Loudoun County supervisors have formally launched a long-awaited process to redraw the airport noise zones around Dulles International Airport, which guide both development policy and real estate disclosures.
As a matter of policy, Loudoun County generally does not allow residential development within the highest-noise Airport Impact Overlay District, which is meant to represent the areas most affected by jet noise from the airport. They are also based on projections of future noise as airport traffic grows and a new runway is built.
However, the maps of airport noise on which that district is based were last updated in 1993, and the airport has seen changes since then—including moving plans for a new runway.
Noise maps are based on a calculation called the Day-Night Average Sound Level, abbreviated in county zoning as LDN, which measures the average level of sound over a 24-hour period, with a penalty for noise at night. The county currently recognizes three gradations of airport noise: the 65-decibel LDN, where residential development is prohibited; the 60 LDN; and a one-mile buffer around the 65 LDN.
A new noise study conducted in 2019 yielded a slight reduction in actual and projected noise contours, reaching further north of the airport but less far to the west, for a net reduction of 39 acres in the highest-impact area, with a total of 476 acres inside the 65 LDN.
However, it does extend that district into some lots where residential development was permitted—and where homes already exist. Real estate sellers are required to disclose when a house is sold in an airport noise zone. Some supervisors worried that could impact home prices.
“If we put their homes in an airport overlay district, it could impact their property values, and they can’t do anything about that because they moved to that area before those lines were put down,” said County Chair Phyllis J. Randall (D-At Large).
Supervisors were also concerned about letting that get in the way of drawing accurate maps.
“I think it’s important that we do go through this exercise,” said Supervisor Matthew F. Letourneau (R-Dulles). “Ultimately, the new contours are driven by science, they’re driven by where the noise is currently and where it’s projected to be as the airport grows. The reason we do this is so we don’t have issues down the road.”
Dulles Airport officials have long supported the practice of restricting some development within the noise zone, hoping to avoid complaints from people living in a noise zone which could lead to FAA restrictions on flight routes and traffic.
There is also an Airport Impact Overlay District around Leesburg Executive Airport, however it is much smaller given the smaller and fewer planes that fly in and out of Leesburg. The 65 LDN is also almost completely within town limits, where the town government controls zoning decisions.
Under the work plan adopted unanimously Tuesday, Feb. 2, supervisors are expected to approve new noise maps in May 2022.