The Dalecarlia Reservoir and Water Treatment Plant

from Army Corps of Engineers via Wikimedia

I went up to the Dalecarlia Reservoir and Water Treatment Plant on MacArthur Boulevard for a tour and to speak with Thomas Jocobus, the General Manager. The Dalecarlia operations are the main location for the Washington Aqueduct. The Washington Aqueduct consists of the Dalecarlia Reservoir and Water Treatment Plant, the Georgetown Reservoir, and the McMillan Reservoir and Water Treatment Plant. The Washington Aqueduct draws water from the Potomac River and treats it to provide finished drinking water to the water distribution companies that buy water from them.

The Washington Aqueduct is a federally owned and operated by the Army Corp of Engineers and Mr. Jacobus like all employees of the Washington Aqueduct is a civilian employee of the Army Corp of Engineers. The Aqueduct was initially built with federal funds, but since 1927 the operating budget and capital budget have been paid for by the Aqueduct’s customers. Today, the operating budget is around $46 million that is supplied by the wholesale water rates charged for the water delivered. The Aqueduct produces an average of 155 million gallons of water per day and sells that water to the District of Columbia (about 75% of the finished water), Arlington County, Virginia (about 15%), and the City of Falls Church, Virginia (10%). In total about one million people a day use water supplied by the Aqueduct.

The maximum capacity of the Aqueduct is 320 million gallons of water per day much more than even the peak demand for drinking water and fire fighting for their customers. Though water use peaked at an average of 180 million of gallons a day about a decade ago, the system was expanded in the 1950’s anticipating serving Montgomery and Prince George counties, but the Washington Suburban Sanitary Commission (WSSC) instead built what is today the WSSC's principal water supply facility, the Potomac River Filtration Plant in western Montgomery County to supply their needs.

The Washington Aqueduct dates back to 1853 when congress appropriated $5,000 to develop the first portion of the system. The first portions of the system were the Dalecarlia Reservoir and Georgetown distribution reservoir. That portion of the system was designed to run on gravity, so that the system did not require pumps until much later when the system and the city expanded and demand for water required the expansion of the system. Even today the energy used is reduced because of the utilization of natural elevations in the design of the system. The Aqueduct first began delivering water in 1862. The Lydecker Tunnel and McMillian Reservoir and water treatment plant were added in 1905. The McMillian slow sand water treatment plant was the first treatment plant in the system and was built to address the increasing outbreaks of typhoid fever that were caused by contaminated drinking water. This was followed by a rapid sand filtration system at Dalecarlia to address the continued population growth after World War I.

Today the water for the Washington Aqueduct continues to be drawn from the Potomac River at the Great Falls and Little Falls intakes. This duel intake location about 10 miles apart allows for some degree of management of the water quality at intake if there should be a fuel spill or other water quality disturbance. On its way from the river intakes to the Dalecarlia reservoir, raw water passes through a series of screens designed to remove debris such as twigs and leaves and whatever trash finds its way into the Potomac River. Then copper sulfate and sodium permanganate are added as algaecides. All water drawn for the system enters the Dalecarlia Reservoir. While the water moves slowly through Dalecarlia Reservoir, much of the sand and silt settles to the bottom. This is called pre-sedimentation. After screening, the addition of the algaecides and pre-sedimentation the water is either pumped to the Dalecarlia or McMillan treatment plants.

The treatment plants filter and disinfect water from the Potomac River to meet safe drinking water standards. The treatment process is not identical at both plant, but it is very similar and includes sedimentation, filtration, fluoridation, pH adjustment, primary disinfection using sodium hypochlorite, secondary disinfection with chloramine through the addition of ammonia, and corrosion control with orthophosphate.

