Water Treatment News
This page provides detailed information on news related to treatment of 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.
- Washington Aqueduct completes treatment change to sodium hypochlorite disinfection and use of caustic soda for fine pH control (July 2011)
In July 2011, Washington Aqueduct completed its conversion from liquid/gas chlorine to sodium hypochlorite at its Dalecarlia and McMillan treatment plants. Conversion from liquid/gas chlorine to hypochlorite represents a safety improvement.
Also in July 2011, Washington Aqueduct completed its conversion to the use of caustic soda for fine pH adjustment at its Dalecarlia and McMillan treatment plants. Use of caustic soda will improve pH control and corrosion of the drinking water distribution system.
For more information, please visit the Washington Aqueduct's website. http://washingtonaqueduct.nab.usace.army.mil/hypochlorite.htm
- 2011 Temporary Disinfectant Change (Spring 2011)
From March 21 through May 1, the Washington Aqueduct made a temporary change in the disinfectant added to the drinking water supplied to its customers. The temporary switch from chloramine disinfection to disinfection with chlorine only is common in utilities that normally use chloramine for disinfection and is intended to dislodge biofilms and sediments in water mains.
- Washington Aqueduct begins Hypochlorite Use at McMillan Treatment Plant (May 2010)
- 2010 Temporary Disinfectant Change (January 2010)
- Washington Aqueduct to Phase-in Treatment Changes (July 2009)
- Spring 2009 Temporary Disinfectant Change (April-May 2009)
- EPA Approves Orthophosphate as Optimal Corrosion Control Treatment (June 2006)
- Chlorine Burn Postponed (March 2006)
- Orthophosphate Dose Decreased (January 2006)
- Pipe Loop Testing Continues (January 2006)
- Information on Coliform Bacteria in Drinking Water (September 2004)
- Orthophosphate Corrosion Inhibitor added System-wide (August 2004)
- Washington Aqueduct begins Orthophosphate Corrosion Control Treatment in Limited Area (June 2004)
- EPA Approves Washington Aqueduct's Request for Zinc Orthophosphate Partial System Application (April 2004)
- Corrosion Control Study Recommends Zinc Orthophosphates (April 2004)
Washington Aqueduct begins Hypochlorite Use at McMillan Treatment Plant (May 2010)
In late May 2010, Washington Aqueduct began its conversion from liquid/gas chlorine to sodium hypochlorite at its McMillan treatment plant. Conversion from liquid/gas chlorine to hypochlorite represents a safety improvement.
This is the first phase of two treatment changes that will be implemented at the Washington Aqueduct’s treatment plants. Conversion to hypochlorite at the Dalecarlia plant, as well as implementation of caustic soda for pH control at both treatment plants are expected to be completed by September 2010.
For more information, please visit the Washington Aqueduct’s website.
2010 Temporary Disinfectant Change (January 2010)
From February 1 through May 17, the Washington Aqueduct will make a temporary change in the disinfectant added to the drinking water supplied to its customers. The temporary switch from chloramine disinfection to disinfection with chlorine only is common in utilities that normally use chloramine for disinfection and is intended to dislodge biofilms and sediments in water mains. The duration of the 2010 temporary disinfectant change is longer than in past years.
For more information, please see news releases from the Washington Aqueduct and DC WASA.
Washington Aqueduct to Phase-in Treatment Changes (July 2009)
Between the fall of 2009 and the spring of 2010, the Washington Aqueduct will phase in two treatment changes at its Dalecarlia and McMillan Treatment Plants. The Washington Aqueduct will convert from its current disinfectant to sodium hypochlorite and will add sodium hydroxide (caustic soda) for fine-tuning pH control. These changes will result in safety enhancements and improved pH control.
For more information on these treatment changes, see the Washington Aqueduct’s website.
Spring 2009 Temporary Disinfectant Change (Spring 2009)
From April 6 through May 4, the Washington Aqueduct made a temporary change in the disinfectant added to the drinking water supplied to its customers. The temporary switch from chloramine disinfection to disinfection with chlorine only is common in utilities that normally use chloramine for disinfection and is intended to dislodge biofilms and sediments in water mains.
