U.S. EPA Contaminated Site Cleanup Information (CLU-IN)

U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

Horizontal Remediation Wells


Technical Guidance

The 2017 How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites: A Guide for Corrective Action Plan Reviewers, published by EPA's Office of Underground Storage Tanks, includes an appendix (Appendix A) that summarizes the use of horizontal wells for remediating underground storage tank (UST) sites. The appendix summarizes the equipment and procedures used to drill, install, and develop horizontal wells. It also describes advantages and limitations of HRWs and their use in conjunction with various remediation technologies. In addition, EPA's 1997 Design Guidelines for Conventional Pump-and-Treat SystemsAdobe PDF Logo includes a section on horizontal and slant wells.

Most states and municipalities have requirements for the licensing of drillers and permitting for the installation and decommissioning of wells that would apply to horizontal wells. Additional specifications for drilling and installing conventional vertical wells for monitoring or remediation might apply. The California Department of Transportation document, CALTRANS Encroachment Permits: Guidelines and Specifications for Trenchless Technology ProjectsAdobe PDF Logo, contains a five-page section on HDD requirements for the installation of utilities. Other states and municipalities generally have guidelines for directional drilling focused on traffic control, noise control, and managing drilling fluids. Environmental practitioners are advised to contact state and local agencies prior to starting HDD projects.

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General Resources

Adobe PDF LogoHorizontal Directional Drilling and Horizontal Wells to Enhance Remediation at Complex Sites
Carlton, K.J. NAVFAC Remediation Innovative Technology Seminar, 100 slides, 2023

The Navy installed horizontal wells at several ER and BRAC sites to remediate petroleum hydrocarbons, chlorinated solvents, metals, and other COCs in conjunction with various treatment technologies, such as ISCO, SVE, and MPE, to mitigate vapor intrusion beneath buildings. The presentation provides an overview of best practices for installing and operating horizontal wells, highlights recent advances in design and emplacement methods, and provides case studies employing horizontal wells highlighting success stories and lessons learned.

Adobe PDF LogoHorizontal Directional Drilling and Well Installation for Substrate Injection
Ombalski, D. | FRC 2021: The 26th Florida Remediation Conference, 17-19 November Orlando, Florida, abstract, 2021

This presentation details proper horizontal directional drilling and well installation techniques along with a screen design case study.

New Perspectives on Horizontal Wells for Assessment and Remediation
Wiley, W.F. ǀ Colorado Environmental Management Society Webinar, virtual, 10 August, 73 minutes, 2021

This presentation details of horizontal well technology, including the key benefits, such as better performance than vertical wells and the ability to access otherwise inaccessible areas, and perspectives that can change when the entire plume can be properly addressed. Case studies are included that demonstrate key benefits and illustrate the ability to tackle plumes more efficiently and effectively.

Adobe PDF LogoApplication of Horizontal Wells to Enhance Site Remediation
NAVFAC Technical Report TR-NAVFAC-EXWC-EV-2103, 37 pp, 2020

Horizontal wells have become a cost-effective and practical tool to facilitate the remediation of contamination at challenging sites where vertical wells alone may not be able to achieve project objectives. This report provides Navy case studies where it was optimal to install horizontal wells and reviews recent advances in design and emplacement technologies for horizontal wells.

Adobe PDF LogoTreatment Well (HRX Well®) For Managing Contaminant Plumes In Complex Geological Environments
Divine, C. ESTCP ER-201631, software, 2021

The HRX Well design tool was developed to provide preliminary site design estimates to practitioners considering implementing the HRX Well. Many HRX Well configurations are possible, but the applicability of any design is subject to site-specific factors. The tool allows the user to optimize the design based on user-provided values using equations. Supplemental literature values can also be used as inputs to support high-level estimations. The tool predicts well length, capture width, and the number of wells required to meet target treatment goals. In addition, the associated costs and sustainability implications are calculated, which can further inform design selection. For many sites, a site-specific numerical flow and transport model may be useful for final design and predict and assess HRX Well performance. Additional information: HRX Well® Design Tool Microsoft Excel

Adobe PDF LogoNew Perspectives on Horizontal to Vertical Well Ratios for Site Cleanup
Laton, W.R.
Remedation 30:27-31(2019).

