ERC calculator mining – Module 9 transcript

Watch the video Mining ERC calculator training – Module 9 – Waste structures to see examples of sheet 7 – waste rock dumps, overburden dumps, spoil piles and stockpiles; sheet 8 – heap leach pads; and sheet 9 – tailing storage facilities.

Welcome back to the training for the 2022  edition of the estimated rehabilitation cost calculator for mining. This is Module 9. This module covers: sheets 7 – waste rock dumps, overburden dumps, spoil piles and stockpiles; sheet 8 – heap leach pads; and sheet 9 – tailing storage facilities.

The waste rock dumps, overburden dumps, and spoil piles and stockpiles sheet has four tables. The first is the default rates of five risk categories of waste rock dump. The second is a user build table for waste rock dumps, and the third is a user build table for overburden dumps and spoil piles, and the fourth is a user build table for growth media stockpiles. The total cost is summed at the bottom of each table and the total cost for the sheet or domain is shown in the top ribbon. The total estimated rehabilitation cost is also shown at the top of the ribbon so the user can see how the overall estimated rehabilitation cost is changing with inputs into this specific sheet.

Let's look at the waste rock dump default table first. As for all input sheets, the first column is the map identification for that particular item. Column D allows the user to enter the name of the waste rock dump. The area column requires the user to input the total area of the waste rock dump that will require rehabilitation. This is a key entry to this table and must be entered for any line the user inputs to. The user must select a risk category from the drop-down menu in the risk category column. The presence of a drop-down menu is indicated by the red ‘select from dropdown’ text.

The risk categories are described further in the user guide. The selection of the risk category is a critical part of the calculation, and the user is encouraged to provide information to support their selection. As you can see, the use of this table is easy. You enter an area and select a risk category and the cost is calculated. As in other input sheets, if an alternate rate is justified for that line item, the user enters it into the alternate rate column and the cost for the line item is calculated based on the alternate rate. Note that the unit for the alternate rate in this case is dollars per hectare, and this gets multiplied by the area. Don't forget to add a justification in the alternate rate justification cell and the user is encouraged to provide sufficient detail to inform the department as to why an alternate rate is justified.

Now we move on to the second table, which is the user build for waste rock dumps. If you enter a waste rock dump into the defaults table we just spoke about, you do not need to enter it into any other table, including this user build table. This is a general principle throughout the calculator, in that you should not have to enter any quantities into more than one table. The user enters the map ID and the name of the waste rock dump. Like all other user build tables in the calculator, this table is broken into sections across the columns to aid understanding. The first set of columns is general details and dimensions associated with the waste rock dump. This is where the user enters the total footprint of the waste rock dump and selects the risk category, which in turn selects an appropriate default for capping thicknesses. The user enters areas and thicknesses of flat areas such as tops and benches, the slopes and batters, and the area of the ramps. You will see that the flat areas is linked to the total footprint of the waste rock dump and that is because generally the flat area will be approximately the total footprint area. However, if the user has more detailed information, they can change the flat area.

This is a general concept throughout the calculator in that if a quantity is typically equal to another quantity, it will be linked, but if the cell is green, the calculator acknowledges the user may have more detailed information and can enter it.

The next section in the table is focused on reshaping and dozing the waste rock dump. The user selects the reprofiled slope angle from the drop-down menu. If the user has specific volume quantities, they can enter it directly. Otherwise the calculator calculates the volume based on the entries added earlier. Similarly, the user can enter their own quantity into the user volume to push slopes column. Otherwise the calculator calculates that quantity. In the reshaped length of dozer push and fleet for reshaped columns, the user selects the dozer size and length of push specific to the reshaping activities.

The selection of these two items determines the dollars per cubic meter rate that will be applied to the total column, and the dozer and slope angle determined the unit rate for slope areas. The first of these comes from subrates table 2 and the user can click on the hyperlink to reference the full range of those rates. Similarly for the slope dollars per hectare rate, the hyperlink takes the user to this table, subrates table 3. The next two columns are the totals for these activities. The cost for dozer push all areas being the volume of material to be pushed by the dozer multiplied by that unit rate. The cost to doze and shape slopes and ramps column is the dollars per hectare rate multiplied by the total area to reshape.

