ARCHIVED REPORTS XR0012973 - Laserfiche WebLink

Home Browse Search

t4le 08 September 2009 AGE -NC Project No. 03-1055 Page 13 of 19 BTEX compounds were reported in samples collected from borings BI 1, B 14 and B 15 at maximum concentration of 16 pg/1 benzene, 9.4 µg/l toluene, 37 pg/1 ethylbenzene, and 59 µg11 xylenes in sample B 11-12. Additionally, MTBE was reported in sample B 11-12 at a concentration of 27 Pg/t. The highest concentrations of contaminants appeared to be down -gradient of the former Chevron site, in the center of Adams Street. Grab ground water samples collected from the 103 West Eleventh Street (currently 107 West Eleventh Street) environmental assessment (B 1 to B3 - 2004), and borings B8, 139, BI I and B15 all demonstrated dissolved benzene concentrations; modeling of this data represents an off-site plume of dissolved hydrocarbons (Figures 12 and 13). Post -destruction of monitoring wells MW -1 through MW -4 in 2003 (and soil excavations), three of the site's ten ground water monitoring wells, MW -6 (installed in 2004), MW -8 (installed in 2005) and MW -11 (installed in 2008), exhibited consistent TPH-g-impacted ground water. TPH-g were reported in well MW -6 at concentrations ranging between <50 µg11 and 1,300 µg/1, in well MW -8 at concentrations ranging between <50 µg11 and 2,300 pg/l, and in well MW -1 I at concentrations ranging between 6,000 pg/l and 4,600 gg/l. Summaries of the analytical results of grab ground water and ground water monitoring well samples collected as part of the former Tracy Diner site investigations are provided in Tables 2 and 4, INWO respectively; analytical results of grab ground water samples collected as part of the former Chevron site investigations are summarized in Table 6. 4.1. MASS OF DISSOLVED PETROLEUM HYDROCARBONS REMAINING Based on grab ground water investigations coupled with ground water monitoring well data, it appears a large mass of impacted ground water emanating from the former Chevron site extends easterly and northeasterly from the former Chevron off-site onto the western sidewalk of Adams Street (MW -I1, B9, B10 and B11), the center of Adams Street (B12 through B15), the eastern sidewalk of Adams Street, north of the former Tracy Diner Site (138), and possibly on the former Tracy Diner site (B5). Impacted ground water emanating from the former Tracy Diner site appears to be concentrated near the former 500 -gallon UST area (MW -2; TPH-g were reported at or below detection limits in the July 2009 monitoring event, however this well is typically impacted with TPH-g), and upgradient in well MW -6. It appears there is considerable commingling of the former Chevron and Tracy Diner ground water plumes in Adams Street in the vicinity of borings B 12 and B 13; however, the former Chevron commingling appears more aggressive in Adams Street. The lateral extent of dissolved TPH-g concentrations prior to and post soil excavations reported in grab ground water and ground water monitoring well samples collected during the former Chevron and Tracy Diner investigations is depicted on Figure 12; a separate model of the residual dissolved benzene on the Chevron site is Advanced GeoEnviromnental, Inc.