When the river ran orange with mine waste in August, city taps still flowed with clean, usable water.

To make sure Durango will have drinking water in a future emergency and to serve eventual growth, city officials would like to build a new $50 million Ridges Basin Water Treatment Plant below Lake Nighthorse.

“It gives the city such great flexibility that it doesn’t have with just one reservoir,” said utilities director Steve Salka.

If both the Animas and Florida rivers were flowing with severely contaminated water or running extremely low, the new plant would provide access to the 2,133-acre-feet of water the city owns in Lake Nighthorse. This additional water would allow the city to serve tens of thousands of additional water customers, said City Manager Ron LeBlanc. The city currently serves about 6,700 customers, Salka said.

Depending on a single plant leaves very little room for error and limited time for repairs because it can never be shut down completely, Salka said.

“If a pipe breaks, it’s an emergency,” he said.

Even scheduled maintenance must take place within restrictive time frames, and there is some maintenance that cannot happen until a new plant is built.

A new water-treatment plant could allow the city to process 15 million gallons of water a day and shut down the existing 60-year-old plant entirely during repairs.

The current plant produces about 8 million gallons on a peak day in the summer, and peak summer consumption is about 7 million gallons. The additional production allows the city to catch up when a water main breaks, said Dave Ferguson, water-treatment plant superintendent.

“If you can only produce what the town demand is, you are never going to catch up,” Ferguson said.

One of the limiting factors of the current plant is the disinfection process. The water must be exposed to the chlorine in the 7 million gallon storage tank. The city plans to build a new 3 million gallon tank at the existing plant to help add capacity.

Some of the preliminary work for the plant has already started. The city is negotiating with the property owner for a site, LeBlanc said.

The city has also started building a water-sampling station at Lake Nighthorse to complete the required two years of monitoring that must take place before a plant can be built.

Keeping heavy metals out

Since the Animas River was declared safe to use for drinking water in mid-August after the mine blowout, the city has been pumping water intermittently as needed, Ferguson said.

But the city doesn’t pump after storms when there is more sediment and heavy metals in the river to prevent them from entering the system.

When a small amount of heavy metals are pumped into the reservoir, the result of ongoing mine pollution, the metals settle to the bottom of the reservoir before entering the treatment process, Ferguson said.

The metals that do make it into the plant are filtered out through the water-treatment process.

Before the water is pumped to customers, the city tests for metals. It published two examples of tests from the month of September on the city’s website.

All the metal levels are far lower than what is allowed by the Environmental Protection Agency.

Paying for the plant

The city will have to ask residents to approve a bond measure to build the plant, and the city would like to put that question on the ballot in 2018, LeBlanc said.

He doesn’t want to see the vote postponed beyond that date.

“It’s not a project we could delay. Water is an essential function, and the purpose of this plant is to provide redundancy,” he said.

City water bills will pay for cost of construction. Water rates increased in 2015 and are expected to increase again in 2016 to boost revenue to the water fund by 15 percent.

The project is the latest in a string of major construction projects for the city, including remodeling or rebuilding the city sewer plant. Remodeling the plant is estimated to cost $58 million, and it could be millions of dollars more if the city chooses to move the plant. City and La Plata County officials have also considered updating Durango-La Plata County Airport terminal, which will likely require tens of millions of dollars to remodel or rebuild.

The new plant could be built in partnership with the La Plata Archuleta Water District, which needs the water to serve customers on the west side of its district.

But the details of the agreement are still being worked out, LeBlanc said.

mshinn@durangoherald.com