Our Expertise > Columbia Tank II: South Boise Water Storage Tank Expansion
Engineering Idaho’s Largest Potable Water Tank
By the Numbers
- #1—Idaho’s largest potable water tank
- ~10 MG total system storage achieved through expansion
- 45+ square miles served
- 100‑year design life
- 0.3% change orders
The Challenge
South Boise was growing faster than its water system could handle. Booming development, airport expansion, and major employers increased water demand beyond what the existing 3‑million‑gallon (MG) high‑elevation tank could supply.
With no backup storage, the system was stretched thin. Modeling showed that during peak use, parts of valley could face low water pressure and reduced fire protection. Homes, businesses, and public safety were at risk.
Veolia, South Boise’s water utility, needed more high‑elevation storage to serve over 45 square miles. And the project had to move fast while navigating steep foothill terrain, long utility runs, active airport and ranch operations, and the need to keep service reliable during construction.
The Solution
Veolia partnered with Keller to design the Columbia Tank, a massive 6.8 MG prestressed concrete structure. Working with the existing tank, it provides nearly 10 MG of coordinated high‑elevation storage.
Prestressed concrete was selected for its durability and low maintenance, offering roughly a 100-year design life. Two 24‑inch bidirectional flow meters give operators real‑time insight into system performance.
Close coordination among Veolia, Keller, and SKAAR Construction kept change orders to 0.3%—an unprecedented accomplishment.
The Results
The Columbia Tank passed its fill test with zero leaks and now delivers a dependable backup storage, stable water pressure, and improved fire protection for South Boise.
Its low‑profile design blends into the foothills while providing long‑term value. The project increases future-readiness, reliability, and lowers lifecycle costs. And it provides a lasting public resource that’ll serve the Boise community for decades.