AWWA ACE61600

Three sources of contamination have resulted in groundwater quality impacts at the New Mexico Department of Transportation (NMDOT) Las Vegas Service Center in Las Vegas, New Mexico. Leaking underground storage tanks, leaking distribution piping, and formerly unlined, salted cinder storage have contaminated groundwater with petroleum hydrocarbons, 1,1,1-trichloroethane (TCA), and total dissolved solids (TDS), respectively. The plumes are distinct at the source areas, but commingle downgradient. The low permeability of the shallow water-bearing zone makes groundwater extraction via wells impractical due to low production rates. The nature of the commingled contaminants and low permeability of the subsurface, were considered in the selection of an extraction and ex-situ treatment remedy for contaminated groundwater. Because a trench has greater access to contaminant flow pathways (fractures and bedding planes) than a single, or multiple wells, trench-based dual phase extraction (DPE) was piloted to evaluate its ability to dewater a significantly larger volume of the subsurface, and to provide a higher groundwater production rate than extraction wells. During a 2-week pilot test, the DPE trench achieved a steady state groundwater extraction rate of approximately 2.5 gallons per minute (gpm). This pumping rate represents an average groundwater extraction rate 10 times greater than was attainable with the previous multi-well groundwater extraction system. Includes tables, figures.