Mitigation of Groundwater-Dominated Lakebed Playas Crossed by the Ruby Pipeline, Utah and Nevada

The Ruby Pipeline is a 42-inch diameter pipeline that will transmit natural gas 675 miles from Opal, Wyoming, to Malin, Oregon. The pipeline alignment crosses landforms designated as playas at several locations in Utah and Nevada. Federal agencies reviewing environmental documents requested mitigation based on the concept that playas collect and hold rainwater on impervious clay bottoms for long periods of time, and that an open-cut trench could drain ephemeral lakes by penetrating impervious clay bottom soil layers and permanently alter the surface water hydrology of the playas. Trench plugs, segregation of excavated impervious soil, limited construction right-of-way, impervious backfill, and construction during the ‘dry’ season were the recommended mitigation measures, presumably to reduce the potential for surface water collected on the playa to drain into the subsurface through a trench cut across the playa. The surface-water hydrology concern may pertain to playa environments in semiarid areas such as the southern High Plains of the United States, notably northern Texas. The playas crossed by the Ruby Pipeline are lakebeds of major ancient lakes (Lake Bonneville in Utah, and Lake Lahontan and Lake Meinzer in Nevada) that were hundreds of feet deep and occupied extensive, topographically closed drainage basins. These lakebed playas are dominated by shallow groundwater. Surface water collects on the playa surfaces but is not responsible for playa formation or preservation. The water tends to be salty in lakebed playas in Utah and Nevada compared to fresh water in the ephemeral playa lakes in northern Texas. This brief case history describing playas dominated by groundwater instead of surface water may help advance the understanding that mitigation useful for surface-water dominated playas is not needed for groundwater-dominated playas. Geotechnical investigation included soil borings, test pits, laboratory testing, and surface geophysical surveys (seismic refraction and refraction microtremor [ReMi] methods).