A Fundamental Investigation of Well Injection Depth Extraction (WIDE) System Performance Aspects in Fine-Grained Soil Contaminated with Trichloroethylene

Abstract

This research consisted of three components: the field demonstration, laboratory experimentation, and finite element analysis. Global WIDE system performance (in-situ ground water and contaminant transport) was investigated during the field demonstration, PVW performance was examined during laboratory experimentation, and contaminant partitioning tendencies were evaluated as a function of time and operational scheme during the finite element analysis.

The field demonstration was conducted at a site located in Ashtabula, Ohio. With the exception of a silt seam located approximately 1.8 m to 2.4 m below the ground surface, the subsurface consisted of clay (CL) and the in-situ permeability was determined to be approximately 1x10-6 cm/s. TCE contamination levels as high as 300,000 mg/kg were detected on the soil, and concentrations as high as 475 mg/L were detected in the ground water. A 21.0 m by 18.3 m WIDE demonstration system was installed over an area that encompassed a TCE plume. The test area was divided into four quadrants and 494 PVWs were installed to a depth of 6.1 m. Concurrent injection extraction, alternating row extraction, and full quadrant extraction operations took place over a nine month demonstration. Vacuum pressure, injected and extracted fluid volumes, TCE concentrations (gas and soluble-phase), and water table levels were monitored.

A 10 kPa laboratory tracer test experiment was conducted using a 1.0 m3 clay slurry sample with a high permeability soil seam, similar to field conditions. The test box was lined with a geocomposite to provide a constant head reservoir boundary around the test sample. Three settlement plates, 23 piezometers, and 27 tracer tubes were installed to monitor settlement, pressure head, and chloride (Cl) tracer concentration, respectively. The zone of influence and PVW geometry effects were evaluated.

NAPL Simulator (a three-dimensional finite element analysis model) was calibrated using hydraulic field data and then used to simulate soluble and gas-phase contaminant transport in saturated and unsaturated soil media. Using a reference case, a parametric evaluation was initially performed to establish the input variables that significantly affect contaminant transport. System performance and contaminant partitioning tendencies were evaluated as a function of time and operational scheme. Finally, a sensitivity analysis, consisting of 36 simulations, was performed to evaluate contaminant partitioning tendencies as a function of the PVW spacing, extraction water flow rate, and mass transfer coefficient.