Calibrating Process and Hydraulic Models to Re-Rate the Big Dry Creek WWTF

The Big Dry Creek Wastewater Treatment Facility (BDCWWTF) is currently permitted to treat a maximum month flow of 11.9 million gallons per day (mgd) and 18,600 pounds per day (ppd) of biochemical oxygen demand (BOD5). Over the past several years, flows have increased at anticipated rates, but the BOD5 load has increased at a rate higher than anticipated, and disproportionate to the flow increase. Recent BOD5 loads have exceeded 80 percent of the permitted capacity, which is the regulatory trigger to evaluate the need for re-rating and/or plant expansion. This paper presents the results of the capacity analysis that was conducted to identify options for a potential plant re-rating and/or expansion. Based on the results, the City applied for an increase in the permitted organic loading to the plant of 21,500 ppd BOD5. The project included training for City staff on how to use the models developed for the study.