Environmental Protection
Agency
Elevated Lead in D.C. Drinking Water: A
Study of Potential Causative Events
EPA is releasing a report with the results of an extensive study evaluating factors that
contributed to elevated levels of lead in drinking water for many residents served by the
District of Columbia Water and Sewer Authority in the early part of the decade. EPA
identified the need to perform this analysis to document, to the extent possible, the cause
or causes of elevated lead in D.C. drinking water in order to help other water utilities
avoid similar situations.
Why did EPA do this study?
The District of Columbia Water and Sewer Authority (DCWASA) owns and operates a
system that delivers water produced by the U.S. Army Corps of Engineers Washington
Aqueduct (WA) to customers in Washington, D.C. During compliance monitoring for the
Lead and Copper Rule (LCR) in July 2000 through June 2001, DCWASA exceeded the
15-|j,g/L action level (AL) for lead at the 90th percentile in home tap sampling.
DCWASA repeatedly exceeded the AL during subsequent monitoring through the period
ending in December 2004. EPA decided to have an independent in-depth analysis
performed that would document and determine, to the extent possible, the source(s) and
cause(s) of elevated lead levels at Washington, D.C. consumers' taps.
What did the study find?
The authors concluded that a combination of factors - not a single source or a single
causative event - contributed to the problematic release of lead in water at consumers'
taps in the D.C. Water and Sewer Authority (DCWASA) system. The primary source of
lead release was attributed to the presence of lead service lines (LSLs) in the DCWASA
service area. Since the mid-1990s, three notable occurrences in the DCWASA system
likely contributed to elevated lead releases during 2000 through 2004:
(1) Increased chlorine residual dosing in the mid-1990s
(2) pH variations and low operating pH in the distribution system
(3) Conversion from free chlorine to chloramines for final disinfection
Why was the free chlorine residual increased in the mid-1990s?
In the mid-1990s, the concentration of residual free chlorine was increased to 4.0 mg/L,
and subsequently maintained in the range of 2.2 to 3.2 mg/L, for the purpose of
controlling coliform occurrence in the water distribution system.
How did high free chlorine residual contribute to the elevated lead levels?
Relatively high free chlorine concentrations likely facilitated the formation of Pb(IV)
scales in the form of lead dioxide (PbC^) in lead service lines. The conventional
understanding that forms the basis for the LCR assumes the presence of Pb(II) as the
dominant scales. Lead scales on the interior of lead service lines are likely comprised of
various forms of lead, including both Pb(II) and Pb(IV), and the chemical composition of
the scales likely changes with varying water quality conditions. Lead dioxide scales
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generally exhibit relatively low lead solubility under high oxidation reduction potential
along with normal ranges of pH and alkalinity in public water systems when compared
with Pb(II) compounds. Once the oxidation reduction potential of the water decreased
(caused by the switch from high free chlorine to chloramines) it likely changed the nature
of the predominant scale from Pb(IV) to Pb(II) and thus facilitated an increase in the
release of lead from the lead service lines into the water at consumers' taps. Oxidation
reduction potential provides an indication of a solution's ability to oxidize or reduce
another material.
How did pH levels contribute to the elevated lead levels?
The pH of the water is an important factor in the control of lead solubility. The pH of the
distributed water in Washington, D.C. exhibited seasonal variations that fluctuated from
approximately 7.0 to 8.9 during 1992 to 2004. The pH levels at the lower end of this
range are not considered optimal for lead corrosion control based on the conventional
understanding of lead solubility per the LCR, assuming that Pb(II) is the dominant form
of scales.
In Washington D.C., relatively high free chlorine concentrations applied to the service
area during the mid-1990s likely facilitated the formation of Pb(IV) as the dominant
scale. Pb(IV) exhibits relatively low lead solubility at the lower pH levels experienced in
the DCWASA system. Consequently, lead levels were low during LCR compliance
monitoring during the mid-1990s.
How did the conversion to chloramines contribute to the elevated lead
levels?
This conversion facilitated a reduction in oxidation reduction potential (ORP) to a range
that favors the predominance of Pb(II) scales. Pb(II) species generally are highly
influenced by low and fluctuating pH levels. This conversion from free chlorine to
chloramines likely facilitated the release of lead in water while the system was operating
with fluctuating pH conditions that were, at times, lower than what would have been
expected to control Pb(II) solubility.
Why did the Washington Aqueduct switch from free chlorine to
chloramines for final disinfection?
The residual disinfectant conversion was implemented primarily for the purpose of
lowering disinfection byproducts to avoid health risks associated with these byproducts.
There are a number of operational and compliance benefits to using chloramines.
