Submarine Ground-Water Discharge of Mercury to Sinclair Inlet, Puget Sound from the Bremerton Naval Complex, Washington, USA

Since the State of Washington Puget Sound Ambient Monitoring Program began monitoring the sediments of Puget Sound in 1989, the sediments at the Sinclair Inlet site, adjacent to the Bremerton Naval Complex (BNC), routinely contained the highest concentrations of mercury. A site investigation was initiated in 1990 and the Record of Decision was signed in 2000. The 2007 Five-Year Review of the BNC Record of Decision indicated that there is insufficient information to determine whether the remedial action is protective of ingestion of mercury in rockfish by subsistence finfishers. In addition, it was noted that a monitoring well adjacent to the shoreline contained concentrations of total mercury as high as 5,240 ng/L. In 2008, USGS began an investigation of possible migration of dissolved and particulate mercury from the vicinity of this well to the adjacent marine water. During sampling in January and May, dissolved mercury concentrations in this well ranged between 450 and 830 ng/L. During intensive day-long monitoring on May 6 over a tidal range of 5 m, the highest concentrations of mercury were measured at the top of the screened interval and decreased with depth down the 4-m screen. The highest mercury concentrations in the well were measured in saline water several hours after higher high tide at the time when the ground-water flow direction switched from landward to seaward. It is postulated that the salts in seawater intruding into the area upland of the well during the rising tide interacted with contaminated fill material to release mercury into the saline ground water. This hypothesis will be tested in a tidal study of mercury in the well and in six lower intertidal piezometers during two days in June 2008 when tidal ranges are again 5 m.