The overall objective of this project was to demonstrate and evaluate the effectiveness of two technologies for characterizing coastal contaminant migration. Specific objectives included: (1) demonstrate that the Trident probe can be used to help delineate areas where groundwater seepage is occurring and Contaminant of Concern (CoC) concentrations in those areas; (2) demonstrate that the UltraSeep system can be used to quantify the flow of groundwater and concentration of contaminants that may be impinging on the surface water system; (3) demonstrate the technology to end-users to determine the utility of these tools for making decisions at Department of Defense (DoD) coastal landfills and hazardous waste sites; and (4) quantify costs associated with technology operation.

Technology Description

The Trident probe is a combined conductivity sensor, porewater sampler, and temperature sensor probe developed to screen sites for areas where groundwater may be discharging to a surface water body. Differences in observed conductivity and temperature indicate areas where groundwater discharge is occurring. The probe allows large areas to be rapidly mapped so areas where groundwater may be migrating are more easily identified. The integral porewater sampler can be used to rapidly confirm the presence of freshwater or other chemical constituents.

The UltraSeep is an integrated seepage meter and water sampling system for quantifying discharge rates and chemical loading from groundwater flow to coastal waters. The technology is innovative in that it couples a state-of-the-art flow-detection sensor with a sophisticated, flow-proportional sampling technique. Traditional seepage technology was modified and improved to include automated multiple sample collection and continuous flow detection with ultrasonic flowmeters. The resultant instrument makes direct measurements of advective flux and contaminant concentrations at a particular location. The data produced are time series, over tidal cycles, of groundwater flow, contaminant concentration, and associated sensor data, which allow an accurate determination of the maximum extent of groundwater contaminant flux into a bay or estuary.

Demonstration Results

The first demonstration focused on evaluation of a volatile organic compound (VOC) plume associated with Area of Concern 1 at Naval Support Activity Panama City. The site was adjacent to St. Andrews Bay, and the plume appeared to be migrating toward the bay. The Trident probe was used successfully to identify areas of groundwater discharge from the site to the surface waters of the bay. Thirty offshore stations were sampled with the probe sensors and water sampler, and the results were validated with shallow piezometers. The UltraSeep was used successfully at this site to quantify groundwater discharge rates and VOC discharge concentrations in two discharge zones identified with the Trident. Although groundwater discharge was detected, all target VOC analytes in all UltraSeep samples were below the detection limit. Results from three shallow piezometers installed adjacent to each UltraSeep station validated the results obtained from the UltraSeep. Overall, the Panama City demonstration was successful in demonstrating the utility of the Trident and UltraSeep in assessing coastal contaminant migration. No DCE discharge into St. Andrews Bay at levels above the Surface Water Cleanup Target Level was detected, and the results from the study supported the selection of monitored natural attenuation (MNA) as a corrective action alternative for the site.

The second demonstration took place at the former Naval Training Center (NTC) Orlando. The CoC at OU4 NTC Orlando was PCE and its degradation products, which had been detected along the shoreline of Druid Lake. The Trident probe was used successfully to identify areas of groundwater discharge from the site to the surface waters of Lake Druid. Detectable levels of VOCs were measured in the sub-surface and/or surface water in the areas of groundwater discharge identified with the Trident sensors. The results from shallow piezometers validated the results from the Trident probe. The UltraSeep was successfully employed to quantify groundwater discharge rates and VOC discharge concentrations in two discharge zones identified with the Trident screening. Validation of the UltraSeep sampling conducted using piezometers indicated general agreement. Overall results for the demonstration show how discharge of VOCs to the lake are regulated by the physical pathway and the chemical attenuation that occurs along these pathways, along with the effects of localized mixing in the lake itself.

Implementation Issues

A cost analysis for the Trident and UltraSeep technologies relative to the baseline technologies was developed on the basis of the demonstration, input from commercial partners, and typical site parameters. The cost analysis assumed a coastal area of interrogation measuring 200 ft by 500 ft with 60 Trident sensor, 15 Trident porewater, and five UltraSeep sampling points. It indicated that the cost of an integrated Trident/UltraSeep survey is expected to be on the order of $120K. This represents a cost savings of about 42% relative to the estimated cost for the baseline technology. In addition, the Panama City demonstration documented an additional cost avoidance of about $1.25M based on support for selection of MNA as the corrective action at the site.

The Trident and UltraSeep generally have found strong acceptance by stakeholders and end users. The direct nature of the measurement technology helps to reduce uncertainties associated with these sites in the past. The ESTCP demonstrations provided an excellent venue for stakeholder and end-user exposure because both of the site teams integrated the technology into their regulatory programs and utilized it in the decision-making process. The results were available for review and comment to relevant local, state, and federal regulators and stakeholders. Since the completion of this project, the technologies have been applied at more than 20 sites throughout the United States, including California, Oregon, Washington, Hawaii, Rhode Island, Massachusetts, Maryland, the District of Columbia, New Jersey, New York, and Florida. (Project Completed – 2008)