Environmental Considerations
of the 450-650 Mineral Blend Decision

Reduced Groundwater Pumping for Both 450 and 650 Blends

Perhaps the most important environmental factor in the use of more Colorado River water is the reduction in ground water pumping this will allow. Reducing pumping will protect our desert environment, let our remaining riparian areas continue to thrive, and reduce the threat of subsidence. We'll see this benefit regardless of which future water blend we choose.

Electrical Power Needs for 450 Blend

Operating a large reverse osmosis plant requires a considerable amount of electrical power, in part due to the need to pressurize the water to force it through the filtering membranes. Large amounts of electricity would also be needed to power the mineral concentrators that help reduce water lost to evaporation. This power requirement could be an important environmental consideration in deciding between the 650 and the 450 mineral level blends.

Mineral Disposal for 450 Blend

If we decide to create the 450 blend, we will have to dispose of the minerals that are removed from the Colorado River water by the reverse osmosis plant. It's estimated there could be as much as 90,000 tons per year of mineral solids to dispose of. The mineral solids might be used in the manufacture of building materials. If not, they would have to be put into a landfill. We'll also need to construct and operate about 100 acres of evaporation basins in central Avra Valley. If we decide to let the mineral level rise to 650, the minerals that would otherwise be removed by the reverse osmosis process will enter our environment through irrigation and wastewater disposal.

*mg/L - Milligrams per Liter. One mg/L = 1 teaspoon in 1,302 gallons.

Reverse Osmosis and Water Loss

Up to 75 percent of the water that goes through a home reverse osmosis unit is lost, but the much larger system Tucson Water would use to remove minerals from our blended water would be much more efficient. The treatment plant, working in combination with the mineral concentration system, would retain 99% of the water that passes through it.