13 november 2017 a holistic look at lead in drinking paul ... · operations affecting corrosion...
TRANSCRIPT
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A Holistic Look at Lead in Drinking Water Distribution Systems Paul Hargette, P.E.
Senior Process Engineer
13 November 2017
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Agenda
• Background and drivers• Factors affecting lead release• What are utilities doing
• Risk evaluation• Water chemistry evaluation• Modeling• Materials inventory
• Demonstration testing• Pipe wall scale analysis• Bench scale testing• Pipe loop testing
• Putting it all together
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Distribution System Considerations
Increased public understanding of distribution system water quality3
• Regulations / public health
• Aesthetics
• Distribution System Integrity
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Lead Release in the News
From a Reuters investigation “The thousands of U.S. locales where lead poisoning is worse than in Flint” – not solely caused by lead release in water
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Lead Release Events – Common Themes
Increased public pressure for action5
• Change in source, treatment, or chemistry • Elevated lead levels at customer tap samples• Deterioration of water quality beyond lead• Simultaneous compliance • Outcomes:
• Increased public awareness and dialogue
• Increased industry knowledge base
• Changes in the regulations “Tap water in Flint’s hospital on October 16” by Joyca Zhu/Flint Water Study in “The Conversation” licensed by CC BY-ND 4.0
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Regulatory Drivers• Lead and Copper Rule
• 1991, 2000, 2004, 2007, 2017?
• Proposed changes to the LCR• Sampling protocols and voluntary sampling• Increase public education and transparency• Expanded OCCT requirements• Single household action level• Revised copper requirements• Proactive LSLR program / full replacement
• State-specific regulations on the rise
Is your utility positioned for compliance with the long-term revisions?6
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FACTORS AFFECTING LEAD RELEASESOLUBLEPARTICULATEMICROBIAL INFLUENCE
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Factors Affecting Lead Release
• Water chemistry and microbiology
• Piping materials
• Operational practices
• Treatment changes
• Know your system-specific risk factors
Need to look at soluble and particulate lead separately8
Hydraulic / Quality Analysis
Risk-Consequence
Prioritized Improvements
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Distribution System Water Quality
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Metals Solubility
• pH • Master variable for all water processes• Lead solubility decreases with
increasing pH (for MOST waters)
• Alkalinity
• Dissolved Inorganic Carbon (DIC)
• Consider secondary complexes
Good indicator of relative potential for lead release10
Figure Source: Water Research Foundation, 2015.
Lead
Sol
ubili
ty, m
g/L
Low DIC
High DIC
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Common “Corrosion” Indices
Additional indices useful in specific cases
• Calcium Carbonate Based• Langelier Saturation Index (LSI)
• Calcium Carbonate Precipitation Potential (CCPP)
• Chloride to Sulfate Mass Ratio (CSMR)
• 𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝐧𝐧′𝑳𝑳 𝑹𝑹𝑳𝑳𝑹𝑹𝑹𝑹𝑳𝑳 = 𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝑪𝑪𝒂𝒂−+𝑺𝑺𝑺𝑺𝟒𝟒
𝟐𝟐−
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Scale Release
Impacted by secondary metals and changing water conditions12
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Biostability
• Temperature, organic carbon, and nutrients
• Disinfectant residual and ORP• Maintain residual throughout system
• Measure overall microbial activity• ATP or HPC• TCR data• Nitrification in chloraminated systems
(NO3-, NO2
-, NH3)
Impacts both soluble and particulate metals release
Dual-species microbial biofilm stained with fluorescent labels
captured with confocal microscopy
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Impacts of Nitrification
• Loss of chlorine residual• Increased HPC and general microbial growth• Formation of nitrite and nitrate• Drop in pH and alkalinity• Increase in rate of corrosion and metals release• Increased potential for legionella
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Corrosion Inhibitors
• Orthophosphates and silicates
• Aid in formation of passivating layer
• Stabilize existing scale; lower lead solubility
• Polyphosphates – sequester metal ions, NOT effective for corrosion control
Need to consider secondary impacts1515
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WHAT ARE UTILITIES DOING?
