No Increased Public Heath Risk Associated with Mercury from Nevada Flooding

Jan. 23, 2017
Water quality samples taken after the January 2017 major flood event have been analyzed by an independent lab and the results were provided to state and federal regulatory agencies for their review and analysis on January 19.

Water quality samples taken after the January 2017 major flood event have been analyzed by an independent lab and the results were provided to state and federal regulatory agencies for their review and analysis on January 19. To clarify, the SouthEast Connector is not a mercury cleanup project. Soil containing mercury surrounds the project. Mercury will continue to flow into the area from Washoe Lake via Steamboat Creek. However, as an added benefit to construction of a new roadway, approximately 300,000 cubic yards of soil containing mercury will be encapsulated under the roadway and no longer exposed to the environment as it was prior to the start of construction. To date, 125,000 cubic yards are encapsulated within the constructed roadway embankment and 70,000 cubic yards were located within stockpiles on site.

“We have concluded there is no increased risk to public health,” stated Dave Emme, administrator of the Nevada Division of Environmental Protection.

The mercury, left over from the Comstock days when it was used in mining operations, has been brought into the Truckee Meadows by sediment flowing through Steamboat Creek water for over 150 years. The mercury is not a public health risk unless the affected water or soil is consumed. Some of the soil with concentrations of mercury had been excavated in preparation for being encapsulated in the roadway when the 45-year flood event on Steamboat Creek occurred earlier this month. There are 12 stockpiles of this soil containing mercury and flood waters reached one stockpile.

“The RTC is doing what they need to be doing and is in compliance with the regulatory controls we have established. They are not responsible for the increase in mercury concentrations which can be attributable to this major flood event,” stated Kristine Hansen, US Army Corps of Engineers. Both state and federal regulatory agencies are in concurrence with the conclusion that there is no increased health risk associated with the construction or the flooding.

Testing showed mercury within the water at 0.0086 parts per million at South Meadows Parkway and 0.013 parts per million at Clean Water Way. South Meadows Parkway is the southern limit of the project and Clean Water Way is the northern limit of the project. While results indicate an increase in total mercury within Steamboat Creek, a drone flyover video filmed on Monday, January 9, 2017, during the peak of the floodwater flows indicates the increase in total mercury was most likely contributed to previously existing soil containing mercury within the Steamboat Creek channel and within soil containing mercury that is located outside of the construction project limits. The floodwater flow paths within the construction site were mostly flowing over soil that either did not contain mercury or were flowing over areas that had significant removal of soil containing mercury.

The RTC is working with regulatory agencies and developing a post-storm recovery plan. The plan will detail methods for handling and properly treating any floodwater still located on the project site as well as methods for handling and properly treating any sediment that is within the project site that was mobilized during the flood event itself. Even after the project, some mercury will remain in the environment and continue to flow into the area via Steamboat Creek or spread by future flood waters.

The SouthEast Connector is a new evacuation route for the community that will be passable in a flood event similar to that which the region experienced in 1997. The primary purpose of the road is to improve regional connectivity and reduce traffic congestion. Flooding is fully expected within the project site as the SouthEast Connector is being constructed in a flood plain. Constructions of the wetlands in the project area will reduce flooding in other nearby areas. The area also needs to have ponding water in order to prevent floods in other parts of the community.

The excavation and stockpiling of soil containing mercury reduced the amount of mercury exposed to flood waters during the recent storm.