Theme: 01. Remediation Technology Innovations

Topic Area: 01c. Permeable Reactive Barriers: Best Practices and Lessons Learned

Formatted Title:

A Site-Specific Solution for In Situ Treatment of Heavy Metals and Chlorinated Solvents in Groundwater at a Brownfields Redevelopment Site

Background/Objectives:

Coastal Metals Finishing, Inc. operated a plating business in the Town of Merrimac, Massachusetts, between 1970 and 2002, when operations ceased. Activities at the facility included precious metal, zinc and chromate plating. The site remained as an abandoned industrial building in a residential neighborhood until 2013 when the town took over the property with the goal of cleaning up and redeveloping it for affordable housing. The town was awarded EPA Brownfields Clean Up Grants to remediate chlorinated solvents and heavy metals impacts at the site and prevent off-site contaminant migration.

Treatment of groundwater contaminated with both heavy metals and chlorinated solvents (CVOCs) can be challenging. Treatments that perform well on metals may not be effective for degradation of CVOCs. Similarly, a treatment based on enhanced reductive dechlorination using organic carbon substrates, may effectively reduce CVOC concentrations but possibly mobilize certain heavy metals by altering the oxidation reduction potential (ORP) and pH. Integrating organic carbon with sources of iron (zero or divalent) becomes critical in addressing CVOCs but also to complex heavy metals. This presentation will highlight how a site-specific solution was developed and implemented by combining reagents and application techniques to treat metals such as Zn, Ni, Pb and Cd as well as tetrachloroethene (PCE) and trichloroethene (TCE). The site-specific goals were to reduce the concentrations of dissolved metals and CVOCs in the source area by an order of magnitude and reduce the concentrations of CVOCs and their potential for migration in the plume area.

Approach/Activities:

The authors will review common approaches to address these commingled contaminants from the perspectives of contaminant chemistry and site geochemistry. The presentation will discuss how reductive technologies were applied in a cost-effective way to reduce contaminant mass in the source area, manage contaminant concentrations in a large plume area, and installing a permeable reactive barrier (PRB) at the property boundary to prevent off-site migration in order to meet the site-specific clean up goals. Source area treatment was targeted using grid injection points. The larger plume was treated using several reactive treatment zones. background geochemical conditions will be discussed and how these played a role in selecting the proper reagents. The remedy was implemented in Fall 2021. Performance data from over two years of monitoring will be presented.

Results/Lessons Learned:

In the source area, removal of soluble heavy metals was achieved by precipitation and complexation via biogeochemical processes as metal sulfides or iron-metal-sulfides. This was achieved by ensuring an adequate supply of soluble iron and free sulfide under appropriate pH and Eh conditions. Soluble metals are also removed by adsorption through direct addition of iron oxides or stimulation of biogenic iron oxide formation. The same minerals that mediate removal of metals also supported abiotic reductive dechlorination of CVOCs. In the plume area, soluble reagents used provided a wider zone of influence to treat the CVOCs via a biological as well as biogeochemical pathways. After two years, the approach has resulted in >95% reductions in PCE/TCE concentrations with little to no vinyl chloride (VC) production in the source and plume area monitoring wells. Reductions in divalent metal concentrations has ranged from 50% to 95% during the same time period. Continued monitoring for the next 12 months will continue to establish further declining trends and push towards monitored natural attenuation (MNA). This project exemplifies how a site-specific solution can be effectively implemented to meet the regulatory and the site redevelopment goals using an adaptive approach.

Neil Frasca

Affiliation

Refine Results

(Group 2, Poster Board #214) A Site-Specific Solution for In Situ Treatment of Heavy Metals and Chlorinated Solvents in Groundwater at a Brownfields Redevelopment Site