Navajo Nation Groundwater Supply

 

Groundwater is water that has landed on the ground and percolated through the soil to the groundwater table. It is water located beneath the surface and is held in the small spaces between soil particles.

It is also an especially important water source for the NN providing for commercial, industrial, agricultural uses and more than 99% of domestic and municipal water supply. According to Cooley et al. (1964), practically all groundwater on the NN occurs in sedimentary rock formations, such as Coconinio and Navajo Sandstone, that overlie impermeable granitic and metamorphic rock formations. Generally, aquifer systems throughout the NN consist of permeable sandstone between nearly impermeable layers of siltstone or mudstone, which act as an aquiclude.
Caption: Illustration of groundwater stored in space between soil particles

 


Four Corners Aquifers

There are several important aquifers located throughout the Navajo Nation including:

 

  • C aquifer - 413 million acre-feet storage
  • N aquifer - 290 million acre-feet storage
  • D aquifer - 50 million acre-feet recoverable volume

 

Caption: Red areas represent aquifer locations on the Navajo Nation (outlined in blue).

 

 

 

C aquifer

The C aquifer is a multiple aquifer system that stores groundwater over an area larger than 27,000 square miles and is the most productive aquifer in the Little Colorado River basin. The aquifer is named for the Coconino Sandstone, which is the primary water-bearing unit within the system and is found continuous in the subsurface for nearly the entire extent of the aquifer. The Coconino Sandstone generally has a thickness ranging between 60 and 900 feet. Upper portions of the aquifer in the Kaibab Formation and Coconino Sandstone have good quality water where as water in the Upper Supai Formation is degraded due to increased dissolved solids from the extensive evaporate in the formation (BOR, 2007).



N aquifer

The N aquifer is found laterally across 5,400 square miles in and around the Navajo and Hopi Reservations including the Black Mesa area and holds an estimated 180 to 400 million acre feet of water (BOR, 2007). The aquifer name is derived from the Navajo Sandstone, which is the primary water bearing unit and is approximately 1,000 feet thick (Macy, Brown and Anderson, 2012). The N aquifer is an important water source for the Black Mesa area of the Navajo and Hopi Indian Reservations. The N aquifer is an important municipal water source for the Navajo and Hopi residents of the area as it has a total dissolved solids concentration less than 500 milligrams per liter and has better water quality than the D aquifer which lies over the N aquifer (Truini and Macy, 2006).



D aquifer

The aquifer is named for Dakota Sandstone which is the primary water bearing unit for the aquifer. The D aquifer lies above the N aquifer and there may be some leakage between the aquifer units. Water-rock reactions, due to weak acid and strong base conditions lead to the dissolution of more solids in the groundwater. As a result, the D aquifer has a total dissolved solid concentration of more than 1,000 milligrams per liter, which exceeds the US EPA recommended level for drinking water (Truini and Longsworth, 2003).

 

Learn more about the impact of groundwater contaminants such as arsenic on Navajo Nation drinking water supply.