Paper describes use of a predicted ZOI using a mathematical and hydrogeological approach to evaluate the cost-benefit of a horizontal versus vertical well system.

Adobe PDF LogoReconsidering Horizontal to Vertical Well Ratios for Site Clean-up
Laton, W.R.
The 29th Annual International Conference on Soil, Water, Energy, and Air, San Diego, CA, March 18-21, 2019 March, 23 slides.

Directional drilling has been used for a variety of purposes; utilities, dewatering, and remedial activities. Cutting costs for remedial activities is always of consideration. The costs to clean-up a site via traditional vertical extraction wells, versus the use of a horizontal well system, need to be reconsidered based upon today's remedial challenges. Traditionally, it has been stated that a single horizontal well is worth 4-11 vertical wells. This seems arbitrary, in that both depth of the system and hydrogeological conditions play a large role that is not considered. A better way to evaluate the cost benefit of one system over another is to base it on the number of vertical wells per linear foot of directional well, and base it more on zone of influence of both designs.

Adobe PDF LogoCALTRANS Encroachment Permits: Guidelines and Specifications for Trenchless Technology Projects
California Department of Transportation, 2018.

Pages 13-18 of this document deals with horizontal directional drilling and covers soil investigations, pre-construction and site evaluation, installation requirements, drilling fluids management, drilling and back reaming, site restoration, and other requirements.

New Perspectives in the Use of Horizontal Wells for Assessment and Remediation
Koenigsberg, S.S., E. R. Piatt, and L.I. Robinson
Remediation 28(4):45-50(2018) [Abstract].

Decreasing costs and a strategic shift, which can be characterized as "greater flexibility," are two factors that have brought about a resurgence of horizontal well systems. Article explains how movement from monolithic single well systems to segmented well systems is a next-generation advancement in site assessment and remediation.

Adobe PDF LogoHow to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites: A Guide for Corrective Action Plan Reviewers
USEPA (EPA 510-B-17-003), October 2017.

Appendix A summarizes the equipment and procedures used to drill, install, and develop horizontal wells for remediating UST sites. It also describes the potential to incorporate HRWs into site remedies such as air sparging and soil vapor extraction, hot air or steam injection, bioremediation, chemical injection, and LNAPL removal, as well as plume containment, injection of treated water, and sampling.

Improved Slant Drilling Well for In situ Remediation of Groundwater and Soil at Contaminated Sites
Furukawa, Y., Mukai, K., Ohmura, K., and T. Kobayashi.
Environmental Science and Pollution Research 24(7): 6504-6511(2017) [Abstract]

The slant well is a potentially useful technique in settings, such as working factories, but its use is technically challenging because of the need for high drilling accuracy and the difficulty in sealing the slanted bores. Study investigated a technique for slant drilling using water-swelling materials as sealants to install wells for treating contaminated soil and groundwater. Tracer tests were also conducted to investigate the accuracy of drilling.

Tips for Calculating Setback in Horizontal Drilling
Bardley, D.S.
National Driller Magazine, October 2015.

Magazine column summarizes the numerous factors involved in calculating the setback distance needed to install a horizontal well.

Adobe PDF LogoEnhancing the Hydraulic Conductivity of Horizontal Remediation Wells
Lubrecht, M.
21st Annual International Petroleum Environmental Conference, Houston, Texas. 20 slides, October 13-16, 2014.

Slide presentation outlines how well design, drilling method, well construction, and development can be performed to enhance recovery of groundwater from horizontal remediation wells.

Horizontal Wells Target the Source: Adobe PDF LogoHorizontal Environmental Well: Drilling Fluids – Is Bentonite a Four Letter Word?
Lubrecht, M.
21st Annual International Petroleum Environmental Conference, Houston, Texas. 18 slides, October 13-16, 2014.

