Automated Low-Volume Chemical Oxidant System Operational at the Former Lowry Air Force Base

Lowry Assumption, LLC, United States Air Force – Denver, CO

Weaver’s Automated Low-Volume Chemical Oxidant Remediation System Operational at the former Lowry Air Force Base to address Recalcitrant Chlorinated Solvents

Weaver Consultants Group’s (WCG) Remediation Services team provides turn-key remedial services from strategy discussions through design, construction, and operation, maintenance, and monitoring (OMM) at the high-profile Former Lowry Air Force Base (AFB) – Operable Unit 5 (the Site). These services are focused on remediating groundwater impacted with recalcitrant Chlorinated Volatile Organic Compounds (CVOCs) within the alluvial and bedrock Water-Bearing Zones (WBZs). WCG specializes in the remediation of recalcitrant chlorinated hydrocarbons from characterization through design, construction, and implementation, which is at the core of our expertise. The primary goals for this project are source area treatment, mitigating potential recontamination of downgradient areas, and maintaining the established protection of human health, the environment, and the areas previously remediated. WCG worked in conjunction with numerous stakeholders, including the Colorado Department of Public Health and the Environment, United States (US) Air Force, US Environmental Protection Agency (EPA), Lowry Redevelopment Authority, City and County of Denver, and the City of Aurora to develop a Phase 2 Corrective Action Plan Addendum and associated US EPA Underground Injection Control (UIC) Program Amendment to remediate residual CVOCs in groundwater.

WCG designed the remedial strategy to address these recalcitrant areas with targeted in-situ chemical oxidation (ISCO) treatment of the former Building 1432/Outfall Source Area (Site), portions of the former main Trichloroethene (TCE) plume, and Carbon Tetrachloride (CT) source area that were experiencing rebounding concentrations of CVOCs following large scale direct-push point (DPP) ISCO and BOS-100® injections completed the early 2010s.

LVCOI

WCG developed and implemented a combined remedy strategy to control and clean up TCE impacted groundwater in low permeability soils at the Site. WCG designed, constructed, and operates a Low Volume Chemical Oxidant Injection (LVCOI) program, pioneered by one of WCG’s Professional Chemical Engineers, Scott Andrews. The LVCOI was designed and constructed in partnership with Weaver Companies’ Supervisory Control and Data Acquisition (SCADA) and pump control systems affiliated company Sligo Systems, LLC, providing top to bottom turn-key remediation services in-house. This capability and approach optimized strategy, design, communication, and scheduling, while also maximizing the clients’ financial resources to instead expend costs toward the goal of site cleanup.

The LVCOI system design enhances the distribution of oxidant daily, maintaining a highly oxidative state in the subsurface year-round. WCG combined the LVCOI technology with thermal in-situ remediation (TISR^SM) system in partnership with ARCADIS, designed to heat the groundwater and accelerate chemical oxidation reactions. The TISR^SM system supplies a heated glycol solution conveyed via subsurface piping to four TISR^SM Borehole Heat Exchange (BHE) well locations. Seven strategically located injection wells and four TISR^SM BHE wells were installed within the Site. Following well installation, WCG implemented a unique approach to Investigative Derived Waste (IDW) management, including the incorporation of treated purge water re-injection into the UIC Amendment, saving our client $10,000s in disposal and waste management costs.

The LVCOI system includes seven individual metering pumps with one pump dedicated to each injection well to optimize the volume, frequency, and concentration of the oxidant solution delivered to each respective location. The LVCOI system has a Programmable Logic Controller (PLC) and remote monitoring telemetry to enable injection of a volume of oxidant solution unique to each injection well several times per day. Further system optimization includes processing diluted water through a carbon filter and ion exchange unit to remove excess chlorine and dissolved solids before mixing with the concentrated sodium permanganate.

The LVCOI system design also incorporates secondary containment of the oxidant from the supply tank to the individual injection wells. A leak detection system is designed within the container, pump housing, and at the top of each injection well to shut down the injection system in the event of a leak in the oxidant delivery system or rising groundwater elevation. The PLC incorporates wireless telemetry, including security cameras, to monitor and control the system remotely. Safety signage is outside the enclosure, and temporary privacy fencing was erected to protect the unit from pedestrian traffic in the park. The LVCOI system is designed to operate 24-hours per day, 7-days per week, injecting target volumes of approximately 1-gallon per well per day of a 1-10% sodium permanganate. The system is designed to require minimal interaction when operating properly. Controls are automated; however, operator response is required when an alarm condition occurs.