For more information, please see the joint news release from the Washington Aqueduct, DC WASA, Arlington County, and the City of Falls Church
Spring 2008 Temporary Disinfectant Change (Spring 2008)
From April 7 through May 12, the Washington Aqueduct made a temporary change in the disinfectant added to the drinking water supplied to its customers. The temporary switch from chloramine disinfection to disinfection with chlorine only is common in utilities that normally use chloramine for disinfection and is intended to dislodge biofilms and sediments in water mains. This temporary switch, sometimes called a "chlorine burn", was performed in conjunction with water main flushing programs being performed by DC WASA, Arlington County, and the City of Falls Church. The last temporary disinfectant change was performed in the spring of 2007.
For more information, please see the joint news release from the Washington Aqueduct, DC WASA, Arlington County, and the City of Falls Church
Spring 2007 Temporary Disinfectant Change (Spring 2007)
On April 7, 2007, the Washington Aqueduct began a month-long change in the disinfectant added to the drinking water supplied to its customers. The temporary switch from chloramine disinfection to disinfection with chlorine only is common in utilities that normally use chloramine for disinfection and is intended to dislodge biofilms and sediments in water mains. This temporary switch, sometimes called a "chlorine burn", is being performed in conjunction with water main flushing programs being performed by DC WASA, Arlington County, and the City of Falls Church. The last chlorine burn was performed in the spring of 2004.
On June 14, 2006, EPA designated [5 pp, 270K, about pdf] orthophosphate treatment as the optimal corrosion control treatment method for controlling the leaching of lead into drinking water. This designation comes after nearly two years of orthophosphate addition, tap monitoring for lead and copper, and distribution system monitoring for a suite of water quality parameters. In August 2004, EPA approved orthophosphate on an interim basis, for the period of distribution system passivation.
In an effort to maintain stable water chemistry with respect to lead, the Washington Aqueduct and its customers (DC WASA, Arlington County, and Falls Church) decided to suspend the 2006 switch to free chlorine. The Washington Aqueduct uses chloramines for disinfection for most of the year, but has traditionally switched to free chlorine for distribution system maintenance purposes for a few weeks each spring. The 2005 chlorine "burn" was also suspended due to concerns over changes in water chemistry that may impact the lead-phosphate scale in the distribution system pipes. A chlorine burn is being simulated in pipe loop experiments to evaluate the impact on lead levels. The Aqueduct and its customers will meet next year to decide on the need for the springtime chlorine switchover in 2007.
The Washington Aqueduct lowered the orthophosphate dose in the drinking water for the first time on January 30, 2006. The initial dose (approximately 3.5 mg/L) was on the high end of normal operations in order to passivate the system. The decrease in dose to approximately 2.4 mg/L (to attain a residual concentration of 2 mg/L in the distribution system) is part of standard operational procedures. The Washington Aqueduct and DC WASA (in conjunction with other members of the Technical Expert Working Group) will examine lowering the dose to a final maintenance dose. Lead compliance data and laboratory pipe loops will be useful when considering these operational changes.
The Washington Aqueduct and DC WASA are continuing to run their pipe loops which simulate distribution system conditions. Conditions can be changed in different loops to assess the effects varying operational parameters (e.g., corrosion inhibitor dosage, chlorine burn).
WASA continues to test various corrosion control strategies in their pipe loops. To date, no corrosion control strategy has outperformed orthophosphate for decreasing lead leaching. Testing continues to examine how changing disinfectants would impact orthophosphate treatment. This is an important research area because the drinking water disinfectant is typically changed from chloramines to chlorine for one month in the spring to help control for bacteria.
The Washington Aqueduct has been conducting flow-through pipe studies at its treatment plant to complement WASA's pipe loop testing. To simulate actual residential water use, water is pumped through the lead service lines and discarded. The water is then held in the lines for several hours and lead levels are measured. The Aqueduct's flow-through studies are focusing on refining the treatment process, selecting a final maintenance dose of orthophosphate, and examining the impact of a temporary switch from chloramine disinfection to free chlorine.
Several District of Columbia (DC) public schools are sampled monthly as part of the extensive city-wide water quality monitoring program that DC WASA is performing to assess the impacts of orthophosphate (added by the Washington Aqueduct in August 2004 to control lead corrosion) on water quality. DC WASA has been monitoring 50 sites in the distribution system, including 11 schools, for over 20 water quality parameters since November 2004.
