2007-11-20_REVISION - M1982015 (12)

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The wells were surveyed by Carroll Lange Company along with staff gauges placed in the St. Vrain River and the quarry ponds for this investigation. Groundwater in the monitoring wells is generally 12 feet below the ground surface. Groundwater at the time of the initial gauging flowed to the north from the St. Vrain River toward the quarry ponds. Groundwater and surface water elevations were gauged again on January 23, 2007. The measurements at the monitoring points demonstrated very little fluctuation since the previous monitoring event. This data confirmed groundwater flow direction heading from the St. Vrain River toward the quarry ponds. The groundwater contours for the January 23, 2007 gauging event are illustrated on Figure 4. Groundwater elevations from the monitoring points are summarized on Table 5. This is also consistent with site observations as groundwater seeps are present in the southwest corner of Quarry Pond #2 (Big Lake). Water has been observed flowing from the bank of the pond to the north since the initial surface water sampling was performed in December 2006. Based on the January 23, 2007 data, the groundwater gradient is 0.026 ft /ft measured from St. Vrain Gauge Station #1 to MW-6. Hydraulic conductivity testing has not been completed to date, however, based on field observations in the saturated zone, the hydraulic conductivity is estimated at 1.0 x 10 4 feet/second for fine sands (USGS Water Supply Paper 2220, 1989). Assuming the porosity is 0.20, the estimated groundwater flow velocity is: V = (K/n) x (dh/dl) = 1.0 x 10-4 ft/sec / 0.20 x 0.026 = 1.3 x 10-5 ft/sec = 4.7 ft/day On January 9, 2007, two test pits (#1 and #2) were excavated to a depth of approximately 8 feet bgs using a track hoe to the west of the pipeline spill area and between the slurry wall and the St. Vrain River. The soils from the test pits were visually inspected and screened using a PID for indications of VOCs. Soil samples from select intervals were placed in a bag for screening using the PID. Soil samples were placed in 2-ounce glass jars in a cooler with ice and transported to ECS for analysis. The samples were analyzed for BTEX and TVPH. Based on the lab results, neither of the samples contained any detectable BTEX or TVPH. There were no field observations to indicate petroleum impacts were present in the test pit soils either. On January 20, 2007, five additional test pits were excavated generally from station markers 14+50 to 17+50 using a track hoe in the immediate area of the slurry wall trench to the west of the pipeline break. The test pits were excavated to evaluate the level and extent of gasoline contamination in the material used to backfill the slurry wall trench, and evaluate lateral migration of gasoline into sidewall soils. The test pit locations are shown on Figure 2. The sidewall soils and slurry wall material were visually inspected and screened using a PID for indications of VOCs. Composite soil samples from approximately 5-foot intervals were placed in a bag for screening using the PID. Soil samples were placed in 2-ounce glass jars in a cooler with ice and transported to ECS for analysis. The samples were analyzed for BTEX and TVPH. The laboratory 10