Appendix A in How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites: A Guide for Corrective Action Plan Reviewers. EPA 510-B-17-003, 47 pp, 2017

Horizontal directional drilling (HDD) can be used to install wells at environmental cleanup sites; these are known as horizontal remediation wells (HRWs) or horizontal environmental wells. HDD uses a specialized drill rig and drill-head locating equipment to create a curved borehole along a pre-determined borepath, producing either a surface-to-surface well or a blind well. HRWs are able to access locations beneath surface obstructions and to place long well screens in contact with the contaminated area. The wells can be thousands of feet long, with hundreds of feet of well screen. The potential for HRWs to complement a site remedy is described with reference to air sparging and soil vapor extraction, hot air or steam injection, bioremediation, chemical injection, LNAPL removal, plume containment, injection of treated water, and sampling. This appendix also provides a detailed overview of equipment and procedures for drilling a horizontal remediation well. https://www.epa.gov/sites/production/files/2017-10/documents/tums-app-a-oct2017.pdf