Integrated DNAPL Site Strategy

Sites contaminated by chlorinated solvents present a daunting environmental challenge, especially at sites with dense nonaqueous phase liquid (DNAPL) still present. Restoring sites contaminated by chlorinated solvents to typical regulatory criteria (low parts-per-billion concentrations) within a generation (~20 years) has proven exceptionally difficult, although there have been successes. Site managers must recognize that complete restoration of many of these sites will require prolonged treatment and involve several remediation technologies. To make as much progress as possible requires a thorough understanding of the site, clear descriptions of achievable objectives, and use of more than one remedial technology. Making efficient progress will require an adaptive management approach, and may also require transitioning from one remedy to another as the optimum range of a technique is surpassed. Targeted monitoring should be used and re-evaluation should be done periodically.

Sites contaminated by chlorinated solvents present a remediation challenge. Chlorinated solvents are among the most difficult groundwater contaminants to remediate, especially at sites with dense, non-aqueous-phase liquid (DNAPL) still present in the source zone. Significant remedial progress requires a thorough understanding of the site, clear descriptions of achievable objectives, and use of more than one remedial technology.

A thorough understanding of DNAPL properties is crucial to designing an adequate characterization program. In developing a thorough site characterization program, it is also critical to determine the relative presence and distribution of DNAPL, vapor, dissolved, and sorbed chemical phases of contamination across the various geologic media and understand that the distribution of these contaminants will change over the lifecycle of the site.

Integrated site characterization is a process for improving the efficiency and effectiveness of characterization efforts at DNAPL sites. It encourages characterization at a sufficient
resolution to capture the effects of the heterogeneities that direct contaminant distribution, fate, and transport, and remediation effectiveness, so that an integrated three-dimensional CSM can be developed and refined.

The Tool Selection Worksheet offers a rapid method of identifying the appropriate tools and information for collecting geologic, hydrologic, and chemical data.

Many technologies have been developed for source and plume treatment, all with specific advantages and limitations. Selecting a treatment technology requires evaluating several factors, including technical site features (e.g., geology, hydrogeology, and contaminant levels), regulatory requirements, sustainability, and community stakeholder interests.

A monitoring approach that relates remedy performance to site-specific（ SMART1） functional objectives is a critical element of an integrated strategy. The monitoring approach must include a spatially and temporally sufficient and reliable data set of the remedy performance.

1. SMART ： smart Methods in Advanced Remediation Technologies