One thing to note for dozer selections, which is common throughout the calculator, is that the smaller dozers cannot push as far as larger ones. So if the user selects a dozer that is not capable of achieving the selected length of dozer push the calculator will communicate an error and the cost totals will also be in error. In this case the user must reselect a larger dozer that can achieve the selected push length.

The next section is the rock armour placed over the waste material to provide stability. The first column, default slope break rock armour cover thickness shows the default thickness drawn from the capping table at the top of the sheet. The user can access this table through the hyperlink shown. The user can enter their own cover thickness in the user slope armour cover thickness column, and if a thickness less than the default is entered, they must provide justification in the capping alert sheet. You can see if we enter 0.5 instead of 1 an alert will be reported against that dump in the capping alert sheet and the user must provide the justification.

You can easily move between sheets as indicated previously by clicking on the contents hyperlink and then navigating back to the waste rock dump sheet. The rest of the rock armour table proceeds similarly to the previous table whereby the user can enter their own rock volume if they can justify it or accept the calculation. The user then selects the fleet size from the drop-down menu, which then selects the appropriate dollars per cubic meter rate and this is multiplied by the rock cover volume to get the total cost for that cover.

The capillary break layer is the next section of the table and operates similarly to the previous sections, whereby the user can enter the area that will be covered with the capillary break layer, and if so provide justification or accept the calculation, which defaults to the area of the waste rock dump. The default capillary break layer thickness is shown and the user can hyperlink to the table to see the range of values against each risk category. The user can enter their site-specific capillary break layer thickness and if it is less than the default, they must provide justification in the capping alert sheet. The user can enter a specific capillary break volume or accept the calculation, and this is multiplied by the dollars per cubic meter rate determined by the fleet selections to obtain a total for the source and prepare capillary break layer material.

This table also includes costs for the haulage of the capillary break layer material, starting with fleet size selection, which determines the appropriate unit rate, and this is multiplied by the volume again to get the costs for that activity. The last bit of this section for capillary break layers is the dozer push for the material and the total cost of which is determined by the fleet selections which determines the unit rate. The total cost for the capillary break layer is the sum of the three activities determined in the preceding columns.

The low permeability layer is the next section of the table and operates similarly to the previous sections, whereby the user can enter the area that will be covered with the low permeability layer and if so provide justification or accept the calculation, which defaults to the area of the waste rock dump. The default low permeability layer thickness is shown in this box and the user can hyperlink to the table to see the range of values against each risk category.

The user can then enter a specific low permeability layer volume or accept the calculation, and this is multiplied by the dollars per cubic meter rate determined by the fleet selections to obtain a total for sourcing and preparing the low permeability layer material. The next section of this table allows the user to select whether the low permeability clay will be obtained locally or must be sourced some distance from the site. If local is selected in the source for low permeability capping column, the calculator sets the long haul rates to zero and accepts the calculation in the source, prepare, place and compact low permeability layer material column.

If long haul is selected, the rate in low permeability unit rate is reduced and the long haul rates are used. For long haul the user must select the one-way distance from the drop-down menu in distance one-way for low permeability capping. The distance to the source site is one way and this selection determines the unit rate in dollars per cubic meter per kilometre. The user can hyperlink to subrates table 9 to see how these rates change with distance. For long haul, the transport costs just calculated is then added to the purchase cost dollars per cubic meter to obtain a total cost for the long haul of the capping material. The user can bypass this calculation and directly enter their own delivered to site costs in dollars per cubic meter in the user clay delivered to site column. If this is entered, they must provide justification. The combination of costs are then added to obtain the total cost for the low permeability layers.

The next section of the table is the top rock capping and this works similarly to the other sections. The surface area for top rock defaults to the surface area footprint for the waste rock dump, but the user can enter a site-specific value if they can justify it. The default layer thickness is determined by the risk category and the range of values is in the capping values table at the top of the sheets accessed by the hyperlink. Similarly to other sheets the user can enter specific thicknesses and volumes with justification or accept the calculations. The load and haul top rock unit rates are determined by the fleet selections and the sub cost determined by multiplication of the rate with the volume.

