In 2010 more than 65,000 acre-feet of water was extracted from the aquifer in the Upper Santa Cruz basin from Green Valley to Sahuarita - about 90 percent by existing mines and farms, according to the Arizona Department of Water Resources.
Natural recharge to the aquifer replaces some of that pumped water in a good year, but none of that pumping was offset by imported renewable supplies. Some was offset by recharge of Central Arizona Project water in Marana.
The unfortunate truth is that mines and farms have no obligation to use renewable water or recharge renewable supplies to compensate for overdrafting of local aquifers. But they can do so when provided the opportunity.
The city of Tucson is faced with an opportunity to approve construction of two pipelines that will carry renewable water supplies down to Green Valley and could have the capacity to offset up to 50 percent of this pumping in the future.
But some with the city believe we should intentionally limit our ability to mitigate that considerable overdraft of our aquifers because of concerns that some of that recharge will offset pumping by the Rosemont Mine. This view is shortsighted and actually subverts our regional water-management goals.
While the pending Rosemont Mine is clearly an important issue for this community and the future of the region, it should not be a determining factor in planning for future water management in the Green Valley area.
We should be seeking to achieve regional water sustainability. This goal is embodied in state law, under the 1980 Groundwater Management Act with its objective of achieving safe yield for our local aquifers by 2025, and in the guiding principles established by the Joint City/County Water Study, which espoused greater regional cooperation to increase our local use of renewable water supplies.
Intentionally limiting our ability to make use of renewable water supplies - especially to offset overdrafting of critical aquifers upstream of the Tucson metro area - to give the appearance of not aiding in the approval of a controversial mining project may appear to be good politics, but that is a very narrow view of policy-setting in this context.
It flies in the face of sound water-resource management. It also subverts the safe-yield goal for our aquifer and the principles established in the water study. I strongly encourage our leaders and our community to get behind the idea of encouraging as much recharge in the Upper Santa Cruz basin as possible. This approach reflects a commitment to water-resource sustainability, which is good for the future of the region.
Christopher Brooks is a hydrologist and attorney in Tucson who served on the oversight committee for the Joint City/County Water Study.