Are current groundwater remediation technologies sustainable?

In situ active remediation technologies such as air sparge/soil vapour extraction (AS/SVE), multi-phase extraction (MPE) and pump and treat (P&T) are widely used for remediating groundwater.

While some of these have been proved successful at achieving remediation end points in a timely manner, these remediation technologies typically incorporate components such as high vacuum extraction pumps and thermal treatment equipment that consume large amounts of power.

As the remediation industry matures and becomes more conscious of the impact of remediation activities on the environment, the question now arises whether these technologies are sustainable remediation approaches to be considered in the future.

Remediation technology trends

The USEPA compiled report titled Treatment Technologies for Site Cleanup: Annual Status Report (12th Edition, Sep 2007), documents the status, achievements and trends associated with treatment technologies at National Priority List (NPL) sites between 1982 and 2005.

A review of the trends and general observations identified the following:

• The selection of in situ treatment technologies for source control continues to increase, accounting for about 60% of new projects between 2002 and 2005;
• From 2002 to 2005, MPE and chemical treatment have increased compared with SVE which has decreased;
• There is a continuous increasing trend in the use of innovative technologies;
• MNA has been increasing since 2002 with almost half of all sites selecting MNA in 2005;
• The most common in situ technologies include air sparging, bioremediation, chemical treatment, PRBs and MPE;
• In situ bioremediation and chemical treatment have increased significantly in recent years, with between 70 and 80% of these projects being selected in the past 6 years.

What the above points illustrate is that remediation technologies are evolving and maturing, their applications becoming more defined, with cost and performance metrics more accurately measured, enabling them to become established. There appears to be a move towards in situ technologies with the use of bioremediation and MNA being more prevalent than before.

What have been the drivers for change?

Less energy-intensive technologies
The most frequently used energy-intensive treatment technologies used at NPL sites are P&T, thermal desorption, multi-phase extraction, AS and SVE. Using data from cost and performance reports compiled by the Federal Remediation Technologies Roundtable and other resources, OSWER estimates that a total of more than 14 billion kilowatt-hours (kWh) of electricity will be consumed through use of these five technologies at NPL sites from 2008 through 2030.

Energy-intensive remediation technologies such as P&T have lost their appeal as a result. Technologies such as MPE and AS/SVE have increased in popularity over the years due to lower energy requirements. In situ chemical injection technologies have increased in popularity for the same reason.

Performance
Another reason for the change in technology selection has been related to the overall performance of remediation technologies in achieving the remediation end points. Of the compiled list of remediation technologies used at NPL sites, more than 70% of P&T projects selected are currently operational. Furthermore, only 10% of P&T projects have been completed; and of this 10%, a number of these projects have been completed because the decision was made to shut down the P&T system, not necessarily because they reached their remediation end points.

By comparison, in situ treatment technologies represent 31% of completed projects, similarly 45% SVE and less than 30% of AS. It was noted that the percentage of completed in situ projects was expected to increase as these technologies only became established in the 1990s.

Current practice for remediation technology selection

The predominant aspects considered in the remediation technology process include:

• Implementability;
• Cost effectiveness and justifiable;
• Technology meets remediation end points;
• Risks are mitigated or removed as appropriate.

What makes a remediation technology sustainable?

The chosen technology achieves the remediation objectives in a cost-effective and timely manner, with minimal impact to the environment. But it must also achieve the most optimum net benefits to society.

Examples of sustainable remediation technologies include: MPE, P&T, ISCO and AS/SVE.

How to achieve sustainable remediation

The key to achieving sustainable remediation is in the application of a holistic approach whereby the true social priorities are incorporated. In order to ensure that remediation technologies are assessed in a non-biased manner, a common unit of measure needs to be used.

This requires a dollar amount be determined and placed on social and environmental benefits. That way, decisions can be better made for weighing up the overall cost benefit analysis, in particular for remedial approaches that achieve clean-up goals faster but involve more intensive short-term emissions.

In order to determine this, the future use of the site (and of the neighbouring properties) needs to be understood. In addition, the needs of the community should also be understood, as their interests may differ from the person involved in the clean-up.

A site-specific approach is necessary with very clear end points identified prior to the remediation technology selection process.

How to implement sustainable remediation

The implementation of sustainable remediation from a regulatory and industry perspective needs a consistent and unified framework so that it doesn’t become fashionable or abused. Examples include limited measuring tools such as carbon emissions or energy usage as a single measuring tool. This could lead to misconceptions that remediation approaches such as monitored natural attenuation (MNA) are treated as the 'silver bullet'.

Similarly, technologies such as P&T, and thermal technologies such as thermal conductive heating, are not automatically discounted due to their high energy-intensive nature.

In addition, a framework needs to include suitable incentives to encourage companies to aim for sustainable remediation outcomes when other economic/social/environmental mechanisms are not naturally considered.

Remediation end points need further clarification from regulatory agencies to improve the remediation technology selection process. Greater emphasis needs to be placed on risk assessment processes and their value in determining suitable remediation end points to mitigate risks.

The same rigorous cost-benefit analysis and holistic approach also needs to occur on treatment requirements for various waste streams, such as vapour treatment. What is the net environmental benefit of using vapour treatment to remove organic pollutants that requires large amounts of energy, which in turn produces significant carbon emissions? Are there other areas where vapour emissions could be alternatively reduced or removed?

Separately, but equally important, there needs to be less pressure placed on auditors and regulatory agencies alike when it comes to achieving site closure. The timeframe required to reach remediation end points and the subsequent time at which the site is available for its proposed future use plays a major role in the overall remedy selection process and interferes with sustainability. Some technologies may in fact be deemed to be more suitable in achieving a sustainable outcome if the timeframe for sign-off is considered to be less than another technology.

Over the last 20 years, remediation technologies have become more sustainable, simply through the introduction of technologies that are more cost effective, less energy intensive and achieve remediation timeframes in a more timely manner. This has, in turn, reduced the overall life cycle costs of remediation. The use of in situ technologies will likely continue to become more prevalent in the years ahead.

*Andrew Thomas, OTEK Australia Pty Ltd.