Appendix A - Table 1.0 and Table 2.pdf
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- Attached to
- PKAA, Walsen Project
- Solicitation number
- DQ1 PKAA 2026000499 2
- Issued by
- Colorado
About this file
This file is an appendix containing detailed feature work lists for the Walsen Project mine closure contract in Colorado. The document outlines specifications for Item 4.0 (Install Mine Closures) encompassing eight distinct mine features (W01 through W08) and Item 5.0 (Install Maintenance Mine Closures) covering three maintenance features. The closure work involves a combination of excavation, backfilling, and erosion control measures tailored to each feature's characteristics. Feature W01 is a 30-by-27-foot sinkhole requiring 754 cubic yards of imported backfill material and 110 linear feet of wattles; W02 is a 61-by-55-foot subsidence feature requiring 261 cubic yards of imported material and 150 linear feet of wattles; W03 is a 41-by-63-foot subsidence feature requiring 251 cubic yards of imported material and 80 linear feet of wattles; W04 is a small 3.5-by-5-foot sinkhole requiring 1 cubic yard of onsite material with no wattles; W05 is a large 201-by-170-foot sinkhole requiring 3,318 cubic yards of imported material and 200 linear feet of wattles; W06 is a 4-by-5-foot sinkhole requiring 2 cubic yards of imported material and 25 linear feet of wattles; W07 is a 21-by-19-foot subsidence feature requiring 23 cubic yards of imported material and 60 linear feet of wattles; and W08 is a 6-by-6-foot sinkhole utilizing a monolithic concrete plug (8 cubic yards of concrete and 10 cubic yards of rockfill) with 190 linear feet of wattles. The maintenance work includes grading approximately 0.35 acres encompassing nine subsidence features with 300 linear feet of wattles, backfilling a 2-by-3.5-foot shaft with 0.3 cubic yards of material, and managing a 35-by-35-foot air shaft requiring removal of 60 cubic yards of debris and backfilling with onsite waste material and 50 linear feet of wattles.
The document specifies detailed closure methods, including machine backfill with imported or onsite material meeting specific grading requirements with medium diameters of approximately 12 inches and sufficient finer particles to minimize voids. Most features are addressed under Section 2.0 specifications, with W08 utilizing Section 7.0 specifications for monolithic plug installation. All backfill volumes are calculated using geometric assumptions such as half-ellipsoid or oval configurations based on feature dimensions and depth. Special considerations include proximity to high-voltage overhead powerlines at features W01 and W02, requirements to preserve existing trees during grading operations, and provisions allowing contractors to reuse existing onsite wattles if they meet bid specifications. The contractor is responsible for obtaining landfill invoices for debris disposal at the air shaft feature and ensuring all concrete samples are provided to the Project Manager for testing purposes.
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Item 4.0: Install Mine Closures Walsen Table 1.0 – Feature Work List
Feature ID Type Description of Mine Opening
Closure Method
General Bid Specifications and
Drawings
UTM
(X,Y) NAD83 Work Description / Notes
W01 Sink Hole
Excavated:30ft by 27ft
Eroded:30ft by 27ft
Present:30ft by 27ft
Depth:32 ft Lining:Other Drainage:No
Machine Backfill
Section 2.0
518148.2825 1179,
4162675.041 28458
The feature is located approx. twenty-five (25) feet north of high voltage, overhead, powerlines. Excavate along perimeter until all sides of feature are bound by stable bed rock.
Excavate ramp down to the bottom of the hole. Ramp is intended to be parallel to existing mine workings; to create a stable and safe work area. Backfill feature with imported material: backfill shall consist of a hard, durable, and well graded material with a medium diameter of approximately twelve
(12) inches and sufficient finer particles to minimize the presents of voids. Install one hundred and ten (110) LF of wattles along downslope perimeter of feature. Rockfill IS NOT Required.
The total backfill volume is estimated at seven hundred and fifty-four (754) cubic yards of imported material. This was calculated by multiplying the surface area of the oval feature by its depth.
