ARCHIVED REPORTS_XR0007400 - Laserfiche WebLink

Home Browse Search

Third Quarter 2000 Ground Water Monitoring Report Cleanup and Abatement Order No 5-00-707 EAI Pro ect No 1232 4.0 DISCUSSION 4 1 Ground Water Elevation Contour Maps Unocal has segregated water at the sites into shallow and deep zones Figures 3 and 4 present ground water elevation contour maps for both the shallow (Figure 3) and deep (Figure 4) zones ' at the sites Shallow zone wells extend across the water table and generally are screened from 30 to 50 feet below grade surface (bgs) Deeper zone wells are generally screened between 50 and 70 feet bgs Table 4 and Figure 5 pi esent the well construction details in tabular form and graphically, respectively On August 22, 2000, at the direction of the RWQCB, the RIW was turned off When ground water was gauged on September 19, 2000, the RTW had not been in use for approximately one month However, the ground water flow direction was still toward the RIW (see Figures 3 and 4) Further, note the ground water gradient increases more rapidly in the shallow zone than in the deep zone in the near proximity to the RIW 4.2 Ground Water Flow Direction and Magnitude ' Figure 6 presents the historic ground water flow direction and magnitude for the two sites During the summer months, the ground water flow direction for the Wards site is southwest and for the Unocal site it is generally south to southwest Figure 6 indicates that during the winter months when the RIW is not in operation, the natural ground water flow direction is easterly and during the summer months when the R1W is in operation, ground water flaws from both sites toward the RIW 4.3 Shallow and Deep Monitoi ing Well Hydrogi aphs ' Figures 7 and 8 present hydrographs for selected shallow and deep ground water monitoring wells These figures also indicate a reversal of ground water flow direction during summer ' months when the RIW is in operation 4.4 TPH-G and Benzene Isoconcenti ation Maps ' Figures 9 and 10 present shallow and deep TPH-G isoconcentration maps for the site, respectively Figure 9 indicates in the shallow zone the highest concentrations of TPH-G are in wells MW-10A (1,770 pg/L) and MW-22S (3,140 pWL) In the deep zone the highest concentration ofTPH-G is in well MW-1 1 (8,270 pg/L) Figures 11 and 12 present shallow and deep benzene isoconcentration maps for the site, respectively The highest shallow zone benzene concentration is in monitoring well MW-10A at 408 pg/L (see Figure 1 1) while the highest deep zone benzene concentration is in monitoring well MW-1 l at 682 �ig/L (see Figure 12) BHM 123280042 7 ENVIRONMENTAL AUDIT, INC