Reactive Gas Process for In Situ Treatment of 1,2,3-Trichloropropane in Vadose Zone Soils

Dr. Paul Hatzinger | APTIM Federal Services

ER-201632

Objective

This project is a joint effort between the Biotechnology Development & Applications Group at CB&I Federal Services LLC (CB&I) and the U.S. Army Corps of Engineers (USACE) Directorate of Environmental and Munitions CX and Engineer Research and Development Center (ERDC). The objective is to demonstrate a novel reactive gas process for remediation of vadose zone source areas containing 1,2,3-trichloropropane (TCP). TCP is an emerging contaminant that is present at Department of Defense (DoD) sites primarily through its application as a solvent for cleaning and maintenance, paint and varnish removal, and degreasing. However, its sources also include chemical manufacturing processes (particularly polysulfone liquid polymers, dichloropropene, hexafluoropropylene, and polysulfides) and production and/or application of pesticides and soil fumigants. TCP is a suspected human carcinogen and emerging DoD contaminant that is generally not amenable to conventional vadose zone treatment processes. The reactive gas process is also expected to be effective for other compounds that are susceptible to alkaline hydrolysis, such as common munitions constituents (e.g., RDX) and some insensitive munitions components (e.g., DNAN).

ER-201632 Photo

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Technology Description

The reactive gas process being demonstrated entails injection of a blend of air and gaseous ammonia (NH3) in order to raise the pH of soil and to promote destruction of contaminants via alkaline hydrolysis. When NH3 is added to soil, it combines with water to produce ammonium ion (NH4+) and hydroxide ion (OH-), subsequently increasing soil pH. Many different contaminants are subject to alkaline hydrolysis, including chlorinated propanes and various explosives. The process may also stimulate cometabolic biodegradation reactions mediated by the enzyme ammonia monooxygenase (AMO) as a secondary effect as pH declines or at the edge of the reactive zone. Thus, this approach will have utility for treatment of any contaminant subject to alkaline hydrolysis, and may also promote cometabolic treatment as a secondary polishing step.

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Benefits

There are currently few reliable options for treating TCP in groundwater, and even fewer options for vadose zone treatment. This demonstration will validate a novel reactive gas approach for vadose zone treatment that will have application for TCP and other compounds that are susceptible to alkaline hydrolysis, including the explosives TNT, RDX, HMX, CL-20, and DNAN. TCP has been detected across at least 45 DoD sites and more than 1,400 wells where testing has been conducted, resulting in a 17% detection rate. At least 27 bases had detections in soil boreholes, amounting to more than 850 detections (7% detection rate). It is likely that there are more DoD sites where TCP is present, but where testing has yet to be conducted.

This project will provide DoD with a new approach to remediate vadose areas with TCP as well as other contaminants susceptible to alkaline hydrolysis. At some sites, this could result in avoidance of the long-term costs required to implement groundwater remediation. Moreover, successful implementation of the process at a training range site could prevent range closure due to contaminants leaching to groundwater. The field demonstration will provide a basis for design of reactive gas treatment systems for other sites. Criteria established during the field demonstration (e.g., percentage ammonia in reactive gas, injection point spacing, treatment zone monitoring protocol) will be published and widely distributed. (Anticipated Project Completion - 2020)

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Points of Contact

Principal Investigator

Dr. Paul Hatzinger

APTIM Federal Services

Program Manager

Environmental Restoration

SERDP and ESTCP

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