Topic Area: 13a. Bioremediation of Munitions Constituents

Formatted Title:

Optimization of In Situ Anaerobic Bioremediation for Source Zone and Barrier Treatment of Perchlorate in Groundwater

Background/Objectives:

Area M at the Naval Weapons Industrial Reserve Plant (NWIRP) McGregor, Texas, is a former manufacturing facility where propellants were mixed to produce weapons and solid-fuel rocket propulsion systems. The plant was first opened in 1942 and ultimately closed in 1995. The closure and subsequent authorization by Congress to initiate property transfer led to site investigation activities to define the nature and extent of environmental impacts. The two most common contaminants released into the environment were volatile organic compounds (VOCs) and perchlorate. Of the two, perchlorate, an ion of ammonium perchlorate, has migrated the farthest down the Station Creek Basin in surface water and groundwater. A bioremediation pilot study was performed at Area M from July 2016 through August 2018 to evaluate the performance of bioborings to reduce concentrations of perchlorate in the groundwater within the shallow unconfined aquifer in the highly weathered limestone underlying the site. The biobiorings, initially constructed with mushroom compost, wood chips, and gravel, were not effective. However, subsequent injection of emulsified vegetable oil (EVO) into the bioborings was demonstrated to be an effective remedy. The objective of this work was to leverage the results of the pilot study and implement a full-scale in situ bioremediation injection program for the treatment of perchlorate in groundwater on the site.

Approach/Activities:

Predesign sampling using temporary groundwater monitoring wells was first completed to better define the limits of perchlorate concentrations that exceed the protective concentration level (PCL) at source zones identified at Area M. Baseline monitored natural attenuation (MNA) parameters and microbial population data were collected, including quantitative polymerase chain reaction (qPCR) for enzymes specific to perchlorate reduction (perchlorate reductase [pcrA]) and next generation sequencing to identify the presence of genera known to be microbial constituents in the bioremediation of perchlorate. Data from this predesign sampling were combined with the annual long-term monitoring (LTM) data, and this combined 2022 data set served as the basis of design for an in situ bioremediation injection program. An optimized injection approach was developed that will utilize injection wells at multiple depths to more effectively distribute substrate and treat perchlorate in groundwater.

Carolyn Scala

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Optimization of In Situ Anaerobic Bioremediation for Source Zone and Barrier Treatment of Perchlorate in Groundwater