The Grass Valley Wastewater Treatment Plant provides service for a population of about 12,000. The area has some unique challenges from mine drainage and heavy flows during the winter storm season in the Sierra Nevada foothills.
The plant uses chain and scraper systems for sludge collection and scum pipes for scum collection. In 2013, the chain and scraper systems were approaching the end of their service life, placing an increasing burden on the system.
Matters came to a head when the collector system in two of the tanks became inoperable due to a breakdown of the triple-ouput shaft drive system. The outage left just one tank operational and threatened to shut down the entire system.