Environmental Background
Work at this site was performed under an Administrative Order on Consent (AOC) between the client and USEPA Region III. This facility is located in Kanawha County, West Virginia. During multiple site investigations, Benzene has been detected in LNAPL and in the dissolved phase in groundwater samples collected from numerous wells at the facility. Benzene concentrations have regularly exceeded the risk-based action level. To address Benzene and LNAPL in groundwater, AGES designed and constructed a Soil Vapor Extraction/Air Sparge (SVE/AS) system at the site and implemented a limited LNAPL collection program (absorbent socks and bailing) for selected wells.
Very high levels of naturally occurring iron are present in groundwater at this site. Sparging with ambient air would, therefore, result in the precipitation of iron oxide compounds and extensive iron fouling of system components. Although the site conditions were amenable to this technology, a routine AS/SVE approach could not be used at this site. AGES, therefore, designed an alternate approach to AS/SVE that includes sparging with nitrogen rather than ambient air. This innovative approach eliminated iron-fouling issues and allowed for the use of the technology at the site.
Groundwater Treatment
The SVE/AS system consists of three (3) treatment zones, with each zone being operated via a separate treatment building. The system includes a total of 51 AS wells and 27 SVE wells and is sparged with nitrogen manufactured in an on-site plant. Recovered vapors are collected and treated by an on-site thermal oxidizer.
To maximize its effectiveness, the system is operated on a rotational basis, with various combinations of two (2) of the three (3) treatment zones operating at any given time. Nitrogen is sparged at an approximate rate of 3 cfm per operational AS well, with sparge pressures ranging from 6 to 19 psi.
To evaluate Benzene recovery rates, gross air samples are collected from piping in each treatment building. These air samples are collected on a weekly basis and sent to the laboratory for analysis of VOCs. The gross air samples are representative of the average vapor collected from all of the SVE wells in each treatment zone. Groundwater samples are also collected from sixteen (16) wells at the site on a monthly basis to evaluate the system’s effect on groundwater quality. System operation and monitoring is continuing.
Special Project Features
1.) AGES communicated extensively with the USEPA and USACE regarding the status and effectiveness of the selected technology.
2.) This innovative groundwater treatment technology, treatment time shortened to 24 months.
