Directional Technogies: Passive Remediation Technologies with Horizontal Wells

Passive Venting and Passive In Situ Treatments with Horizontal Wells

Horizontal Placement Flexibility Enables Green Remediation

By placing screen along rather than across the principal plane containing the problem at hand, horizontal wells make passive treatment technologies, including passive venting and passive in situ treatments possible. This principle spans the gamut of environmental problems—from subslab mitigation to in situ remediation.

The Problem with Vertical Wells and Passive Remediation Technologies

Before horizontal mitigation solutions became available, subslab depressurization of larger commercial buildings required dozens if not hundreds of vertically emplaced fan units that were driven by blowers. Not only was their installation disruptive to operations at the facility, the PVC conduits were unsightly and the fan units were challenging to operate. Additionally, the vertical systems required a perpetual power supply. Attempts at designing passive venting using vertical screens typically failed because vertical screens cannot be placed in the natural plane of the problem. The natural plane is the gravel or sand layer located beneath the large horizontal slab of a building that is used to protect the building from vapor intrusion.

Horizontal Wells and Passive Remediation Technologies

Horizontal well screens, placed with one or two ends open to the atmosphere, present design alternatives that address the effects of the building footers, foundation cracks, graded foundation gravel, utility lines and other preferential pathways that allow vapor to intrude and compromise the air quality within the building. Horizontal Passive Venting systems are now quite common.

In Situ Bioremediation with a Horizontal Remediation System

A new development site in San Jose, California illustrates the potential of horizontal wells as passive delivery tools for in situ bioremediation. Placement along sedimentary depositional horizons harvests the energy of the natural hydraulic gradient in groundwater to disperse biotreatment agents without compressors, blowers, or pumps that use power and are expensive to operate. Immobilized bed reactor systems (IMBR or ISBR) harbor dense microbial colonies that take advantage of a porous biocarrier substrate providing high surface area for the microbial colonies to attach and grow. Placed within permeable zones carrying the bulk of dissolved contamination, these in situ bioreactors can treat contaminated groundwater as it passes through the reactors, driven by nothing more than the potentiometric head gradient under static conditions in the absence of any pumping or other induced flow.

Directional Technologies, Inc. (DTI) recently installed twelve horizontal ISBR wells totaling 1550 feet in length at an industrial facility in San Jose, California. The horizotal wells were constructed of 4-inch schedule 80 PVC with screen sections that utilized recent advances in well screen manufacturing. The well screens provided the optimal open area to allow groundwater to flow through the screened horizontal pipe containing the biocarrier substrate. ISBR delivery equipment was installed inside the 4-inch PVC screens. To accommodate logistical site constraints, DTI used the blind well installation method. The blind well installation method allows the wellbore to terminate in the subsurface at the end of the horizontal screen. All twelve wells were drilled from a common starting point and disruptive movement of horizontal drilling equipment within the close quarters of the waste processing site was avoided. DTI maintained accurate well paths avoiding vertical wells and subsurface utilities. DTI’s environmental directional driller surveyed successfully across an abrupt 7-foot elevation change at the site to place the horizontal wells within a thin target zone.  Activities at the busy industrial facility continued during the entire horizontal drilling operation. This application is one more among the growing list of horizontal well delivery and recovery methods for in situ remediation.