1. No category

Discolored Water: A Colorful Issue
Gert van der Walt, PE : DC Water
John Civardi, PE : Hatch Mott MacDonald
AWWA NJ Annual Conference March 19, 2015
Presentation Agenda
• DC Water Overview
• Project Background
• Discolored Water Evaluation
• Addressing Discolored Water
• Current Activities
• Next Steps
• Lessons Learned
• Questions
DC Water Overview
3
DC Water Overview
Water Supply
• Source - Potomac River
• Treatment by Washington
Aqueduct (WA) of ACOE at
two plants:
• Dalecarlia WTP – 240 MGD
• McMillan WTP – 120 MGD
• Distribution by DC Water
• WA wholesales to Arlington
and Falls Church, VA
4
DC Water Overview
Water Treatment
5
DC Water Overview
Water
System
Water
Treatment
6
Project Background
7
Project Background
• Spring 2013 Town Hall Meetings – High
customer discolored water complaints
• Summer 2013 Water Quality & Water
Services Committee Presentation by the
Department of Water Services
8
Project Background
• Discolored water complaints occur
throughout system
• Complaints are related to
unlined cast iron mains
o Total 715 miles
(66% of small mains)
• Problems concentrated
where water age is greatest:
• Pressure Zone Boundaries
• Outskirts of System
• Dead ends
Current WQ Problem Areas:
Unlined Cast Iron Mains In
Red In Background
9
Project Background
Pipe coupons – both installed in 1940’s
Unlined Cast Iron
(1942)
Factory Lined Cast Iron
(1949)
Project Background
Customer Complaint* Trends by Year
300
Discolored Water Complaint
Other Complaint
200
Decreasing
Trend?
150
Not
necessarily…
100
6 months data
New Complaint Sites
250
50
0
2004
2005
2006
2007
2008
2009
2010
2011
* New complaint addresses added to database each year
2012
2013
11
Pb in DC
© M.J.Clarke, Boston College
Project Background
Motivation and Goals of Evaluation
• “Rising” frequency of discolored water complaints
• Higher iron concentrations in complaint samples
• More areas with chronic water quality problems
• Existing response protocol is resource intensive and
reactive, not addressing root cause
• Need to identify underlying issue(s) and implement
appropriate solution
• Incorporate treatment and operational changes data
analysis
 Involve the Experts – Dr Alexa Obolensky & HMM13
Discolored Water Evaluation
Water Quality Analysis
and Hypothesized Causes
14
Discolored Water Evaluation
Interacting Processes and Impacts
Scale
Development
& Properties
Iron
Corrosion
Microbial
Activity
Iron
Release
Hydraulics
Water
Quality
15
Discolored Water Evaluation
Chronology of Treatment and Operational Changes
Mid 1990’s
Free chlorine dose
raised due to high
coliform
1990’s
2000
Distribution system
disinfectant changed from free
chlorine to chloramine
(OCCT is pH adjustment by
lime addition)
2000
1999
Unidirectional Flushing
Program started
following TCR violation
* Annual chlorine burn conducted in April
2001
2001
Elevated lead
levels first
detected
2003
Lead Service Line
Replacement Program
begins
2004 (August)
Orthophosphate added at
a dose of 3.5 mg/L
2002
2003
2004 *
2004
Distribution system monitoring
and data gathering increased
16
Discolored Water Evaluation
Chronology of Treatment and Operational Changes
(continued)
2005
Water Quality
Division created,
extensive monitoring
and data collection
begins
2005
2007
Distr. System operational changes
• Hydrant insp. and ops program
(DC Fire Dept. & DC Water)
• Hydrant flow testing program
• Valve operations
2011
Fluoride dose lowered from 1.0 to
0.7 mg/L (CDC recommendation)
2010
4-month extended
chlorine burn (Jan-Apr)
2006
2007 *
2008 *
2006 (January)
Orthophosphate dose lowered to 2.5 mg/L
(white cloudy water problems attributed to
high iron/ phosphate/ calcium/ aluminum
complex)
* Annual chlorine burn conducted in April.
