A Marriage of Remediation Technology
Horizontal drilling adds to classical drilling methods for groundwater remediation approaches
- By Charles Cohen, Thomas E. Jamrok
- Sep 01, 2002
Isn't the number of remedial technologies that actually exist to remediate and protect groundwater amazing? Not only does industry have a wide selection of pump and treat options, there is a full array of in-situ technologies that engineers continue to conceive and refine. It seems that every year there are new acronyms added to the string of remedial approaches in use. In the corrective action/remediation field there are:
- Air Sparging
- Soil Vapor Extraction
- Dual Phase Extraction
- Soil Washing
- Surfactant Flushing
- Enhanced Natural Attenuation
- Reactive Gates
- Oxidation/Reduction Compound Treatment
- Reactive Barriers
- Density Driven Convection
This list does not include all the consultant or trademark products and could go on and on; but luckily for the readers, I won't.
In general, all remedial technologies can be broken down into three general technologies: physical, chemical or biological. The application of these technologies is how to get the contaminant out of the medium or how to get the treatment to the contaminant. All the technologies listed do have merit and are applicable in given situations. What prompts the development of these approaches are the unique site needs that present themselves and the problem-solving vision of the remediation engineer.
Classically, groundwater has been addressed by pump and treat technologies. However, recent technology advances have shifted many approaches to in-situ methods. Whether groundwater remediation is accomplished by pump and treat or in-situ methods, the obstacle to overcome is how to get the contaminants to the treatment or the treatment to the contaminant.
The majority of remedial projects extract water or introduced treatments using conventional soil drilling rigs and vertical well installations. Well fields are typically placed within the area of contamination to draw contaminants to the wells or at a down gradient location that facilitates intercepting the contaminant plume and allowing the contaminants to come to the well. At times both source collection and barrier wells are used to control a contaminant plume.
The question becomes: How can you optimize the radius of collection or influence? More wells, longer screens? With the advances in directional drilling, the marriage of horizontal wells and remedial technology is here, even though few are attending the party.
Literature presents several good articles on horizontal drilling which describe successful solutions and general advantages, namely cost. While these articles are well written, the value of horizontal drilling is the versatility of the technology. Horizontal wells are not just for air sparging applications. The well installation technology can enhance the application of any remedial approach. From sparging and de-watering to setting oxidizing/treatment barriers. The long screen length of a horizontal well places the treatment within intimate contact of the contaminants.
Where time is money, remediating a site in a matter of months verses years can have a significant effect on the bottom line. Not even considering the differences in installation costs, the reduced operation and maintenance (O&M), energy, monitoring and reporting costs can be a significant savings alone.
While classical drilling methods are still needed for monitoring and make sense for some remediation approaches, horizontal drilling significantly adds to the consultants' toolbox when properly considered and deployed.
The advantages are more appreciated at sites that have limited access or where surface access is not practical. Whether contamination exists under buildings, roadways, manufacturing and processing facilities or landfills, lagoons and tank farms, horizontal wells may be the only logical choice.
Versatility of the technology is impressive. While boreholes of four to eight inches are most common in environmental applications, projects have been completed with bores from as small as one inch to a monstrous 42 inches in diameter. The beauty of the technology is the ability to put the horizontal well where you want it, whether it is immediately under a building foundation or at depths of 40 to 50 feet. Operators can control drift to within inches (0.06 inch/100 linear feet) and can hit target elevations on runs exceeding 4,500 feet.
Directional drilling has progressed to the point that installations in urban settings are possible as long as utility locates and infrastructure concerns are properly identified. With precautions, crossing or paralleling existing utilities is possible. This is extremely advantageous in situations where the migration pathway is associated with the utility conduit. In some situations, horizontal drilling might well be the only method to mitigate off-site contamination. It allows access under roadways, railroads and airport runways without disrupting public use.
The installation is equally functional when completed above or below a water table. Custom well casing and screening are commonly available and can range from plastic to ductile iron pipe.
A cost analysis of various applications shows that horizontal drilling is economically feasible. When considering the net present value of a project, horizontal applications can typically show economic advantages over conventional remedial methods. The favorable economic value is directly related to the technologies' ability of getting the treatment to the contamination rather than trying to get the contaminants to the treatment.
Horizontal well drilling technology is here. I leave it in the capable hands of the engineers to make the applications of the technology as diverse as the remedial approach.
This article originally appeared in the 09/01/2002 issue of Environmental Protection.