ATTACHMENT 1 WILSON MINE LECROY AREA SEMIPERMANENT DEWATERING SYSTEM Reclamation plans for the Wilson Mine Lecroy area were approved by the Arkansas Department of Environmental Quality with a passive barrier to treat groundwater. The barrier, designated as the sulfat.e-reduci~g barrier (SRB), is shown on Sheet 2, of the drawings in the submittal for a construction permit. '\ The effectiveness of the SRB must be monitored for several months before final modifications, if any, can be designed and constructed. The monitoring is necessary to determine if the lateral and vertical extent of the barrier is adequate and to determine the effectiveness of the materials in the barrier to improve groundwater quality. During this monitoring period, some groundwater in the vicinity of the SRB must be collected and pumped to East Wilson Pond prior to discharge through the pond's National Pollutant Discharge Elimination System (NPDES) discharge point. ~ The drawings submitted support our request for a permit to consti1lct a system to collect3q4 pump the groundwater to East Wilson Pond. The major components of the design include a line of well points at the east and west end of the existing SRB, a tank for storage of water prior to FOnd. p~ng, Theand storagea pump tanktoandlifthethepump water will over be the sizedhill after between data isthe collected Lecroyduring area and construction the Wilson the volume of water that.n~.q~ping. We anticipate that this system will have a life of between one and possibly three years. We anticipate a time period of no more than six months to a year to collect the necessary data to evaluate the need for a reconfiguration of the existing SRB. The additional time will be required for design, contracting, and the availability of corporate funds for reclamation. Assuming the availability of corporate funds, we think the most likely time frame to begin construction of a revised barrier would be the summer of2007. The goal of the new barrier will be to clean up the shallow groundwater entering Indian Creek downgradient of the site. When this goal is accomplished, there will no longer be a need to pump water from the Lecroy area back to East Wilson Pond. C:\PF\962-05\ \131Ia\Pennit Application Revision\Attachmentl.doc NPDES PERMIT FilE NPDES # fir CJO '-I R95 ()c... AFIN # ;;10-60;;;-17 ----",- ---- Permit PN Correspondence ----Technical Backup I -.:15-01 ~ Dafe Scanned
ATTACHMENT 2 vvl~i MEMORANDUM To: From: Date: Re: Umetco Wilson Mine Lecroy File 962-051.131 Waste Engineering, Inc. T. Andrew Earles, Ph.D., P.E. ~ ~ ~I;:.S.. ~ ~\\ ~4AJ\!O. 12329~..".~ -..:.J.DAEW ~~,I' P;,-"y,,11 Basis of Design for Erosion and Sediment Controls for Stabilization Phase of Parcels C, D, E and Borrow Area Reclamation ~ This memorandum provides the basis of design for erosion and sediment control measures for the stabilization phase of reclamation work on Parcels C, D, E and the Borrow Area of the Umetco Wilson Mine Lecroy area in Hot Springs, Arkansas. The purpose of erosion and sediment control during this phase is to reduce erosion and promote sedimentation from the time grading activities at the site are completed to the point where stable vegetative cover of disturbed areas is established. Figures, drawings, and reports describing the location of the project, details of construction activities including grading and drainage plans, and approved construction drawings are included in the project file and are incorporated in this memorandum by reference. GUIDING DOCUMENTS The following regulatory documents were the primary guiding documents used in preparation of this memorandum: National Pollutant Discharge Elimination System (NPDES) General Permit No. ARR150900 (Medium and Large Construction), Arkansas Department of Environmental Quality (ADEQ), 2005. NPDES Permit No. ARt048950, Authorization to Discharge Under the NPDES and the Arkansas Water and Air Pollution Control Act for Umetco Minerals Corporation d/b/a Wilson Mine, ADEQ, 2006. Storm water Pollution Prevention Plan (SWPPP) for Site Activities at: Umetco Minerals Corporation Lecroy and Indian Creek Area, Wilson Vanadium Mine, Garland County Arkansas, Remedial Construction Services, Inc., April 2005. City of Hot Springs, Arkansas, Storm water Management Manual, Section 1100 Sediment and Erosion Control, City of Hot Springs, Arkansas, Internet version from June 2006. Waste Engineering. Inc. 2430 Alcott Street, Denver, CO 80211 Tel. 303/433-2788; Fax. 303/480-1020, e-mail:krwright@wrightwater.com
