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As DoD proceeds with remediation at contaminated groundwater sites, it is becoming apparent that long-term monitoring (LTM) is a significant part of remediation lifecycle costs. The need for LTM is in part due to the reality that complete cleanup of significant dense nonaqueous phase liquid (DNAPL) source zones has not and - at least for the foreseeable future - will not, be possible. In most cases, even after the most successful remediation efforts, some LTM is still required.
The number of monitoring wells at an installation can range from 250 to 3,000. The Air Force alone has an estimated 50,000 wells. At $2,500 per sampling event per well, the estimated long-term monitoring cost for all of DoD is more than $100 million per year.
At present, most LTM approaches are relatively conventional, involving the installation and maintenance of monitoring wells, labor intensive sampling, and costly laboratory analysis. The most common sampling and analysis approaches are based on technology originally developed for site characterization efforts more than 25 years ago. In addition, the most common analytical techniques are designed to detect a wide range of organics for characterization. Once a site is in the LTM phase, however, the number of contaminants of concern is generally much smaller. As a result, measurements may be needed for only a limited number of compounds.
To improve the current LTM approach, more efficient data collection methods and more effective ways to use data once it is collected are required.
Recent advances in sensor technology are applicable to LTM. Researchers are exploring the development and use of sensors or sensor systems designed for the more limited and specific needs of LTM. These advances could lead to field-based monitoring systems with real-time reporting capabilities. To be effective, such systems need to be robust and reliable, capable of operating with little maintenance for long periods of time and under a wide range of subsurface environmental conditions.
It is also important to improve sampling approaches and to determine if these sampling and new sensors provide an accurate representation of contaminant concentrations in the aquifer. Various environmental parameters or sampling methods will affect the sensor’s ability to function. It is essential to understand the relationship between these various parameters and measured contaminant concentrations in order to optimize the use of sensors for compliance sampling. SERDP and ESTCP research efforts are making progress in improving sampling techniques. These efforts also are improving the understanding and the predictive capabilities needed to determine which environmental parameters and sampling methods will provide accurate groundwater contaminant measurements for compliance sampling.
The efficiency of LTM can be improved by ensuring that only the essential data needed for monitoring current conditions is collected. This goal can be achieved by eliminating redundant sampling locations and/or frequencies. ESTCP demonstrations focus on optimizing the LTM sampling approach to address such issues.
Reductions in the cost of LTM programs have the potential to greatly reduce DoD’s long-term liability. LTM costs are increasing, and now represent a significant percentage of the total and future restoration costs.