denver water’s preparation for the stage 2 disinfectant by-product rule bruce hale (dw) steve...
TRANSCRIPT
![Page 1: 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)](https://reader030.vdocuments.mx/reader030/viewer/2022032611/56649efe5503460f94c12506/html5/thumbnails/1.jpg)
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)
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Important Stage 2 features
• New Distribution System (DS) definitions
• Locational Running Annual Average (LRAA) MCLs
• Significant Excursions• Phased compliance• Initial Distribution System
Evaluation (IDSE)
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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
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IDSE options
•Standard Monitoring Program (SMP)
•System-specific Study (SSS)
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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
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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
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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
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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
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Monthly DS Max. TTHM profile
0
10
20
30
40
50
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
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Hypothetical LRAA w/ monthly DS Max values
0
10
20
30
40
50
60
70
80
Year
co
nc
. (u
g/L
)TTHM
HAA5
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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)
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Key APM products
•At any DS location, percent composition by water source (WTP)
•Water age at any DS location.
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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
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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
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September 9, 2003Water Age Analysis
Moffat WTP
Marston WTP
Foothills WTP
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September 9, 2003Foothills WTP Source Trace
Moffat WTP
Marston WTP
Foothills WTP
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September 9, 2003Moffat WTP Source Trace
Moffat WTP
Marston WTP
Foothills WTP
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How many sites will DW’s SSS cover?
• Under the “DS entry point” scenario: 24
• Under the “population-based” scenario: 32
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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
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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
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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
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Foothills WTP
Moffat WTP
Marston WTP
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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)
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HAA5 vs TTHM (all sites)
R2 = 0.8192
0
10
20
30
40
50
60
0 20 40 60 80 100
TTHM (ug/L)
HAA5
(ug/
L)
HAA5 max
TTHM max
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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
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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.
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Acknowledgements
Royce BennettRhonda BirdnowFred SanchezJanice VaughnGreg Zempel