From the Army Corp of Engineers

The raw water from the Potomac River contains suspended solids, sediment, bacteria, and microorganisms that must be removed to produce finished drinking water. These are removed by the water treatment processes of the Washington Aqueduct after the initial screening and pre-sedimentation water treatment consists of:

Coagulation - A coagulant, aluminum sulfate (alum) and powdered activated carbon, is added to the water as it flows to sedimentation basins. Coagulants aid in the removal of suspended particles by causing them to consolidate and settle. Alum contains positively charged atoms called ions which attract the negatively charged particles suspended in water causing them to gather into clumps of particles heavy enough to settle. The activated carbon controls odor in the water.

Flocculation – The water is gently stirred with large paddles to distribute the coagulant; this causes particles to combine and grow large and heavy enough to settle. This process takes approximately 25 minutes. Cationic polymer and nonionic polymer are added.

Sedimentation – The water flows into quiet sedimentation basins where the flocculated particles settle to the bottom. After about four hours, approximately 85% of the suspended material settles out. Until recently, the sediment recovered was returned to the river, now the sediment residuals are collected from Dalecarlia, McMillan and Georgetown locations and then pumped to a central processing facility at Dalecarlia.  Residuals processing, including gravity thickening and dewatering, occur at the newly constructed Residual Management building. Following processing, trucks haul the residuals off-site to permitted land-disposal areas.

Filtration – Water at the top of the basins flows to large gravity filters, where the water flows down through filter media consisting of layers of small pieces of hard coal (anthracite), sand, and gravel placed in the bottom of deep, concrete-walled boxes. Filtered water passes through to a collecting system underneath. The filters are back washed every four days.

Disinfection – Chlorine in the form of sodium hypochlorite is added with precision equipment to kill pathogenic microscopic life such as bacteria or viruses. Ammonia is then added. The chlorine and ammonia combine to form chloramine compounds. This is the most recent significant change in the water treatment process and was required by changes in the Safe Drinking Water Act in the 1990's. The concentration of chloramines in the water is closely monitored from the time it is added at the treatment plants to points near the furthest reaches of the distribution systems.

The Dalecarlia operation has an EPA certified laboratory to perform the tens of thousands of analysis required each year under the Safe Drinking Water Act. One of the coolest features of the tour was seeing the surveillance of the water treatment train. In one of the laboratories is a trough sink with 15 spigots continually running. Each spigot continually draws water from one step in the treatment process. If a problem arises water at every point can be checked to make adjustments.

Fluoride, in the form of hydrofluorosilicic acid, is added to the finished water to reduce tooth decay; this is especially beneficial for children. Orthophosphate is added to control corrosion in pipes, service lines, and household plumbing throughout the distribution system. It works by building up a thin film of insoluble material in lead, copper, and iron pipes and fixtures. This thin film acts a barrier to prevent leaching of metals into the water. Calcium hydroxide (lime) is also added to adjust the pH of the water to ensure optimal performance of the orthophosphate.

After the water has completed its path through the treatment process, it is referred to as finished water and meets all requirements under the Safe Drinking Water Act. Because the Washington Aqueduct is in Washington D.C. it is directly regulated by the US EPA Region 3 office. The Washington DC regulators do not have primacy. Unlike most large urban water systems the Aqueduct does not have state regulators to answer to and its customers are the three water distribution systems DC Water, Arlington and Falls Church section of Fairfax County. Falls Church has come to an agreement to turn over their distribution system to Fairfax Water who will continue to buy water for that portion of the system from the Aqueduct. The Washington Aqueduct does not currently engage in any advanced water treatment, but is studying the options.  

The History of Drinking Water in Washington DC

In the first decade of the nineteenth century a group of residents of Washington DC were granted permission to pipe water from the city spring to their neighborhood in the 600 block of Pennsylvania Avenue. Shortly thereafter the city built a pipe to convey water from a city spring to the northwestern Pennsylvania Avenue vicinity, between 9th and 14th streets. These, were the first instances of water deliveries in Washington DC and the beginning of the water system in our nation’s capital. The city-wide delivery of fresh water was still another fifty years away and would arrive with the Washington Aqueduct.

