Mixing water – CAP project under way in region - The Explorer: Desert Times

Mixing water – CAP project under way in region

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Posted: Thursday, August 7, 2014 3:53 pm | Updated: 10:18 am, Fri Aug 8, 2014.

As water levels continue to drop from regional-area groundwater wells, the City of Tucson and Metro Water District are in the beginning stages of counteracting the decrease by exploring how to combine groundwater with CAP (Central Arizona Project) water, which delivers about 1.5 million acre-feet of water annually from the Colorado River.

In the Metro Water District, which spans from roughly Lambert Lane to the north, River Road to the south, Thornydale to the west, and Oracle Road to the east, water reserves have continued to drop about two feet per year for the last two decades. 

While by no means is the decrease considered an emergency, water officials are saying the time is now to begin preventative measures. 

“Ultimately something will need to be done to make sure the aquifer levels don’t get to a depressed level,” said Metro Water District General Manager Joe Olsen. 

Metro Water District has consequently developed a 10-year timeline to complete a $36.1 million project that will recover CAP water that is recharged at the Avra Valley Recharge Project, and blend it with groundwater at the Herb Johnson Reservoir before being delivered through water mains to homes.

Metro Water’s Board of Directors approved the project’s timeline in April.

Until the conversion is set in motion, Metro will continue providing its approximate 17,000 customers with water from groundwater basins – the two major locations being the Tucson Basin and Avra Valley Basin – though the water reserve in such basins is depleting faster than it is being restored from rainwater and melted snow. 

The project will be broken down into three stages. Land acquisition to accommodate new infrastructure is anticipated to take two years. Project design would span the subsequent three years, and construction, beginning in 2021, is expected to take three years. 

To the public eye, the most noticeable piece of construction will be that of the new transmission main, Olsen said. 

While the project will make use of blended water, Olsen added that due to continued filtering precautions, there would be no additional health concerns, though some may experience different levels of Total Dissolved Solids (TDS) than they are used to, however, this is a measure of water taste above anything else.

TDS is a measure of the water’s “hardness” based on the amount of mineral content within it. Metro’s current TDS levels range from 200 TDS in milligrams per liter to in excess of 550 TDS.

In a study by World Health Organization, a panel of tasters rated levels less than 300 TDS as tasting excellent, 300-600 TDS as good, 600-900 TDS as fair, 900-1,200 TDS as poor, and above 1,200 TDS as unacceptable.

Upon the project’s completion, Olsen estimates an average TDS of 400mg/liter in the district. 

While still in the preliminary stages of determining the amount of water the CAP blend will add to groundwater levels, the initial addition is estimated to be 4,000 acre-feet.

The project will be paid for in large part from modest annual increases to the company’s Water Resources Utilization Fee, which is charged to customers based on their volumetric water usage. 

Olsen said as the project goes underway, Metro Water will continue its public outreach. 

“We want to be as transparent as possible and use the 10 years as a time to educate the public,” said Olsen. 

Tucson is also undergoing changes with its water supply. Most recently, the city completed a master plan for the development of recycled water as a future drinking water resource, expected to take several years to complete. While Tucson already makes use of recycled water, the updated master plan explores ways to expand upon using unused effluent as a source of drinking water.

“We’ve been studying this for some time,” said Tucson Water Director Alan Forrest. “The ongoing drought and dropping water levels in Lake Mead, and planning for the impacts of climate change are making it a higher priority than originally planned.”

In order to safely drink effluent, additional treatment would be required, but Tucson officials say they are already equipped to do so. 

“This program will build on 30 years of success, applying advanced technology, recharge, and blending with other water supplies to secure a high-quality and renewable water resource,” said Jeff Biggs, interim Tucson Water deputy director.

Like Metro Water, Tucson Water will also rely heavily on CAP water to meet consumer needs. 

More information on these projects can be found at www.tucsonaz.gov/water and www.metrowater.com.

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