In a previous article, How is the Tucson Water Conservation Fund Money Spent?, I noted that Tucson Water customers are being charged a “conservation fee” that is apparently being poorly spent on actual water conservation.
One of the eco-fads promoted by the program is rainwater harvesting at residences. So far, that program has resulted in no measurable reduction in water use. But perhaps, if that idea was used on a larger scale, it could help recharge our aquifers. Why don’t we collect storm-water runoff from city streets and in ephemeral flows in the Santa Cruz River and pump that water back into the aquifers via dry wells?
That idea is discussed by Chuck Graf, Senior Hydrologist, Arizona Department of
Environmental Quality in a short article in the Spring Issue of Arizona Water Resource Newsletter (link to article).
This idea is not new. Phoenix began recharging storm-water in the 1930s and now has more than 50,000 wells in operation. Many other communities also use this recharge method. Why not in Tucson and Pima County?
The practice of dry well recharge in Phoenix went largely unregulated until 1987 when legislature directed the Arizona Department of Environmental Quality (ADEQ) to license dry well installers and establish a registration program for existing and newly constructed dry wells. The law expressly limited the use of dry wells to the disposal of storm water. This limitation was intended to prevent disposal of hazardous chemicals into dry wells, which in the past had caused severe groundwater contamination plumes (some of which are still under remediation).
Graf explains the dry well method as follows:
“The dry well borehole is drilled in alluvial sediments, through any intervening fine-grained and cemented zones, into a permeable layer of clay-free sand, gravel, and cobbles. The permeable layer serves as the injection zone for the storm water. ADEQ requires at least 10 feet of separation between the bottom of the injection zone and the water table. Because groundwater commonly occurs at great depth in Arizona’s alluvial basins, installers often have considerable leeway to find an exceptionally permeable zone above the water table that maximizes dry well performance while maintaining a much greater separation distance than the 10-foot minimum.”
Graf goes on to write:
“Potential adverse groundwater quality impact is the biggest concern about dry wells. Although the definitive water quality study probably remains to be done, a number of studies, including a 10-year study in Los Angeles conducted by the Bureau of Reclamation and others, found little evidence for groundwater contamination. A 1985 study in Phoenix found that dry wells had a beneficial effect on groundwater quality with respect to major chemical constituents.”>
This idea should be considered. Perhaps then, our involuntary contribution to the “Conservation Fund” would actually conserve some water.