The horizontal reactive media treatment well (HRX Well^®) for passive in situ remediation: Design, implementation, and sustainability considerations

Abstract

A new in situ remediation concept termed a Horizontal Reactive Media Treatment Well (HRX Well®) is presented that utilizes a horizontal well filled with reactive media to passively treat contaminated groundwater in situ. The approach involves the use of a large‐diameter directionally drilled horizontal well filled with solid reactive media installed parallel to the direction of groundwater flow. The engineered contrast in hydraulic conductivity between the high in‐well reactive media and the ambient aquifer hydraulic conductivity results in the passive capture, treatment, and discharge back to the aquifer of proportionally large volumes of groundwater. Capture and treatment widths of up to tens of feet can be achieved for many aquifer settings, and reductions in downgradient concentrations and contaminant mass flux are nearly immediate. Many different types of solid‐phase reactive treatment media are already available (zero valent iron, granular activated carbon, biodegradable particulate organic matter, slow‐release oxidants, ion exchange resins, zeolite, apatite, etc.). Therefore, this concept could be used to address a wide range of contaminants. Laboratory and pilot‐scale test results and numerical flow and transport model simulations are presented that validate the concept. The HRX Well can access contaminants not accessible by conventional vertical drilling and requires no aboveground treatment or footprint and requires limited ongoing maintenance. A focused feasibility evaluation and alternatives analysis highlights the potential cost and sustainability advantages of the HRX Well compared to groundwater extraction and treatment systems or funnel and gate permeable reactive barrier technologies for long‐term plume treatment. This paper also presents considerations for design and implementation for a planned upcoming field installation.

Groundwater Remediation in Low‐Permeability Settings: The Evolving Spectrum of Proven and Potential

“…The Horizontal Reactive Media Treatment Well (HRX Well; Divine et al ; Divine et al , ) is a new passive flux‐control technology that utilizes large‐diameter horizontal wells filled with solid‐phase reactive media to treat contaminated groundwater in‐situ. The HRX Well is installed parallel to the direction of groundwater flow and the design leverages natural “flow‐focusing” behavior induced by the engineered contrast in hydraulic conductivity between the high in‐well reactive media and the ambient aquifer hydraulic conductivity to passively capture and treat proportionally large volumes of groundwater within the well.…”

“…The HRX Well concept has been evaluated with numerical models and physical sand tank experiments (e.g., Divine et al , ), and the first field‐scale installation of this technology was completed in August 2018 at Vandenberg Air Force Base (VAFB) in Central California. This site was selected to control contaminant flux in a thin (7‐ to 12 ft‐thick) low‐permeability aquifer impacted by trichloroethene (TCE) at concentrations up to about 50 mg per liter (mg/L).…”

“…The HRX Well consists of 85 ft of inlet screen and 70 ft of outlet screen separated by 165 ft of casing, with treatment media cartridges (35% ZVI) are installed in 70 ft of the cased section. Divine et al () present design details for this application, and the simulated capture zone for a HRX Well is greater than 50 ft (Figure , left). For this site, the HRX Well concept compared favorably in sustainability considerations relative to pump and treat (P&T) and PRB approaches: because the system operates passively in situ, the recurring and cumulative energy requirements, carbon footprint, life‐cycle water consumption, recurring material use, and waste generation are low.…”

Grain Size Analysis and Permeametry for Estimating Hydraulic Conductivity in Engineered Porous Media

“…A recent example of a technology requiring engineered porous media is the Horizontal Reactive Media Treatment Well (HRX® Well). The HRX Well is a passive groundwater remediation technology that utilizes a horizontal well containing a highly permeable, reactive treatment medium (Divine et al ; Divine et al ). Establishing and maintaining a large contrast (factor of 100 or more) in K between the media within the well and the aquifer is required to achieve the design objective of maximizing the capture zone in the aquifer.…”

Theoretical evaluation of chemical and physical feasibility of an in situ ultrasonic reactor for remediation of groundwater contaminated with per‐ and polyfluoroalkyl substances

“…Operating energy can be avoided because water capture is passive, unlike in ex situ systems requiring continuous pumping. Water capture and potential for groundwater remediation applications were further described for the HRX Well ® concept by Divine, Roth, et al (2018) and Divine, Wright, et al (2018).…”