The next section of the table is for additional capping that may be entered. The additional capping will be determined by the user. The entries here are very simple in that the area for each particular type of capping, geofabric, geosynthetic layer, and geomembrane are entered and the rate for those is drawn from subrates table 5. The total is then displayed in the total for geo layers column. The next section of the table is for management of drains and water management, and again these are simple entries whereby the total area is entered and multiplied by the default unit rates. The user can enter a water management earthworks cost as a total cost, and justification must be supplied.

The next section of the table is for the application of growth media, soil amendments, and vegetation. The growth media section of the table works similarly to other sheets. A default thickness is supplied and reference from the capping values table at the top of the sheet. The user can enter their own thickness or their own volume, and the calculation uses whichever combination is entered. The growth media load and haul rate is drawn from subrates table 1, depending on the selection of haulage distance and fleet size the user selects. The growth media table includes a local and long haul selection similar to that described previously, and allows an alternate rate of dollars per cubic meter for growth media to be entered directly. The combinations of entries entered determines the total cost for growth media.

The next section of the table is for soil amendments and includes the options you can see in the drop-down menu. The table allows three soil amendments to be added, so the user can enter a combination of amendments and enter the specific area upon which that soil amendment will be added. In each case, the user can enter a site-specific dollars per hectare rate and provide justification for its use. The soil amendments include assumptions for the application rates, and these are shown in subrates table 14. The user cannot change the application rate in the waste structures table, but can enter a site-specific example to the general land rehabilitation sheet and change the application rate in that sheet. Consequently if required, the user could add the soil amendment for a waste rock dump or other structure in the general land rehabilitation sheet and enter their own application rate there. If the user chooses to do this, please provide information for the department to review.

The default for seeding is pastureland, but the user can change the mix depending on what the specific land type that area will be returned. The alert if land types do not equal 100% column alerts the user if they have added numbers that are greater than 100% of the land area. If the waste rock structure is in a desert area where vegetation is not expected, the user enter 0% in the proportion pasture land and proportion native land and this will create 100% proportion arid land, setting the seeding cost to 0. Depending on the selection the calculator uses the rates for seeding of pasture or native land, or zero if 100% arid, or takes the alternate rate entered by the user. If an alternate rate is added, the user must provide justification. The last section of the table is for permeability testing, engineering and other activities. The area for the permeability testing column defaults to the footprint of the waste rock dump and the number of points per hectare defaults to the number shown. The user can enter their own number of points per hectare and must provide justification.

Depending on these selections, the total cost for permeability testing is then calculated. The rate for engineering, which includes items such as groundwater assessments, modelling studies, landform design, engineering plans, work plans, and supervision references the capping values table at the top of the sheet. The user can enter their own dollars per hectare rate with justification. The user other activity columns allows the user to enter any other costs that must be attributed to the waste rock dump, and the user is encouraged to provide information to alert the department as to what these costs are. The total cost for waste rock dump is then shown in the total cost waste rock dump column and that cost is divided by the total footprint area to give a dollar per hectare rate. There is a check column which shows an error if incorrect entries have been added. This is primarily an incorrect dozer selection, which will be shown in those sections. If an error is shown, the user must go back and rectify. Justification for alternate rates can be added to the next column. The third and fourth tables in the waste rock dump, overburden dump, spoil piles and stockpiles are simple versions of the waste rock dump user build and use the same concepts as described for the user build table.

The heap leach pad and tailing storage facility sheets operate almost identically to the first two tables in the waste rock dump and piles sheet. There is one addition to heap leach pads and that is flushing. The flushing of the heap leach pads assumes the area is the footprint of the pad, but the user can enter their site-specific area. The user enters the thickness of the pad to be flushed and the calculator calculates the volume. If the user enters a site-specific volume the calculator uses that volume. The volume is multiplied by the heap leach pad flushing default rate to obtain the total cost for flushing, and this is added to the heap leach pad total. As with all the sheets, the totals in each table are added up and the total for each sheet or domain reported to the summary sheet.

As always, for more information or specific instructions, please consult the user guide, which is also available on the Business Queensland website below the download for the calculator.

See you in the next module.

Watch the video: Module 9 – Waste structures.