Trap & Treat® BOS 200+® was applied using direct push technology (DPT) methods at a former retail gasoline site in Knoxville, TN. Since installation, there has been a 57-99% reduction in total BTEX, a 42-99% reduction in naphthalene, and an average increase of almost 200% in dissolved CO2 over the project monitoring period. The State of Tennessee issued a No Further Action (NFA) status for the project in 2022.
To mitigate LNAPL and reduce hydrocarbon concentrations below the Site-Specific Clean-up Levels (SSCLs) to expedite site closure.
LNAPL mitigation (Note: LNAPL was not detected in the monitoring wells but was suspected to be present based upon OIP results and saturated soil analytical data)
TDEC Soil SSCL: 3.8 mg/kg benzene
TDEC Groundwater SSCL: 0.885 mg/L benzene
APPROACH
Initially, High Resolution Site Characterization (HRSC) using the combined Optical Image Profiler (OIP)/Hydraulic Profiling Tool (HPT) was completed for qualitative assessment and delineation in September 2020. Following the HRSC work and the data interpretation, a Remedial Design Characterization (RDC) was performed to quantitatively determine the overall lateral and vertical extent of the speciated compounds and total contaminant mass within the source area and the dissolved plume.
High-density soil and groundwater sampling was completed in October 2020. Samples were collected from 76 soil sample intervals in 6 borings, and 8 groundwater wells were sampled. All samples were analyzed at the Remediation Products, Inc. (RPI) Project Support Laboratory in Golden, CO at no cost to the project.
Using the data from the RDC, a surgical injection design was developed for the site using BOS 200®+. Coupling of the soil and groundwater data during the remedial design process allowed AST to consider the total contaminant demand within the treatment area. Remedial implementation occurred in May 2021 and consisted of 107 injection points (10 gals. per shot, 12.5-25 lbs. per injection) and 20,300 lbs. of BOS 200® injected.
RESULTS
Lower (1-9.9 mg/L) total BTEX in groundwater at baseline
96-99% reduction in total BTEX
98-99% reduction in naphthalene
223-297% increase in dissolved CO2
Upper (> 10 mg/L) total BTEX in groundwater at baseline
57-92% reduction in total BTEX
42-97% reduction in naphthalene
53-217% increase in dissolved CO2
The areas with the higher baseline hydrocarbon concentrations in groundwater also had higher concentrations in saturated soil mass; lower decreases in groundwater concentrations were observed over the monitoring period
No Further Action status approved by the State of Tennessee
