1900
The City of Nampa constructed sanitary sewer lines using local improvement districts to fund. Shortly thereafter, a community septic tank was constructed. This tank was located about 1/4 mile east of the existing treatment plant site.

1950
The existing plant was constructed in 1948 and 1949 and began operating in 1950. This plant was one of Idaho's earliest efforts for reducing fecal count, total solids and/or ammonia with some form of biological or chemical treatment (secondary treatment).

1964-1965
Due to industrial development and population growth, Nampa enlarged the plan to handle the increased waste loads.

Primary clarification, trickle filters, secondary clarification and increased digestion capability were added to the treatment facility.

1968
A pre-aeration basin was constructed due to settlebility of strong organic industrial waste.

1969
A polishing digester was constructed to further contain the solids removed from this highly industrial loaded plant.

1976-1982
A modernization and expansion project began in 1976 and was completed in 1982. This expansion included a centralized instrumentation system which monitors all process equipment, new screw pumps for power efficiency, a large aeration basin for ammonia removal, and jet chlorination for improved disinfection.

A new administrative building was also constructed in the old aeration basin using the existing wall structures. This maximized land use and saved on overall costs.

The modernization allowed the Nampa Treatment Plant to meet higher state and EPA standards for ammonia removal, residual chlorine content, and oxygen content. Overall treatment reliability has been increased.

The modernization was $17 million.

With the expansion, a population equivalent of 250,000 can be served.

1999
A sodium hypochlorite system was installed to replace the use of chlorine gas. The system consists of four - 1,800 gallon tanks with containment tanks for storage and two pumps to distribute the bleach at a rate of up to one gallon per minute. The product is delivered weekly by bulk tankers.

Sodium Bisulfite was also installed to neutralize the hypochlorite. This system consists of two 1,600 gallon tanks with containment, and two pumps to deliver bisulfite to the #4 water station for chlorine neutralization. Sodium Bisulfite is also delivered weekly by a tanker.