Corrosion Control Research

This page provides detailed information related to on-going and planned research related to corrosion control for District of Columbia drinking water. Please check back often for updates and additional information. For a general update on lead in DC drinking water, please see the home page.

Background on Corrosion Research

According to the most recent information available, the previously elevated levels of lead in District of Columbia drinking water were due to increased water corrosivity, and were aggravated in some homes by the presence of lead service lines. The District of Columbia Water and Sewer Authority (DC WASA), the agency responsible for the distribution of drinking water in the District of Columbia, the Washington Aqueduct (operated by the Army Corps of Engineers), the agency responsible for treating drinking water in D.C., and EPA recognize the need for additional research into corrosion control in light of previous lead action level exceedances in the District of Columbia.

Technical Expert Working Group

WASA, the Aqueduct, and EPA continue to work with subcontractors and other Federal and D.C.-area agencies in a Technical Expert Working Group (TEWG). The TEWG is charged with facilitating and expediting the necessary corrosion control research. The TEWG is comprised of an Advisory Team and three Technical Research Teams.

TEWG Action Plan - PDF [18pp, 374K, about pdf]

Interim Optimal Corrosion Control Treatment Report

The interim optimal corrosion control treatment (OCCT) report examines the effectiveness of the interim OCCT using orthophosphate. This report reviews the research performed to investigate previously elevated lead levels in Washington, DC, and summarizes chemical and biological water quality data. The data reviewed are from early 2003 through the period of the interim OCCT designation, which ended in December 2005. In addition, the report provides an overview of the DC drinking water system and the history of OCCT designations for DC water systems.

Review of the Interim Optimal Corrosion Control Treatment for Washington D.C.
Cover page, Table of Contents, and Chapter 1 (Introduction and Background)- PDF [12pp, 112k, about pdf]
Chapter 2 (Summary of Research Relevant to the D.C. Lead Issue) - PDF [42pp, 780k, about pdf]
Chapter 3 (Review of Relevant Water Quality Data) - PDF [55pp, 695k, about pdf]
Chapters 4 and 5 (Conclusions and Recommendations; References) - PDF [8pp, 49k, about pdf]
Appendices - PDF [96pp, 2.6M, about pdf]

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Galvanic and Grounding Currents Study

A study was performed to examine the potential impacts of galvanic and grounding currents on lead release from lead service lines. Galvanic currents may result from the coupling of dissimilar metals, such as in the case of partial replacement of lead service lines with new copper pipes. Similarly, an electrical current may be impressed on a service line when a household's electrical system is grounded to plumbing components. Actual sections of lead service lines from the DC distribution system were used in these experiments. The study found that under the conditions in the DC distribution system (low conductivity water and highly-passivated service lines) galvanic and grounding currents likely have no meaningful impact on lead release.

Final Report: Effects of External Currents and Dissimilar Metal Contact on Corrosion from Lead Service Lines (PDF) [26pp, 899K, about pdf]

Note: EPA Region 3 learned in March 2008 that a statement made on page 15 of this report regarding DCWASA's use of dielectric couplers during partial lead service line replacement (PLSLR) is incorrect. DCWASA does not use dielectric couplers when performing a PLSLR.

Pipe Loop Experiments

Working with the Technical Expert Working Group (TEWG), both WASA and the Washington Aqueduct have set up pipe loop experiments to test the effects of different water treatment schemes on lead levels in tap water. Experimental conditions in both sets of pipe loops are compared to the control condition of finished water – containing orthophosphate, chloramines, and fluoride – from the Washington Aqueduct.

Pipe Loop Studies
Because lead service lines were known to be a contributing factor to elevated lead levels in District of Columbia drinking water, sections of lead and copper service lines were being used in corrosion control experiments. One of the ways that corrosion control methods were evaluated was through the use of electrochemical pipe loop studies. The studies were designed to measure the amount of lead and copper being leached from the small (2-3 inch long) sections of pipe. The sections of lead and copper pipes used in the experiments represent service lines connecting water mains to homes.

Electrochemical pipe loops operate using a recirculation pump that moves water from the holding tanks through the pipe sections and back into the holding tank. The water is changed out of the tanks every day.

A control loop is operated for comparison against different water treatment regimes. The effects of pH and phosphate on lead leaching in the presence of chloramines are important to determine, as increasing pH and the addition of phosphate are two methods commonly used for corrosion control. The flow regime mimics the water flow in service lines to homes with periods of active use followed by prolonged periods of quiescence. Samples are drawn after these periods of stagnancy to replicate household first-draw samples. Samples are analyzed for pH, total and dissolved lead, alkalinity (as calcium carbonate), chlorine species, dissolved oxygen, and several other water quality parameters.

