HOW GEOSCIENCE STOPPED A FEDERAL HIGHWAY PROJECT OR THE SINKHOLE THAT (ALMOST) ATE LINDBERGH HILL

A $12 million federal highway project in Grand Canyon National Park (GRCA) was suspended when Geoscience studies related to the park’s Trans-Canyon Water Line (TCWL) infrastructure project identified serious potential groundwater vulnerabilities. Expansion of a proposed staging area and construction of a “mobile” asphalt plant to support the paving project were halted.

The TCWL, one of the largest infrastructure projects in the National Park Service, will replace virtually the entire aging GRCA drinking water system. The drinking water supply relies solely on groundwater discharges from deep karst perennial springs below the Kaibab Plateau on the North Rim of the Grand Canyon. Springs are also the primary water supply for backcountry travelers and support exceptionally diverse ecosystems.

Ongoing studies are characterizing the hydrogeology of the entire Kaibab Plateau. The aquifer system consists of two “stacked”, primarily karstic, aquifers from the surface up to 1200 m deep. The aquifers are connected by faults and collapse features that have propagated through intervening aquitards and allow groundwater to travel from the surface to the deep karst aquifer. A dye trace study in 2016 established connections between plateau sinkholes and multiple springs below the canyon rim, up to 40 km distant from the sinks, and revealed a highly complex hydrologic system.

Depressions on the plateau were delineated from a LiDAR DEM and characterized as sinkholes using GIS and machine learning algorithms. Sinkhole density correlates with proximity to fault zones.

GRCA’s world-class cave system provides a window into the subsurface. GRCA is collaborating with academic partners to acquire underground LiDAR data of hydrologically important cave systems, characterize their sub-surface stratigraphy and geologic structure, and integrate this data with airborne LiDAR into a comprehensive, interactive 3-D hydrogeologic model of the Kaibab Plateau.

GRCA is using GIS modeling to identify alternate, more suitable sites for consideration as staging areas. By locating development away from known sinkholes and faults, GRCA is significantly reducing the potential risk for fuel, chemicals, human waste, and other contaminants to enter and contaminate groundwater and the park’s drinking water supply.