By Tomas Will, Sr. Environmental Scientist
Efforts to remediate dissolved petroleum hydrocarbons at a gas station site in the southeastern US had failed to achieve the desired results. Five vertical wells had previously been installed at the site with three wells used for Multi-Phase Extraction (MPE) and two wells used for Air Sparge (AS). While multiple Mobile Enhanced Multi-phase Extraction (MEME) events had reduced the total concentrations of hydrocarbons in the groundwater, the existing system was insufficient to achieve remediation targets. With various downgradient private water supply wells in the immediate area, the consultant needed to find an effective solution to remediate the groundwater plume and began evaluating all their options.
In their search for a solution that could achieve better performance, the resourceful consultant explored the possibility of implementing a horizontal MPE well. Directional Technologies’ initial review of the project found the use of horizontal wells to be feasible. Using their proprietary custom well screen design technology, a site-specific screen design was developed to deal with the tight lithology at the site. The consultant, having evaluated the various available options, determined that a horizontal MPE well would allow them the best chance for success.
Directional Technologies installed a single horizontal MPE well with approximately 100 feet of screen set at a target depth of 10 feet. The horizontal well was installed directly alongside the gas station pump islands. Had the gas station not been out of business at the time of installation, the horizontal well would have been installed without any interruptions to the fueling operations at the site. Following the completion of the horizontal MPE well, two rounds of MEME pilot testing were scheduled to be conducted. The pilot tests, scheduled three weeks apart, would compare the performance of the vertical wells and the horizontal well.
The first round of MEME pilot testing occurred using the three vertical MPE wells and the second round occurred using the newly installed horizontal MPE well. During both pilot tests, an air sparge unit was connected to two nearby vertical AS wells for a portion of each event so that ambient air could be injected to further enhance the vapor recovery. The pilot tests were each broken into four 6-hr parts: 6-hrs of low vacuum MEME, 6-hrs of low vacuum MEME with AS, 6-hrs of high vacuum MEME with AS, and 6-hrs of high vacuum MEME.
The two pilot tests revealed the following conclusions:
- The single horizontal MPE well outperformed the combined output of the three vertical MPE wells as measured by both system flow rate as well as hydrocarbon removal rate. Over 17 pounds of hydrocarbon compounds were extracted from the horizontal well during the horizontal pilot test.
- Once the air sparge was added to the MEME, the hydrocarbon removal rate increased.
- Optimal recovery rates occurred during the combined application of low-vacuum extraction with air sparge.
With performance results from the pilot testing verifying that the relatively short horizontal well was providing performance over three times greater than a single vertical well, the consultant could proceed with confidence that they had found a solution that could finally help them achieve their remediation goals. Various low-vacuum MEME events were scheduled over the course of the next year to bring the site to closure.
Do you have project sites where vertical wells have failed to provide the results you needed? Call our horizontal remediation well experts at 1-877-788-4479 to discuss your current project needs or visit our website to reach out with questions, review case studies, and learn more.