Grand Canyon Springs and Exceedence of Maximum Contaminant Level Drinking Water Standards - Implications for Resource Management

Document Type

Conference Proceeding

Publication Date


Publication Title

2018 UCOWR/NIWR Annual Water Resources Conference

Publisher Location

Pittsburgh, PA

First page number:



Historical information from 1950 to 2017 on Grand Canyon spring water quality and quantity was examined to determine the number of times the U.S. Environmental Protection Agency’s Maximum Contaminant Levels (MCLs) for drinking water standards were exceeded, and the factors that might influence water quality in the springs. MCLs are the legal threshold limit on the amount of a substance permissible in public water systems under the Safe Drinking Water Act. MCLs were exceeded at least 136 times in Grand Canyon springs over the 67 years evaluated, with arsenic concentrations exceeding the MCLs most frequently (78 times). MCL concentrations were also exceeded for beryllium, uranium, cadmium, lead and mercury. Locations for the highest concentrations of these elements included Pumpkin Spring, Monument Spring, Horn Spring, Big Spring and Milkweed Spring. Many of the exceedences were recorded from springs issuing from the Redwall-Muav aquifer stratigraphic region. Some isotopic analyses suggest anthropogenic influence on water quality. The highest historical arsenic concentration was reported as 350 times the MCL, the highest beryllium concentration was 32 times the standard, uranium over 13 times higher, cadmium over 3 times exceeding the drinking water level, lead over twice the level, and mercury 1.9 times the MCL. The more stringent Maximum Contaminant Level Goals (MCLGs) for drinking water quality, which are the levels for drinking water which are associated with no or minimal risk, were exceeded regularly in spring water samples. Examining the data further, many of the exact locations of sampling for each spring were not consistent through the years, nor were meteorological and hydrological conditions before and during sampling. These spatial and temporal inconsistencies in sampling, along with large data gaps, make trend and correlation analysis difficult.


Hydrology | Natural Resources and Conservation