The Dalecarlia Water Treatment Plant (WTP) in Washington, D.C., is one of two plants at the Washington Aqueduct that serve the district and surrounding areas. The federally owned plant will host a facility tour at this year’s AWWA ACE11 conference. Here Washington Aqueduct Deputy General Manager Patricia Gamby discusses the plant and its plans for the future with WWD Associate Editor Kate Cline.
Kate Cline: What is the plant’s history? What population does it serve?
Patricia Gamby: The Dalecarlia WTP was constructed in 1925. It was authorized as an expansion of the Washington Aqueduct treatment system beyond the McMillan WTP to serve the growing population in the northwest part of Washington, D.C., and to serve Arlington County, Va.
It has a capability of approximately 180 million gal per day and could serve the entirety of the Washington Aqueduct service population of 1 million. Normally it works in conjunction with the McMillan WTP. Dalecarlia provides about 60% of the daily demand of the wholesale customers.
Cline: The plant is federally owned. Does this present special challenges for maintenance or management?
Gamby: Washington Aqueduct is owned by the federal government as a consequence of its founding in 1853. The employees are federal civil servants and part of the Army Corps of Engineers. There are no appropriated funds involved in the operations or capital improvements of Washington Aqueduct. Financially and strategically, Washington Aqueduct is underpinned by a wholesale customer board comprised of the three customer jurisdictions: D.C., Arlington County and the city of Falls Church, Va. It is regulated by EPA [U.S. Environmental Protection Agency] Region 3 as a public water system.
Cline: How does the plant handle specific treatment challenges?
Gamby: We treat Potomac River water, which is generally good. In high-water events we have to contend with increased raw water turbidity, but the Dalecarlia Reservoir mitigates that to an extent. Taste and odor control in summer is problematic at times. Washington Aqueduct has engaged in a major study to evaluate future treatments that might be desired or required to meet expectations and future regulations concerning emerging pathogens and other chemicals finding their way into the water supply.
Cline: What contaminants and treatment methods are being considered?
Gamby: This study is a groundbreaking effort to engage technical experts, stakeholders and customers to: develop a deliberate process to develop drinking water quality goals beyond compliance; identify promising future treatment processes; determine the effectiveness of processes in achieving goals; develop associated capital and operating costs; and make informed choices for treatment options to improve public health protection and perception in a cost-effective and systematic way based on regulatory compliance needs, operational challenges and input from industry experts and major stakeholders.
The major areas of consideration addressed in the project are public health protection, finished water aesthetics, distribution system compatibility (including impacts on lead leaching), energy use, environmental effects, cost and affordability and opportunities to protect and improve source water and distribution system water.
Through the process outlined above we considered hundreds of contaminants, both currently regulated and emerging or beyond regulation, in the categories of microbial contaminants, inorganic compounds, radionuclides, pesticides, pharmaceuticals and personal care products, other organic compounds, nanomaterials and disinfection byproducts. We evaluated numerous treatment alternatives and combinations of treatment alternatives, including UV, ozone, RO, IX, GAC, AOP, BAF, Cl2 versus chloramines and more.