New dam embankment and foundation drilling guidelines released
The Federal Energy Regulatory Commission recently released a new guideline for drilling on embankments or into foundations of water retaining structures. The drilling guideline is intended to “do no harm” by reducing the potential for hydraulic fracturing and/or creating seepage paths that could lead to internal erosion and possibly an uncontrolled release of the reservoir.
To mitigate chances of internal erosion occurring, the FERC now requires a Drilling Program Plan be approved prior to starting the investigation. The DPP must be submitted 30 days prior to doing the work. The plan may also require approval from the FERC staff in Washington D.C., which will likely require a longer review period. In addition, the FERC strongly encourages a face-to-face meeting or conference call to discuss project details during preparation of the program. The DPP must be prepared by an experienced geotechnical engineer or geologist.
In addition to the typical information needed for a subsurface program – such as boring location, depth, sampling intervals, etc. – the plan must also include:
- Procedures for risk identification and mitigation
- A communication plan
- Resumes of field personnel
- Relevant historical subsurface information
Depending on the project and subsurface exploration details, some drilling methods maybe prohibited or restrictions may be required. After drilling, all boreholes must be backfilled with cement and/or bentonite grout placed by the tremie method.
One of the more stringent requirements in the new guideline is that a qualified geotechnical engineer is required to be present during drilling. The qualifications of on-site personnel depends on if the dam is low or high hazard. For high hazard dams, a Bachelor of Science in civil engineering or geology is required. The on-site representative must also have four years of experience drilling in embankment dams with knowledge of identifying and mitigating potential hazards associated with performing subsurface explorations within embankment dams and foundations.
ABOUT THE AUTHOR
Marty Kemps, P.E., is a senior engineer and client manager with nearly 20 years of geotechnical and project management experience. He has served as project manager for upgrades to existing dams, new dams and has performed numerous safety inspections along with construction administration oversight. When not working on dams and hydroelectric projects, Marty enjoys motorcycling and skiing.
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