WASA Pipe Loop Studies

Begun in March 2004, WASA's experimental pipe loops, set up at their Ft. Reno facility, tested the effects of different treatment scenarios on lead service line corrosion. Each pipe loop had water with different chemical characteristics flowing through it. The parameters that were varied were disinfectant type (chlorine, chloramines), corrosion control strategy (orthophosphate, coatings), and chemical dosages. Both flow-through and electrochemical experiments were performed to determine changes in corrosion rates and lead release with different treatment chemicals. Results indicate that orthophosphate is effective at reducing lead corrosion from lead water service lines.

Additional Information on WASA's pipe loops (August 2006)(PDF) [2 pages, 32K, about pdf]

Electrochemical pipe loop testing apparatus at the D.C. Water and Sewer Authority (WASA) Fort Reno Office, 3900 Donaldson Place, NW.

Replicate loops are set up for these corrosion control experiments. In this picture, dull grey lead pipe sections, shiny copper pipe sections, Nalgene holding tanks, and tubing are visible.

Washington Aqueduct Pipe Loop Studies

CH2M Hill, a contractor to the Washington Aqueduct, prepared a plan [PDF, 9 pages, 102K, about pdf] to investigate the effect of several parameters of interest on lead corrosion.

These experiments subjected excavated sections of District of Columbia lead service lines to different regimes of corrosion inhibitor and disinfectant. The studies were designed to mimic actual conditions in lead service lines connected to customer homes, with the intent of evaluating refinements in corrosion control treatment. The Washington Aqueduct began the conditioning phase of the pipe loop tests in January 2005 and experiments began in March 2005. The pipe loops were set up at the Washington Aqueduct's Dalecarlia treatment plant. These experiments examined scenarios with varying disinfectant types (chlorine/chloramines), corrosion inhibitor types (orthophosphate/zinc orthophosphate), and corrosion inhibitor doses. Results indicated that orthophosphate is effective for decreasing lead levels. Experiments were also conducted to assess the effect of a "chlorine burn" (temporary switch to free chlorine as a disinfectant) and incremental decreases from the initial orthophosphate dose to a lower maintenance dose.

Additional information on the Washington Aqueduct's pipe loops (PDF) (August 2006) [2 pp, 53K, about pdf]

Changes in Lead Levels during Switch to Free Chlorine
The Washington Aqueduct's 2004 springtime switch from chloramines to free chlorine presented the D.C. Water and Sewer Authority (WASA) with an opportunity to examine the relationship between disinfectant type and lead levels in tap water. Data indicates that the conversion to chloramine disinfectant in November 2000 may have stimulated the release of lead previously immobilized due to the presence of free chlorine.

Lead Profile Studies

In addition to the required lead tap sampling and the pipe loop studies, WASA has been sampling at homes to determine which part of the plumbing between the water main and the tap is contributing to elevated lead concentrations. Lead profiling is a type of sampling that collects each liter of water from the tap, through the home's plumbing system, and out through the service line to the water main. Lead profiles have been performed to assess the effectiveness of orthophosphate addition and lead service line replacements. For more information on lead profile studies, see the Research Newsletter [PDF, 8 pages, 437 K, about pdf].

Impacts of Zinc Orthophosphate on the Environment

Based on a desktop study, the experience of other utilities, and after a review by water treatment experts, zinc orthophosphate (ZnOP) was initially approved as the corrosion inhibitor for use in the District of Columbia. However, the addition of zinc and phosphorus to drinking water prompted concern over the impacts of the additional nutrient and metal loading to streams and wastewater treatment plants in the District of Columbia, Arlington County, and Falls Church, Virginia. Orthophosphate, the original recommendation of the TEWG, was ultimately selected for use by the Washington Aqueduct.

A study [PDF, 60pp, 486 K, about pdf] was performed to assess the impacts of the proposed additional zinc and phosphorus loading to streams (through combined sewer overflow or potable water discharges) and to wastewater treatment processes. Although there are currently no plans to use ZnOP, this study provides an evaluation of zinc and phosphorus impacts in the event of future treatment process changes.

Impacts of Zinc Orthophosphate on Wastewater Treatment

Although orthophosphate is currently being used for corrosion control, DC area utilities were interested in the potential impacts of zinc orthophosphate on wastewater treatment processes. Metals in general (and zinc, specifically) are known to inhibit sensitive biological nitrogen removal processes. Studies performed at the Arlington (VA) Water Pollution Control Plant (WPCP) evaluated the effects of zinc loading on nitrogen and organic carbon removal.

The studies were designed to examine changes in nitrogen and carbon removal at zinc concentrations typical of what would be discharged to the WPCP if zinc orthophosphate were to be added to the drinking water supply as a corrosion inhibitor. Batch inhibition tests and respirometry studies were used to determine the effects of additional zinc loading on nitrogen removal at the Arlington WPCP. The studies indicate that the levels of zinc that would enter the wastewater treatment process due to ZnOP addition to drinking water should not have an adverse effect on the nitrogen removal process. The results of these studies will be useful in the event that the zinc orthophosphate is considered as a corrosion inhibitor in the future.

Final Report: Evaluation of Zinc Inhibition on Nitrification and BNR (PDF) [59pp, 1.8MB, about pdf]