Restoring Flow in Dam Relief Wells with the Patented Packer-Purge System™

SME’s innovative Packer-Purge System™ technology (U.S. Patent No. 11,021,937) provides  a cost-effective alternative in the redevelopment and maintenance of relief wells.  The system reduces pore-water pressures under dam structures and powerhouses to support compliance with the Federal Energy Regulatory Commission’s (FERC’s) allowable limits, known as Design Basis Value (DBV), for dam safety and stability.

Challenges

In 2000, the client installed three relief wells with an underdrain adjacent to the existing powerhouse of a hydroelectric dam to reduce aquifer potentiometric levels beneath the foundation. Slope stability analyses were performed, and piezometers were installed to monitor pore-water pressures at the powerhouse.

Over the next decade, relief well flow rates slowly declined while pore-water pressures increased to levels exceeding the FERC DBV. In 2011, the dam owner had the three wells redeveloped, which reduced the pore-water pressures to acceptable levels, yet only for a couple of years.

In 2014, SME was retained to oversee a second round of relief well redevelopment. SME’s analyses indicated the well screens were becoming clogged with formation particles due to deteriorating gravel packs, thus reducing the relief wells’ capability to fulfill their function of maintaining acceptable pore-water pressures across the area.

Project Outcome and Value Added

SME designed and installed the Packer-Purge System™, an innovative relief well purging system using packers and natural gradients to restore flow to the relief wells and maintain pore-water pressures below the FERC DBV. The purging system uses packers to halt, then release, the flow in the well, thereby creating an instantaneous surge across the well screen. The surge removes particles from the screen area and restores flow to the well. A PLC system governs the packer method and purging frequency for year-round pore-water pressure control, with little or no well maintenance.

Installation of the Packer-Purge System™ produced significant favorable operational results:

• Well screen clogging was reduced as evidenced by 1) clogging particles being purged from the screened areas of the relief wells, and 2) an increase in flow from the wells of over 10 percent;
• Potentiometric levels at the relief wells have been maintained below allowable FERC Design Basis Value; and
• Significant financial cost savings have been realized as no further investment in relief well redevelopment has been required since the installation of the Packer-Purge System™.