AZTEC — City commissioners will decide tonight whether to spend nearly $1 million on a new water tank.

Located at the municipal airport, the existing 250,000-gallon tank is more than 50 years old and in such bad shape that the cost of maintenance was more than an investment in new, improved equipment, according to city documents.

The current 1959 tank is made of steel, which has corroded substantially on the inside through decades of use.

An early budget request called for installation of a million-gallon tank, but after considering the city's needs, the size was scaled back.

As a result, the $1.2 million budgeted for fiscal year 2013 would be more than enough to complete the project.

According to a staff summary report, more than $300,000 from the original budgeted amount will be saved and held in the city's Joint Utility Fund for other water-related projects this fiscal year. If the money isn't used, then it reverts back to cash reserves for the following fiscal year.

"This is a good example of an excellent bidding process and project," said Austin Randall, purchasing agent for the city. "Though we had many good competitive bids, we landed one that saves the city a lot of money."

Through the bidding process, Mike Huber, city engineer and public works director, explored two designs — a glass-fused-to-steel design that is bolted together or one made of pre-stressed concrete.

Although it added $30,000 to the price tag, Huber chose the concrete tank for its strength and lower maintenance costs.

While both designs need interior cleaning, glass-fused-to-steel tanks require periodic maintenance on seams and seals and inspection of bolts. Concrete tanks have no coatings that can be damaged or corrode.

The proposed tank replacement will double the city's existing storage capacity to 500,000 gallons and supply potable water to West and North areas of the city.

As part of the project, a new distribution main line would be added. The line will connect North Oliver Pump Station to the proposed tank.

"The airport water tank is vital to the overall efficiency of our city's water system," City Manager Joshua Ray said. "We have worked for the past four years trying to secure funding to build a new water tank at this location but have not been successful. In turn, we have been successful in saving sufficient funding to make this project come to fruition for our citizens."

The commission meeting begins at 6 p.m. in City Hall, 201 W. Chaco St.