Application of Air Circulation Technology for Remediation of BTEX Plume in the Groundwater at a Natural Gas Plant, Winkler County, Texas

MINNERY GREGORY A., ChevronTexaco Exploration & Production Company, 15 Smith Road, Midland, Texas 79705, phone: 432-687-7385, fax: 432-687-7660, [email protected], HUGH B. ROBOTHAM, and DAVID B. VANCE, ARCADIS G&M, Inc., 1004 N. Big Spring St., Suite 300, Midland, Texas 79701

Results of a site investigation at a natural gas plant in Winkler County indicated remediation would be driven by three factors: constituents of concern (COC) BTEX and TPH; the 70-foot depth to groundwater; and geology of the impacted water bearing zone and overlying vadose zone consisting of unconsolidated eolian sands capped by caliche. This combination of COCs and site setting make application of air circulation technology ideal for remediation of dissolved-phase COCs because the COCs are biodegradable under aerobic conditions, the underlying sands are permeable and have relatively low ratio of horizontal to vertical hydraulic conductivity, and the 70-foot vadose zone capped by caliche provides sufficient vertical space to use the geologic matrix as a fixed film bioreactor to degrade the COCs instead of surface recovery and treatment.

Air circulation technology was pilot-tested at the site in 2001 with the results indicating positive hydraulic and biogeochemical impact with minimum radius of influence of 50 feet for each circulation well. Biogeochemical impact was evident in reduction of BTEX compounds, soluble iron and total organic carbon (TOC) in the circulation well and decline in several parameters in nearby observation wells.

With positive results from the pilot test, in 2002 ChevronTexaco re-activated air circulation in the pilot well and installed a distal end plume cut-off remediation system. The current system appears to be exerting influence beyond the area for which it was designed with the observed radius of influence of 180 feet or greater versus a design of 50 feet.