ARCHIVED REPORTS_XR0012741 - Laserfiche WebLink

Home Browse Search

WAX Mill f Mr. Kyle Christie March 9, 1990 Page 7 Field and Analytical Results--October 1989 Depths to groundwater were approximately 60 feet below ground surface in October 1989, and the groundwater flow direcdor, was to the southwest under a hydraulic gradient of about 18 feet per mile (35 percent). Dissolved BETX concentrations in groundwater samples collected during October 1989 are included in Tabic 1. October 1989 benzene concentrations are shown on Figure 1. Complete laboratory reports of the 01 1989 groundwater sample analyses are enclosed as Exhibit A. October 1989 analytical results show benzene concentrations in groundwater in monitoring wells W-2,W-2A,and W-3 are greater than the California Department 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-2, W-2A, and W-3. The action leve!.for toluene is 100 ppb. Ethylbenzene and xylene concentrations, where i detected, were below their respective MCLS. t 13ETX were not identified in groundwater in off-site trnnitoring wells W-4,W-5,W-6,and V4-7. r BETX concentrations in ground,;rater from monitoring well W-2A are considerably greater than from monitoring well W-2. 'These two wells are 5 feet apart. The screened 'interval of monitoring w;.11 W-2 extends about I5 feet above, and 5 feat below the screened interval in monitoring well W-lA. 5 Conclusions BETX concentrations in groundwater in on-site monitoring wells screened across the water table are less than the BETX concentrations identified during the last quarterly sampling in July 1989. The approximate 1-foot drop in the water table since July 1989 has significantly affected BETX r concentrations. The majority of hydrocarbons appear to remain pooled beneath the site near the water table and in the vadose and capillary fringe 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 when the groundwater level drops. e >. BETX concentrations, which are considerably greater in monitoring well W-2A than in r monitoring well W-2, could be due to the fact that the sample was taken after only I.4 well volumes were jc f evacuated. Lack of water and slow recharge har of ' ------- -W-2A made purging and-sampling difficult. Thus,the sample of into..rnonitoring-well- -- ----- - __...._ groundwater that was analyzed may not be representative of the formation fluid. I Brawn and Caldwell Consultants