Excavation will require a larger excavator such as a CAT 325 Excavator (or approved equivalent).
Description of Mine Opening
Closure Method
General Bid Specifications and
Drawings
UTM
(X,Y) NAD83 Work Description / Notes
W02 Subsidence Feature
Excavated:61ft by 55ft
Eroded:61ft by 55ft
Present:61ft by 55ft
Depth:4 ft Lining:Rock +
Timber Drainage:No
Machine Backfill Section 2.0
518138.6115 41593,
4162613.075 49521
The feature is located underneath overhead powerlines. Excavate to determine extent of subsidence. Machine backfill with imported material; backfill shall consist of a hard, durable, and well graded material with a medium diameter of approximately twelve
(12) inches and sufficient finer particles to minimize the presents of voids. Install one hundred and fifty (150) LF of wattles along downslope perimeter of closure. Rockfill IS NOT Required.
The total backfill volume is estimated at two hundred and sixty-one (261) cubic yards of imported fill material. This was calculated by assuming the feature is a half ellipsoid and calculating the volume.
W03 Subsidence Feature
Excavated:41ft by 63ft
Eroded:41ft by 63ft
Present:41ft by 63ft
Depth:5 ft Lining:Other Drainage:No
Machine Backfill Section 2.0
518125.4431 41507,
4162692.865 82402
Machine backfill with imported material;
backfill shall consist of a hard, durable, and well graded material with a medium diameter of approximately twelve (12) inches and sufficient finer particles to minimize the presents of voids. Install eighty (80) LF of wattles along downslope perimeter of closure.
Rockfill IS NOT Required.
The total backfill volume is estimated at two hundred and fifty-one (251) cubic yards of imported material. This was calculated by assuming both sides of the figure 8 shaped feature are individual, half-ellipsoids and summing the two volumes.
Description of Mine Opening
Closure Method
General Bid Specifications and
Drawings
UTM
(X,Y) NAD83 Work Description / Notes
W04 Sink Hole
Excavated:3.5ft by 5ft Eroded:3.5ft by
5ft Present:3.5ft by
5ft Depth:3 ft
Lining:Other Drainage:No
Machine Backfill Section 2.0
518101.1039 09745,
4162723.938 91824
Machine backfill with onsite material; Total backfill volume is estimated at one (1) cubic yard. This was calculated by assuming the feature is a half-ellipsoid.
Wattles are NOT required. Rockfill IS NOT Required.
W05 Sink Hole
Excavated:201ft by 170ft
Eroded:201ft by 170ft
Present:201ft by 170ft
Depth:5 ft Lining:Other Drainage:No
Machine Backfill Section 2.0
517901.9583 7195,
4162870.817 18573 well graded material with a medium diameter of approximately twelve (12) inches and sufficient finer particles to minimize the presents of voids. Install two hundred (200) LF of wattles along downslope perimeter of closure. Rockfill IS NOT Required.
The total backfill volume is estimated at three-thousand, three-hundred and eighteen (3,318) cubic yards of imported material. This was calculated by summing the areas of the six subsidence features, assuming each feature takes the shape of a half-ellipsoid.
Description of Mine Opening
Closure Method
General Bid Specifications and
Drawings
UTM
(X,Y) NAD83 Work Description / Notes
W06 Sink Hole
Excavated:4ft by 5ft
Eroded:4ft by 5ft Present:4ft by 5ft
Depth:3 ft Lining:Other Drainage:No
Machine Backfill Section 2.0
517878.3652 53244,
4162897.578 09966 well graded material with a medium diameter of approximately twelve (12) inches and sufficient finer particles to minimize the presents of voids. Install twenty five (25) LF of wattles along downslope perimeter of closure.
Rockfill IS NOT Required.
The total backfill volume is estimated at two
(2) cubic yards of imported material. This was calculated by multiplying the surface area of the oval feature by its depth.
