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Gross Dam Expansion

The Big Picture

While the expansion of the Gross Reservoir will have a great impact on Boulder County over the next seven years or longer, the "extra" drinking water supply stored in the expanded reservoir will exclusively serve Denver Water customers at the expense of Boulder and surrounding areas.

The project was intended to address an expected water shortfall that would have hit in 2016. However, due to conservation efforts, that shortfall never happened. Sustainable water management practices are required in this era of drying climate. Expanding Gross Dam is using 20th century technology to solve a 21st century challenge. The project is also claimed to solve an imbalance between Denver Water's north and south supply systems, however in the now likely event that the expanded capacity reservoir remains "unfillable", their imbalance will remain. 

Rather than spending $380 to $450 million (and maybe more) on a dam expansion project that threatens our local environment, we should concentrate our efforts on continuing water conservation efforts in the Denver area and look for ongoing, sustainable solutions to support a growing population in a world affected by climate change. Climate scientists tell us that by the middle of this century there will likely not be enough water to fill even the existing reservoir, let alone a larger one. This ill advised project, should it proceed, may well result in Denver Water "building" a big, dry hole.  

Gross Dam Expansion: Welcome

A Documentary made for PBS by Boulder cinematographer Len Aitken, gives an overview of the controversy over the expansion of Gross Dam and Reservoir.

Gross Dam Expansion: Video

Current Status

On 2 November 2021, Boulder County Commissioners voted to accept a settlement agreement with Denver Water. The agreement was conditional on Boulder County dropping any legal action against Denver Water, challenging them to go through Boulder County's 1041 process.

Click here for Boulder County's Project page

Click here for the County's Project Document Repository

The 1041 process was the final hurdle for Denver Water to overcome, and with that out the way and having all other required federal permits, construction is scheduled to start in April 2022

Gross Dam Expansion: Welcome

Gross Dam Expansion Campaign Website

Gross Dam Expansion: News


This link takes you to the document repository for the Environmental Impact Study. The repository of documents is huge, however the final report can be downloaded by clicking here: FINAL REPORT

The federal permit issued by the Federal Energy Regulatory Commission (FERC) approving the project

The federal permit issued by the U.S. Army Corp of Engineers approving the project

Gross Dam Expansion: List
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