Clemson Symposium

April 12, 2018

The Madren Conference Center
Madren Center Drive, Clemson, SC 29634

Oral and poster presentations will take place at the Madren Center located on the Clemson University campus. The presentations will cover a diverse assortment of topics including characterization, monitoring, remediation and many others at various scales (lab to watershed). 

MORE INFORMATION AND REGISTRATION

 

Combined Remedies with Passive Sustained Release ISCO Technology Treatment for Chlorinated Solvents Site in Canada

 

Pamela J Dugan, Ph.D., P.G.,Carus Corporation;

Timothy Colgan, Carus Corporation (tim.colgan@caruscorporation.com);

 Grant Walsom, XCG Consulting Limited (Ontario, Canada)

 

Background.  XCG Consulting Limited was retained by the owners of a commercial real estate property to remediate impacts related to the property’s former use as a dry-cleaning facility. Historic operations resulted in sub-surface releases of chlorinated solvents, including perchloroethylene (PCE), and its breakdown products, trichloroethylene (TCE), cis&trans-1,2-dichloroethylene (cis1,2-DCE, trans-1,2-DCE), and vinyl chloride (VC).  The initial contaminant concentrations in groundwater were in the order of five to 10 times higher than the standards for the given land use. Remediation of this property presented several significant challenges, including:

  • High concentrations of contaminant species having relatively low remedial target concentrations;
  • Continued commercial use of the building space overlying the impacted area;
  • Subsurface utilities in close proximity to the impacted areas;
  • Shallow water table (~three feet) below the floor slab of the commercial space;
  • Fine-grained soil conditions, resulting in low hydraulic conductivity, a tendency for contaminants to be retained in the soil matrix, and limited remedial access to contaminated zones due to preferential groundwater flow patterns

 

Approach/Activities. Initial remedial activities included in situ chemical oxidation (ISCO) through the advancement of temporary subsurface injection points at interior locations through the concrete floor slab of the building, and at exterior locations through the asphalt surface. Solutions of oxidizing compounds (sodium persulfate and potassium permanganate) were injected at low pressure through the temporary injection points.  These remedial activities were generally successful, with contaminant concentrations in groundwater reduced by approximately 50% to 100%. However, residual groundwater impacts persisted, due to back diffusion from fine-grained soil conditions. This resulted in contaminant concentrations exceeding the remediation target of 17 ppb. To address the lingering contamination a passive remedial treatment option was chosen in the form of the sustained-release (SR) plus ISCO technology. The SR+ technology consists of a wax matrix that has oxidants compounds (potassium permanganate and sodium persulfate) evenly dispersed within in the form of a cylinder.

 

Results/Lessons Learned. Remedial progress of the slow-release ISCO technology was monitored through periodic collection of water samples and analyses of chlorinated solvents within and near the remaining impacted areas. In addition, water quality parameters were also analyzed such as pH, electrical conductivity, and ORP at monitoring wells. Measurement of field parameters taken before and after the ISCO treatments indicates the conditions in the areas of the remaining groundwater became much more favorable for the oxidation of chlorinated solvents. Immediate and continuing increases in the electrical conductivity and oxidation-reduction potential in the groundwater of the treated areas have been observed, indicating the continued release of oxidizing compounds from the dissolving reagent cylinders. After the application of SR+ technology in 2015, an additional source area was found and treated with sodium permanganate. Following the 2017 injections, groundwater sampling results have shown a sustained decrease in the total mass of chlorinated solvents at the monitoring well locations with the remedial target concentration of 17 µg/L reached and pending site closure. Lessons learned include that a low-cost passive treatment option can be used to complement active remediation activities in a combined remedies approach and assist with addressing the effects of "rebound" and back diffusion of chlorinated solvents from low permeability media.