Bioremediation in Fractured Rock: 1. Modeling to Inform Design, Monitoring, and Expectations

Abstract

Field characterization of a trichloroethene (TCE) source area in fractured mudstones produced a detailed understanding of the geology, contaminant distribution in fractures and the rock matrix, and hydraulic and transport properties. Groundwater flow and chemical transport modeling that synthesized the field characterization information proved critical for designing bioremediation of the source area. The planned bioremediation involved injecting emulsified vegetable oil and bacteria to enhance the naturally occurring biodegradation of TCE. The flow and transport modeling showed that injection will spread amendments widely over a zone of lower-permeability fractures, with long residence times expected because of small velocities after injection and sorption of emulsified vegetable oil onto solids. Amendments transported out of this zone will be diluted by groundwater flux from other areas, limiting bioremediation effectiveness downgradient. At nearby pumping wells, further dilution is expected to make bioremediation effects undetectable in the pumped water. The results emphasize that in fracture-dominated flow regimes, the extent of injected amendments cannot be conceptualized using simple homogeneous models of groundwater flow commonly adopted to design injections in unconsolidated porous media (e.g., radial diverging or dipole flow regimes). Instead, it is important to synthesize site characterization information using a groundwater flow model that includes discrete features representing high- and low-permeability fractures. This type of model accounts for the highly heterogeneous hydraulic conductivity and groundwater fluxes in fractured-rock aquifers, and facilitates designing injection strategies that target specific volumes of the aquifer and maximize the distribution of amendments over these volumes.

Bioremediation in Fractured Rock: 2. Mobilization of Chloroethene Compounds from the Rock Matrix

“…characterization can be synthesized using a groundwater flow model, groundwater fluxes can be used to design the injection and distribution of remediation amendments, and identify monitoring locations and expectations at monitoring wells (Tiedeman et al 2017b). characterization can be synthesized using a groundwater flow model, groundwater fluxes can be used to design the injection and distribution of remediation amendments, and identify monitoring locations and expectations at monitoring wells (Tiedeman et al 2017b).…”

“…characterization can be synthesized using a groundwater flow model, groundwater fluxes can be used to design the injection and distribution of remediation amendments, and identify monitoring locations and expectations at monitoring wells (Tiedeman et al 2017b). Site characterization and groundwater flow and chemical transport modeling discussed in the companion article (Tiedeman et al 2017b) are used to formulate the CE mass balance in the rock volume targeted in the bioremediation experiment. The purpose of this investigation is to demonstrate that results of a detailed groundwater flow model in a fractured sedimentary rock aquifer can quantify CE fluxes and provide estimates of the CE mass depleted from the rock matrix following amendment injections associated with biostimulation and bioaugmentation (collectively referred to as a bioremediation experiment).…”

“…Furthermore, quantifying groundwater fluxes permits the calculation of chemical fluxes under pre-and postremediation conditions to evaluate the contaminant mass mobilized by remediation treatments. The detailed characterization of the groundwater flow regime is intended to provide reasonable constraints on the distribution of Lacombe (2000), Lacombe and Burton (2010), and Tiedeman et al (2017b) describe the hydrogeology and the source zones of TCE contamination in the Lockatong mudstone underlying the NAWC. The investigation is conducted in the Lockatong mudstone underlying the former Naval Air Warfare Center (NAWC), West Trenton, NJ (Figure 1), which is a site of groundwater contamination with TCE (Lacombe 2000).…”

“…The purpose of this investigation is to demonstrate that results of a detailed groundwater flow model in a fractured sedimentary rock aquifer can quantify CE fluxes and provide estimates of the CE mass depleted from the rock matrix following amendment injections associated with biostimulation and bioaugmentation (collectively referred to as a bioremediation experiment). TCE, as a NAPL, was detected in the West Area source zone ( Figure 1C) and aqueous phase concentrations of TCE in fractures also suggest the presence of TCE as a NAPL at other locations in the West Area Tiedeman et al 2017b). Site characterization and groundwater flow and chemical transport modeling discussed in the companion article (Tiedeman et al 2017b) are used to formulate the CE mass balance in the rock volume targeted in the bioremediation experiment.…”

“…The investigation is conducted in the Lockatong mudstone underlying the former Naval Air Warfare Center (NAWC), West Trenton, NJ (Figure 1), which is a site of groundwater contamination with TCE (Lacombe 2000). Goode et al (2014) and Tiedeman et al (2017b) used geologic, geophysical, hydraulic, and biogeochemical information to identify groundwater flow paths through permeable fractures and the distribution of CE in the mobile groundwater in fractures and the immobile groundwater in the rock matrix. Investigations of rock core at the site indicate the majority of the CE mass is resident in the rock matrix .…”