During the summer and fall of 1998, stormwater runoff from a recently constructed retail site in Stone Mountain, Georgia resulted in the release of soil material from the site. The material ended up 0.1 miles downstream in a small cove area in Lake Lucerne. Lake Lucerne is a private lake held and managed by the Lake Lucerne Homeowners Association.
In October 2000, the U.S. EPA issued a Consent Agreement (CA) to the retail site developer for the actions of its site contractor that led to the release of the materials. The CA required, among other stipulations, that the developer submit to the U.S. EPA for approval a Sediment Removal Plan to evaluate and remove siltation (sediment) from the small cove in Lake Lucerne. In addition, the CA found that the developer, during construction of the retail site, had utilized fill materials containing small percentages of foreign material which constituted a pollutant. The remedial actions consented to required the developer to enhance the existing stormwater basin and on-site wetland and to create a new wetland stream channel. The objectives were to protect downstream uses and receptors by improving the stormwater basin's sediment retention, enhancing the existing wetlands, and creating a new wetland/stream. The developer selected a team led by Geosyntec to design, permit, and implement all of the elements required in the CA.
Geosyntec's Scope of Services
After considering various sediment removal options, Geosyntec selected underwater dredging or excavation to remove the sediment from the lake bottom by mechanical means. We selected this approach because the Lake Lucerne Homeowners Association did not support lowering the water level in the lake for a "dry" sediment excavation due to the potential for risk to wildlife.
In order to achieve a natural lake bottom in the cove, Geosyntec removed over 4,000 cubic yards of sediment from the lake. This removable quantity brought the sediment level to the natural lake bottom within the cove area as defined in the Sediment Removal Work Plan. Geosyntec monitored the lake surface water turbidity monitoring during the sediment removal work to observe the level od suspended solids discharge during sediment removal activities. we established water column monitoring locations, consisting of a combination of three pre-established monitoring points defined in the U.S. EPA-approved sediment removal plan, immediately outside of the floating silt turbidity curtain within Lake Lucerne.
A track-mounted excavator was used to transfer the material from the cove to haul trucks for transportation back to the retail site. Sediment was also pumped into geotubes from the excavation area to the retail site for staging and drying of the material. Once decanted, the material was used for general fill for future property development by the developer.
In addition to the sediment removal work, Geosyntec enhanced the existing stormwater basin and the on-site wetland, and created a new wetland/stream channel at the retail site. We designed these activities to further protect downstream uses and receptors by improving the existing stormwater basin's sediment retention characteristics, enhancing the existing wetlands through improvements in hydrology, creating a new wetland/stream channel, and providing a method with which the water quality could be monitored as directed in the CA.
Through the efforts of Geosyntec and our team, the developer successfully met the terms of the CA by returning the level of the lake cove bottom to what it was prior to the event. Also, our activities enhanced the ability of the wetland and stream system to retain sediment. By providing the developer with a single point of contact for the execution and completion of the project, Geosyntec allowed our client the freedom to focus on their core business objectives.