W07 Subsidence Feature
Excavated:21ft by 19ft
Eroded:21ft by 19ft
Present:21ft by 19ft
Depth:3 ft Lining:Other Drainage:No
Machine Backfill Section 2.0
518176.6481 05027,
4162596.825 23708
Excavate to find the extent of the void.
backfill shall consist of a hard, durable, and well graded material with a medium diameter of approximately twelve (12) inches and sufficient finer particles to minimize the presents of voids. Install sixty (60) LF of wattles along downslope perimeter of closure.
Rockfill IS NOT Required.
The total backfill volume is estimated at twenty-three (23) cubic yards of imported material. This was calculated by multiplying the surface area of the half ellipsoid feature by its depth.
Description of Mine Opening
Closure Method
General Bid Specifications and
Drawings
UTM
(X,Y) NAD83 Work Description / Notes
W08 Sink Hole
Excavated:6ft by 6ft
Eroded:6ft by 6ft Present:6ft by 6ft
Depth:6 ft Lining:Other Drainage:No
Monolithic Plug Section 7.0
518275.8593 82076,
4162522.771 70515
Excavate the perimeter and bottom of the feature to find the full extent of the void.
Secure opening with a monolithic plug (eight
(8) cubic yards concrete and ten (10) cubic yards of imported rockfill).
At least seven (7) days after the concrete has been poured, the contractor may backfill the remainder of the opening with onsite materials.
Install one hundred and ninety (190) LF of wattles along downslope perimeter of closure.
The contractor may re-use the existing wattles onsite if they meet specifications in Bid Item 3.0.
The Project Manager will take cylinder samples of concrete.
Item 5.0 Install Maintenance Mine Closures - Walsen Table 2.0 – Feature Work List
Description of Mine Opening
Closure Method
General Bid Specifications and
Drawings
UTM
(X,Y) NAD83 Work Description / Notes
107Walsen -Area1SF1
Subsidence Feature
Excavated:25ft by 12ft
Eroded:25ft by 12ft
Present:25ft by 12ft
Depth:6 ft Lining:N/A
Drainage:No
Grade N/A
517960.6447 06412,
4163167.107 08708
The area consists of nine (9) individual subsidence features requiring maintenance.
Grade the site to eliminate the saddles between each feature, ensuring improved drainage, and blend the depressions seamlessly into the surrounding topography.
Finally, install three hundred (300) LF of wattles along the downslope perimeter for erosion control.
Area to be graded is approximately 0.35 acres. Take care not to disturb the existing trees.
704 HL-06 Shaft
Excavated:2ft by 3.5ft
Eroded:2ft by 3.5ft
Present:2ft by 3.5ft
Depth:1.5 ft Lining:N/A
Drainage:No
Machine Backfill Section 2.0
517707.1943 21651,
4162920.940 51989
Excavate around the perimeter of the feature and backfill with onsite material. Backfill will require 0.3 cubic yards of material. Wattles are NOT Required. Rockfill IS NOT Required.
Item 5.0 Install Maintenance Mine Closures - Walsen Table 2.0 – Feature Work List
Description of Mine Opening
Closure Method
General Bid Specifications and
Drawings
UTM
(X,Y) NAD83 Work Description / Notes
748 RH-03 Air Shaft
Excavated:35ft by 35ft
Eroded:35ft by 35ft
Present:35ft by 35ft
Depth:5 ft Lining:Rock Drainage:No
Machine Backfill Section 2.0
516570.2116 09127,
4165463.248 90167
An estimated sixty (60) cubic yards of debris must be removed from feature. All trash and debris shall be hauled to a county approved landfill. Landfill invoices shall be provided by the Contractor.
Excavate the sinkhole to a solid bottom and machine backfill with the on-site waste pile material located approximately three hundred
(300) feet south-east of feature 748 RH-03.
Install fifty (50) LF of wattles along the downslope perimeter. The contractor may reuse existing onsite wattles if they meet the specifications outlined in Bid Item 3.0.
Rockfill IS NOT Required.
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