ERC calculator mining – Module 8 transcript

Watch the video Mining ERC calculator training – Module 8 – Water storage and treatment to see examples of the water storage and the water treatment and pumping sheets.

Welcome back to the training for the 2022 edition of the estimated rehabilitation cost calculator for mining. This is Module 8. In this module we will work through some examples in the water storage and the water treatment and pumping sheets.

The water storage sheet includes three tables. The first is water storage by category and capacity, the second is by crest area, and the third allows the user to build their own rate. The first two rows in the first table are different to the remainder of the table and allow for any small clean water type structures.

Rows in the remainder of the table include three drop-down menus defining the water structure or group of structures. The first drop-down menu determines the type of dam or pond. This selection primarily determines the thickness of sediment or sludge and whether the dam or pond is lined. The assumption is process and raw water dams are lined, and evaporation and other dams are not lined.

The next column is the selection of the water capacity at crest level and this determines quantities such as the volume of soil in bund walls that has to be moved. The last drop-down column is for the land type. If arid is selected because the site is in a desert area, no growth media or vegetation are included in the costs. The combination of the selections determines the default rates and this is multiplied by the number of structures in the row to get the total cost for that row.

The next table allows the user to enter dams and ponds based on whether they are lined or unlined and by area. The area quantity is the crest area of the dam or pond, or group of dams and ponds. The last table allows the user to build their own rate using some defaults set by the calculator. The calculation works out the cost of one dam or pond in the row and then multiplies it by the number of structures entered into this column. This is important because the entries throughout the table are for one dam or pond and only at the very end is the cost multiplied by the number of structures entered by the user in that row.

This is different to the other tables in this sheet. The user must enter at least a 1 in the number of structures column to make this calculation work. The top of water structure area, as in the crest area, is a key entry required to make the calculation work. The user then selects whether the dam is lined or unlined and can enter a specific liner area or accept the default. If the user enters a liner area less than the crest area an alert is shown and either the user needs to change the entries or explain why the liner area is less than the crest area. The liner area is multiplied by the default rates to calculate the cost for demolishing the liner and managing the waste.

The wall push in section is the bunds being demolished and pushed in for backfill. The wall height above ground service, width at top, and slope are key parameters that make the calculation work. The user can enter a specific cross-sectional area, in which case those values do not need to be entered. The linear length of bund wall is calculated by a simple square root of the area, but the user can enter a specific linear length of bunds. From these entries, the volume of soil in the bunds is calculated and this is multiplied by the default rate to obtain the total cost for this activity. The next section of the table is for sediment or sludge removal and management, and the user can enter their own thickness or accept the default as shown. The combination of crest area and sediment thickness calculate the sediment volume and this is multiplied by the default rate to calculate the total cost for sediment and sludge removal.

The growth media and revegetation section of the calculator works the same as the other tables in other sheets. The growth media area defaults to the crest area, but the user can enter a specific value or a specific growth media thickness. The combination of entries creates the growth media volume and this is multiplied by the default rate to calculate the cost associated with the application of growth media. Similarly with the seeding area, the default is to the crest area, but the user can enter a specific seeding area.

The selection of land for rehabilitation works the same as the other sheets in that the user enters percentages to pasture and/or native or sets these to 0 if the land is in arid desert land. The land investigation section requires the entry of the area to investigate and the share or fraction of the upfront cost of the investigation. This second column allows for campaign type investigations whereby full upfront costs are not necessarily applicable if, for example, small dams are grouped together and the cost would be shared across those structures. This is further explained in the user guide.

In its simplest form, the share fraction of upfront cost is set to 1 and this means all the upfront costs associated with the investigation are assigned to that row. If, for example, the share is set to 0.5, the calculator assigns half of the upfront cost to the investigation for that row.

The next section of the calculator is fleet selections, with the first being the haulage distance and fleet size for sediment removal. Keep in mind that anywhere there is a distance selection for fleet it is for a one way trip as the calculator will calculate the return trip in the background. For example, if the distance to haul is 1.5 kilometres, the user would select the greater than 1000 to less than or equal to 1500 meter range.

