ARCHIVED REPORTS_XR0011010 - Laserfiche WebLink

Home Browse Search

^ KLEINFELDER 6 CONCLUSIONS AND RECOMMENDATIONS On September 13, 14, and 15, 2004, 10 monitoring wells and 3 piezometers were purged and sampled. Water samples obtained from each location were submitted for chemical analysis. Based on the data obtained during our assessment, the following conclusions and recommendations have been formulated: 1. Groundwater flow direction at the site is calculated to be towards the east to southeast with a relatively flat gradient of approximately 0.0002 ft/ft. 2. The seven-downgradient well samples (MW-DIS-lls, MW-DIS-11d, MW-DIS-12, MW-DIS-13, MW-DIS-14s, MW-DIS-14d and MW-DIS-15) all showed-decreasing concentrations of 1,2-DCA and non-detectable concentrations of BTEX compounds, EDB, and oxygenates. Only MW-DIS-Ils showed an increased concentration of TPH-g and 1,2-DCA. The 1,2-DCA concentration in MW-DIS-14s continued to show a decreasing trend during the 2004 monitoring period (down to 2.0 ug/l from 3.4 ug/1). It should be noted that the concentration of 1,2-DCA reported for MW- DIS-15 was the lowest since monitoring this location began(2.1 ug/1). Significant decreases in the concentrations of TPH-g, 1,2-DCA, and the BTEX compounds were noted in the source area wells MW-DIS-1 and MW-DIS-2 (excluding benzene). Many of the decreases were in excess of 50% and as high as 79% (1,2-DCA MW-DIS-1). The benzene concentration noted in MW-DIS-2 had increased slightly from 1.7 ug/1 in 2/19104 to 2.3 ug/l, but still remained well below the previously recorded concentration of 4 ug/l in March 5, 2003. The three piezometers sampled this quarter (NP-70', NP-80', NP-90') all showed decreased concentrations of TPH-g, ethyl-benzene, and xylene compared to last quarter, and further showed a .fluctuating pattern of detected concentrations over time. The benzene and toluene concentrations increased slightly in NP-70' and NP- 80'; whereas in NP-90' benzene decreased and toluene remained the same. The samples showed non-detectable results for the fuel oxygenates TBA, MTBE, DIPE, ETBE, and TAME. The 1,2-DCA and EDB concentrations in the piezometers increased this quarter, with the exception of NP-80' where the'EDB concentration decreased. The increased concentrations of benzene, toluene, 1,2-DCA, and EDB in NP-70' and NP-80' appears to be from a lifting effect as seen in the past caused by the air sparging and soil vapor extraction remedial action on the source side of the plume, evidenced by the decreasing concentrations in NP-90'. 3. Kleinfelder recommends that monitoring of the site should be continued in accordance with the "Groundwater Monitoring Frequency Decision Tree" at this time. 12280.MON/ST04R1610/7Z:ly Page 11 of 13 { 0 2004,Kleinfeider,Inc. December 10,2004