Chloramines can provide the following benefits:
• Since chloramines are not as reactive as chlorine, they form fewer disinfection
byproducts. Some disinfection byproducts, such as the trihalomethanes (THMs)
and haloacetic acids (HAAs), may have adverse health effects and are closely
regulated.
• Because a chloramine residual is more stable and longer lasting than free chlorine,
it provides better protection against bacterial regrowth in systems with large
storage tanks and dead-end water mains.
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• Chloramines, like chlorine, are effective in controlling biofilm, which is a coating
in the pipe caused by bacteria. Controlling biofilm also tends to reduce coliform
bacteria concentrations and biofilm-induced corrosion of pipes.
• Because chloramines do not tend to react with organic compounds, many systems
will experience fewer taste and odor complaints when using chloramines.
• Chloramine technology is relatively easy to install and operate. It is also among
the less expensive disinfectant alternatives to chlorine.
Because of this switch, THM levels reported by DCWASA have decreased from a high
quarterly average value of 84 ppb in 1999 to 46 ppb in 2006. The highest single samples
collected by the utility also decreased from 207 ppb in 1999 to 85 ppb in 2006.
What have DCWASA and WA done to address the problem of elevated lead
levels?
DCWASA and WA, in conjunction with the USEPA and a Technical Expert Work
Group, conducted a series of studies to identify solutions to reduce and control lead levels
at consumers' taps. As part of these studies, DCWASA conducted a partial system
application of the corrosion inhibitor orthophosphate in a portion of the distribution
system beginning on June 1, 2004. Based on results of this demonstration test,
orthophosphate was subsequently added as treatment at the WA water treatment facilities
to cover the entire DCWASA system beginning August 23, 2004 for the purpose of
lowering lead levels at the tap. Based on recent compliance monitoring information,
DCWASA has been below the LCR lead action level since the first full monitoring period
after commencing system-wide addition of orthophosphate.
What is EPA doing to make sure this does not happen again?
EPA is addressing concerns with the impact of treatment changes on corrosion control in
the proposed short-term revisions to the LCR and in the Simultaneous Compliance
Guidance Manual for the Long Term 2 and Stage 2 DBF Rules. One of the proposed
revisions to the LCR requires that systems provide advanced notification prior to and
receive State approval for treatment changes or additions of new water sources. The rule
was proposed in 2006 and should be released as final in the fall of 2007.
The Simultaneous Compliance Guidance Manual for the Long Term 2 and Stage 2 DBF
Rules (http://www.epa.gov/safewater/disinfection/stage2/compliance.html) provides
recommendations to systems that are switching to a different residual disinfectant in
order to minimize increases in the rate of lead and copper corrosion:
• The water system should perform an optimal corrosion control treatment study
prior to introducing chloramines into the distribution system.
• Add chemicals to the finished water to form a protective coating on the pipes,
such as an orthophosphate corrosion inhibitor.
• Optimize the chloramination process to minimize the possibility of nitrification
that can reduce pH and increase corrosion.
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Also, in addition to its own research, EPA is evaluating studies from the open literature to
determine how changes in treatment can impact the corrosion of lead in pipes and
household plumbing.
Do the report findings or recommendations suggest any major problems
with the Lead and Copper Rule?
The report findings do not suggest that there are problems with the LCR. However, EPA
is identifying research needs associated with the impacts of treatment changes on lead
corrosion in drinking water systems and the formation of different types of lead scale
formation. EPA will consider new information and research findings when making long-
term changes to the rule. EPA is addressing concerns with the impact of treatment
changes on corrosion control in the proposed short-term revisions to the LCR and in the
Simultaneous Compliance Guidance Manual for the Long Term 2 and Stage 2 DBF
Rules.
How did EPA assure an independent review for this study?
EPA contracted with an engineering firm to analyze the data and draw conclusions for the
report. Additionally, prior to completion of the report, it underwent an independent peer
review. The final document incorporates the comments received as a result of the peer
review and includes the actual comments from peer reviewers in an appendix.
Where can I find additional information?
The report, Elevated Lead in D.C. Drinking Water: A Study of Potential Causative
Events, is available on EPA's Web site on the Lead and Copper Rule page at
http://www.epa.gOv/safewater/lcrmr/lead_review.html. The site also includes summaries
of EPA's evaluation of monitoring data for utilities provided by state drinking water
programs and summaries of expert workshops conducted through 2005. The site also has
links to EPA's proposed revisions to the LCR and guidance to help implement the rule.
Office of Water (4607M) EPA 810-F-07-002 August 2007 www.epa.gov/safewater
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