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Oct 22

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Denver Basin Water Supply Planning: A Cost Comparison to Renewable Water and Recent Water Level Trends

Stephanie Luce, Leonard Rice Engineers, Inc.

Dating back to the mid 1800s, ground water pumping has been a flourishing practice; although originally the wells were shallow and pumped via windmill for mostly livestock and homesteads. By the 1950’s ground water pumping was far more advanced and commonplace, and by the 70s and 80s the practice was popular enough in the Denver Basin that regulations were imposed through Senate Bill 213 and Senate Bill 5.

The longer pumping went on, the more Geologists learned about the finite supply of the Denver Basin and its dynamic inner-workings. The yield of a particular well was determined to be a function not only of its location within the Basin and hydrogeology, but also its proximity to neighboring wells, and the rate and duration of use.

Due to the rapid growth during the 1990s and 2000s, ground water became an integral part of municipal supply for the greater Denver area. As the use of ground water increased, levels in the Denver Basin began to show an equally rapid decrease leading to worry that the artesian pressure head of the aquifer would be drawn down such that the aquifer would become–in essence–unconfined. With the looming threat of permanently depleting the supply of the Denver Basin, many municipalities sought alternate sources to alleviate the stress on the aquifer. As such, recent studies have shown a localized moderation of water level declines. In some cases the water level decline trends decreased. This decrease in declining trends may have been due in part to decreased or stabilized pumping of Denver Basin ground water wells; the transition of some aquifers from artesian to unconfined; and/or vertical leakage between the aquifers within the Denver Basin.

Despite the slowdown of declining water level trends, the rapid population growth in Colorado still required the municipalities in the area to become creative with their resources. Through the purchasing of surface and ground water rights, pumping and piping, lease agreements, and change cases, Colorado municipalities have found the real pivot point to the balancing act of water resources in economics. Surface water rights in Colorado are predominately over-appropriated, at which point the economist’s bread and butter comes into play: supply and demand. The use of surface water rights requires a significantly greater financial burden associated with the acquisition and start-up cost than with ground water rights. At which point, the question becomes: Is the initial financial investment worth the stability of a renewable water supply source?

The cost elements associated with surface water supply vary based on seniority of the right; distance from the source to the storage facility and/or users; amount of necessary treatment; expense of storage, etc. Conversely, the acquisition of a ground water rights requires only well permitting and construction, leading to a much lower initial cost. After the start-up costs of a ground water supply, the primary expenses to maintain the source are operation and maintenance, and necessary treatment.

On July 27, 2010 Chris Sanchez and Daniel Niemela, of Bishop-Brogden Associates, presented at the AWRA Colorado Section monthly Luncheon Program. A comparison of four scenarios was performed to help further depict the long-term costs to a water right user. The scenario defining criteria were varied with options of a municipality relying on either a “near” or “far” surface water supply; with either senior or junior priority, as well as either low or high Total Dissolved Solids (TDS). These surface water scenarios were compared to a non-renewable ground water supply from the Denver Basin with either low or high yields.

For each scenario it was found that the cumulative capital cost and operation and maintenance for a ground water supply was $0.00 for year 1, and ranged from approximately $400M to $850M by year 50. The surface water supply scenarios for year 1 ranged from about $150M to $200M and reached somewhere between $325M to $725M by year 50. Although these results, over the 50-year study period, were not linear, when further analyzed, these results show that a municipality is faced with the decision of supplying a greater start-up cost for a surface water supply source, or incur a typically larger cumulative monetary burden over the term of a water supply plan.

The solution that many municipalities in Colorado have found to be effective is the idea of project cooperation or piggybacking. By using current infrastructure and working with other entities to share the cost of new or expanded infrastructure as well as a combination of ground and surface water supplies, many municipalities have managed to deliver their constituents a necessary water supply without burdening themselves, or their users, with too much of a monetary responsibility, as well as lessening the stress put on the Denver Basin put on by intense ground water pumping.

Permanent link to this article: http://www.awracolorado.org/denver-basin-water-supply-planning-a-cost-comparison-to-renewable-water-and-recent-water-level-trends/