Successful Urban Injection with Horizontal Well

By: Kyle Carlton, PG, Senior Geologist

For environmental sites in highly developed urban settings, horizontal remediation wells continue to be selected as the preferred in-situ remedial method to provide the necessary access and influence coverage of the target treatment areas.

In the fall of 2017, Directional Technologies, Inc. was contracted to provide design assistance and installation of a horizontal injection well beneath a major thoroughfare in a congested commercial and residential area. The site presented several challenges which are commonly encountered by environmental consultants when planning and executing remediation at sites in urban areas.

Background

The former operations of an industrial facility contributed to a significant trichloroethylene (TCE) contaminate plume in groundwater extending over 1,300 feet east to west and 1,400 feet north to south. TCE concentrations near the source zone ranged from 110 micrograms per liter (µg/L) to 170 µg/L.

Remedial Challenges

The site setting is within a highly developed area with multiple commercial businesses and residences.

Variable groundwater flow in the area enabled migration of the TCE to form a highly irregular shaped plume beneath 50 individual properties and state and local roadways.

A significant portion of the source zone is located beneath a major thoroughfare. Multiple subsurface utilities in the area were also a concern and limited the feasibility of vertical injection points. Additionally, a complex subsurface lithology with unpredictable occurrences of cobble and gravel posed challenges to the drilling processes.

Approach and Activities

Based on a long-standing relationship with a nationwide leading consulting firm, Directional Technologies was contracted to provide horizontal well design assistance and turnkey installation services.

Factors in horizontal injection well design included the layout, well diameter, screen length, screen design, target depth, placement for avoidance of utilities and preferred access to injection wellheads. The design phase of work concluded with selection of one 4-inch diameter horizontal injection well, 700 feet in total length, with 340 feet of screen. The well screen design specified 0.067 percent open area with longitudinal slots. The machine cut, engineered slotting of the injection well ensures even distribution of injected fluids throughout the entire length of screen, therefore, influencing the entire target area.

Directional Technologies, Inc. mobilized a Ditch Witch JT 4020 horizontal directional drill rig with 15-ft drill rods to install the pilot bore along the pre-determined well path. Steering adjustments were made in the field to obtain the target well layout and injection depths. The horizontal well path was safely advanced below multiple subsurface utilities within the street and rights-of-way. Traffic on the roadway continued without any lane closures or barricaded areas. The activities of the surrounding businesses continued without interruption as well.
The well was installed via-entry exit method, so that well vaults exist on both sides of the well, providing two access points for injection.

Initial Remediation Results

The horizontal injection well was completed within 3 weeks, and initial injection events began in late 2017. A proprietary injectable product specifically designed for the in-situ treatment of TCE in groundwater was injected through the horizontal well on a regular basis.

Initial analytical results are pending; however, greater than expected groundwater mounding observed at nearby monitoring wells indicates the subsurface formation is receiving the injections extremely well.

In comparison, injecting within this target zone with traditional vertical injection points would have caused significant logistical problems for the local street department, through traffic, and the normal activities of businesses and residents. Additionally, vertical injection could result in gaps within the radius of influence resulting in reduced remedial coverage.