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Yr n5"`m r .tt - "__ 'r. ^•s rr € - d.- _ 'ISC'Xa%istd"d `"r &;.l&il Mr. Kyle Christie September 13, 1989 - Page 7 Field and Analytical Results--July 1989 Groundwater levels were measured at approximately 59 feet below ground surface in July 1989. In July 1989, groundwater flow direction was to the southwest and west under a hydraulic gradient of about 14 to 15 feet per mile (.27 to .29 percent). Dissolved BETX concentrations in groundwater samples collected dudg July 1989 are included in Table 1. July 1989 benzene concentrations are shown on Figure 1. Complete laboratory reports of the July I989 groundwater sample analyses are enclosed as Exhibit A. July 1989 analytical results show benzene concentrations in groundwater in monitoring wells W-1, W-2, W-2A, W-3, and W-5 are greater than California Departmwnt of Health Services' (DHS) Maximum Contaminant Level (MCL). DHS MCLs for benzene, ethylbenzene, and xylene are 1.0 ppb, 680 ppb, and 1,750 ppb, respectively. Toluene was identified in concentrations greater than the DHS drinking water action level (action level) in monitoring wells W-1, W-2, and W-3. The action level for toluene is 100 ppb. Ethylbenzene and xylene concentrations, where detected, were below their respective MCLS. BETX were not identified in groundwater in off-site monitoring wells W-4, W-6, and W-7. Benzene was the only constituent identified in an off-site well (W-5), at a concentration 6.7 ppb. BETX concentrations in groundwater from monitoring well-W-2 are considerably greater than from monitoring well W-2A. These two wells are 5 feet apart (see Figure 1) and are accessible to groundwater near the surface of the aquifer(see Figure.2). The screened interval of monitoring well W-2 extends about 15 feet above and 5 feet below the screened interval in monitoring well W-2A. Conclusions BETX concentrations in groundwater in on-site monitoring wells screened across the water tw table are approximately half of the BETX concentrations identified during the last.quarterly sampling in April 1989. The approximate 4-foot drop in the water table since April 1989 has significantly affected BETX concentrations. The majority of hydrocarbons appear to s , remain pooled beneath the site near the water table and in the vadose and capillary fringe r zones. BETX remaining in the vadose and capillary fringe zones are relatively inaccessible to groundwater, thus causing a relative reduction in BETX concentrations in groundwater samples. 'sXylene was identified in very low concentrations in the 74- to 88-foot depth interval (W-213). Benzc�ie was identified at a Iow_concentration-in-off-site-mo�zitoring welE-W-S• The fact that BETX concentrations are considerably greater in monitoring well W-2 than in monitoring well W-2A suggests that the vadose zone, which is screened by monitoring well .a W-2, but not monitoring well W-2A, is a major source of hydrocarbons found in samples from well W-2. i BROWN AND CALDWELL �� 723SSTREE7 SILRAMENTQ CALIFORNIA g5gt4Mg2•(ytfij l4;pt23 -