About This Project
I want to focus on a small area from a petroleum LNAPL site where BOS 200+® was injected. The goal is to emphasize the rhythm of the characterization process. The circle in Figure 1 delineates the area and the three types of data collected from the area.
Site Overview: The site exhibited petroleum contamination entrained within clay and clay silts, with the water table located approximately 18 feet below the surface. Historically, site characterization was based on monitoring wells, supplemented by soil core samples taken during monitoring well installation. The monitoring wells extended to 20 feet bgs. After examining the site data, it was determined that additional characterization was appropriate.
Characterization Approach: To accurately identify and delineate the extent of the LNAPL, Ultraviolet Optical Screening Tool (UVOST®) was employed to pinpoint contamination. We found that the contamination extended deeper than 20 feet in the processes. In Figure 2, a strong return is evident below 20 feet. Using this and similar UVOST data, nested monitoring wells were installed. Soil cores were collected, and samples from those cores underwent comprehensive analysis at the RPI Laboratory in Golden, Colorado, enabling us to quantify petroleum mass and identify various analytes, including alcohols, fatty acids, and gases. Our findings indicated an estimated petroleum mass of 725 ± SD 75 Kg, in the area shown in Figure 1.
Application of BOS 200+: BOS 200+ was systematically injected in situ using a 7.5-foot triangular grid throughout the contaminated area in Figure 1 and through the vertical thickness of LNAPL contamination illustrated in Figure 2. All site monitoring wells were cleaned or rehabilitated after site injection. The results are presented in Figure 3. The petroleum-associated contaminants exhibited an immediate reduction of 100 to 1000-fold, and these low levels have been sustained over a year. All data not presented are consistent with Figure 3.
Conclusion: This case study exemplifies the effectiveness of combining advanced characterization techniques with cutting-edge remedial technologies like BOS 200+. Monitoring of the site continues.
Figure 1 presents the spatial relationship between the data collection points in the LNAPL area. The outer circle indicates the approximate area of remediation on which we are focused. The vertical thickness of the contamination, not depicted by the illustration, was about 12 feet.
Figure 2 compares the UVOST, electrical conductivity, and the rate at which the probe descended. We’ll focus on the percent return. The signal is evident at about 16 ft to 27 ft interval. The strongest return picks up at about 22 ft and tails off about 24-25 ft. The most significant mass of petroleum is ingrained below the clayey silt layer at 20 ft. The two blue lines mark the lithology that corresponds to the strong UVOST return.
Figure 3 shows BTEX from MW-2, which has a history of having the highest petroleum concentrations of any monitoring well on site. BOS 200+ injection was initiated at time zero “0.” Depending on the contaminant, the BTEX in groundwater immediately declined 10 to 100-fold. Benzene is the most soluble of the BTEX constituents, and it has a lower heat of adsorption to activated carbon, so it is often the last to fall.