AN INTEGRATED APPROACH FOR DETERMINING NPDES AMMONIA LIMITS FOR THE CITY OF TOPEKA扴 OAKLAND WWTP

摘要

Recently, the Kansas Department of Health and Environment (KDHE) reclassified thernKansas River because of new and revised stream designations. Consequently, KDHErnissued a draft National Pollutant Discharge Elimination System (NPDES) permit forrnthe city of Topeka's Oakland wastewater treatment plant (WWTP). The OaklandrnWWTP抯 previous NPDES permit did not include ammonia limits. To meet this permitrnchallenge, the city of Topeka chose to initiate an integrated process to developrnenvironmentally protective and economically reasonable ammonia limits for thernOakland facility. The objective of this site-specific ammonia study is twofold: first, tornestablish a scientific process to apply site-specific data to modify permit requirementsrnwhere appropriate and second, to direct scare public dollars towards the greatestrnenvironmental benefit. The city used the following elements to achieve its objective:rn?Ω 12 Λ168 Λ192 Λ240 Λ288 Λ336 Λ384 Λ432 Λ480 Λ528 Λ576 Λ624 Collaborative Processrn?Mixing Zone StudyrnBioasessment/Habitat Surveyrn?Water Quality Samplingrn?Low Flow AnalysisrnThis paper describes the field sampling program, study results, alternatives analysis,rnNPDES permit limit considerations and project benefits.rnCORMIX3 was used to predict the mixing zone at low flow conditions. Duringrnregulatory low flow conditions, the mixing zone is long and thin, and it hugs the riverrnbank. An alternative analysis comparing treatment, a modified outfall and cost impactsrnwas conducted. To enhance mixing, the city is exploring the feasibility of installing arndiffuser.rnPermit limit considerations include: seasonality for river low flow, three-times factorrnfor winter continuous criterion (CCC), modified outfall impacts, WWTP improvementsrnand mixing zone length of 10-times the stream width. The city of Topeka is the firstrncommunity in Kansas to complete a site-specific study for development of NPDESrnpermit limits. In collaboration with KDHE, the implementation of this project will servernas a model for other communities across the state allowing for flexibility in the permitrnnegotiation process.