In 1997, the Ferris passive treatment system complex was installed to address four abandoned mine discharges emanating from an old deep mine in the coal mining ghost town of Ferris in the Slippery Rock Creek Watershed in Butler County.
This complex consisted of two series of Vertical Flow Ponds, one set treating the SR85 and SR86 discharges and the other set treating the SR87 and SR88 discharges.
These VFPs then flowed into a large aerobic wetland created using an abandoned railroad grade as an embankment. Eventually, the treated water empties into the main stem of Slippery Rock Creek.
This system was evaluated by BioMost, Inc. after the Slippery Rock Creek Watershed Coalition noticed possible water quality issues. The field pH at the outlet of wetland 2 on 2/18/17 was 3.78. After further investigation it was determined that maintenance to the SR 85/86 treatment cell was necessary.
Initially, flow from the forebay through VK1 was not present, causing raw water from the forebay berm to bypass both vertical flow ponds directly to the treatment wetland. VK1 maintained a high water level but did not flow to VK2, which indicated the treatment media and/or the underdrain was plugged. Several attempts were made to unplug the pipe and media.
A flush pipe was located within the forebay and found to be closed or blocked on the inlet side.
An emergency overflow pipe was located and cleared within VK1 using a power snake attachment, which dropped the water level in the pond approximately 2 feet. The treatment media was backflushed using a 3” pump for approximately 20 minutes during three separate attempts to gain a flow path within the media to the underdrain.
This netted a minimal increase in flow to the underdrain pipe.
After further backflushing attempts proved unhelpful in reestablishing flow through the system, it was decided that exposing the underdrain pipes and examining the quality of the treatment media would help to determine the next course of action.
A temporary berm to divert flow from the forebay was installed and VK1 was drained over the course of a few days to accomplish this.
Once VK1 drained, an excavator was used to examine the quality of the treatment media within the pond. The media was separated into two layers. The top layer was highly degraded with no structure, and the lower layer was highly compacted and minimally permeable.
After determining it had little viability in continuing to provide water treatment, a significant amount of the top layer of media was removed from the pond using a 6” shredder pump.
The lower layer of media was then removed to examine the underdrain and surrounding stone. This revealed a cemented together layer of stone with 4” perforated underdrain pipe that still had no flow exiting the flush pipe. A redesign of VK1 was determined to be necessary to regain treatment within the component.
A spillway was installed between VK1 and VK2 to allow water treatment in VK2 without flowing through the VK1 media. Stop logs regulating water level within VK2 were removed to help determine the permeability of the stone within the pond.
A layer of sediment approximately 6-8” thick was discovered on top of the treatment media stone.
Although VK2 drained, it would benefit from stirring the media and removing sediment using a 6” shredder pump to rejuvenate the stone. This was performed after work was completed within VK1.
Hopefully, in the coming year, additional funding can be acquired to make the necessary changes to this treatment system.
(Reprinted from the October edition of The Catalyst newsletter, Slippery Rock Watershed Coalition in Butler County. Click Here to sign up for your own copy.)
No comments :
Post a Comment