About This Project
ABSTRACT
Trap & Treat® BOS 100® was used to successfully reduce contaminant mass in a localized Trichloroethylene hot spot as part of a pilot test at a former missile site in Nebraska. Over 99% reduction has been achieved in the pilot test well over three and a half years.
PROJECT SNAPSHOT
Key Dates
• Remedial Design Characterization (RDC) – December 2015
• Injection of BOS 100® – April 2016
• Monitoring period – 1,305 days
Treatment Area = Approx. 1,300 ft2
Lithology: Low plasticity clay till
Depth to Perched Water Table: 50 ft below ground surface (bgs)
Primary Contaminant: Trichloroethylene (TCE)
Implementation Method: Pre-Drill/DPT Injection
CHALLENGES & OBJECTIVES
TCE source with suspected Dense Non-aqueous Phase Liquid (DNAPL) was unidentified; a raw water storage tank was suspected. Historic high concentration in pilot test well (MW-18) was 240,000 μg/L (2013).
Since DPT refusal was encountered above the perched groundwater table (approximately 35 ft bgs), the use of a pre-drill technique was required. A solid stem auger (4.25 inch) was advanced to a maximum of 70 ft bgs and the annulus was backfilled with hydrated bentonite chips (2 to 3 ft lifts). Fourteen injection locations were advanced to 70 ft bgs and 7 injection locations were advanced to 54 ft bgs.
The project objective was to evaluate the effectiveness of BOS 100® for remediation of TCE contamination and potential TCE DNAPL present in saturated soil and groundwater in the perched zone at the north-central area of the site in the area of well MW-18.
APPROACH
As part of the RDC, 6 soil borings were advanced to a maximum of 70 ft bgs. Continuous soil samples were collected using a hollow stem auger and split spoon approximately every 2 ft, with samples collected for laboratory analysis based upon field observations and PID readings. A total of 115 soil samples were collected and sent to the RPI Project Support Laboratory in Golden, CO. Analyses were performed at no cost to the project.
Four (4) permanent monitoring wells and 1 Solinst Continuous Mutli-Channel Tubing (CMT) multi-level well (7 channels, 22 to 70 ft bgs) were installed in the soil borings.
A total of 7,560 lbs of BOS 100® was applied in 21 injection locations at varying triangular spacing (5, 7.5, and 10 ft) in a top down progression (1.5 to 2 ft vertical intervals) at flow rates that ranged from 35 to 84 gallons per minute (gpm).
During the field effort, pressure transducers were used to monitor radius of influence. Post-injection monitoring included TCE, daughter products, chloride, and dissolved gases such as ethylene and acetylene.