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PollutionEngineering November 2012 : Page 39

Advertorial DIRECTIONAL TECHNOLOGIES INC. HOWTO: Rapidly mitigate Vapor Intrusion Exposure Using Horizontal Remediation Wells 1-877-788-4HRW • V apor intrusion ( VI) in buildings of toxic contaminants, such as chlorinated solvents and petroleum hydrocarbons, is a critical exposure pathway that can threaten the health of children, workers and other human receptors at many contaminated sites. Mitigation of the VI exposure pathway is often confounded by the presence of the building itself, which limits the types of remedies that can be put in place. This article shows how horizontal remediation wells (HRW) can be used in a smart, fast and cost-effective way to extract (or treat) harmful gases from the subsurface and mitigate risk to occupants without affecting the integrity of the building. Two typical HRW projects rapidly miti-gated VI issues in commercial structures using single, long horizontal sub-slab wells with impressive results. In the first project, the owner of a high-end office building leased the structure to an inter-national corporation that used the build-ing as its US headquarters. The structure is located in a highly urbanized area that was at one time used for industrial manufacturing and then later redevel-oped into an office park. The structure measures approximately 320-feet by 100-feet, slab on grade construction. The owner became aware that VI may be an issue in the building and the owner’s environmental consultant recommended that an active VI mitigation system be installed. The building owner agreed but was adamant that the tenant’s operations could not be interrupted or disturbed in any way and that the VI mitigation system could not be installed inside the building. Directional Technologies mobilized its medium-size horizontal directional drill-ing rig to the building’s parking lot and advanced a single 320-foot long horizon-tal boring beneath the building’s center-line. The horizontal boring terminated at the opposite end of the building approxi-mately three feet below the floor slab, as illustrated in Exhibit 1. Directional Technologies next withdrew the drill string and installed the three-inch diam-eter polyvinylchloride horizontal well screen and riser by pushing it into place with the drill rig. result that mitigated the risk of exposure to workers (see Exhibit 2). Exhibit 2. Radius of Influence of HRW Vapor Intrusion Mitigation System. Exhibit 1 Horizontal VI Mitigation Well Orientation The owner’s consultant installed and began operating the surface-located vapor extraction blower system. Tests subsequently confirmed that the single horizontal well’s zone of influence was sufficiently extensive to depressurize the entire slab. DTI successfully completed this assignment in three days. In a second project at a multi-hundred thousand square foot former manufac-turing facility (now a warehouse), chlo-rinated solvents were found beneath the floor slab, creating a VI issue. Directional Technologies installed a single 800-foot long horizontal well beneath the building’s centerline. Test results indicated that the horizontal well’s zone of influence was suf-ficient to depressurize the entire floor slab. In other words, the ZOI extended approxi-mately 400-feet on either side of the horizontal well screen – an extraordinary Directional Technology’s horizontal directional drilling experience, engineered well-screen design expertise and hori-zontal well installation methodology has a decades-long successful track record. Horizontal remediation wells are finding new applications such as Vapor Intrusion Mitigation because of their unique capa-bilities related to site/structure access, business-disruption avoidance, acceler-ated site closure and enhanced site safe-ty. In addition, horizontal remediation wells consistently out-perform vertical wells because they provide an effective delivery mechanism to reach previously inaccessible contaminants such as those contaminants found beneath buildings. Cost-effective and expedited mitigation of the VI exposure pathway using HRW is a true advance in remediation technology. Contact Directional Technologies at 1-877-788-4HRW or email them at to utilize their 20 years of experience in designing and installing horizontal remediation systems for your next in-situ project. 39 NOVEMBER 2012

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