The original portions of the Washington Aqueduct were planned and built by Lieutenant Montgomery C. Meigs of the Army Corp of Engineers. The Dalecarlia Reservoir was completed in 1858 and water first reached the District through the Washington Aqueduct system on January 3, 1859. Initially the reservoir provided water to the city from the adjacent Little Falls Branch, but this soon was inadequate and flow from the Potomac River was added in 1864. At that time the city government believed, the Washington Aqueduct system would be sufficient for all the future water needs of the city. Today the Washington Aqueduct is a division of the Baltimore District, U.S. Army Corps of Engineers. The Aqueduct is a federally owned and operated public water supply agency that produces an average of 180 million gallons of water per day at two treatment plants located in Washington DC and sells the water to the District of Columbia, Arlington County, Virginia, and the City of Falls Church, Virginia.

 After the initial construction of the Washington Aqueduct the surge in population of Washington DC during the Civil War, quickly created a human waste problem in the city and there were epidemics of smallpox, malaria, and typhoid from human waste contaminating the water supply which took many thousands of lives during the war years. Dr. John Snow had discovered and proved the connection between cholera and contaminated water during the 1850’s in London, England. Nonetheless, the general belief was that if water looked, tasted and smelled fine it was good and though the Potomac River provided dilution disease survived. The Washington Aqueduct was originally built as a water transportation system, to bring the river water into the city. However, in 1895 the flow from Little Falls Branch was diverted away from the Dalecarlia Reservoir to prevent disease in conjunction with development of the sanitary sewer system. Despite these steps it was clear that, the Washington Aqueduct needed to be expanded and have a filtration system. The Washington Reservoir, which is now called the McMillan Reservoir, was built in 1902 to increase supply and in 1905, a 75 million gallon per day slow-sand filtration system was added at that reservoir and the Bryant Street high-lift pumping station was built.

After World War I an 80 million gallon per day rapid-sand filter was added at the Dalecarlia Reservoir to address the problems created by continued population growth and the sheer amount of raw sewage that was being pumped into the river. Primary waste treatment began for Washington DC at Blue Plains sewage treatment plant in 1937. The continuous population growth of Washington DC during World War II made it necessary to continue to expand and improve the water supply system. In February 1946, Congress approved comprehensive plans from the Army Corp of Engineers and the City Engineer to construct, improve and add to the existing water system. For more than thirty years, implementation of the plan underwent periodic modifications through changing requirements and increases in necessary funding by Congress. This awkward and inefficient oversight and funding was still in effect when I briefly lived in the District in the early 1970s when the water and sewage agency was known as the District of Columbia Department of Environmental Services. Later, in 1985, the District Government established a new Department of Public Works, of which the Water and Sewer Administration was a part of until 1996.

In 1996, the District Government initiated the creation of the District of Columbia Water and Sewer Authority (DC WASA re-branded DC Water in 2010), an independent authority of the District of Columbia providing water delivery and sewage services to the region. On April 18, 1996, following a 30-day Congressional review period, the District Council enacted DC Law 11-111, "The Water and Sewer Authority Establishment and Department of Public Works Reorganization Act of 1996." This allowed DC WASA to have a separate and dedicated source of funding-water and sewer rates. It was envisioned that DC WASA would then be able to use that funding to meet its statutory obligation to provide sanitary sewer services and deliver potable water to the Washington Metropolitan Area. The Washington Aqueduct remains   federally owned.

