DGM Services: Vieques Island
NAEVA was contracted to map most of the beaches and some select interior roads inside the Former VNTR totaling approximately 300 acres. The objective of the investigation was to accurately detect any subsurface Munitions and Explosives of Concern (MEC) at the beaches and roads as part of the preparations for opening them to the public. NAEVA’s responsibilities included performing a geophysical prove-out (GPO) prior to the investigation, collecting and processing digital geophysical data over the entire site, selecting targets, and reacquiring 100% of the targeted anomalies.
NAEVA selected the EM61 MK2 equipped with 1m x 0.5m coils as the most appropriate DGM technology for this investigation. The system was configured to collect four bottom coil time gates. Since data collection was performed under varying terrain and vegetation conditions, several positioning methods (Real Time Kinematic (RTK) Global Positioning System (GPS), Robotic Total Station (RTS) and on-ground control (fiducials)) and system transportation configurations (wheel and litter-mode) were deployed.
Prior to the start of geophysical mapping, NAEVA successfully performed a GPO demonstrating the data collection and processing methods for the project. The GPO was made up of two 30-meter by 30-meter grids. NAEVA demonstrated successful detection and accurate targeting for each of the positioning methods in both wheel and litter-mode configurations.
Once NAEVA’s performance in the GPO had been successfully demonstrated, DGM in the field area commenced. In most cases, NAEVA was able to observe tracks in the beach sand from the wheeled coils to ensure complete data coverage. In locations where ground cover obscured the tracks, painted ropes are used to maintain straight-line profiling. NAEVA’s field personnel inspected each grid block for quality and to ensure that no positioning drop-outs or data gaps existed. Complete grid blocks were then transferred to NAEVA’s offices for final processing and target selection. All mapping, processing, and QC information were entered into the Munitions Response Site Information Management System (MRSIMS).
Throughout the course of the project, NAEVA performed a series of Quality Control (QC) procedures designed to demonstrate the adequate performance of all equipment and personnel. All of the QC checks were based on US Navy guidelines and met the requirements detailed in the Site-Specific Work Plan. Tests were performed prior to, during, and after all data collection sessions.