Through WCG’s experience and continued optimization of the designed systems, an innovative approach to the initial loading of the targeted WBZs was initiated via the injection of dilute hydrogen peroxide into the injection wells to address residual chlorinated ethane constituents. Following the hydrogen peroxide injections, low-pressure injections of sodium permanganate were completed to provide the initial treatment of residual chlorinated ethene constituents and initial oxidant loading of the WBZs into the targeted subsurface areas during the construction of the LVCOI system.

WCG employed a unique approach to the challenging location of the Site now located within a Denver city park, through complex coordination and permitting with Denver Parks and Recreation for mobilization of equipment, materials, and subcontractors required to provide a power supply and support subgrade infrastructure construction activities. A cost analysis modifying the electrical supply installation and associated restoration footprint from trenching to directional boring provided further efficiency of our client’s financial resources. WCG constructed a complex subgrade conveyance system and manway vaults from the LVCOI to the injection wells, consisting of permanganate discharge piping, leak detection, and high-level alarm systems, and TISR^SM system distribution manifold and supply/return piping. The LVCOI system is powered by standard electrical power to provide heat to support operation during the winter months.

WCG successfully designed, constructed, and initiated the operation of the LVCOI under challenging timelines during the global COVID-19 pandemic, with limited issues sourcing materials and equipment.  The LVCOI was designed in April 2020 and began operation in November 2020. Initial performance monitoring of the Site has demonstrated the successful distribution of the oxidant throughout the subsurface and reductions in CVOC concentrations.

Supplemental DPP Treatment

Supplemental remediation was also completed to address residual concentrations of dissolved phase TCE and CT within the alluvial and bedrock WBZs across the former main TCE plume and CT source areas that have not yet achieved the applicable site-specific groundwater standards. To expedite the client’s site cleanup goal, an ISCO injection and BOS-100® trap and treat remediation program was designed to target seven treatment areas and influence areas surrounding CVOC impacted groundwater wells and target impacted WBZs in both the alluvium and bedrock. The program included field management of the oxidant and introduction of dilute solutions of sodium permanganate (5-10%) into strategically located direct-push injection points within the CVOC impacted groundwater. The BOS-100® injection program was designed, in consultation with Remediation Projects, Inc. (RPI), to influence recalcitrant areas within the CT source area via strategically located DPP injections.

During the technical review of data collected by others, it was apparent to the WCG that declining concentrations of CVOCs in certain wells during compliance monitoring was attributed to well functionality. WCG’s unique approach indicated that the recent groundwater data was not representative of the true water-bearing formation through the silting of select well screens. This thorough technical review of historical data and trends allowed WCG to rehabilitate the wells, re-collect representative groundwater samples, address the issue before regulatory agencies, and ultimately require the redemonstration and extension of the monitoring program duration to confirm compliance achievement.

WCG designed the supplemental treatment program and successfully advanced forty-six ISCO/BOS-100® DPPs within the alluvial and bedrock WBZs to target depths across the former Lowry AFB footprint under challenging timelines during the global COVID-19 pandemic intermittently over approximately two months. To efficiently allocate and optimize our client’s resources associated with the compliance groundwater monitoring program, WCG proposed and implemented a modification to the monitoring program via “no-purge” techniques while demonstrating the agreeability and correlation of the previous and modified sampling methodology to the regulatory oversight agencies.

WCG designed and costed the supplemental DPP treatment program in July/August 2020 and implemented the ISCO program in late September 2020. The BOS-100® program was postponed and implemented in November 2020 at the request of the client. Subsequent performance monitoring of the seven target areas has demonstrated the successfully targeted distribution of the sodium permanganate within the targeted WBZs and associated reductions of CVOC concentrations. WCG successfully completed the supplemental DPP treatment program before schedule and under budget while continuing to provide our client with the foremost technical expertise and OMM services for the performance of the ISCO and BOS-100® programs to achieve their ultimate goal of Site cleanup and the protection of human health and the environment.