ARCHIVED REPORTS XR0009266 - Laserfiche WebLink

Home Browse Search

Geological Technics Inc. Page 4 Groundwater Monitoring Report Project No.723.2 September 30,2002 As required under AB2886, the laboratory data were submitted electronically to GeoTracker on September 11, 2002 - confirmation number 6928664684. 2.0 FINDINGS AND DISCUSSION The results of the groundwater sample analysis show the following: • The concentrations of BTEX and TPH-G continue to fluctuate in individual monitoring wells from one sampling event to the next. • Intermediate well MW-101 continues to contain stable TPH-G concentrations, but benzene and toluene concentrations have fallen to non-detectable levels. 0 Deep well MW-201 continues to experience a decline in contaminant concentrations. Benzene, toluene and TPH-G concentrations have fallen to levels below the laboratory reporting limits. Ethyl Benzene and Xylene were present at 0.3 and 4.8 ug/l, respectively. MTBE was present at 2.4 gg/l but this was not confirmed by EPA method 8260. The contamination is probably a drilling artifact created by the use of mud rotary drilling. It is noted that the contaminant concentrations in MW-201 have declined by an ,r order of magnitude since the first monitoring event in December 2001, which supports the conclusion that the high concentrations were from a drilling artifact. • Figure 4 illustrates TPH-G and Benzene concentrations versus elevation in well MW-3, which lies near the core of the plume. There appears to be a direct relationship between the water table and the TPH-G concentrations. Benzene concentrations have stabilized in the well. • Figure 5 illustrates TPH-G and Benzene concentrations versus elevation in well MW-4, which lies up gradient of the core of the plume. The contaminant concentrations have stabilized in this well. 4 • Figure 6 illustrates TPH-G and Benzene concentrations versus elevation in deep well MW-101, which lies near the core of the plume. The concentrations are approaching stability. The steep decline in the initial concentrations suggests that the contaminants detected in the well were initially a drilling artifact • Figure 7 illustrates the TPH-G concentrations in the shallow wells. The high �. concentration in well MW-3 creates a localized node. Additional investigation is needed to gain a more accurate site conceptual model. 3.0 CONCLUSIONS & RECOMMENDATIONS Conclusions 1. Groundwater flow trends to the northeast to east. The southerly flow direction recorded on December 4, 2000, appears to be anomalous. 2. High levels of BTEX and TPH-G are present in the groundwater of all six water table .r monitoring wells. It is noted that the groundwater elevation exceeded the level of the w.