The highest nitrite levels detected in a few schools in summer 2005 ranged from 0.4 to 0.7 milligrams per liter. These slightly elevated nitrite levels are not system-wide, but rather localized in certain buildings that may have been closed, underused, or located in low-flow or dead-end areas of the distribution system. EPA has published a safe drinking water standard for nitrite which is 1 milligram per liter (mg/L) measured in water leaving the treatment plant. The water distributed city-wide has consistently met that EPA standard. Nitrite levels are in compliance with the drinking water standard and do not constitute a public health emergency. Harmless bacteria present in many distribution systems can convert ammonia to nitrite through a process called nitrification. Elevated summertime temperatures and low water use while buildings are unoccupied (for example, schools closed over summer months) appear to allow growth of these harmless bacteria. This is not an uncommon occurrence in systems where chloramine disinfectant (produced by combining chlorine and ammonia at the treatment plant) is used. Water leaving the Washington Aqueduct treatment plants does not have detectable levels of nitrite.
The drinking water standard for nitrite is protective of the most sensitive population - infants under 6 months of age. In the first few months of this monitoring, three test results from one of the 11 schools monitored ranged from approximately 1.1-1.2 mg/L, but flushing of the school plumbing quickly reduced nitrite levels within the building. DC Public Schools and DC WASA continue to monitor this building closely to ensure that water quality is maintained. The building systems are also being assessed for cross-connections with boiler and heating systems to ensure that the drinking water supply does not mix with other non-potable water.
The data gathered, and lessons learned from the supplemental monitoring program resulted in precautionary notices sent to all of the public and private school facility managers in DC, as well as some additional large building owners in DC. They advise the owners to take relatively simple steps to perform maintenance activities when there is no or very low water use in a facility over an extended period. Additional testing and flushing continue and results will be carefully monitored to determine the scope of the issue.
During September 2004, sampling by the District of Columbia Water and Sewer Authority (WASA) has indicated that the number of tap water samples containing coliform bacteria is above the 5% maximum contaminant level (MCL) set by EPA. WASA has issued public notification to their customers through a letter [PDF, 1p, 25K, about pdf] and an official notice, has submitted the notice for publication in newspapers, and has notified EPA that they are in violation of the Total Coliform Rule monthly MCL for September [PDF, 2pp, 81K, about pdf].
Although drinking water (especially that from surface water sources) is treated through a variety of processes to remove microbial contaminants, it is not sterile. Coliform bacteria are able to grow in a variety of soil and water environments and are indicators of biological activity in the distribution system. Coliform bacteria are generally harmless, but they may indicate the presence of other potentially harmful bacteria. Violation of the monthly MCL for coliform bacteria does not present an acute health risk – neither WASA, the District of Columbia Department of Health (DCDOH), nor EPA are recommending that water be boiled before drinking or cooking. If you have specific health concerns, you should consult your physician.
EPA regulates coliform bacteria in drinking water under the Total Coliform Rule. The rule includes requirements for routine and repeat monitoring and for public notification if an MCL is exceeded. This link provides more information on the Total Coliform Rule.
What is the water system doing about coliform bacteria?
WASA is increasing their bacterial monitoring beyond what is required to determine the extent of the problem and the best way to resolve the issue. In conjunction with increased monitoring, WASA is performing an extensive flushing program to remove bacteria, sediment, and iron from the distribution system. WASA will also issue public notification to their customers.
Is this related to orthophosphate addition?
To decrease lead levels in drinking water, the Washington Aqueduct began adding orthophosphate to the water supply in late August 2004. The Aqueduct, WASA, and EPA were aware that increased numbers of samples detecting bacteria, including coliform bacteria, and "red water" were possible temporary side-effects of the treatment. Orthophosphate has the ability to soften iron oxides and biofilms in the distribution system, causing them to be released and mobilized in the distribution system pipes. WASA's flushing program will help move the corrosion inhibitor through the distribution system as well as remove rusty or dirty water and bacteria.
In an August 3, 2004 letter [PDF, 9pp, 36K, about pdf ] to the Washington Aqueduct and the D.C. Water and Sewer Authority (WASA), EPA designated orthophosphate (OP) as the interim optimal corrosion control treatment (OCCT) method that will be used to combat lead leaching in the water distribution system. After months of review, research, and a partial system application of OP in the 4th high pressure zone of Northwest, the Technical Expert Working Group (TEWG) recommended [PDF, 1p, 1.5 MB, about pdf] to the Aqueduct and its wholesale customers that OP be added to finished water distributed to the entire District and to Falls Church and Arlington County, Virginia. An independent peer review panel of outside experts concurred with this recommendation. The treatment is expected to begin on or about August 23, 2004.