Slide presentation describes two common drilling fluids for horizontal wells bentonite-based and bio-polymer and outlines the factors that affect selection of these drilling fluids at contaminated sites.

Adobe PDF LogoIn-Situ Testing, Operation and Troubleshooting of Horizontal Remediation Wells
Sequino, M. and K. Martin.
21st Annual International Petroleum Environmental Conference, Houston, Texas. 18 slides, October 13-16, 2014.

Slide presentation summarizes testing (e.g., remedial feasibility testing, vertical well testing, in situ as-built testing, and follow-up testing), troubleshooting techniques, and well development procedures to ensure horizontal remediation wells meet intended goals.

Adobe PDF LogoHorizontal Environmental Drilling 101: An Introduction to the Means and Methods for Horizontal Environmental Well Installation
Bardsley, D.
2014 Arizona Institute of Professional Geologists and Arizona Hydrological Society National Conference, Prescott, Arizona, 23 slides, September 2014.

Slide presentation outlines the techniques and materials used to drill and install horizontal wells for environmental applications. Advantages, disadvantages, and installation challenges of the technology also are discussed.

Directional Drilled Horizontal Wells and Engineered Horizontal Remediation Wells Screens Accelerate Site Closure
Van Heest, G. and M. Sequino.
29th Annual International Conference on Soils, Sediments, Water, and Energy, University of Massachusetts at Amherst. October 21-14, 2013.

Paper discusses the use of HRWs (four air sparging and three SVE wells) to treat a large gasoline release at an airport. Suggests the importance of the larger zone of influence of HRWs over vertical wells.

Horizontal Directional Drilling
NiSource Multi-Species Habitat Conservation Plan, Appendix J, 42 pp, June 2013.

Appendix J summarizes how horizontal wells are drilled and installed for habitat conservation projects for the NiSource utility company. It includes a 1994/95 paper by C.W. Hair, "Site Investigation Requirements for Large Diameter HDD Projects." This paper was prepared for New Advances in Trenchless Technology: An Advanced Technical Seminar, held February 5-8 in St. Joseph, Missouri.

Horizontal Directional Drilling: A Green and Sustainable Technology for Site Remediation
Lubrecht, M.D.
Environmental Science & Technology 46:2484-2489 (2012)

Article highlights the potential for horizontal wells to improve sustainability of site remediation by maximizing the net benefit of human activities by reducing energy consumption, preventing or mitigating environmental damage, and addressing local economic and social factors.

Adobe PDF LogoHorizontal Wells for Groundwater Remediation: How A Technology That Revolutionized the Oil Industry is Used to Remediate Groundwater
Van Heest, Gary.
EM Magazine, 23 pp, June 2013.

Paper explains the process of drilling and installing HRWs, their advantages, and how they've been adapted for site remediation.

Adobe PDF LogoResearch and Development for Horizontal/Angle Well Technology
Williams, D.E.
U.S. Department of the Interior, Bureau of Reclamation, Desalination and Water Purification. Research and Development Program Report No. 151, 72 pp, 2008.

Report reviews angle wells, horizontal directionally drilled wells, and other extraction technologies to determine their suitability for seawater desalination facility construction. It reviews their capabilities, challenges, and potential improvements; assesses key design and construction needs; identifies key areas for specialized testing and development; and identifies next steps for technology development.

Construction of Horizontal Wells in Municipal Solid Waste Using A Directional Drill
Ho, Pei-Yi Joy, Master's thesis, University of Waterloo, ON, Canada. 118 pp, 2007.

