Investigation Of The Hadlock Pond Dam Failure
Investigation Fact Sheet
Prepared by the New York State Department of Conservation
On July 2, 2005, the dam on Hadlock Pond in the Town of Fort Ann failed. The New York State Department of Environmental Conservation (DEC) contracted with Clough, Harbour & Associates to conduct an engineering investigation to gather information on the events leading up to the failure. A report summarizing their findings has been released.
The engineering investigation and report provides results of the physical examination of the site, including a topographic survey, test borings and trenches, and geophysical testing. The report also collects and analyzes design and construction documentation, including engineering reports, plans, specifications, construction inspection reports, contractor logs, photos, and videos. The purpose of the report is to identify, as much as possible, how the failure occurred. The report's purpose is not to identify blame, liability or specific compliance activities. This fact sheet answers some of the most common questions about the report.
Q: What is Clough Harbour's opinion as to what led to the failure of Hadlock Pond Dam?
A: Based on their analysis of conditions at the dam site, construction records and eyewitness accounts, Clough Harbour determined that Hadlock Pond Dam failed because of internal erosion.
Q: What could have caused the internal erosion?
A: Internal erosion happens when water finds a path to seep through or under a dam. As more water seeps through, it carries soil away and enlarges the opening. The more water that flows through this pathway, the bigger it becomes. As a result of the dam failure and the water flowing through the area where the dam was breached, Clough Harbour engineers were not able to see evidence of the exact path of the failure. Engineers did determine that the failure could have happened in any of the following four ways. Water seeping through or under the dam could have found a path:
- between the new and old parts of the earthen dam if large stones used in the previous dam's construction were left in place;
- through backfilled soil that was not thoroughly compacted next to the roller-compacted concrete wall or base;
- through coarse material like gravel that may have been left in place from a construction access road and buried inside the dam instead of being removed; and/or
- through spaces left by the thawing of frozen soil that may have been buried during construction.
Q: What other scenarios for the dam failure did the investigation look at?
A: In addition to internal erosion, Clough Harbour investigated five other situations that could have caused the dam to fail: water flowing outside of the spillway, settling of the dam embankment, unstable embankment slope, seismic events such as earthquakes, and intentional vandalism. Clough Harbour found no evidence that these possibilities occurred or contributed to the failure.
Q: How did DEC ensure that the investigation and findings are accurate?
A: DEC hired two well-respected engineering firms-Clough, Harbour & Associates and O'Brien & Gere. Clough, Harbour & Associates, which led the engineering investigation, is headquartered in Albany and has a 53-year record of providing professional engineering services. O'Brien & Gere, an engineering firm with extensive dam engineering experience, provided peer review for the field investigation and final report. Peer review is a process used for checking the work performed by professionals to ensure it is accurate and unbiased. After reviewing the data and Clough Harbour's investigative approach and analysis, O'Brien & Gere agreed with the report's findings and conclusion.
Q: What are DEC's roles and responsibilities with regard to the regulation of dams in general?
A: DEC and dam owners each have specific roles and responsibilities when dams are constructed, reconstructed or rehabilitated. The DEC does not issue dam safety permits for dams themselves. DEC issues dam safety permits for the construction, reconstruction, or rehabilitation of dams. First, DEC reviews the dam owner's engineering plans and specifications, also called the "design." If they meet DEC standards, DEC accepts the design and issues a dam safety permit. In addition, DEC requires the owner to have a licensed professional engineer supervise the construction or reconstruction of the dam to ensure that the dam is built according to the approved design. During the time that construction is occurring, DEC conducts site visits at certain specified dams to observe compliance with general permit conditions. When construction is completed, the dam owner must notify DEC and include a certification from the dam owner's engineer that he or she supervised the construction and that it was done according to the approved design. For selected dams, a satisfactory inspection by DEC and a DEC letter of approval to fill are required before the owner is allowed to refill the waterbody behind the dam.
Q: What are a dam owner's responsibilities with regard to dams in general?
A: The owner of a dam is responsible for making sure the dam is maintained and operated in a safe condition at all times. If reconstruction or rehabilitation of a dam is necessary, the owner hires a licensed professional engineer to develop an appropriate design for the dam work and to apply for all local, state and/or federal permits needed to carry out the project. To comply with a New York State dam safety permit, the dam owner is responsible for ensuring that the dam is being properly constructed according to the design that was approved by DEC. The owner and hired contractors are required to follow the conditions of the DEC permit that was issued, including following the engineering plan that was approved by DEC. The owner is responsible for providing construction inspection and oversight as needed in order to monitor and evaluate conditions as they are encountered and to observe material placement and workmanship as construction progresses. When the reconstruction or rehabilitation is completed, the owner's engineer sends DEC a certification that the work has been completed.
Q: What has DEC's role been regarding the Hadlock Pond Dam?
A: Hadlock Pond Dam is classified as a high hazard dam, which means dam failure can cause loss of life or serious damage to structures. In 1979, the U.S. Army Corps of Engineers identified the dam's spillway as too small, posing a risk of dam failure. DEC worked with the Hadlock Improvement Association, and later the Town of Fort Ann, to address this problem. In 1998, the Town was awarded $300,000 from the 1996 Clean Water/Clean Air Bond Act to help with the cost of construction to fix the problems. In October 2003, DEC issued the Town a dam safety permit authorizing the repair and rehabilitation of the dam. In addition, the Town received approvals from the U.S. Army Corps of Engineers and the Adirondack Park Agency.
Construction began in September 2004. DEC staff conducted four site visits during construction to observe the construction and site conditions. The last DEC site visit was on April 13, 2005. DEC did not receive a notice of completion or the engineer's certification, and did not conduct a final inspection or issue a letter of approval to fill.
Q: What are DEC's next actions?
A: If the Town determines that it wants to re-construct the dam, DEC will work with the Town to ensure that it is constructed consistent with DEC's regulations and guidelines. In addition, DEC will continue to work with the Town of Fort Ann, State Department of Transportation, and the Army Corps of Engineers on projects to replant and stabilize streambanks downstream of the dam.
Where to Find More Information
Copies of the full Report of Engineering Investigation of the Hadlock Pond Dam Failure are available for the public to review during normal business hours at the Fort Ann Library in Fort Ann, the Hudson Falls Free Library in Hudson Falls and the Crandall Library in Glens Falls.
