Title: Site Characterization Text: Naval Weapons Station Charleston, Solid Waste Management Unit (SWMU) 12, was used for treatment of wooden ammunition boxes using pentachlorophenol (PCP). As a result of this and other activities, groundwater at SWMU 12 has been contaminated with high concentrations of chlorinated volatile organic compounds (VOCs). A former 500-gallon UST is the source for the chlorinated solvent contamination, and was removed in 1998. Delineation of the contaminated plume was conducted using several non-invasive, cost-effective, innovative technologies, including tree coring, seismic reflection, membrane interface probes, and water-to-vapor diffusion samplers. Visual Description: Aerial photograph of SWMU 12 site.

Title: Tree Coring (1 of 2) Text: At SWMU 12, the contaminated groundwater located approximately 10 feet below ground surface moved into a lowland forest 100 feet down gradient. Tree coring was used as a qualitative screening tool to assist in plume delineation at SWMU 12. Water extracted from the ground by the tree roots moves up the trunk of the tree as a result of transpiration processes. The coring technique involves the collection of tree cores in 20 milliliter VOA vials and subsequent analysis of the vapor released from them. Core samples were taken from mature trees at the site and analyzed for VOCs. After sample analysis, the tree coordinates were obtained through either global positioning system or traditional surveying. Maps of the analytical results of the tree cores provided the basis for a more efficient, and cost effective subsurface investigation by identifying the general location, orientation and extent of the plumes. Visual Description: Rotating photos of a technician coring a tree and tree core in vial.

Title: Tree Coring (2 of 2) Text: Collection of tree cores distributed throughout the site allowed for identification of potential locations of contaminated groundwater without unnecessarily cutting down trees to use conventional intrusive sampling approaches such as direct push technology and monitoring wells until they could be more precisely located. The map shows the results from tree cores collected at SWMU 12. The blue circles represent non-detect samples while the orange circles represent TCE contaminated tree core samples. The contamination follows a banana shape that was later confirmed with groundwater samples using direct push technology. Deployment of this tool appears to have the most promise for sites in which contamination consists of volatiles and is located in a shallow groundwater environment with a population of trees sufficient to map the plume. Many of the Navy’s sites contain old landfills and or disposal areas that have since grown over with trees. Tree cores may be a useful first reconnaissance tool at these sites. The United States Geological Survey in Columbia, South Carolina and the Southern Division Naval Facilities Engineering Command conducted this work. Visual Description: Aerial photo of SWMU 12 site showing tree core sample locations.

Title: Using Seismic Reflection to Detect DNAPL (1 of 2) Text: Seismic reflection is a non-invasive way to map subsurface stratigraphic features and detect DNAPL. In seismic reflection, an artificial source on the ground surface generates elastic waves, which bounce off subsurface layers and return to the surface, where they are received by geophone sensors. These geophones, spaced about the area of interest, record the amplitude and arrival time of the waves. This information is then processed using a data analysis method called Amplitude Versus Offset (AVO), which can be used to detect the presence of DNAPL contamination. Several hundred carefully spaced geophones are typically required to create a seismic picture of high resolution. Visual Description: Rotating photos of the use of seismic reflection to detect DNAPL.

Title: Seismic Reflection (2 of 2) Text: At the NWS Charleston site, seismic reflection with AVO modeling was used to detect a hot spot of DNAPL. A confirmatory water sample collected in the area of the suspected hot spot showed concentrations of 600 mg/L of total chlorinated hydrocarbons. Seismic reflection is a useful tool for site characterization because it can generate detailed images of subsurface lithology, including potential migration pathways for DNAPLs, using non-invasive methods. More information about geophones More information on using seismic reflection to detect DNAPL. Visual Description: Seismic reflection with AVO modeling reveals a hot spot of DNAPL. Detailed images of subsurface lithology is shown.

Title: Membrane Interface Probes (1 of 2) Text: The MIP system provides real-time, continuous, stratigraphic conductivity logging and vertical profiling of total VOC contamination. The MIP investigation at NWS Charleston SWMU 12 was used to identify lithological zones of preferential subsurface contaminant migration, to evaluate the distribution of VOCs to determine appropriate placement of a monitoring well, and to evaluate the presence of DNAPL in the vicinity of the former UST. A total of 32 MIP borings were made, at depths ranging from 15 to 31 ft bgs. The MIPs had 3 detectors in series: photoionization detector (PID), electron capture detector (ECD), and flame ionization detector (FID). Visual Description: Rotating photos of membrane interface probe (MIP) and map with MIP points.

Title: Membrane Interface Probes (2 of 2) Text: Results from the MIP points at NWS Charleston showed that the interval from 8 to 12 feet bgs has the highest VOC contamination. Locations and depths of groundwater monitoring wells were based on results from the MIP study. Using membrane interface probes to delineate the plume eliminated costs associated with installation of superfluous groundwater monitoring wells. Visual Description: Photo of map of MIP points and groundwater monitoring well results.

Title: Water-to-Vapor Diffusion Samplers (1 of 2) Text: Water-to-vapor diffusion samplers are screening tools used to look for VOCs in bottom sediments of surface water bodies in areas of groundwater discharge. These samplers consist of a polyethylene membrane separating a 50 mL vial. This vial is placed in the bottom sediments of a surface water body, allowed to come to water-vapor equilibrium, then the resulting vapor is analyzed using a gas chromatograph. Water-to-vapor analyzers are inexpensive and can determine whether VOCs are discharging from groundwater into a surface water body. Visual Description: Picture of marsh, picture of water-vapor sampler with flag on top.

Title: Water-to-Vapor Diffusion Samplers (2 of 2) Text: At NWS Charleston, water-to-vapor diffusion samplers were used to determine if VOCs were present in the marsh. Water-to-vapor diffusion samplers are useful for indicating the presence of VOCs, but confirmatory sampling must be conducted to accurately determine concentration levels. Visual Description: Picture of marsh, picture of water-vapor sampler with flag on top.