Employing HDD techniques in landfill applications provide several challenges, including unknown waste material density, unknown waste material hardness, and unknown drilling operation and waste material interaction. Conventional HDD studies cannot be directly applied as the drilling medium parameters are virtually unknown. This research incorporated a trial site to gather field data. The trial site is located at the Region of Waterloo Landfill site located on Erb Street in Waterloo, Ontario. The installations took place at the Original Landfill Area, which is currently inactive and capped. The vertical wells, originally installed to control the leachate, have degraded, resulting in inefficient operation of the landfill gas collection system. The field installation of two horizontal wells (in opposing directions) was put in practice not to replace the vertical wells, but to assist in capturing and collecting leachate. The installations were monitored, and key parameters were recorded.

Adobe PDF LogoHorizontal Environmental Well Design and Installation
Directed Technologies Drilling.
Horizontal Environmental Well Handbook, 35 pp, December 2004.

Handbook chapter provides a history of horizontal drilling and descriptions of drilling equipment and approaches, locating techniques and equipment, drilling materials, remediation technologies that use horizontal wells, well development procedures, and health and safety concerns.

Horizontal Environmental Wells: Part 1Adobe PDF Logo, Part 2Adobe PDF Logo, and Part 3Adobe PDF Logo
National Driller Magazine, June, July, and August 2002.

In 2002, National Driller Magazine published a 3-part series that analyzed information contained in a catalog of horizontal environmental wells. The catalog, initiated with a survey in 1993 and subsequently updated, identified 1,142 horizontal environmental wells that were installed in the United States through the end of 2000. While not a complete listing, the catalog provided a record of how the industry had evolved since the late 1980s. Part 1 identifies summary points based on the data, a history of horizontal well use, and descriptions of environmental applications; Part 2 describes well design and drilling; and Part 3 describes well materials, drilling fluids, and well development, and contains an analysis of wells installed to date, including their locations, depths, remediation applications, well materials, and geology.

Remediation of Contaminated Sites Using Horizontal Directional Drilling
Ariaratnam, S.T. and E.N. Allouche.
Construction Congress VI: Building Together for a Better Tomorrow in an Increasingly Complex World, ISBN: 9780784404751, pp 435-444, 2000.

In recent years, a growing number of consultants and owners have considered the use of horizontal remediation wells as an alternative solution to the removal and containment of contaminants. Currently, engineers rely on complex systems of vertical wells or barrier wall systems which inject and/or extract subsurface water or vapor for on-site soil and ground water remediation. However, in sites containing fine-grained soil or widespread contamination, numerous vertical wells are required to adequately treat the plume. Horizontal directional drilling makes it possible to install a single horizontal well to contact a much larger contaminated area. Because fewer wells are required, the cost of extraction and treatment over the life of the project may be substantially reduced, In addition, horizontal wells can be installed beneath buildings or environmentally sensitive areas, to reach contaminants inaccessible by other methods. Construction of such wells may be achieved using horizontal directional drilling, a remotely guided drilling technique that makes it possible to drill horizontal boreholes over long distances along straight or curved profiles and alignments. An overview of horizontal environmental well technology including discussion of the advantages and limitations of this technology is presented. Greater utilization of horizontal wells depends on the availability of design and construction guidelines. Parameters and design principles that should be considered in such installations are presented.

Adobe PDF LogoHorizontal Wells
Miller, R.R.
Ground-Water Remediation Technologies Analysis Center, TO-96-02, 17 pp, October 1996.

Technology summary report provides a brief overview of an environmental remediation technology, including an introduction to its general principles, reported applicability and utilization, and cited advantages/disadvantages.

Adobe PDF LogoInnovative Technology Summary Report: Horizontal Wells
U.S. Department of Energy, DOE/EM-0378, 28 pp, 1998.

Report summarizes demonstration projects conducted at several DOE sites. It describes how horizontal wells are installed, their performance, and technology applicability and alternatives.

Adobe PDF LogoDesign Guidelines for Conventional Pump-and-Treat Systems
Robert M. Cohen, James W. Mercer, Robert M. Greenwald, and Milovan S. Beljin
EPA Ground Water Issue, EPA/540/S-97/504, 38 pp, September 1997.

Guidelines on use of pump and treat for contaminated water includes a section on horizontal and slant wells.

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