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Recommendation for Site Closure Achieved within One Year Using EHC-O^TM

UST Area, Feley Farm Site - Bark River, Michigan.

Lead Consultant - PAZ Technology Group, Dallas TX

Injection Contractor - ORIN RemediationTechnologies, LLC - Madison, WI

Summary:
Soil and groundwater at the former Feley Farms Site (Michigan, USA) was impacted by gasoline constituents that originated from former USTs. The leaking tanks were removed in 1995; based on the reported petroleum-contaminated water seeping into the excavation hole along the surface of the bedrock during the tank removal process, groundwater monitoring was recommended. The results of the 1996- 97 monitoring effort showed that groundwater had been impacted at the source of the gasoline tank leak, which was located between the farmhouse and the farm water well. Benzene levels and those of other gasoline- associated pollutants substantially exceeded Michigan standards. Due to the danger of the gasoline leaking into the farm water supply, USDA contracted with The PAZ Group for additional services to delineate, monitor and remediate the contaminants. Accordingly, a soil vapor extraction system operated for 96 months followed by a groundwater pump-and-treat system (November 2000).

A drop in remedial performance of the pumping system was encountered hence, in October, 2006. EHC-O was used to remove residual benzene and other constituents from an average concentration of 50 ug/L (ppb) to below their regulatory limits (MCLs of 5 ppb). EHC-O was the preferred source of slow-release oxygen due to its ability to supply oxygen plus inorganic nutrients and buffering capacity in a more cost effective manner (US$4.50/lb; US$9.90/kg for EHC-O). Within 6 months of EHC-O treatment, benzene concentrations were reduced by 99%, below the State of Michigan standards.

Post-treatment monitoring showed no re- bound > 1 year post EHC-O application, with all monitored constituents being below the analytical detection limits. This timely and cost-effective remedial action facilitated a clean closure and freedom for future property transfer. At US$4.50/lb (US$9.90/kg), the EHC-O product cost was US$0.20/ft3 (US$18/m3).

The Challenge:

Feley Farms in Bark River, Michigan became a USDA site through foreclosure on a loan in 1994. The USDA hired a contractor through the US Army Corps of Engineers to remove the gasoline tank. The tank contained product, but the contractor lifted the tank out of the ground and the tank ruptured, spilling gasoline into the tank pit. It is unclear what action was then taken by the USACE, but PAZ was hired by USDA in 1997 to examine the spill area and to monitor the groundwater in the event the release had not been properly remediated. PAZ installed 13 wells on the property with two upgradient wells and 11 downgradient wells.

Traces of gasoline were found in Well #7 consistently over the past many years. In 1998, PAZ was hired by USDA to install a vapor extraction system to help mitigate the plume of contamination that had moved approximately 100' from the source. Benzene was the primary constituent of concern and levels at that time in Well 7. Following conventional remedial actions (including soil excavation, SVE, and groundwater pump-and-treat) benzene remained present in the groundwater at levels exceeding the Michigan Department of Environmental Quality's regulatory limit of 5 ppb. These impacts were mainly in Well #11 (at the former source area) and Well #7 (at the collection area). The soils in the area were characterized as nearly level to moderately steep, well drained to somewhat poorly drained, loamy soils; and nearly level, very poorly drained organic soils.

The Solution:

In October 2006, a total of 966 lbs EHC-O was added to 18 injection points within the targeted hot spot measuring about 50 ft wide x 50 long x 10 feet deep (from 5 to 15 ft bgs). Approximately 815 USG of EHC-O slurry was introduced into the subsurface using GeoProbe direct push technology where 1 ¼-inch diameter steel rods with disposable tips were advanced to a target depth or first encountered bedrock. Depth of bedrock at the site ranged from 4.5 to 8.3 feet below ground surface. Approximately 50 gallons of Adventus EHC-O at 14.5-percent solution was injected at each point as the rods were retracted from the resultant borehole. Exact injection point locations and volume of injected solution varied depending on site conditions and soil matrix.

The Result:

Approximately 4 months following EHC-O injection, the concentration of benzene in groundwater decreased by >99% in both monitoring wells (< 0.4 µg/L - data not shown). One year post treatment monitoring showed that the concentration of benzene (and other constituents - data not shown) remained below the analytical detection limits (Figure 1). There was NO REBOUND and the Site is recommended for closure with no further investigation or remedial action necessary.

The Timeline and Cost:

• The EHC-O injection was completed in one day. Following EHC-O additions the concentration of Benzene decreased about 99%, and the concentrations of all constituents were below the State of Michigan groundwater standards.
• The site is recommended for closure and no further investigation or remedial action is necessary.
• At US$4.50/lb (US$9.90/kg), the EHC-O product cost was < US$0.20/ft3 (US$18/m3).