The Maryland Department of the Environment says 19 dams in the state are a potential hazard to the lives and homes of people living nearby.
Where are those dams? That's a secret.
The dams, although rated in "poor" or "unsafe" condition and a "high" or "significant" hazard, pose no immediate threat to life or property, according to MDE dam safety experts.
Those experts, fearing that the dams would make attractive targets for terrorists, took out most of the identifying information from a set of dam inspection reports released recently as part of a public information request. Names of the dams were blacked out, as were the owners. The heights of the dams were deemed classified. Length was not.
"The reason is security," according to Cas Taherian, an engineer with the department's dam safety program. "We can't disclose the names and locations. I can't make any comments on that. If the information is available other places, we have no control over that."
The information, or most of it, is available in other places.
One of those places is the Internet. A comparison with the Army Corps of Engineers' online inspection database yields the names of 16 of the 19 dams censored from the department's reports. Another Web site, this one from the Maryland Emergency Management Agency, gives details about the people and places that would be affected if the specific dams were to fail.
The Army Corps database is available for download online, and includes latitude and longitude for each dam, names and owners, along with other details. Owners of several of the dams were able to confirm that their dams were the ones reported by MDE.
One of those owners was the Army Corps.
Spokeswoman Mary Beth Thompson said the Corps was working on updating its Jennings Randolph Dam in Bloomington. MDE lists it as "unsafe" because of an inadequate spillway, although it says "the dam may otherwise be in good or excellent condition."
"The Corps of Engineers disagrees with the term `unsafe,'" Thompson said. "It's structurally sound and performs as it should."
Ken Pensyl, manager of Maryland's dam safety program, said the designation "unsafe" was a technical term - part of a ranking system set up by the Corps of Engineers. While high-risk dams such as Jennings Randolph pose a threat if the dam were to fail catastrophically, the designation is not related to the condition of the dam.
"When you use the word `unsafe'," Pensyl said, "that raises a huge [unwarranted] alarm."
MDE's criteria for safety, handed down by the federal government, are partly based on a "probable maximum flood" - a storm dropping about 28 inches of rain in six hours. The Jennings Randolph Dam, according to the report, would be unable to handle half that amount.
In cases where the unsafe rating was because of spillway conditions, Taherian said the danger lies in the dam being overtopped by a large storm.
The T. Howard Duckett Dam in Prince George's County matches all of the available information with a dam rated unsafe in an MDE report. Neither the department nor the owner, Washington Suburban Sanitary Commission, would confirm that it is the same dam, although it is the only dam in the Corps database that meets the criteria.
A 2004 Hazard Mitigation Plan from the Maryland Emergency Management Agency, available on the agency's Web site, says the Duckett dam, which forms Rocky Gorge Reservoir, is a particular concern. The report lists 48 high-hazard dams along with populations and critical facilities within their flood zones.
"Of all Maryland's high-hazard dams," the report says, "the Rocky Gorge Dam has the largest population within its danger reach." If the dam failed, the report continues, "an estimated 19,103 persons would be affected." The flood zone contains three schools, a nursing center and a volunteer rescue company.
Pensyl said that plans were in place for owners and state and local government agencies who would be involved in an evacuation.
"All we're trying to do is protect the dam owners as far as security issues," he said. "Measures are always taken to make sure the dams are safe."
Of the 19 dams in MDE's inspection reports, three are listed as being in "imminent danger of failure." They were confirmed by the owners to be the Loveton Farms storm water management facility in Baltimore County; Crabbs Branch storm water management facility in Montgomery County; and Coulbourn Mill Pond Dam in Wicomico County.
Gene Gopenko, senior engineer of storm water facilities in Montgomery County, said the county was aware of problems at Crabbs Branch and is working to correct them.
"If there's a significant problem then time is of the essence," he said. "We have some time, that's why we've decided to do some additional planning."