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 http://www.epa.gov/safewater/stage2/index.html

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?

Annual TTHM profile (monthly avg. of all DS data points)

0

10

20

30

40

50

60

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

conc

. (ug

/L)

2000

2001

20022003

Monthly DS Max. TTHM profile

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60

70

80

90

100

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

co

nc

. (u

g/L

)

2000

2001

2002

2003

Hypothetical LRAA w/ monthly DS Max values

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10

20

30

40

50

60

70

80

Year

co

nc

. (u

g/L

)TTHM

HAA5

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, 2003Water Age Analysis

Moffat WTP

Marston WTP

Foothills WTP

September 9, 2003Foothills WTP Source Trace

Moffat WTP

Marston WTP

Foothills WTP

September 9, 2003Moffat 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, 2004

• 32 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

Conductivity vs TTHM DS sites w/ TTHM < Platte WTP effluents

R2 = 0.9197

0

20

40

60

80

0 50 100 150 200 250 300 350

Specific conductance

TTHM

(ug/

L)

HAA5 vs TTHM (all sites)

R2 = 0.8192

0

10

20

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50

60

0 20 40 60 80 100

TTHM (ug/L)

HAA5

(ug/

L)

HAA5 max

TTHM max

Chlorine vs HAA5 DS sites w/ mostly Foothills WTP effluent

0

0.4

0.8

1.2

1.6

2

0 20 40 60

HAA5 (ug/L)

Cl2 (

mg/

L)

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 BennettRhonda BirdnowFred SanchezJanice VaughnGreg Zempel