPPH were not detected in the groundwater sample from monitor wcV MW-3. The highest concentration of bcazenc was detected at 4,100 ppb in samples from well MW-1 at the south side of the site. Well MW-1 also contained 480 ppb toluene,1,5'0 ppb total xylenes,and 920 ppb cthylbenzene. BTEX were also detected in samp!cs frim well: IVIW.2 and MW-5,where ,i benzene. concentrations were 3,200 ppb and 16 ppb, resp,;ctivcly. In additia:,benzene and 1,2-DCB were detected at 1.7 ppb and 5.3 ppb,respectively,in the groundwater sample coll-cted from well MW- 4. A trace amount of EDC was also detected in the groundwater sample collected from well MWA. 9 1 R R GROUNDWATER FLOW M All monitor wells on the site were surveyed for top-of-casing elevations by John Koch,a licensed land surveyor(#LWII)on 28 March 1989 to the City of Stockton benchmark#218. Figure 5 shows the potenteumctric surface of the shallow-water-bearing zone based on depth- to-water measurements taken on 7 September 1989 (Table 2). The approbmate direction of groundwater flow is the to the cast at a gradient of about 1%. Sample calculation A shows bow the gradient was derived.' ' SAMPLE CALCULATION A: GROUNDWATER GRADIENT CALCULATION From Figure 5,reference line C-C' W Gradient = = 0.75 ft = 0.006 I '30 It or about 1% h -1550 ft--16,25 ft - 0.75 It 1 a 130 It(distance along C-C') 1WRINo9 a �'