Passive Remediation: Advanced Solutions for In Situ Treatment

By Tomas Will, Sr. Environmental Scientist

Diligent consultants are often rewarded for remedial actions that can both save money on implementation and avoid costs from disrupting operations at active commercial and industrial sites.  This progressive approach to vadose zone remediation might involve injection, extraction, thermal, or soil vapor extraction systems. While effective, these systems can often require expensive equipment to operate. The installation for these systems is typically costly, disruptive to facility operations, unsightly, and often requires a constant source of power resulting in a need for long term operational budgets. In the case of one consultant, they sought out an approach that would avoid these problems for their client’s large commercial property.

Elevated volatile organic compound concentrations had been measured beneath the client’s tank storage area. Contamination in the vadose zone located directly beneath the storage area’s concrete pad had been detected in areas that were difficult to access from the surface. To help avoid the expense of installing a costly active remediation system to address the large contaminant plume, the consultant wanted to explore the possibility of a passive treatment design that incorporated bioremediation. The consultant’s well designs were based around the inclusion of chambers containing beneficial microbes to promote the growth of dense bacterial colonies capable of breaking down the trapped contamination in the tight soils of the vadose zone. The chambers would be inserted within the well screen segment that was placed within the zone of contamination. These in situ systems can distribute the bacterial treatment to contaminated soils beneath the existing structures, driven by nothing more than the growth of the microbes propagating out into the vadose zone in the absence of any continual pumping or other induced flow.

Unfortunately, the consultant’s initial efforts to design a passive bio treatment system using traditional vertical installation techniques came across various problems. One of the main issues with using vertical installation methods for passive bio treatment systems is that a vertical approach is inherently restricted by the limited amount of screen that can be placed in direct contact with contaminated zone. In order for their approach to be effective, they would require a significant number of vertical points to properly address the soil layer beneath the tank storage area. Their other major issue was that there was very little accessible square footage within the tank storage area, severely restricting the well locations that could be installed with a vertical drill. The consultant’s efforts to implement a passive treatment approach were significantly bolstered once they began to look into implementing their designs through horizontal remediation wells. When properly designed, horizontal well screens can take advantage of the natural gradient in groundwater flow to disperse biotreatment agents over large areas without the need for compressors, blowers, or pumps.

The consultant sought out Directional Technologies’ expertise in horizontal remediation wells to help them finalize their designs for a horizontal passive remediation system for their client’s property. Following approval of the system design, directional Technologies installed twelve horizontal in situ bio-remediation wells beneath the tank area. Following well installation, the chambers containing beneficial microbes were placed inside the screened segments of the horizontal well to break down the contaminants in the vadose zone. The horizontal wells totaled 1,550 feet in length and provided coverage throughout the footprint of the affected area. The horizontal well screen segments were designed with the optimal open area to allow groundwater to naturally flow through the sections of the pipe containing the biocarrier substrate and distribute it along the zones of contamination. To accommodate logistical site constraints, Directional Technologies used a blind (single-entry) well installation method, which allowed the wellbore to terminate in the subsurface at the end of the horizontal screen. All twelve horizontal wells were drilled from a common starting point, avoiding any disruptive movement of horizontal drilling equipment within the close quarters of the facility. Normal operations at the busy facility continued uninterrupted during the horizontal drilling operation.

Thanks to their inventive thinking, the consultant was able to provide their client with an effective solution that avoided the drawbacks that are typically associated with active remediation systems.

Is there a cost-effective alternative for your soil and groundwater remediation projects that can take advantage of horizontal design techniques?  Call our horizontal remediation well experts at 1-877-788-4479 to discuss your current project needs.