Hydrogen Release Compound (HRC™) Research

"Validating a New, Low-Cost Remediation Tool"

Does the breakthrough bioremediation product — Hydrogen Release Compound (HRC™) — really stop plume migration and reduce source contaminants in chlorinated solvent-impacted soil and groundwater?

To determine that question, MWH teamed up with its technology alliance partner, Regenesis (San Clemente, CA). Together, they applied, monitored and assessed the overall impact of HRC™ as a remediation tool. The $31 thousand research project lasted from April 1998 through January 1999.

The project — which validated HRC™ as a low-cost and long-term cleanup alternative — garnered a Honor Award at the 2000 Engineering Excellence Competition held by the Wisconsin (U.S.) Association of Consulting Engineers (WACE). This MWH project also received National Finalist status in the American Consulting Engineers Council 2000 Engineering Excellence Competition.

The Process

The MWH team conducted the research project at Cedarburg Drycleaners in Cedarburg, Wisconsin, a northern suburb of Milwaukee. The site was contaminated with high levels of the chlorinated hydrocarbon, perchloroethene (PCE).

To remediate the PCE, MWH applied glycerol polylactate ester (GPL), an HRC™ bioremediation product, which provided a time-released source of hydrogen. Under the right conditions, GPL has proven to promote enhanced rates of reductive dechlorination.

The HRC™ product was injected by Geoprobe‚ with 240 pounds of a slightly flowable formulation of GPL-HRC™. This was applied using a direct push injection at 20 pounds per hole in 12 holes.

Upon injection, HRC™ comes in contact with water and is acted upon by microbes to release lactic acid. This lactic acid further converts to other organic acids, releasing hydrogen at each step. The hydrogen helps a specific population of reductive dechlorinating bacteria, naturally occurring in the aquifer, degrade PCE and its daughter products.

The Results

The Cedarburg Drycleaner’s field test successfully demonstrated HRC™ to be a simple, passive, low-cost and long-term option for anaerobic bioremediation of chlorinated hydrocarbons via reductive dechlorination. The test also showed HRC™ could significantly reduce the overall cost and maintenance of solvent remediation.

When our remediation team analyzed the contaminants and their breakdown (daughter) products, they noted an increase in lactic and other metabolic acids (acetic, propionic, and pyruvic) at the HRC™ delivery point and at downgradient locations.

Additionally, groundwater pH analysis showed a shift to the acid side and that redox levels had dropped steadily. Within five months, the remediation team noted an 80 percent mass removal with good field mass balances. Risk to groundwater was significantly diminished.

Researchers found that injection of HRC™ resulted in a more rapid and significant degradation rate of PCE throughout and downgradient of the injection zone. It also impacted the daughter products. Ultimately, the daughter products' plume sizes are reduced relative to their potential spread under conditions of monitored natural attenuation. The remediation team found an enhanced rate of natural attenuation was clearly demonstrated and shown to be persistent.

Ultimately, the team determined that HRC™ offers a simple and effective approach to the remediation of CAHs and, soon after, introduced the product to the commercial industry.

HRC™ Offers Viable Alternative

Not surprisingly, the product's success has sparked industry interest in applying HRC™ at dry-cleaning sites and other chlorinated solvent impacted facilities.

The new bioremediation tool offers municipalities and industry a viable alternative to groundwater cleanup; to meeting state and local regulations; and to providing safer water resources to the public.