US ARMY FUEL TERMINAL
Haines, Alaska

Over its operational lifetime, extensive soil and groundwater contamination had occurred at a now decommissioned US Army fuel terminal, located near Haines, Alaska, on the Lutak Inlet. In conjunction with other clean-up activities at the site, Remedial Construction Services, L.P. (RECON) was retained to install an air sparging system between a benzene-contaminated groundwater plume and the Inlet to treat the contaminant in-situ and thus halt offsite migration.

Air Sparging Technique
Air sparging involves the injection of clean air into the saturated subsurface soils to meet two objectives: increase microbial activity by the introduction of oxygen into the subsurface; and increase the volatilization of hydrocarbons by passing air through the contaminated groundwater (air stripping). The off gas is collected by means of a vacuum pump and either passed through a vapor phase treatment system that allows moisture to settle out and organics to be adsorbed by granular activated carbon, or it can be discharged, as was the case of this project.

Air sparging is particularly suited to the lighter gasoline components, such as benzene because they easily transfer from the dissolved to the vapor phase.

System Installation
The air sparging system was configured to maximize the efficiency of the system and consisted of a series of 10 injection point risers, manifolded at the top and connected to a blower. T-connectors at the injection point inverts were fitted with horizontal sparge piping extending 20 feet in either direction.

The system was installed using the biopolymer (BP) slurry trench method. The slurry exerts hydraulic pressure against the trench walls and acts as shoring to prevent collapse. BP slurry is biodegradable, and does not reduce the final permeability of the in-situ soil or backfill materials.

The 410-foot long trench was excavated through BP slurry to the top of bedrock, at up to 25 feet below working grade. Filter fabric was installed on both sides of the trench to minimize clogging. The air sparge system was then installed through the slurry, ahead of graded backfill placement.

Despite the adverse weather conditions typical of Alaska in the Fall season, the project was completed on schedule and without incident.

GROUNDWATER/SOIL VAPOR EXTRACTION RECOVERY SYSTEM
Navasota, Texas

Remedial Construction Services, L.P. (RECON) was contracted to construct a groundwater and soil vapor extraction recovery system to remove hydrocarbon contamination from the subsurface groundwater and underlying soils. The area of removal encompassed the a Diamond Shamrock retail fueling station.

RECON installed 1,600 linear feet of PVC groundwater recovery piping and 1,000 linear feet of PVC vapor extraction piping to 35 onsite and offsite recovery wells. The existing pavement was saw-cut, to an average depth of 8-inches and  removed in order to excavate the trenches for the recovery system piping.

Using conventional open-trench construction most of the onsite and offsite piping was installed. Piping that crossed the State Highway was installed using a directional boring technique. This method was chosen due to the offsite locations of some of the recovery piping in the Texas Department of Transportation (TxDOT) easement, which would minimize traffic disruptions.

RECON installed a portable recovery treatment system composed of an air stripper, oil/water separator, carbon vessels along with electrical pump motors and blowers with controls.

A major hurdle on this project, was the installation of the recovery system piping underneath and through the median of State Highway 105 and working in the TxDOT right-of-way.