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I EC ® R i SIECOR The current maximum concentration observed during the first quarter 2005 was 11,000 „* ppb (wells MW-5 and MW-7). 5.2.2 Lateral Distribution of Benzene in Shallow Groundwater The lateral extent of benzene in the shallow water zone is delineated by the existing monitoring well network. Historical maximum dissolved concentrations of benzene were ' been observed in well MW-2 at 650 ppb. During the first quarter of 2005 the maximum benzene concentration was observed in well MW-1 at 180 ppb. 5.2.3 Lateral Distribution of MtBE in Shallow Groundwater 1 The lateral extent of MtBE in the shallow water zone is delineated by the existing monitoring well network. Historical maximum dissolved concentrations of MtBE were been observed in well MW-2 at 79,000 ppb. During the first quarter of 2005 the maximum MtBE concentration was observed in well MW-16 at 580 ppb. ry ' 5.2.4 Vertical Delineation of Hydrocarbons in Groundwater wA, In February 2005 two deep direct push soil borings (DGP-1 and DGP-2) were completed to depths ranging from 70 to 75 and feet bgs, and hydropunch groundwater samples were colleted. Hydropunch groundwater samples were collected from DGP-1 at depths of 52 feet and 72 feet bgs and from DGP-2 at depths of 46 feet and 70 feet ' bgs in an attempt to complete vertical delineation odrocarbons in groundwater. 1 Hydropunch groundwater samples from boring DGP-1 at 52 feet bgs contained TPHg, benzene, TBA, and MtBE at concentrations of 1,400 ppb, 0.76 ppb, 5.4 ppb, and 29 ' ppb, respectively. Groundwater samples from boring DGP-1 at 72 feet bgs contained F' TPHg and MtBE at concentrations of 260 ppb and 6.1 ppb, respectively. The hydropunch groundwater sample from boring D_GP-2 at 46 feet bgs contained TPHg, benzene, toluene, ethylbenzene, and total xylenes at concentrations of 110 ppb, if 0.51 ppb, 0.76 ppb, 2.2 ppb and 12 ppb, respectively. The hydropunch groundwatere ' sample from boring DGP-2 at 70 feet bgs reported detections of TPHg, benzene, 3. toluene, ethylbenzene, and total xylenes at concentrations of 1,300 ppb, 0.64 ppb, 1.3 7.; ppb, 13 ppb and 100 ppb, respectively. - K1% C .5 + Based on the results of analysis of groundwater samples collected from borings DGP-1 and DGP-2, vertical delineation of the plume has not been completed. 5.3 Shallow Zone Dissolved Concentration Trends Graphs of TPHg, benzene, and MtBE for vs time for wells MW-1 through MW-7, MW-9, MW-12, Iand MW-16 (impacted wells) all show stable or decreasing concentrations overtime with the exception of MTBE in well MW-16.Graphs of concentrations vs, time and groundwater elevation vs. time are included in Appendix H. 1205 SCM.doc 10 -A ;ai