Today, the Aqueduct draws water from the Potomac River at the Great Falls and Little Falls intakes and treats the water at two treatment plants, Dalecarlia and McMillan. The Aqueduct filters and disinfects water from the Potomac River to meet current safe drinking water standards. The treatment process includes sedimentation, filtration, fluoridation, pH adjustment, primary disinfection using free chlorine, secondary disinfection with chloramine through the addition of ammonia, and corrosion control with orthophosphate. The EPA sets national limits on residual disinfectant levels in drinking water to reduce the risk of exposure to disinfection byproducts formed when public water systems add chemical disinfectant for either primary or residual treatment. These levels are known as Maximum Residual Disinfectant Levels (MRDLs). The EPA also sets EPA sets limits on the contaminants regulated under the Safe Drinking Water Act to ensure that the water is safe for human consumption. These limits are known as Maximum Contaminant Levels (MCLs). During calendar year 2011, no MRDL nor any MCL violations occurred in the Washington Aqueduct system.

By 1996 some portions of the water delivery system were 100 years old and the sewage system was almost the same age. The water and sewage rates in place in the Washington Metropolitan Area covered the costs to deliver the water and treat the sewage and replace 0.33% of the system each year, an unrealistic and irresponsible repair and replacement rate.  DC Water averages between 400 and 500 water main breaks per year, and they thought that a plan to replace the system over a 300 year time span was meeting their statutory obligations. 

Water delivery systems have a long life span, they are just pipes, pumps and valves, but the life span is not infinite. We reward short sighted behavior. In order to have cheaper water and sewer, a replacement cost schedule was not built into the customer rates for the past 78 years which coincidentally is the current average age of a water main in Washington DC. There are water pipes north of the White House that are reported to have been laid before the Civil War. This past Spring DC Water announced that they have tripled the replacement rate to 1% (with of course the increase in water rates) so that in 100 years the system will be replaced. Sewage rates were increased to finance the District’s portion of the $7.8 billion Blue Plains improvement program called the Clean Rivers Project that will meet the reduced total nitrogen released requirements of their operating permits and increase the control of the system during rain storms in addition sludge treatment will be improved and sewer piping improved in many areas. In truth, according to an interview with the General Manager, George Hawkins on National Public Radio, DC Water has gotten so far behind that they cannot to catch up- it will take decades. It is likely, given the age of the water system in Washington DC the increase in replacement rate was probably necessary to address what was failing each year. One hundred years is longer than the predicated life of a water distribution system, piping systems are rated at 80 years and the average water main in Washington DC is 78 years old. The water pipes in DC are old. They leak. DC Water is trying to use a predictive modeling to determine which pipes need to replace first to keep the good quality* water they are buying from the Washington Aqueduct flowing to the homes and businesses in the District.

Washington DC (and most of America) has always thought about the cost of water wrong, there should have always been a plan for maintenance, upgrade and replacement of the system and the care and protection the water resources; instead we have all taken water (and sewage) for granted. Every pipe should have been on a schedule to be replaced before it exceeded its life and broke. The water rates need to cover these capital replacement and maintenance costs. If we do not maintain our infrastructure we will not have on demand water. DC Water sees persuading customers to pay for the maintenance and improvement of the water and sewer system as their biggest challenge. The investment into water and sewer infrastructure is simply one of the best investments that any community can make.

* Dr. Marc Edwards a professor of engineering at Virginia Tech discovered while doing research in the mid-1990s to identify the cause of an increasing incidence of pinhole leaks in copper water pipes, that chloramine was causing the accelerated pipe deterioration and extreme lead concentrations in DC drinking water. Chloramine-treated water picks up lead from pipes and solder and does not release it, resulting in elevated levels and deterioration of the pipes. The change to chloramine was made after the EPA issued regulations concerning disinfection by-products formed when chlorine reacts with organic matter in drinking water; the EPA considered these byproducts to be a potential health threat. Chloramines do not produce disinfection byproducts. The lead problem was addressed in 2004 by the Washington Aqueduct adding additional treatment steps to the water to prevent the chloramine from dissolving lead in the water mains, solder joints, and fixtures. In addition, DC WASA spent $97 million to replace a portion of 15,000 pipes and 2,000 full pipe replacements. Then after the dust settled on this re-branded themselves as DC Water.