A standardized test marine underwater site is required to evaluate the performance of technologies designed to detect unexploded ordnance (UXO) in underwater environments. The Marine Sciences Laboratory (MSL), a division of the Pacific Northwest National Laboratory (PNNL), has been funded to evaluate Sequim Bay, Washington as a potential underwater test site. The MSL is located on the shore of Sequim Bay, a small embayment on the Strait of Juan de Fuca in northwest Washington State, which has a wide range of depths and sediment types relevant for evaluating UXO detection technologies.

This was a preliminary design study conducted by Pacific Northwest Laboratory (PNNL) at its Marine Sciences Laboratory (MSL) on the Olympic Peninsula in Washington State. The objective was to acquire information to further inform the design of a final test site for evaluating underwater unexploded ordnance (UXO) detection technologies and equipment for the Strategic Environmental Research and Development Program (SERDP).

The technical approach for the preliminary study consisted of three tasks: 1) obtain information about typical underwater UXO sites and their substrates, 2) characterize Sequim Bay and locate areas of substrates similar to those described at typical UXO sites, and 3) propose test areas in Sequim Bay that could be used in a final test site design.

Task 1 focused on determining the sediment properties at a representative sample of current and former military sites where underwater munitions are a concern. This information was collected from reports provided by or publicly available from the Military Munitions Response Program, the U.S. Environmental Protection Agency, the Naval Facilities Engineering Command, various state agencies, and scientific literature. While the reports primarily focused on the sediment types available at these sites, additional information about the bathymetry, currents, tides, and wave action was included when available. This survey of the Munitions Response Site Inventory found that a large majority of the underwater sites of UXO concern lie in rivers, lakes, and coastal waters of the continental United States. The bottom compositions at these sites are mixtures of sand, soft sediments, and gravel, consistent with the range of sediments found in Sequim Bay.

Task 2 included underwater video, diver surveys, and substrate coring to find flat bottom areas that have a consistent substrate type for a linear distance of at least 150 m to 200 m. Locations surveyed covered approximately 8 hectares of bottom area. Researchers documented the presence of mud/silt in central Sequim Bay, silt and sand along Travis Spit, gravel and sand near the PNNL facility at the entrance to Sequim Bay, and mixed substrate (sand and gravel) near Middle Ground. This information was recorded and mapped. Additional video surveys documented sandy substrates outside Sequim Bay.

Task 3 identified six areas of varying sizes, depths, and substrate types as potential test site areas. One area south of Travis Spit in Sequim Bay may meet more prerequisites expressed by SERDP, but any of the sites could potentially be developed. Environmental permits and approvals would be required for most of the proposed areas. The test site design, number and type of objects, specific locations of objects, the methods of emplacement of objects, monitoring for movement, and retrieval of objects must all be addressed prior to approaching the stakeholders for permits. SERDP will need to review the proposed areas and make final recommendations regarding test site areas.

The overall conclusion, however, is Sequim Bay could be a unique test facility for testing technologies designed to locate UXO materials. The location is marine, nearshore but relatively protected, has a variety of sediment types, and is located near a federal marine sciences laboratory that can support operations.