RISK ASSESSMENTS
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Proactive Corrosion Risk Assessment
Goal: Always remain in compliance and ahead of regulation changes17
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Lead Risk Assessment Components
• Distribution system materials evaluation
• Distribution system monitoring plan
• Desktop water quality analysis
• Hydraulic modeling / Operations Review
• Risk management strategies prioritization
How optimized is your distribution system?18
Utility-specific
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Materials Evaluation• Distribution piping and service line material
• Plumbing, fixtures, and faucets
• Re-selection of Tier 1 homes
• Updating service line material inventory – WRF #4693
Galvanized pipes downstream of replaced LSLs can continue to release lead19
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Distribution System Monitoring Plan• pH, alkalinity, DIC
• Calcium, magnesium, silica, phosphate
• Chloride and sulfate
• Iron, manganese, and aluminum
• HPC, disinfectant residual, temperature• Ammonia, nitrate, nitrite
• Residential lead sampling to supplement LCR sampling
Selection of representative sampling sites is key20
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Water Quality Evaluation
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• Seasonal patterns • Spatial patterns
• Historical compliance data review • System-specific modeling
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Benefits of Water Quality Modeling• Identify high water age and focus sampling sites
• Trace introduction of new source(s)
• Identify changes in velocity or flow direction
• Evaluate benefits of potential operational changes
• “What-if” scenarios to find most effective solution
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Operations Affecting Corrosion & Lead Release
• Water age / Tank water levels
• Flushing program
• Operational parameters or treatment changes• Enhanced coagulation / Switch in coagulants• Addition of a new source / Change in source• Change in disinfectant type• Addition of new treatment process• Maintenance in the distribution system• LSL replacement programs
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WHAT ARE UTILITIES DOING?
DEMONSTRATION TESTING
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Optimal Corrosion Control Treatment
Narrow down the options before you begin testing
From USEPA, March 2016
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Demonstration Testing Considerations• Pipe wall scale analysis
• Harvested pipe samples
• Bench scale testing• Quickly screen water quality conditions and materials• Typically static conditions and shorter testing duration• Can use new or harvested materials
• Pipe loop testing• Captures hydraulic effects; reflects full scale conditions• Longer testing period, can capture seasonal results• Can use new or harvested materials
Testing program designed to meet specific project needs26
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Pipe Wall Scale Analysis
Most common tools for scale analysis include SEM – EDS, XRD, elemental analysis27
Typical XRD patterns for lead-containing scalesPipe sections are cut longitudinally for analysis of internal scale
From AWWA Manual M58 From AWWA Manual M58
SEM-EDS Analysis
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Bench Testing Configurations
Metal coupon placed in a small container filled with various test waters28
“Storage Stability of Fuels”, book edited by Krzysztof Biernat under CC BY 3.0
Flintwaterstudy.org
Source: Black & Veatch Source: Black & Veatch
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Hybrid Bench/Pipe Loop Scale Systems
• Can create stagnating and flowing conditions
• Compact design
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From WRF #4286 - Distribution System Water Quality Control Demonstration
Welter, G., Giammar, D., Wang, Y., and A. Cantor. 2013. Galvanic corrosion following partial lead service line replacement. Project 4349. Water Research Foundation, Denver, Colorado.
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Pipe Loop Configurations
From Zhang et. al., JAWWA 2012
From WRF 4317 Non-Intrusive Methodology for Assessing Lead and Copper Corrosion
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From Welter, Schock, Miller, Razza, and Giammar, WQTC 2015
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Pipe Loop Configurations
From Integration of desalinated seawater into a distribution system: A corrosion pilot study. 2008. Journal – AWWA. From Zhang et. al., JAWWA 2012
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• Use data to compare lead release from various test cases and conditions.• Must include statistical representation; Replicates are important.• Need to allow for sufficient time for steady state conditions to establish and persist• Use secondary water quality parameters to help explain results
0
50
100
150
200
250
300
350
1 2 1 2 1 2 1 2 1 2
Tota
l Pb
(µg/
L)
Mean
Condition 5Condition 3Condition 2Condition 1 Condition 4
max
median
min
75th percentile
25th percentile
Modified from Wang, Mehta, Welter, and Giammar Journal AWWA, 2013
Example Data Analysis
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SUMMARY
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Understand How To Use Available Tools
• Factors affecting lead release
• System-specific risk assessment
• Demonstration testing
• Consider using pipe loops as standard practice
• Shift from compliance to optimization mindset
• Understand public concerns and increase communication
Provides an opportunity to limit lead release34