Proposed sewer plant upgrades carry a price tag of $55 million, according to engineers hired to advise Durango City Council.
In addition to the staggering estimate, the construction must be completed by December 2017 to meet state regulations for higher water quality.
Currently, the plant is releasing more nitrogen and phosphorous into the Animas River than the new regulations allow.
If the plant does not meet the new rules, it could be placed under a consent order by the state and will not be allowed to build any more sewer taps. This would halt any city growth. It could also equate to a $25,000 daily fine, said Utilities Director Steve Salka.
The regulations were approved in 2012 because high levels of nitrogen and phosphorous causes algae to bloom faster than ecosystems can handle. Too much algae deprives fish and other aquatic life of oxygen, said Meghan Trubee, community relations liaison for the Colorado Water Quality Control Division.
“We’re affecting the base of the food cycle in the wild,” said John Sandhaus, wastewater treatment plant superintendent for the city of Durango.
To remove what is effectively too much fertilizer, the sewer plant will need greater capacity and new technology, he said.
The upgrades should make the plant quieter and reduce the sickening smell that occasionally wafts across Santa Rita Park.
“If this plant is built the way we suggest it be built, you won’t even know it’s here,” Salka said.
Designs include 11 new structures, including a new administration building that may be built near the park to distance the public from the process, Salka said.
The capacity of the plant also will be increased from 3 millions gallons of water per day to 4 million, so it would be prepared for growth.
The new structures will add more equipment to almost every step of the treatment process.
When raw sewage enters the plant, it flows into a headworks building where the current flow-measurement device is too small to handle peak times. It also violates state standards because it cannot be cleaned or calibrated because it is underneath the concrete floor, Sandhaus said.
Once inorganic matter is removed, the waste flows into stilling basins, called primary clarifiers. Here, solid waste is separated from the liquid waste. These would not be replaced, but they would be covered with domes to filter the air.
The water then flows into an aeration basin where micro-organisms digest the waste in the water.
“We call ourselves bug farmers,” Sandhaus joked, while looking out across the dark-brown bubbling basins.
Four new aeration basins must be built with about five times the capacity of the existing basins, Sandhaus said.
Management also plans to replace the blowers that pump air into the basins from direct current to alternating current for efficiency, Salka said.
Solids are then removed from the water again in secondary basins, and the plant will need two more of these basins.
The water is then sterilized with ultraviolet light. A secondary sterilizer will be part of the upgrades because the plant is violating state regulations without one.
Sludge is processed separately from water in a digester. Much as the name suggests, here micro-organisms feed on the waste. The upgrades call for another digester that will prevent the stench currently caused by cleaning and maintenance.
Under the plan, processed waste will be dried in another new building. Here, human waste will be turned into dry pellets that can be sold as fertilizer.
Currently, the plant produces four to five tanker truck loads a day of mostly water mixed with 2.5 percent processed human waste. The plant pays $250,000 a year to truck this waste away.
The preliminary designs also call for a station where restaurants could send grease instead of pouring it down a drain. This can be used to increase the production of methane and produce more electricity.
All of these improvements would be scheduled, so that the plant can continue processing waste during construction. April 2016 is the earliest that construction may start.