Holes and cracks scar Black Mesa landscape

May indicate overdrafting of N-aquifer

by Tanya Lee and S.J. Wilson
Black Mesa, Arizona (NFIC)

Marshall Johnson first noticed the holes in the ground six years ago when he was building a new house for his mother in To Nizhoni Ani (Beautiful Spring Speaks) Valley on Black Mesa in northeastern Arizona. He put old posts in a dozen holes around his mother’s house to keep her sheep from falling in and injuring themselves. Then he began to wonder.

And to walk the land, eventually tracing two startling series of hundreds of holes and cracks running for approximately 30 miles southwest to northeast across the mesa. There may be more, he says, explaining that he has had time to investigate, inch by inch, only a small part of the landscape that is home to the Hopi Tribe and about 27,000 Navajo.

The N-aquifer

Under Black Mesa lies the N-aquifer, the sole source of drinking water for the Hopi and thousands of Navajo. Both tribes pump water from the N-aquifer for municipal use, but more than half of the water that is removed from the aquifer each year is pumped by Peabody Energy to support its coal mining operations on Black Mesa just a few miles north of where Johnson first discovered the holes.

According to a United States Geological Survey Investigations Report 02-4211, in the year 2000, total water withdrawals from the N-aquifer were 7,740 acre feet. Of that amount, less than half – 3,250 acre feet – was pumped by the Hopi and Navajo Tribes for municipal use. The remaining 4,490 acre feet was pumped by Peabody, which uses water from the Naquifer to slurry coal from the Black Mesa Mine to the Mohave Generating Station in Laughlin, Nevada.

Signs of decline

The N-aquifer also feeds the seeps and springs that are essential to the religious and ceremonial life of both tribes. Over the past several years, religious practitioners have observed that many of their once vibrant sacred springs have dried up, and yet more are producing less water than in the past.

Farmers have seen a similar phenomenon in Moencopi Wash. The waterway in which their elders once swam now flows only part of the year, and even then the flow is much less than the elders remember.

Add to these observations a 2000 report, “Drawdown: Groundwater Mining on Black Mesa” prepared by the Natural Resources Defense Council. The NRDC report, which analyzed data on the N-aquifer collected by the U.S. Department of the Interior’s Office of Surface Mining Reclamation and Enforcement, the USGS, and Peabody itself, found that the criterion that is supposed to be used by OSMRE to judge the structural stability of the aquifer had been exceeded in six of the 15 monitoring wells set up to track whether the aquifer is in danger.

The criterion is that “the measure of water pressure known as the potentiometric head, the height to which confined water will rise when tapped by a well, should rise at least 100 feet above the aquifer’s top.”

In six N-aquifer monitoring wells, the potentiometric head is less than 100 feet. The NRDC report also stated, “A 1993 study conducted with the aid of Hopi elders found that the outflow from springs sacred to the tribe had been dropping significantly. Little Burro Spring and Burro Spring, sources of water for the Hopi Grey Flute Society ceremonies, were depleted, as were the springs at Rock Ledge, Moenkopi, and Pasture Canyon. Rock Coyote Spring, marked by a commemorative shrine, was virtually dried up, although water could be seen in the bottom of the original impoundment structure.”

The observations of religious practitioners and the NRDC report have led many to ask if the N-aquifer is in danger of sustaining irreparable harm from too much pumping (overdrafting). Add Johnson’s observations, and the answer may be “yes.”

Aquifer overdrafting and land subsidence

Dr. Lon House of Water & Energy Consulting, a California-based company, explained overdrafting of an aquifer this way: “There are three principal surface symptoms associated with overdrafting of an aquifer. The first symptom is that the water level in the aquifer starts dropping (water levels in wells drops).

“Associated with that are surface expressions that the water in the aquifer is being reduced – springs start drying up. The technical term is the piezometric head is being reduced. Both of these symptoms are an indication that withdrawals from the aquifer are exceeding recharge.

“However, if the overdrafting is stopped at this level of symptoms, the aquifer’s integrity has not been compromised and allowing sufficient recharge will refill the aquifer. “The third principal surface expression is ground subsidence or sinkholes.” Dr. Blaine Reely is a civil engineer and hydrologist in Tucson. After seeing the photographs (one published with this article), he said, “Such cracks and holes in the ground are typical surface manifestations of ground movement that indicates land subsidence.”

He noted that such manifestations often occur along parallel tracks. The most common reason for land subsidence, he said, is water being removed from an aquifer. The Center for Land Subsidence and Earth Fissure Information, explains on its website (http://www.azgs.as.gov/CLASEF.htm) how land subsidence occurs.

“As water is pumped from an aquifer, the water occupying the spaces between the rock particles is removed and the water level, described as the water table, drops. Without the water, the particles then become more tightly packed together. In other words, the particles compact and consolidate.

“With the continued pumping of groundwater without adequate recharge, the sediments become increasingly compressed, causing the land to settle or subside. This lowering is called land subsidence and is caused by the compaction of the aquifer. Subsidence occurs gradually and spreads over wide areas.”

That the holes and fissures on Black Mesa are occurring over a wide area is evidenced by Marshall Johnson’s maps. That it has been a gradual, and quite recent, development, is suggested by the comments of his mother, Lorraine Johnson. She is 78 years old and has lived on Black Mesa, tending sheep, her whole life. She said that she too first noticed the holes six years ago near her summer camp where she built a new house. She said she had not seen such holes before that time, despite her long and close familiarity with the landscape of Black Mesa.

What land subsidence is

Dr. House said that land subsidence “is a very serious development. This means that the aquifer itself is collapsing. Water is being pumped out of the interstitial spaces and the remaining structure is insufficient to support the weight above it, so it collapses.”

He continued, “This is a very serious development, because it is irrevocable and permanent. Once this happens, the aquifer in that area is ruined (the caverns have collapsed) and you can’t put more water back into the aquifer even if you stop pumping. Wells and springs that depend upon the collapsed part of the aquifer are gone forever.”

After seeing the photographs, Dr. House said, “Something is happening (on Black Mesa) and it isn’t good, and it is widespread.”

The worst-case scenario is that the N-aquifer has begun to collapse because too much water has been pumped from it to maintain the water pressure that ensures the aquifer’s structural stability. This scenario is possibly supported by the NRDC report, which found that the criterion used by OSMRE to determine the structural stability of the aquifer has been exceeded. Dr. House, Dr. Reely, and Dr. Abe Springer, a hydrologist at Northern Arizona University, said that more work needs to be done, including identifying the holes and cracks using a GPS unit for more accurate mapping and comparison of the information thus obtained with satellite imagery.

But it was not sophisticated scientific equipment that brought this potentially devastating development to light.

It was a man who walked the land with his eyes open.