2009 *
2010
2011
Conversion from Cl2 gas to
sodium hypochlorite
completed
2011 *
2012 *
2013 *
2011
Conversion from lime to caustic soda
for “fine” pH adjustment at Dalecarlia
WTP and for full pH adjustment at
McMillan WTP
17
Discolored Water Evaluation
Evaluated Water Quality Parameters
Alkalinity
Manganese
Aluminum
Monochloramine
Ammonia-Free
Heterotrophic Plate Count (HPC)
Ammonia-Total
Iron
Calcium hardness
Nitrite
Calcium precipitate
Orthophosphate
Total hardness
Orthophosphate - dissolved
Chloride
Oxidation Reduction Potential (ORP)
Color
pH
Conductivity
Sulfate
Chlorine-free
Temperature
Chlorine-total
Total Dissolved Solids (TDS)
18
Discolored Water Evaluation
Customer Tap Samples for Iron 2006-2013
Iron
Complaint Tap Samples
total N = 1,853
100
P25-P75
Median
Iron (mg/L)
10
*
N < 10
Whiskers
P10-P90
1
0.1
0.01
2006
2007
2008
2009
2010
2011
2012
2013
19
Discolored Water Evaluation
Water Quality Issues : Structure of Iron Scale
Top Surface Layer
Shell-like Layer
Fe(OH)3; γ-FeOOH; Ca03
Silicates; Phosphates; NOM
FE3O4; α-FeOOH; γ-Fe2O3
Fe(III) phases:
α-FeOOH; γ-Fe2-O3
Porous Core
Fe(II)-Fe(III) phases:
Fe3O4; Green Rusts
Loosely attached
iron particles
Hard, impermeable
barrier to ion
diffusion
Dissolved constituents
diffuse in/out,
can harbor biofilms
Fe(II) phases:
Fe(OH)2; FeCO3
Corroded Floor
Pipe metal lost
to corrosion
Reference: H Sontheimer, W Kolle and VL Snoeyink, 1981. The siderite model of
the formation of corrosion resistant scales. Journal AWWA 73:11:572-579 VL
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Discolored Water Evaluation
Treated Water Corrosion Index over Time
McMillan Finished Water
Larson Ratio: (2*[sulfate]+[chloride])/[alkalinity]
total N = 1,721
4
P25-P75
Median
Larson Ratio
3
*
N < 10
Whiskers
P10-P90
2
Treatment consideration:
control of anions (chloride
and sulfate) would reduce
corrosion index
1
Threshold for
“corrosive” water
0
2006
2007
2008
2009
2010
2011
2012
2013
21
/WAfinished/WAYrLI006.emf
Discolored Water Evaluation
Biological Activity and Chlorine Loss
Prevalence of Nitrification, high HPCs and low Cl2 at TCR Sites
1.0
Total Cl2 < 2 mg/L
0.9
Nitrification Evidence
HPC > 1000 cfu/mL
Chlorine
Residual Loss Cycle:
Fraction of TCR Sites
0.8
 Number of areas with
low chlorine is increasing
0.7
0.6
0.5
 Bacteria levels increase
0.4
 Nitrification follows
0.3
o
Consumes chlorine
0.2
o
Allows more bacteria growth
0.1
 Bacteria increases iron
corrosion
0.0
2006
2007
2008
2009
2010
2011
2012
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Discolored Water Evaluation
Positive Feedback : Corrosion and Bacterial Growth
Corrosion
and Iron
Release
bacterial activity
consumes oxygen,
promotes corrosion and
iron release
Bacterial
Growth
corrosion products exert
significant chlorine
demand
disinfection
compromised
Low
Chlorine
23
Discolored Water Evaluation
Forensic Analysis Trends and Findings
• Discolored water occurrence increased through 2006-2011
and seems to hold steady since 2012
– No consistent seasonal pattern
• Microbiological activity increased since 2006
and is now widespread throughout system
• Chlorine residuals have declined with severe loss in some
complaint areas
– Areas or sites with high water age
• Concern that road salt application could make source water
more corrosive
– Corrosion index of chloride, sulfate, and alkalinity
may be useful tool (Larson’s Index)
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Discolored Water Evaluation
Hypothesized Causes
• Water Stagnation
• Nitrification
• Microbially Induced Corrosion
• Ion Conditions (elevated Chloride and Sulfate, high Larson
Ratio and Conductivity)
• Shifts in Redox Potential from Seasonal Oxidant Switch
• Physical Operational Activities
