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2020-06-16_REVISION - M1978091UG
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2020-06-16_REVISION - M1978091UG
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Last modified
12/27/2024 8:51:55 PM
Creation date
6/17/2020 11:17:10 AM
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Template:
DRMS Permit Index
Permit No
M1978091UG
IBM Index Class Name
REVISION
Doc Date
6/16/2020
Doc Name
Request for Technical Revision
From
LKA Int'l, Inc.
To
DRMS
Type & Sequence
TR4
Email Name
SJM
THM
AWA
Media Type
D
Archive
No
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discharges to Deadman Gulch.The 3"pipe will be anchored to the ground at appropriate points with <br /> anchors(e.g. helical screw anchors)to prevent gravity and flow shear from pulling the pipe down the <br /> hill. <br /> Precipitate(sludge consisting of residual soda ash,floc agent,and precipitated metals)in the treatment <br /> tank will be cleaned out as needed....more often in the early part of the season and much less toward <br /> the end of the season.A 250-gallon galvanized stock tank will be used for this purpose.As needed,this <br /> tank can be easily cleaned with a shovel and the sludge properly disposed of. <br /> Stormwater from the mine pad and building will be captured in a second,lined (N45B)retention pond <br /> of approximately 24,000 gallons in volume(see blue rectangle)and will be located on the pad just <br /> downstream from the minewater retention pond and the treatment tank.Water from this pond will be <br /> allowed to evaporate and if needed treated separately,or based on capacity constraints, pumped into <br /> the treatment tank and treated in the same manner as minewater,separately or in combination with <br /> the minewater. It will also serve as secondary containment for the upstream containment features.The <br /> sump/weir at the base of the existing limestone channel also contributes to this purpose. <br /> Currently,all water that contacts the pad and building flows to the previously installed limestone <br /> channel and reports to the sump/weir at the lowest point of the permitted area.The mine pad was <br /> previously contoured to accommodate this flow pattern. Rainfall-produced runoff from the mine pad <br /> has been measured over the past four years with the largest event producing about 13,000 gallons. It is <br /> estimated that 1"of rainfall runoff from the approximately 24,000 sq.ft.pad area would yield about <br /> 15,000 gallons.According to USGS Streamstats,the 6-hr 100-yr rainfall event for the site is 1". The 6-hr, <br /> 2-year rainfall event is 0.79". Based on these values,and assuming zero infiltration and 100%runoff,a <br /> 24,000-gallon basin will easily capture expected runoff from the pad. Water captured by this new <br /> retention pond (2nd)will be treated with soda ash and neutralized as needed,allowed to settle,sampled, <br /> and then discharged through its own 3"pvc pipe to the sump/weir where it too will be measured (flow <br /> rate and pH)as it discharges to Deadman Gulch. Precipitates will be cleaned out and disposed of at the <br /> end of each season or more frequently,based upon observation,on an as-needed basis. <br /> Seeps located just uphill from the existing lined sump,concrete weir and H flume(installed in 2015 at <br /> the base of the mine dump)yield very small flows of low pH water.These seeps typically dry up by mid- <br /> July or often earlier. Presently,these seeps mix with flows from all sources(minewater,stormwater, <br /> and native flows from Deadman Gulch)in the lined sump/weir.Consistent with best practices,it will be <br /> necessary to isolate these hard to capture and sample low pH seeps from the other water sources. It is <br /> proposed that the existing lined sump, immediately below the seeps(installed in 2015 and filled with <br /> limestone gravel)be cleaned out and reconfigured (isolated)to create a separate basin to capture this <br /> seepage for treatment. A wall or berm(lined,cement filled blocks or other suitable impermeable <br /> materials)will be constructed across the cleaned-out sump so that seep water can be captured and <br /> treated on the upstream side of the wall/berm while the piped,treated water from the two mine pad <br /> treatments(treatment tank and stormwater retention pond)be discharged into a smaller basin on the <br /> downstream side of this berm where it will enter the existing 0.5' H flume for discharge into the gulch. <br /> As seepage water slowly and gradually collects in the cleaned-out upstream portion of the sump,it will <br /> be neutralized as needed and then transferred into the smaller basin(via a small pump or channel <br /> 3 <br />
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