Combined remedies leverage multiple technologies to achieve a common remedial goal, and innovations in combined remedies are currently being used to optimize existing remedies and develop successful cleanup strategies. Combinations can take three forms:
- Spatial: Multiple technologies are “mapped” to different areas within a contaminated site, based on site characteristics or contamination nature and extent. For instance, a site’s remedial footprint might include in situ thermal remediation (ISTR) to address concentrated sources, but the volume treated with this energy-intensive and expensive technology could be reduced by using in situ bioremediation (ISB) in parallel to treat lower concentration fringe areas.
- Temporal: Multiple technologies are applied in a sequence, often referred to as a treatment train approach. Remediation usually begins with an aggressive technology and then transitions to more passive, cost-effective technology. This stepwise approach allows the aggressive and expensive technology to be applied until it reaches a “point of diminishing return” in contaminant removal rates, which is often still above remedial goals. Subsequently, the polishing technology is used to reduce contaminants further until remedial goals are achieved.
- Integrated: Different technological approaches are integrated to take advantage of synergy and make the overall treatment more effective. For example, integrating ISTR with in situ chemical oxidation (ISCO) or ISB can reduce the above ground infrastructure required to extract and treat contaminants during ISTR, and increased temperatures can improve contaminant mass treatment rates by accelerating chemical or biological reactions in situ. These synergies can be used to develop an integrated strategy that is often more efficient than implementing either technology alone.
How technologies are deployed is as important as which tools are used, and a combined remedy should be considered as part of any remedial strategy for today’s complex contaminated sites.
Dismissing misconceptions
With the growing number of successful combined remedy implementations, many misconceptions are being dismissed. One belief was that by combining technologies you increase treatment costs. From a life-cycle perspective, the traditional path of applying different technologies until one works is actually inefficient and expensive; it's more cost-effective to research and implement the right combination of technologies. Another is that certain technologies cannot be combined. For example, it was believed that more aggressive technologies, such as ISTR or ISCO, would have a negative effect on more passive technologies, like ISB. However, research has proven these synergistic technologies can effectively be integrated with careful design considerations.
How technologies are deployed is as important as which tools are used, and a combined remedy should be considered as part of any remedial strategy for today’s complex contaminated sites. Combined remedies should be applied in a flexible, adaptive and attentive manner. Incorporating multiple technologies and strategies can maximize the net environmental benefits of cleanup actions.