Horizontal Bioremediation at a Military Base

By Tomas Will, Sr. Environmental Scientist

When faced with replacing a horizontal bioremediation system at a military base, a consultant was tasked with selecting the best alternative to replace the aging system. The existing system, which had been operating for over 23 years, consisted of a horizontal extraction well connected to a bioreactor. Therefore, the consultant needed to assess the best replacement option and design a replacement that could continue long-term operation.

 

Background and Setting

The existing horizontal remediation well system was used to treat a chlorinated solvent groundwater plume located beneath a hangar building and a portion of an aircraft runway. Lithology at the site consisted of sandy clay underlain by mudstone and an impermeable shale layer. The contaminant plume was documented to be at an average depth of 23 feet below the ground surface. It was primarily located within a layer of fractured shale located directly above the impermeable layer of shale. The system was designed for low-flow extraction of groundwater that was piped to a nearby bioreactor. The existing horizontal remediation well was installed with a blind installation (single entry) using HDPE pipe and continues to operate effectively after 23 years.

 

Problem

The base intended to build a new hanger building, and its proposed footprint meant that the existing horizontal extraction well would have to be decommissioned, and a new remediation well or wells would need to be installed at a nearby location. However, nearby location choices were limited due to the new building construction and the proximity to the airfield. Therefore, in addition to a relocation, the new remediation infrastructure had to meet multiple challenging requirements: it would need to be designed to exceed the performance of the previous system, minimize installation costs, be capable of long-term operation, avoid impacting operations at the military facility, and minimize the downtime between decommissioning the existing well and connecting the new well(s) to the bioreactor.

 

Solution

After evaluating the possible options, the consultant determined that the most effective approach to achieving their criteria for success on the project was to continue to use horizontal wells. Directional Technologies was selected for the project due to their expertise with horizontal well installations in bedrock and DTI’s input on the horizontal well design from their in-house engineer.

Directional Technologies’ team pointed out that replacing the existing horizontal well – which had been installed using mid-1990s techniques, materials, and technology – with a more modern substitute highlighted many of the advantages that horizontal wells have gained in the past few decades.

With advancements in the field, modern horizontal wells:

• Can be installed in shorter periods of time and more cost-effectively.
• Can be installed more accurately, allowing for more precise installations that target hot zones.
• Can mitigate the risk of fouling with site-specific drilling mud programs and advanced well development techniques.
• Can be designed for use with a wider variety of well materials in both entry-exit and blind installations.
• Can be custom-designed using Directional Technologies’ site-specific screen engineering process to significantly improve the zone of influence and increase performance.
• Can be installed to lengths greater than 1,000 feet, allowing significantly more screen to be placed within the target zones and reducing the need for additional wells.

 

Well Design

Preliminary designs for the replacement well consisted of an entry-exit installation that would have required temporarily shutting down the airfield runway. With input from Directional Technologies, the design was revised to a blind installation (single entry) that would avoid the need to interrupt airfield activities. The final well design included approximately 350 feet of the screen and 100 feet of riser. Steel pipe would be used to ensure the longevity of the new installation. The entry point for the design of the new horizontal well would need to be offset from the plume due to limited available space but would be curved to follow the geometry of the plume so that the screen segment would directly target the areas of highest concentration along the center of the plume. The lithology in the final 50 feet of the well screen interval transitioned from a fractured shale to an alluvium. Therefore, the final portion of the screen interval would need to be angled upwards towards the surface to promote water collection and more efficient extraction from the less transmissive layer. Due to these factors, accurate tracking and positioning of the bore path for the well was critical.

 

Results

Directional Technologies used modern drilling equipment and techniques to address the subsurface conditions and accurately install the well to the consultant’s specifications. Facility operations were able to continue uninterrupted during the directional drilling process, and the horizontal wellhead was installed out of the way of the operating areas to prevent any future limitations to the nearby operations. With the new horizontal well hooked up the bioreactor, the project was on a trajectory to achieve the project’s remediation goals.

 

Conclusions

The consultant was able to leverage the modern advances in the field of horizontal wells to provide their client with a bioremediation solution that will be able to overcome the various challenges posed by their site.

 

How can the advantages offered by decades of technological advancement in the field of horizontal wells benefit your project? Call our horizontal remediation well experts at 1-877-788-4479 to discuss your current project needs, or email us at drilling@directionaltech.com with questions, review case studies, and to learn more.