- Erosion & Sedimentation Control/NPDES Permitting
- Geotechnical Engineering
- Integrated Project Delivery
- Utility Design
- Clean Water Act, Section 401/404 Permitting
- Threatened & Endangered Species Surveys/Wildlife Surveys
- Groundwater Monitoring and Assessment
- Hydrogeology and Groundwater Modeling
- NPDES Permitting Support
- Site Characterization
- Soil/Groundwater Remediation Systems
- Erosion & Sediment Control Design and Inspection
- Industrial Wastewater Treatment
- As-built Surveys
- Construction Surveys
- Horizontal and Vertical Control Surveys
- Topographic Surveys
- Construction Management
- Construction Services
- Design/Build Services
- IBC Inspection Services
The client is a large national energy corporation that creates value through best-in-class operations, reliable and efficient electric generation, and a retail platform serving residential and commercial businesses.
The client’s generating station is located on a plateau approximately 30 feet above a river in southwestern Pennsylvania. Portions of the site are located on top of an area historically used for disposal of coal refuse. Groundwater encountering the old mine waste was shown to become contaminated and seeped into the river as acid mine drainage (AMD).
Driven by regulator-imposed corrective measures, the owner sought assistance with the design and construction of a groundwater collection system along the bank of the river that would intercept the affected groundwater seeps and transport them for treatment. The project also required the design and construction of a plant to treat the collected water prior to on-site reuse or permitted discharge into the river.
A terrace, approximately ten feet above the river, provided a good location for installation of a drain to collect AMD seepage. However, test pits located on the terrace encountered unstable sands, gravels, and alluvial boulders, making standard trenching operations difficult and unsafe. CEC and its contractor recognized the potential dangers and limitations of installing the collection pipe using standard methods with the difficult and unstable subsurface conditions.
CEC proposed using a “one-pass” method of installing the drainpipe, which used specialized equipment to excavate a trench, place a pipe at the desired depth, and backfill the trench with sand. This method removed the need to place workers in a trench. To eliminate the concern regarding excavation of large boulders using the “one-pass” approach, the design team also recommended pre-excavating the trench to remove oversized material in advance of using the “one-pass” equipment.
CEC designed the collection system to have three separate collection trenches, each approximately 700 feet long with a separate collection sump with twin pumps set up for lead-lag operation. The pump operating levels were controlled by a process logic control system that could collect the AMD seeps without drawing significant amounts of clean water from the river.
The collection system allowed the client to meet the requirements imposed by the Pennsylvania Department of Environmental Protection. The system efficiently collects AMD seepage and controls its discharge to the river. The treatment system designed by CEC has demonstrated that it can treat water, as necessary, and discharge it based on very stringent water quality standards established for the system.