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Your Assimilative Capacity Has Been Reached

2013 March 29

By Pam Lazos

On a recent excursion to Santa Fe, N.M. I was struck by how dry it was even in the late fall. Yes, the climate ranges from arid to semi-arid, but should snow feel dry? For me, it accentuated what’s true of much of the western half of our nation: they’re running out of water.

The Ogallala aquifer, a 10-million-year-old deposit, provides water to New Mexico and seven other High Plains states and is the most important water source in the region, serving an area of 174,000 square miles. Eighty-two percent of the people living in the High Plains get drinking water from this aquifer yet most of the Ogallala is used for agriculture. About 80 percent of the food grown in the U.S. comes from this part of the country.

No wonder the Ogallala is being depleted at a rate 14 times faster than it’s recharging. Population growth, and contaminants like pesticides and nitrates, have contributed to its decline.

Failure to recharge means not only less water but also degraded water quality. Recharge occurs through rainwater and snowmelt combined, a paltry one inch per year. With eight states tapping into one aquifer, at this rate of withdrawal and recharge the Ogallala will be depleted in a few decades and once depleted there is no turning back.

The main barrier to further recharge is impermeability. Currently, the specific yield of the Ogallala — meaning what’s available for use — is 15 percent. The rest of the water is locked up in the unsaturated zone where it’s inaccessible due to impermeability.

Until technology is developed to move this water to the saturated zone, the high quality Ogallala, once used for drinking without either filtration or treatment, will continue to degrade. If a water body is unable to refresh, the water quality tanks, or to put it in scientific parlance, its assimilative capacity, the level at which the water can no longer cleanse itself, has been reached.

Here in the water abundant eastern states drought conditions last seasons, but in the western higher elevations, arid land droughts can last for years, turning an acute issue into a chronic one. Without attention, chronic problems tend to become emergencies. While some inroads have been made regarding the impermeability puzzle, it’s only been achieved on a small scale. It’s time to focus our attention locally before our most valuable global natural resource is beyond recharging.

About the author: Pam Lazos works in Region 3’s Office of Regional Counsel chasing water scofflaws and enforcing the Clean Water Act. In her free time, when her family allows, she writes both fact and fiction, but mostly she likes to laugh.

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog.

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5 Responses leave one →
  1. Kevin permalink
    March 29, 2013

    Great read!

  2. Nazrul I. Khandaker permalink
    March 29, 2013

    It is quite alarming and thanks for sharing with us. Global climate change scenario is causing a complicated and unpredictable weather pattern in many parts of the world and Santa Fe is perhaps no exception. Your comments on Ogallala aquifer are valid and what I gathered from local Hydrogeologist working in Nebraska is also shocking. It is getting depleted due to excessive withdrawal and lacking much needed recharge and citizens are targeting deep aquifers within the Ogallala often extending 1200 feet plus. Ultimately it will be barren and we have to look for alternatives. The consequences related to excessive withdrawal of underground water are certainly forcing many Midwestern and rocky mountain regions to explore deep into the aquifer which is very costly and not always yielding safe water, often associated with high chlorides or other dissolved ions deposited within the formation water during entrapment of water within the porous sediments. In addition, leaving aquifer unreplenished has serious detrimental ecological and landscape obliteration aspects such as subsidence, generation of mild earthquakes, local-scale desertification, etc. I would like to recommend the following conference paper as a reminder to all of us in connection with this topic.
    Managing Drought and Water Scarcity in Vulnerable Environments:
    Creating a Roadmap for Change in the United States
    Geological Society of America
    September 2006 • Boulder, Colorado, USA

  3. iwallmount permalink
    April 1, 2013

    nice post

  4. Gianni Nocchi permalink
    April 3, 2013

    the US government have to think so good about this water reservoir, because from it depends so many and really important human activities..

    Gianni from Italy

  5. pam lazos permalink
    April 3, 2013

    Thank you. I will take a look at the paper. It’s good to know that people are thinking seriously about this issue.

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