By Sarah LazoFebruary 25, 2019
In an unassuming blue trailer just a few miles north of the heart of the District of Columbia, work is underway to improve the drinking water that serves more than 1 million people in and around the nation's capital.
This effort is part of the Advanced Treatment Pilot Study for the Washington Aqueduct - a unique mission steeped in history. Washington Aqueduct has been owned and operated by the U.S. Army Corps of Engineers for nearly 160 years. Capt. Montgomery C. Meigs, an Army Corps officer and an 1832 graduate of the U.S. Military Academy at West Point, was personally directed by Congress to design and build an aqueduct to provide Potomac River water to the nation's capital. He did so in just a matter of years, with service beginning Jan. 3, 1859, supplying fresh water via gravity from Great Falls for domestic and commercial use,
as well as firefighting.
"Washington Aqueduct, today, still benefits from Meigs' visionary engineering - with key elements of the original gravity-based system still being used," said Tom Jacobus, Washington Aqueduct general manager.
Washington Aqueduct now provides 135 million gallons of safe, reliable and cost-effective drinking water daily across 150 square miles to the District; Arlington County, Virginia; and other areas in northern Virginia to include portions of Fairfax County.
All funding for operations, maintenance, studies and capital improvements for Washington Aqueduct comes from revenue generated by selling drinking water to its three wholesale customers: DC Water, Arlington County and Fairfax Water.
The complex, multimillion-dollar pilot study, which began in summer 2018 and runs 24/7, carries out testing first envisioned within a 2009 study.
The Future Treatment Alternatives Study (FTAS) involved Washington Aqueduct staff and customers; water treatment experts from private industry, utilities, regulatory agencies and academia; and representatives from advocacy groups and the public health sector.
"Our goal has always been to achieve excellence, from source to tap," said Jacobus. "We do this by working closely with our customers."
FTAS prioritized 14 of more than 750 potential water contaminants for further study, and an even smaller subset that could be addressed through treatment changes.
"The study investigated all foreseeable water quality and treatment challenges and prioritized them based on risk specific to Washington Aqueduct, and the outcomes paved the way for the current pilot study," said Margaret Sharkey, Washington Aqueduct environmental engineer and pilot study team member.
The primary goals of the Advanced Treatment Pilot Study include reducing taste and odor compounds; enhancing disinfection through a multi-barrier approach to provide additional protection from potential contaminants in the source water; and achieving year-round water production capacity of 120 million gallons per day at the McMillan Water Treatment Plant (WTP). The pilot study is also designed to evaluate changes in disinfection byproducts and corrosion in the distribution system piping that might result from new treatment processes, if implemented.
"We are and have been meeting safe drinking water standards; however, to be proper stewards of our customers' money, we must anticipate the needs of the future and continue to modernize our processes and infrastructure," said Sharkey.
Within the little blue trailer at McMillan WTP, engineering consultants ARCADIS and CDM Smith have personnel on site testing three advanced treatment processes: ozone contact (gas generated on site that oxidizes organic carbon and other contaminants), biofiltration (natural treatment) and ultraviolet light disinfection (as an additional barrier alongside chlorine).
"Experts involved in FTAS and the subsequent advanced treatment study concluded these are the best treatment processes to mitigate the highest risk contaminants, while renewing aging infrastructure at Washington Aqueduct," said Sharkey.
Ten gallons of water per minute or 0.02 percent of the full-scale operation at McMillan WTP is being diverted for pilot testing. Controls in the workspace are set up to compare current processes with future processes for both filtration and disinfection.
The first year of pilot testing is anticipated to wrap up in summer 2019 and consists of ozone and biofiltration operations at McMillan WTP. The second year will entail ultraviolet light disinfection and distribution system corrosion control testing in which synthesized "finished" drinking water is run through an assortment of pipes made of lead, copper and cast iron to monitor degrees of corrosion. Similar testing will also be executed at Washington Aqueduct's other WTP, Dalecarlia.
"Pilot testing is necessary to confirm performance and establish design and is just one of the many steps needed to implement new processes," said Anna Hayden, Washington Aqueduct engineer and pilot team member. "Fitting in these new processes and squeezing new infrastructure into tight spaces without interrupting operations are just some of our future potential engineering challenges."
Depending on the outcomes from this pilot study, stakeholder input and future funding opportunities, both treatment plants may eventually be retrofitted to implement various recommended improvement measures.
"I understand the gravity of what we're doing every day here at the Washington Aqueduct," said Laura Gallimore, Washington Aqueduct physical scientist. "Water is life, and we're providing that."