LRE Water
Posted On June 25, 2019

Colorado ASR: Closing the Gap

Water storage has been identified as a critical need for Colorado to overcome the projected gap between future water supplies and demand.  The 2016 State Water Plan identified 400,000 acre feet of water storage needs by 2050. The South Platte Basin has the majority of Colorado’s water demand with most of the population and a significant portion of its agriculture. Identifying storage opportunities in the South Platte Basin is a crucial component of closing the State’s future water supply gap. The South Platte Basin Implementation Plan ( calls for storage projects, including underground water storage or aquifer storage and recovery (ASR):

The Metro and South Platte Basin Roundtables strongly advocate for the development of additional surface and groundwater storage, further research of aquifer storage and recovery (ASR), and investigation into additional off-channel storage and reservoir sites in the basin. Additionally, they encourage the consideration of alternatives to “State Water Projects” such as regional collaboration on and financing of water projects.


Many types of projects will be needed to solve Colorado’s future water storage challenges.  Underground water storage has several advantages over surface storage:

  • Decreased permitting costs and schedule repercussions
  • Rapid project implementation
  • Fewer environmental impacts
  • Decreased land use impacts
  • Reduced evaporative losses
  • Potentially lower capital investment requirement

Underground water storage in the South Platte Basin can have statewide benefits.  It will reduce the pressure to consider new trans-mountain diversions from the Western slope, and will put water supplies closer to the demand centers.  South Platte water storage will also help to meet compact requirements.

There has been a buzz of recent activity in Colorado’s groundwater rules and regulations indicates a movement towards using scientific data and methods to maximize possible storage benefits from aquifer systems. This evolution in Colorado’s water administration is leading to renewed interest in developing Aquifer Storage and Recovery (ASR) for water storage.


Colorado’s administration of aquifers originated through application of the Prior Appropriation System during the 20th century when data was sparse and the potential negative impacts of unchecked groundwater pumping were recognized. The adaptability of the Prior Appropriation system can handle conjunctive use of surface water and groundwater use, but it requires that we estimate the timing, location and amount of well pumping impacts to the surface water system (depletion).

The South Platte River basin’s water resources were developed in the dark days before scientific data and methods could accurately estimate depletion. In an attempt to protect water rights during the second half of the 20th century, the industry developed hyper-precise and knowingly erroneous impact analyses through “conservative” over-estimates of well pumping depletion. These methods evolved in a highly litigious environment that has honed our ability to model surface water / groundwater interactions. In the South Platte River basin, well pumping administration necessarily continues to follow the conventions developed before modeling advancements.

Administration in other basins benefits from lessons learned and have improved use of scientific data and models. The Rio Grande Basin, for instance, benefits from the use of a complex surface water / groundwater modeling system that is updated/calibrated annually with hydrologic observations. This model is used to estimate well pumping impacts to the Rio Grande River, resulting in informed, important and sometimes difficult mitigation decision making.

Figure showing a Denver Basin cross section developed using geophysical well logs.


Over the past two years, updates to rules and regulations have incorporated hydrologic data collection and scientific analysis into requirements for aquifer storage and recovery (ASR). The 2018 Artificial Recharge Extraction Rules allow for different rules based on whether the aquifer is located in confined or unconfined conditions. The 2019 Designated Basin Rules will include ASR provisions that require baseline aquifer characterization, water level & water quality monitoring, and predictive modeling of recharged water movement.

The US Environmental Protection Agency (EPA) has also increased stakeholder communications regarding Underground Injection Control (UIC) permitting related to ASR. In a recent public meeting, the EPA clarified UIC application requirements and the process to obtaining project approval.

Although some may feel that these new regulatory requirements are overly restrictive, they are giving water providers legal and regulatory certainty to confidently develop underground water storage. The successful planning, permitting, and implementation of ASR projects is likely to increase in coming years and will make rapid progress towards closing Colorado’s water storage gap..