Topic Area: 3a. Bioremediation in Complex Geological Settings

Formatted Title:

Evaluation of Injection Hydraulics and Remedial System Effectiveness for EVO Injections Adjacent to a Railroad Right of Way

Background/Objectives:

The site is at an active grain mill in the coastal plain of North Carolina that operated from the 1960s through the present. Chlorinated ethenes and ethanes originating from two source areas at the mill have contaminated two separate aquifer zones (Surficial and Black Creek Aquifers) beneath the site, and have impacted surface water in several perennial ditches downgradient of the facility. The mill’s operations prevented access to some of the source zones. Also, a railroad spur right-of-way (ROW) prevented access to areas upgradient of the surface water ditches (i.e., areas that would have been optimal for the placement of injection wells). Terracon designed a multi-phased enhanced reductive dechlorination (ERD) remedy that used emulsified vegetable oil (EVO) injections to address the chlorinated volatile organic compound (CVOC) in portions of the Surficial Aquifer, combined with monitored natural attenuation (MNA) to address the CVOCs within the railroad ROW, surface water ditches, and the Black Creek Aquifer. This presentation will describe the process used to design the EVO injection strategy for the Surficial Aquifer, and will evaluate and discuss the effectiveness of a combined EVO/MNA remedial strategy for the Surficial and Black Creek Aquifers, and surface water in the ditches.

Approach/Activities:

In 2017, Terracon performed a laboratory-scale treatability study to assess the efficacy, loading rates, and buffer requirements for an initial ERD remedial strategy for the site. In May 2018, Terracon injected 4,800 gallons of EVO-based injectant into 12 temporary monitoring wells as an ERD pilot test. The injectate included EVO, a fermentation product, magnesium hydroxide, and the KB-1 Plus^® microbial consortium. The injections were performed initially through Geoprobe^® rods at low pressures, which required very low injection rates to avoid excessive mounding. In October 2019, Terracon performed a single-well injectability pilot test to determine allowable injection pressures and flow rates, and injection radius of influence (ROI) for a permanent injection-well network. In situ pressure transducers were installed in the injection well and adjacent monitor wells to assess groundwater mounding during the pilot study. We evaluated and compared the observed water‑level rise in the injection well and associated monitor wells with the theoretical water-level rise. We also utilized potassium bromide as a conservative tracer to understand the migratory ROI based on spatial and temporal changes in bromide concentration during the single-well injection test. Bromide data from post-injection monitoring events were used to evaluate mobile porosity of the surficial aquifer.

Alexander Manolukas

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(Group 2, Poster Board #65) Evaluation of Injection Hydraulics and Remedial System Effectiveness for EVO Injections Adjacent to a Railroad Right of Way