Transcript My talk

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
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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)
60
conc. (ug/L)
50
40
2000
2001
2002
2003
30
20
10
0
Jan Feb Mar Apr May Jun
Jul
Month
Aug Sep Oct Nov Dec
Monthly DS Max. TTHM profile
100
90
80
conc. (ug/L)
70
60
2000
2001
2002
2003
50
40
30
20
10
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
Hypothetical LRAA w/ monthly DS Max values
80
70
TTHM
HAA5
50
40
30
20
10
Year
03
20
03
20
03
20
02
20
02
20
02
20
01
20
01
20
01
20
00
20
00
20
00
0
20
conc. (ug/L)
60
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
–5
–5
–4
Max residence sites
Avg residence sites
Sites of max residence w/ blends
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
Moffat WTP
Marston WTP
Foothills WTP
Conductivity vs TTHM
DS sites w/ TTHM < Platte WTP effluents
80
2
TTHM (ug/L)
R = 0.9197
60
40
20
0
0
50
100
150
200
Specific conductance
250
300
350
HAA5 vs TTHM (all sites)
60
HAA5 (ug/L)
50
2
R = 0.8192
40
HAA5 max
30
TTHM max
20
10
0
0
20
40
60
TTHM (ug/L)
80
100
Chlorine vs HAA5
DS sites w/ mostly Foothills WTP effluent
2
Foothills’ first
customer
Cl2 (mg/L)
1.6
1.2
0.8
0.4
0
0
20
40
HAA5 (ug/L)
60
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