UNINTENDED CONSEQUENCES OF CONSERVATION DROUGHT DESIGN AND AGE

UNINTENDED CONSEQUENCES OF CONSERVATION, DROUGHT, DESIGN, AND AGE ON WASTEWATER COLLECTION SYSTEMS Urban Water Institute, Inc. 2018 Spring Conference Palm Springs, CA February 7 -9, 2018 George Tchobanoglous Department of Civil and Environmental Engineering University of California, Davis

FACTORS RESULTING IN UNINTENDED CONSEQUENCES FOR COLLECTION SYSTEMS • • • Water conservation Decentralized (distributed) reuse Changing waste generation patterns Drought and collection system age Basic sewer design

CURRENT AND PROJECTED PER CAPITA WATER USE IN THE UNITED STATES ISSUE - REDUCED FLOW

SATELLITE SYSTEMS FURTHER REDUCE FLOW IN COLLECTION SYSTEMS EXTRACTION TYPE INTERCEPTION TYPE ISSUE - REDUCED FLOW

VARIATION IN FLOWRATES OBSERVED AT WASTEWATER TREATMENT PLANTS ISSUES – CHANGING WASTEWATER GENERATION AND FLOWRATE PATTERNS

LEAKY SEWER PIPES ALSO REDUCE FLOW IN WASTEWATER COLLECTION SYSTEMS, ESPECIALLY IN PERIODS OF DROUGHT Consider the effects of using PVC formed with varying amounts plasticizer for clay pipe joint material ISSUE – EXFILTRATION FROM OLD SEWERS

COLLECTION SYSTEM DESIGN ISSUES • Reduced flowrates • Changing water use patterns • Flowrate peaking factors not based on use of low-flow fixtures ISSUE – EXISTING DESIGN APPROACH NEEDS TO BE UPDATED

IMPACT OF WATER CONSERVATION AND DROUGHT: SOLIDS DEPOSITION, H 2 S FORMATION, AND SERIOUS DOWNSTREAM COLLECTION SYSTEM CORROSION ISSUE – REPAIR AND REPLACEMENT COSTS FOR LARGE SEWERS

IMPACT OF WATER CONSERVATION AND CHANGING WEATHER PATTERNS ON DESIGN OF WASTEWATER TREATMENT PLANTS • Increased waste strength • Changing waste characteristics • Treatment plant washout

CONSEQUENCES OF CONSERVATION AND CLIMATE CHANGE • Must RETHINK design of existing and new wastewater collection systems and treatment facilities • Must LEARN TO LIVE and deal with higher levels of environmental pollution Thank you for listening