Page 2 In addition Waste Engineering, Inc. (WEI) incorporated selected guidance ITom the following references in developing the erosion and sediment control strategy for stabilization of Parcels C, D, E and the Borrow Area: Conservation Practices for the Reclamation of Surface Mines in Arkansas, ADEQ (J.F. Stephens, R.S. Rogers and P.K. Fields), 2001. Water Environment Federation (WEF)/American Society of Civil Engineers (ASCE) Manual of Practice (MOP) 87, Urban Runoff Quality (WEF/ASCE MOP), WEF /ASCE, 1996. Denver Urban Drainage and Flood Control District (UDFCD) Urban Storm Drainage Criteria Manual, Volume 3, UDFCD, 1999. EROSION AND SEDIMENT CONTROL STRATEGY The following section describes erosion and sediment control best management practices (BMPs) that will be used for the final stabilization of Parcels C, D, E and the Borrow Area. For each BMP, the description includes the purpose of the BMP, the design criteria for the BMP, and maintenance recommendations. BMPs are shown on the drawing that is included as Attachment 1. Seeding and Mulching Seeding with a permanent seed mixture and mulching are the primary erosion control BMPs for Parcels C, D, E and the Borrow Area. The purpose of seeding and mulching is to establish permanent ground cover that will be resistant to erosion in a manner that is similar to vegetative cover in adjacent areas that were not disturbed as a part of construction. All disturbed areas will be seeded and mulched in accordance with Section 02930 of the project specifications, dated September 2004. Seeding and mulching are expected to occur in May and June 2006. The primary inspection/maintenance activities associated with this BMP will be monitoring success of revegetation and reseeding/re-mulching of areas where revegetation has not been successful. Revegetation progress and reseeding/re-mulching (if any) should be documented in required SWPPP inspections (at least once per week and following any storm event of 0.5 inch or greater). Silt Fence Silt fence will be used as perimeter control on the down gradient side of disturbed areas and will be used along contours on slopes to reduce rill and gulley erosion. Locations for silt fence are shown on the attached drawing. Silt fence around the downgradient perimeter of disturbed areas will provide sedimentation (via filtration) for runoff leaving the site, and silt fence along contours of graded slopes will provide filtration of runoff and may serve to reduce the effective length of the slope. Silt fence will be installed according to Section 1105.2 of the City of Hot Springs, Arkansas,
Page 3 Stormwater Management Manual. Spacing of silt fence on graded slopes shall conform to the following criteria: Slope (Horizontal:Vertical) 2:1 3:1 4:1 5: 1 and milder Spacing (Feet) 25 75 125 200 Silt fence should be inspected during weekly SWPPP inspections and after any storm event of 0.5 inch or greater. It should be inspected at least once every 24 hours during prolonged rainfall events. Repairs should be made as soon as practical following the inspection, preferably as the inspection occurs. When the height of sediment trapped behind the silt fence reaches one-third of the total height of the barrier, accumulated sediment should be removed. Sedimentation/Detention Basins Two sedimentation/detention basins will serve as BMPs for approximately 24 acres of the site 17.4 acres tributary to the East Pond and 6.9 acres tributary to the South Pond. The remainder of the area addressed by this memorandum is less than 5 acres and will use sediment traps created by check dams rather than a formal sedimentation basin as a BMP. The East and South Ponds are shown on the attached drawing. The purpose of the ponds will be to promote sedimentation by creating extended detention. The ponds will also provide peak attenuation, which will promote downstream channel stability. Existing detention pond outlets will be modified to provide a 48 hour drawdown time for the design volume. The 48-hour drawdown time exceeds typical drawdown time for extended detention facilities (typically 40 hours [UDFCD 1999]) and represents a high level of treatment based on the sizing methodology in the WEF/ASCE MOP. The design volumes for the two ponds were determined by applying the sizing criteria in the City of Hot Springs, Arkansas, Storm water Management Manual of 3,600 square feet of storage per disturbed acre. Design volumes are 1.4 acre-feet for the east pond and 0.6 acre-feet for the south pond. This sizing is conservative because all of the tributary drainage areas to the ponds were assumed disturbed when, in reality, there are some areas that have not been disturbed. As a check, WEI applied the water quality capture volume (WQCV) sizing methodology in the WEF/ASCE MOP assuming a 48-hour drain time and 80 percent effective imperviousness (to account for soil compaction, lack of cover, and the underlying liner over a large portion of the area). The WQCV calculations agreed very closely with the design volumes determined using the City of Hot Springs' criteria. For the East Pond, the 1.4 acre-foot design volume will be drained over a period of 48 hours using an orifice plate or perforated riser with 1 column and 6 rows of 2.25-inch-diameter circular orifices. The invert elevation of the bottom orifice will correspond to the existing pond outlet invert of 430.00 feet, and orifices will be arranged in a vertical column spaced 4 inches on center. An