EPA, WASA, the D.C. Department of Health (DOH), and the Washington Aqueduct, are jointly sending out a public announcement [PDF, 2pp, 32K, about pdf], accompanied by a tip sheet [PDF, 1p, 836K MB, about pdf], to describe the treatment process, the continuing consumer advisory, and actions that residents should take in the event of discolored (red- or rust-colored) water, a possible temporary side effect of the OP treatment. Please see the Frequent Questions page for answers to several frequently asked questions about red water and orthophosphate.
Public Meetings held on Orthophosphate Treatment
Two public meetings were held in late August to discuss the District-wide implementation of corrosion control treatment. The meetings consisted of an "open house" informational session followed by a more formal presentation and Q&A session. Meetings were held in the NW and SE sections of the District.
On June 1, 2004, the Washington Aqueduct began feeding orthophosphate (OP), a corrosion control chemical, to decrease lead leaching from lead service lines and lead plumbing components in homes. Orthophosphate is only being applied to the 4th High Pressure Zone [PDF, 1p, 2.8M, about pdf] in the NW section of the District. Drinking water in this area is being closely monitored for lead levels, additional metals, bacteria, pH, and other parameters.
Although orthophosphate was the initial recommendation of the TEWG, EPA originally approved zinc orthophosphate (ZnOP) due to its successful use in other large systems. EPA subsequently approved orthophosphate [PDF, 4pp, 401K, about pdf] as the corrosion control chemical due to concerns over the potential impact of increased zinc loading on wastewater treatment processes. EPA and the wastewater treatment authorities continue to study the impacts of zinc in case there is a need to revert back to ZnOP.
To date, there have been no customer reports of changes in water quality during the partial system application of orthophosphate and all testing results have shown no indication of problems caused by the new treatment. Full system application of OP is scheduled to begin in August.
Chemical feed pumps deliver orthophosphate to the 4th High Pressure Zone, a small portion of the NW quadrant of the District.
This connection is the point where orthophosphate is injected into finished water leaving the Fort Reno Pumping Station
These instruments monitor the pH and oxidation-reduction potential (ORP) of water before and after orthophosphate addition. These measurements are indicators of the acidic or basic nature of the water and the oxidizing or reducing conditions that will exist in the distribution system. Both pH and ORP are important in controlling lead leaching and scale formation inside the distribution system pipes. The target pH is approximately 7.8.
EPA Approves Washington Aqueduct's Request for Zinc Orthophosphate Partial System Application (April 2004)
Jon Capacasa, Director, Water Protection Division, approved on April 30 [PDF, 8pp, 32K, about pdf] the Washington Aqueduct's interim modification to its corrosion control treatment. Based on the April 23, 2004 recommendations of a group of corrosion control experts and upon EPA review, the partial system application of zinc orthophosphate in the 4th High Zone [PDF, 1p, 2.8M, about pdf], a relatively small, hydraulically isolated area of the distribution system in the NW area of the District, is approved. Full system application of this corrosion inhibitor will be evaluated and addressed separately.
In a letter dated April 15, 2004 , the Washington Aqueduct requested EPA's approval of a corrosion control plan that would involve using zinc orthophosphate as a corrosion inhibitor in a limited area of the district beginning on or about June 1, 2004. This corrosion control plan was developed in a meeting of the Technical Advisory Working Group held in response to the Independent Peer Review Panel's review of the CH2MHill desktop analysis. If the treatment is approved and successful, it could be implemented to the entire Washington Aqueduct water treatment system as early as July 15, 2004.
The corrosion control treatment will first be deployed in a small area of the distribution system called the 4th High Pressure Zone [PDF, 1p, 2.8M, about pdf]. Public information sessions on the proposed treatment were held in late April.
A corrosion control study report [PDF, 39pp, 600K, about pdf] was written on behalf of the Washington Aqueduct for the multi-agency team working to develop a strategy to reduce corrosion in the D.C. water supply. It includes comments from an independent peer review panel of corrosion experts from throughout the country.
The team - called the Technical Expert Working Group – has reviewed this report and recommended that the Washington Aqueduct present it to EPA for final approval. The report recommends a new treatment program to correct corrosion of lead into water.
This report includes an evaluation of past corrosion control studies done for the Washington Aqueduct and an evaluation of options that have worked successfully in other locations. It recommends zinc orthophosphate as the chemical regime likely to provide the greatest lead reduction while minimizing adverse impacts.
The technical team consists of representatives from EPA, the Centers for Disease Control and Prevention, D.C. Water and Sewer Authority (WASA), the Washington Aqueduct, D.C. Department of Health, Virginia Department of Health, and a variety of independent experts and contractors.