Horizontal Remediation = Faster Redevelopment

By Tomas Will, Sr. Environmental Scientist

Our client faced the challenge of remediating LNAPL and DNAPL plumes spread out over a large area. The property was scheduled for redevelopment pending remediation of the considerable subsurface contamination. The previous site building had been demolished and the clock was ticking on the start of construction of a new building. Faced with various challenges surrounding how to avoid delaying the property redevelopment without compromising the efficacy of their remedial solution, the consultant began evaluating their potential options.  

Problem:

PCE was present at very high concentrations and vapor intrusion was a significant concern for the pending redevelopment of the property as an educational institution. Redevelopment of the property could not begin until it could be demonstrated that the vapor intrusion concerns had been brought under control. The redevelopment plans called for a large building that was directly over top of the center of the contaminant plume. The developer was eager to begin work on new construction at the site, however, the remediation challenges facing the site were significant.

The subsurface contaminants had a vertical distribution of over 30 feet and the size of the plume was over 250,000 square feet wide. Lithology in the area of the site consisted primarily of poorly graded sands and clay, with clay concentrations increasing down to 60 feet below ground surface. An initial evaluation of vertical wells would have required dozens of wells to be placed in the area where the newly proposed building was to be constructed; either requiring that the start of construction be delayed until contaminant concentrations went down or for a two-phased approach where an initial set of wells would be installed, then abandoned for the construction of the new building, then reinstalled through the new building slab.

Solution

The consultant determined that they could address these challenges and fast-track the redevelopment of the site by using directional drilling to install a network of horizontal soil vapor extraction (SVE) wells to access the plume.

In coordination with Directional Technologies, a system design was engineered that consisted of twelve horizontal remediation wells set at varying depths between 15 and 50 feet below ground surface. The wells included both entry-exit and blind (single entry) configurations to reduce impacts to the planned redevelopment. All twelve wells were drilled from a common location located near the remediation equipment shed located in the far corner of the property, allowing for easy future O&M and minimizing the need for conveyance piping. The well screens were custom-engineered using Directional Technologies’ proprietary screen design software to produce a site-specific design that would provide optimal performance. In order to overcome the difficulties of tracking the bore paths beneath the thick concrete slab of the previous site building and ensure accurate system installation, Directional Technologies used state-of-the-art handheld walkover locating technology. This cost-effective approach avoided the need for prohibitively expensive wireline locating techniques without compromising on drilling accuracy.

The horizontal SVE wells allowed the consultant to accomplish the following:

• Significantly reduced the time it would take before the site could be redeveloped.
• Provide a remediation solution that will outperform the vertical well alternative by providing enhanced contact with the affected areas.
• Deliver a cost-effective design that reduced costs to their client compared to alternative remedial approaches.
• Demonstrate to their client that they are effective problem solvers, and that remediation doesn’t need to adversely impact the redevelopment process.  
• Centralize the wellhead locations allowing for easier O&M and unintrusive system configuration.

Do you have clients that have time-sensitive remediation requirements? Call our horizontal remediation well experts at 1-877-788-4479 to discuss your current project needs.