Denver Water’s Preparation for the Stage 2 Disinfectant By-Product Rule Bruce Hale (DW) Steve Lohman (DW) Arnold Strasser (DW) Edward Koval (B&V)

Important Stage 2 features New Distribution System (DS) definitions Locational Running Annual Average (LRAA) MCLs Significant Excursions Phased compliance Initial Distribution System Evaluation (IDSE)

Finding new Stage 2B monitoring sites w/ IDSE Under “early schedule”, IDSE results due 2 yrs from promulgation See EPA Stage 2 Guidance Manuals

IDSE options Standard Monitoring Program (SMP) System-specific Study (SSS)

Denver Water stats 3 Surface water treatment plants (WTPs) Max. treatment capacity: 710 MGD, chloramine Max. day: 500 MGD Base day: 120 MGD Total “combined” pop. served: ~1.1 million, ~50% in over 60 consecutive systems Water may be served from any operating WTP to any part of “combined” DS Any, or all WTPs may operate at the same time

Denver will opt for a SSS IDSE DW combined system too complex for SMP DW has computer model to assist w/ site selection –Water age provided by model, main factor influencing DBPs from respective WTPs DW already has much data IDSE is intended to uncover

Routine DS monitoring programs Regulatory DBP (HAA/THM) monitoring: 12 sites, monthly VOC monitoring: 9 sites, 8 times/year Sp. Conductance checks: 20 sites, weekly Regulatory total chlorine monitoring: ~ 500 samples/month

What months have highest historical DS DBPs?

Monthly DS Max. TTHM profile

Hypothetical LRAA w/ monthly DS Max values

Rationale for evaluating sites with a single sample event Unable to identify “typical” DS operations Sample when all plants in service Sample when DBPs are high, to make differences between sites more evident Historical data available for context Sites chosen & evaluated with “all-pipes” model (APM)

Key APM products At any DS location, percent composition by water source (WTP) Water age at any DS location.

APM Validations – Extended Period Simulations (EPS) Hydraulic validation: max day Water Age validation: base load day Source trace validation: 3 potentially high DBP production days

Basis for choosing IDSE sample sites Prior knowledge: –Foothills WTP produces highest DBPs –Foothills WTP treats the most water & has largest service area –HAAs & THMs trend the same in the DS APM’s water age representation APM’s source water identification

September 9, 2003 Water Age Analysis Moffat WTP Marston WTP Foothills WTP

September 9, 2003 Foothills WTP Source Trace Moffat WTP Marston WTP Foothills WTP

September 9, 2003 Moffat WTP Source Trace Moffat WTP Marston WTP Foothills WTP

How many sites will DW’s SSS cover? Under the “DS entry point” scenario: 24 Under the “population-based” scenario: 32

Distribution of 32 sample sites using SMP guidelines 1 “first customer” site for each WTP Priority given to sites likely served by Foothills WTP –9 Max residence sites –5 Avg residence sites –5 Sites of max residence w/ blends –4 Sites of avg residence w/ blends 2 Max residence sites each, from Moffat and Marston WTPs

Distribution of 32 sample sites (cont.) 2 Avg residence sites each, from Moffat and Marston WTPs Blends of Moffat and Marston insignificant ~50% are new sites not used in DW monitoring programs No Stage 1 sites

DW tests SSS strategy in Aug, sites sampled on one day All sites tested for HAAs & THMs Field tests at each site –Specific conductance –Total chlorine –Temperature

Foothills WTP Moffat WTP Marston WTP

Foothills’ first customer

Study Conclusions Study was successful –Reflected bias towards Foothills’ DS –Found some sites with high DBPs Level of TTHM LRAA MCL was exceeded at one site only, and not at all for HAA5 No site exceeded proposed excursion levels Confirmed THMs and HAAs act similarly The ratio of Foothills water is the main influence on DBPs at any single site.

Acknowledgements Royce Bennett Rhonda Birdnow Fred Sanchez Janice Vaughn Greg Zempel