In December 2018, DTD installed a dual purpose horizontal well as part of a remediation pilot test at a chemical facility in the southeast United States. Crews installed the 250′ long well beneath an active tank farm. The pilot study will evaluate remediation options in a shallow contaminant plume just above the water table. The client plans to use the well to test two separate remediation strategies. First, they will apply a vacuum to initiate soil vapor extraction (SVE). Secondly they plan to use the well for in-situ injection of remediation substrate. Results from the pilot study will help guide the full-scale design program. The engineer expects the full-scale effort to involve some degree of both SVE and injection technologies.
Prior to mobilization, DTD and the client worked closely together to ease regulators’ concerns over horizontal well technology in general. The regulators had little to no experience with this type of drilling or well installation and were understandably cautious. The lengthy approval process, which took upwards of a year, emphasized the need to get as much data as possible out of this initial pilot project. So the dual purpose horizontal well really provides the most “bang for the buck” compared to other strategies considered.
The above ground storage tanks sit in a lined containment berm, that precluded any vertical drilling within the tank farm itself. Vertical wells installed around the perimeter of the berm have a limited lateral influence thanks to tight clays in the subsurface. So a directionally drilled well stood the best chance of getting good contact with the the heart of the plume underneath.
DTD completed this project with a Vermeer 24×40 directional drilling rig coupled with a single phase mixing system. The project team elected to place the entry location with more horizontal setback than strictly required in order to eliminate interruption of the facility’s deliveries or operations. Infrastructure at the terminus of the well precluded an exit pit, so the crew completed the installation single-ended (or “blind”). Materials consisted of 3-inch SCH80 PVC with 100′ of custom slotted well screen.
The first phase of the pilot study (vapor extraction) starts in February of this year. Following that, efforts will switch to the second (injection) phase of the dual purpose horizontal well.