The Grand Canyon National Park (USA) water corridor: water supply, water quality, and recharge along the Bright Angel Fault

The “water corridor” of Grand Canyon (Arizona, USA) includes the Transcanyon Pipeline, which conveys water from Roaring Springs (North Rim) to Grand Canyon Village (South Rim) to supply the park’s 5–6 million annual visitors. The North Rim water has been reclaimed at the South Rim Water Reclamation Plant (WRP) since the 1960s. This report describes a hypothesis in which the returned pipeline water infiltrates along the Bright Angel Fault and intermingles with groundwater. Geochemical tracers (major ions, stable isotopes) are used to define end members and develop mixing models for South Rim groundwater. It was found that Havasupai Gardens Spring water, discharging below the South Rim along the Bright Angel Fault (~1 km below the WRP), is ~40% North Rim water. Other South Rim springs below the rim also have 10–60% anthropogenic North Rim contribution. Similarly, Coconino Plateau groundwater wells in the town of Tusayan and the Pinyon Plain uranium mine may contain tens of percent of North Rim water. Compatible with this hypothesis, pharmaceutical and personal-care products present in discharge from the WRP, and also in Havasupai Gardens Spring and Pipe Creek Spring below the rim, were found in trace amounts. This study explains the hydrochemical variability of South Rim springs and groundwater as primarily due to anthropogenic groundwater mixing and secondarily due to variations in local recharge, as proposed by others. The hypothesis suggests that uranium mining, local groundwater pumping, and management of the pipeline and WRP infrastructure are all part of an interconnected South Rim groundwater system.