25
Discolored Water Evaluation
Water Quality Issues: Complaints and Operations
350
40,000
New Discolored Water Complaints
35,000
Total Physical Operations
300
Valve Operations (Excluding Flushing)
Number Of Activities
DC Water Hydrant Inspections
250
Hydrant Operated During Flow Tests
25,000
Water Main Breaks
200
20,000
150
15,000
100
10,000
50
5,000
0
0
2006
2007
2008
2009
2010
2011
2012
Number of New Complaints
FEMS Hydrant Inspections
30,000
Discolored Water Evaluation
Water Utility Bench Marking : Key Findings
• 6 Utilities contacted all using chloramine disinfection
– Blacksburg, Charleston, Greenville, Philly, Raleigh, Richmond
• None reported significant discolored water complaints
• Most of those that did, said that operational adjustments
alleviated them
• Some do an annual chlorine burn, some do not have any
chlorine burn
Discolored Water Evaluation
Options to Address Discolored Water
• Water Main Rehabilitation
• Small Diameter Water Main Replacement
• Small Diameter Water Main Cleaning and Lining
• Reduce Water Age to Improve Chlorine Residual
• Modify pumping and transmission of water
• Install Auto Flushers
• Improve Flushing and Valve Operations
• Reduce sudden flow changes so scale is not dislodged
• Optimize unidirectional flushing steps
• Modify Chemistry at the Treatment Plant
Current Activities
29
Current Activities
Small Diameter Water Main
Replacement
• Unlined Cast Iron Mains
• 700+ miles
• Replacing 11 miles / year
• Major Water Quality Areas
• 50 miles identified
• 8 miles replaced since 2000
• 13 miles currently under
design or construction
• Currently replacing about
4 to 5 miles / year
Current Activities
Cleaning and Cement Mortar Lining
• Colonial Village & Hawthorne (1.5 Miles)
– Emergency C&L project managed by
Department of Water Services (DWS)
– Coordination Started: Spring 2013
– Construction Phase 1: Fall 2013
– Construction Phase 2: Spring /
Summer 2014
• AU Park NW (2.0 Miles)
– Next “fast tracked” C&L project
– Emergency C&L project managed by
Department of Water Services (DWS)
– Design Started: Summer 2014
– Construction Planned: Spring /
Summer 2015
Current Activities
Other DC Water Operational Activities
• Optimize Flushing of WQ Areas by Trailing Spot Flush
• Install auto-flushers to remove loose scale and
improve chlorine residual
Next Steps
33
Next Steps
• Evaluate and Optimize Current Flushing Program
• Analyze Water Age
–
–
–
–
Recalibrate hydraulic model
Pressure and flow monitoring
Additional water quality monitoring
Conduct tracer study
• Improve Operations to Minimize Water Age
• Introduce Clean and Line Program
• Dialogue with WA to discuss modifications to water
chemistry to reduce impact to our infrastructure
• Evaluate Chlorine Burn Benefits
Lessons Learned
1. Minimizing discolored water is more than just flushing
2. Collect data to understand the causes, evaluate
hypotheses and implement solutions
–
Standardize data capturing
3. Chloraminating systems provide extra growth potential
for nitrifying organisms and minimizing biological activity
should reduce discolored water.
4. System operations can exacerbate discolored water
5. Minimizing discolored water will involve multiple
solutions involving new infrastructure and operational
changes
6. Benefits of the changes will not only reduce discolored
water but likely result in additional benefits such as
reduced non revenue water, more stable chlorine
residual
Acknowledgements
OBOLENSKY CONSULTING
• Alexa Obolensky, PhD : Principal Investigator
DC WATER
• Maureen Schmelling : Supervisor Water Quality
• Jessica Edwards-Brandt : Manager Water Quality
• Jodye Russell : Manager Planning
Hatch Mott MacDonald
• John Wujek
• Rich Luettchau
Questions / Discussion
37