Sizing is slightly more complicated for processing ponds using in the mining industry than for other types of water features. Like cooling and evaporation ponds, processing ponds must be oversized for safety or serious environmental damage could occur during an unusual storm or power outage event. Building processing ponds too close to the minimum requirements for holding capacity, risks overflow and damage to the surrounding area and structures if there’s a flood or rainfall event. Consider all of the following factors when sizing mining, processing ponds for your facility.
One Day’s Supply Plus Overflow
Most modern processing ponds are sized to contain one full day’s standard flow of leachate. This is usually backed up by an overflow facility of anywhere from 2% to 5% of the total volume of the system. Keep in mind that this total size is spread out across the entire range of processing ponds. If the ponds can absorb 10,000 gallons a day in total, that’s five 2,000 gallon ponds, or ten 1,000 gallon ponds if there are 10 in the system. For a 10-million-gallon system, the overflow capacity can measure anywhere from 200,000 to 500,000 gallons. In climates with catastrophic flooding risks, the overflow capacity may need to go as high as 10% for safety.
Zero Discharge Facility
Very few mining processing facilities built today get permission to aim for any design other than a zero-discharge system. Residues from solution leaching of ores and minerals are not considered candidates for discharge into the ground or an existing body of water, even after processing is complete. Zero discharge facilities generally reuse the barren solution left over at the end of processing by simply adding more water and other chemicals as needed. If the waste leachate becomes too thick to effectively pump back up for recycling, it’s generally removed by tanker truck for disposal or processing at another site. Zero discharge facilities rely on leak-free lining to achieve their goal of keeping chemicals out of the soil and water around the ponds and ditches.
Barren and Pregnant Ponds
Since the flow of leachate is largely controlled by gravity rather than pumps in these systems, the flow of liquid is steady to both the barren and pregnant ponds. There shouldn’t be major differences in the total flow capacity or volume required for either type of pond unless the system is designed around that factor. In a system with very slow rates of leaching solution application, the barren holding ponds may need to be significantly larger than the pregnant processing ponds. However, this is an unusual setup since most systems maintain a relatively steady flow of water through both types of ponds.
Stormwater Overflow Areas
Berms and secondary containment areas are generally sized for stormwater overflow in case of emergencies. This is based on the 100-year flood levels for the area where the processing system is built. Records for rainfall and flooding conditions are consulted for the past 100 years. Even in relatively dry desert areas where gold and silver mines are commonly built, rare flooding events can damage or completely ruin a hydrometallurgical operation. Careful protection of the leach pad and processing ponds with surrounding berms can make the difference between surviving a major flood or losing it all. Processing waste is often high in sulfuric acid, arsenic, and cyanide, making it a hazardous material that can have a long-term impact on the environment if it is flushed out by a flood.
Don’t underestimate the complexity of calculating surface area, depth, and total volume for your processing ponds. This planning step, in a gold or silver ore facility, is best handled by hydro engineers experienced with the challenges common to the mining processing industry. Regardless of the size of the ponds you end up building, BTL Liners products can be custom fabricated to fit your needs and to ensure as quick of an installation process as possible.