Page 4 engineered riprap channel designed to dissipate energy in East Pond outflows for up to the 100-year event provides outlet protection. Additional outlet protection is not necessary. For the South Pond, the 0.6-acre-foot design volume will be drained over a period of 48 hours using an orifice plate or perforated riser with 2 columns and 3 rows of 1.75-inch diameter circular orifices. The invert elevation of the bottom row of orifices will correspond to the existing pond outlet invert of 386.00 feet and orifices will be arranged in a vertical column spaced 4 inches on center. An engineered riprap channel designed to dissipate energy in South Pond outflows for up to the 100-year event provides outlet protection. Additional outlet protection is not necessary. Regular observation and maintenance will be required to assure that pond outlets are functioning as intended. The outlet should be inspected weekly, as required by the SWPPP, and after any storm event of 0.5 inch or greater to assure that it is free of debris and accumulated sediment and that orifice openings are not obstructed. During these inspections, accumulated sediment in the pond should be estimated, and sediment should be removed before it accumulates to more than one-half of the design volume. (The depth of sediment relative to the design depth above the invert of the lowest orifice is a conservative surrogate for the volume of accumulated sediment.) Once vegetation has been successfully established (minimum of 70 percent of pre-disturbance vegetative cover), sediment from the pond should be removed to restore the design capacity of the pond, and temporary modifications to pond outlets should be removed to allow permanent outlets to function as designed. Check Dams A series of rock check dams will serve as the primary BMP for the 2.I-acre disturbed area southwest of the South Pond. These check dams are shown on the attached drawing. Check dams will be constructed at approximately 100-foot intervals along the drainageway, running from the northwest to the southeast. The terminal check dam, located at the point where the channel leaves the area of disturbance, is intended to serve as a sediment trap and to create shallow ponding in the relatively flat area north and east of the structure. Rock check dams will have a minimum boulder size of 36-inches in diameter and will serve stream stabilization functions even after vegetation is successfully established on disturbed areas. A straw bale check dam below the terminal rock check dam, installed in accordance with City of Hot Springs criteria, will provide a final layer of filtration before runoff leaves the project area. The purposes of the check dams are to promote channel stability and sedimentation by slowing runoff and backing up water, which allows sediment to settle rrom runoff. Check dams should be inspected and maintained, as necessary, during weekly SWPPP inspections and following any storm event of 0.5 inch or greater. Maintenance may include removal of sediment accumulated behind check dams (before accumulated sediments exceed onehalf of the available storage capacity) and replacement of straw bales for the straw bale check dam below the terminal rock check dam.
Page 5 CONCLUSIONS The erosion and sediment control strategy outlined in this memorandum and attachments meets and exceeds the minimum regulatory requirements for the project area. BMPs should be installed in accordance with City of Hot Springs criteria, and inspection and maintenance, as described above, are essential. This erosion and sediment control plan is intended to minimize slope erosion and sediment transport from the area of disturbance for relatively frequently occurring events (i.e. up to the 2-year event); this is consistent with the national and local states of the practice. Larger events may cause runoff and erosion that exceeds the design capacity of the BMPs described above. Attachments Attachment 1 (Drawing): Erosion and Sediment Control Plan for Stabilization Phase of Parcels C, D, E and Borrow Area Reclamation cc: David Jubenville, P.E., Project Manager Jeff Nelson, P.E., Project Engineer C:\PF\962'{)51 \131Ia\l'ennit Application Revision\Attachment2AE.doc