Installation of Permeable Reactive Barriers in Urban Residential Environments Surrounding Federal Installations

摘要

A full scale iron permeable reactive barrier (PRB), of over 2,000 feet in length comprised of three segments, was constructed down to a depth of approximately 40-feet below ground surface (bgs) in an off-Base residential area surrounding the former Kelly Air Force Base (AFB) in San Antonio, Texas. The two main objectives of the remediation strategy included preventing further off-Base migration of groundwater contaminated with volatile organic compounds (VOCs), primarily trichloroethene (JCE) and tetrachloroethene (PCE) and to ensure groundwater concentrations in off-Base areas meet acceptable groundwater standards. The PRB was constructed by azimuth controlled vertical hydraulic fracturing technology in a residential neighborhood with numerous subsurface and overhead utilities. Trenching was considered a less desirable installation option because of the numerous underground and above ground utilities. The site is in a busy urban area with businesses, schools, and residences; and minimal work space (a two-lane road) where one lane had to remain open during the day and both lanes had to be reopened at night. All sections of the PRB were constructed to the design specifications of approximately three (3) inches in thickness from a depth of approximately twenty (20) feet to a total depth of forty (40) feet bgs. Daily requirements during the drilling portion of the project included limited work hours and the requirement that all equipment be removed from the City of San Antonio (COSA) right-of-way (ROW) on a daily basis. The site conditions existing during frac well installation and PRB construction presented unique challenges to the project and involved the coordination and management of numerous activities from utility clearances, traffic control, material and equipment handling, and environmental controls; while at all times minimizing citizen disruptions to their normal daily environment. This paper describes the construction challenges and logistics that had to be managed to satisfy site-specific constraints for installing an in situ PRB within a residential neighborhood as part of the overall site remediation strategy for the former Kelly AFB.