Capital Crescent Trail Erosion Repairs
The National Park Service and Arlington County Department of Environmental Service (DES) will be undertaking work to address severe erosion to an area of the Capital Crescent Trail (CCT). The erosion, stemming from stormwater run-off both upslope and at grade of the area, is compromising the stability of the hillside near mile marker 7.0 on the CCT. The erosion is threatening to impact a 48" water main, located underneath the CCT, which provides water for 200,000 customers of the Arlington County, Virginia system.
Existing stormwater drains, located within National Park Service property at this location, are insufficient or non-functioning. In order to avert potential damage to the water main, the NPS and Arlington County plan to work in three phases. Phase I and III will be completed during the Fall of 2007. Phase II will follow in 2008.
Phase I - This phase includes the construction of a pedestrian/bicycle bypass trail so that the CCT can remain in use during the project. Upon installation of the bypass trail, work will commence to stabilize the large erosion void on the west slope, between the CCT and Clara Barton Parkway. An existing storm drain system for that slope will be replaced. The outfall of the storm drain system will have a velocity dissipation device. It is anticipated that this drain would accommodate the runoff for a 10 year storm event.
Phase II – If engineering analysis concludes that the depression on the east side of the CCT needs additional drainage, beyond what can be accomplished by Phase I's storm drain, then the project will install a 15 inch storm drainpipe. This depression, adjacent to the CCT, is directly across the trail from the large erosion void addressed under Phase I. The drainage pipe for this depression would transport stormwater south, along the CCT, to an existing drop inlet located near Manning Street and the CCT. This storm drain would adequately convey excess runoff when the Phase I pipe capacity is exceeded for a combined Phase I and Phase II conveyance of a 25 year storm event. This storm drainpipe will replace an existing drain that is not adequate.
Phase III - Install slope stability measures adjacent to the Phase I. This action will prevent the slope from further movement and insure improved global stability of the Phase I and III immediate area.
At the conclusion of the project, asphalt repairs will be made for the CCT and a final overlay of the total paved area will be accomplished. The pavement will be sloped to insure runoff is directed to the newly installed storm drains. The bypass pathway will be removed once the permanent section of the CCT is reopen for users.
Approximately 85% of the proposed work will be accomplished from a work entrance off the Clara Barton Parkway. The remaining work, including the establishment of the bypass trail, will need to be undertaken from the CCT.
The project's Interdisciplinary Team from Chesapeake and Ohio Canal National Historical Park and George Washington Memorial Parkway has reviewed the project for impacts to natural and cultural resources. The project does not pose any serious or long-term effects to the environmental, historical, cultural, archeological, or visual resources. It meets categorical exclusion #C.16 – Installation of underground utilities in areas showing clear evidence of recent human disturbance or areas within an existing road prism or within an existing overhead utility right-of-way.
For further information about this project, please contact Park Engineer, at 1850 Dual Highway, Suite 100, Hagerstown, MD 21740.