The next is the push lengthened dozer size for pushing in the bund walls, and the last set of selections are associated with growth media. The volumes calculated at the beginning of the table are multiplied by the default rates determined by the fleet selections to get the total cost for each activity for that row. If the best assumption is that water will be present in the dam and it must be pumped, this can be added to this column. The totals for both tables are added together and reported to the summary sheet for addition to the ERC total.

The water treatment and pumping user input sheet has several options for water treatment, including adjustment of low pH water and removal of salt and organics. Correction of low pH water assumes the use of neutralisers and two rates are available, one for initial pH of 4.5 or greater and one for pH of 5.5 or greater. If a site has lower pH water, the user must supply an alternate rate.

Removal of salt is assumed to be by reverse osmosis equipment, and if this rate is used, the user must also enter the mass of salt to be loaded and hauled and disposed to a waste facility by entering the salt disposal gate fee and adding a mobilisation entry to account for the cost of implementing and decommissioning the mobile treatment unit. Removal of organics assumes the use of an oil/water separator and activated carbon.

Two evaporation rates are included for reduction of water in ponds and dams. The first assumes natural evaporation and the rate allows for a technician visiting the site periodically to monitor water levels. The rate is by dam or pond and assumes a time period to set a rate. The second rate is enhanced evaporation using a device such as an atomiser. The rate allows for power, and a technician visiting the site periodically to monitor water levels and maintain equipment. The selection of either of these rates is the choice of the user. If there is likely to be obvious time pressure on the removal of water from the ponds, then enhanced evaporation is likely to be a more appropriate rate to use.

The water pumping and transfer rate allows for water that must be managed and is not included in other input sheets. Pumping and treatment requirements for pits can be included in the user input sheet for pits. Pumping of water from dams and ponds can be entered to the user build for water structures, but treatment is not included and the default rates do not include pumping or treatment of water. If preferred, the user can enter all water management requirements in the water treatment sheet.

Rates are included for removal of evaporation fans and other water management infrastructure, dewatering plant decommissioning, and an allowance for management, establishment, engineering and operation and maintenance costs.

The dewatering plant rate is for decommissioning of company owned dewatering plants. The entry is by capacity of the system. If multiple systems are present, the user can enter the sum. For example two times 1 megaliter per day plant would require an entry of 2. There is also a user build dewatering table that we will talk about later.

In general, if any of the water treatment and management options in this table are selected, the water management, engineering, establishment, and operation and maintenance rate should also be used unless the user can justify its emission. The entries to this table are simple quantity based, but please take note of the units for each column with salt disposal by mass, the treatment and pumping rates being by volume, and the evaporation rates by dam or pond.

Mobilisation of the reverse osmosis plant if salt removal is selected is typically a 1, with these costs being adequate to support multiple mobilisations to separate sites. The quantities part of the table allows multiple entries. For example, if water contains organics and low pH, the user enters quantities to both these columns. The total for all treatments in management options is added up in the total cost column and the user can enter an alternate rate with justification for the entire area, which bypasses all the individual treatment and management options. Water management scenarios will vary from site to site depending on the mine type and degree of processing undertaken.

The user should provide sufficient information to support the determination of the volume of water to be pumped, and selection of water treatment options which will be informed by water quality results and an understanding of the mine processes. The user can enter alternate rates for each treatment or management option in the cost part of the table, and as usual, must provide justification to the right of the table if they are used.

The dewatering table allows the user to build their own rate for a company owned dewatering system for which they will be responsible for decommissioning. The table requires entries including the number of downwell pipes, the type and length of piping, and the type and number of any tanks or dams and ponds specifically associated with the dewatering system that are not included in other sheets. There is also an option for a diesel generator if this is how the dewatering system is powered. If the dewatering system is powered from the site grid, then the decommissioning of services rate in the infrastructure sheet is assumed to cover disconnection of this item. If there are no other services on the site, then it is reasonable to either use the remote services rate in the infrastructure sheet or assume a diesel generator.

As in other sheets, the totals in each table are added up and the total for the 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 8 – Water storage and treatment.