Active treatment system solves tough stormwater challenge at mining operation
An aggregate mine in Coquitlan, British Columbia, produces large amounts of material for the construction industry, particularly sand and gravel.
|Turbid water entering the system can range up to 20,000 NTUs. Treated water is consistently below 20 NTU.|
by Frank Kneib
An aggregate mine in Coquitlan, British Columbia, produces large amounts of material for the construction industry, particularly sand and gravel. Throughout the mining process, fine particles are removed from the rock using clean water, which flows into multiple treatment ponds throughout the facility. Those ponds all flow into the company's main overflow pond for treatment prior to discharge into local water systems including rivers, waterfalls and dry-beds.
Unfortunately, the system put into place by the mining operation could not handle the additional water that resulted from rain events. The turbidity levels after a rain storm consistently reached well over 5,000 NTUs and often reached 10,000-20,000 NTUs. Heavy rains increased the flow rate past treatability with the existing treatment system. This highly turbid water often overflowed into nearby streams and did not meet discharge requirements by enforcing agencies.
A solution was needed to bring the turbidity level below the 50 NTU specification required by the Department of Fisheries and Oceans Canada, the Ministry of Environment, and the city of Coquitlan. The city randomly inspects the site, especially after rain events.
StormTec Filtration was selected to install a new treatment system to treat the overflow and protect the nearby rivers and creeks. Testing revealed that using HaloKlear DPS chitosan to flocculate the sediment, followed by sand media filtration, was the most efficient and effective solution.
The patented HaloKlear chitosan formula is a polymer made from crab shells. It helps coagulate suspended particles by neutralizing the negative static electrical charge on particles, allowing them to flock together and settle out. The HaloKlear products are approved by the Washington State Department of Ecology as well as the Florida Department of Transportation for treatment of stormwater.
A feed pump was set up to bring overflow water to the first mix station where HaloKlear BHR-P50 is injected and mixed. Treated water then flows to the second mix station at which point LiquiFloc 1% is added and mixed. The treated water then flows through settling tanks before passing through a bank of sand filters that remove remaining suspended solids to an approximate level of 20 to 25 microns.
The system is designed to handle up to 800 gallons of water per minute during storm events. Turbidity levels after treatment are consistently below 20 NTUs and mostly below 5 NTUs. Once turbidity levels start to rise to 30-40 NTUs, an alert is sent out indicating that the system is clogging with mud. The system can typically treat 800,000 to 1 million gallons of water and accumulates about 30,000 gallons of mud.
|The treatment system uses HaloKlearDPS chitosan to flocculate the sediment, followed by sand media filtration.|
A proprietary mud removal system cleans the system and removes the mud to ensure the system continues to work properly.
The StormTec system was set up almost one year ago and has been running on an as-needed basis.
"The mining operation is very happy with the solution we provided," said Ian Eggertson, project manager at StormTec who oversees the system.
The system has worked well during rain events and has also been helpful when earth banks collapse and excess turbid water accumulates into the overflow pond. The system has even acted as a backup system when the project's regular pumps have failed.
About the Author: Frank Kneib, MBA, has been managing the HaloKlear stormwater business for HaloSource Inc. since 2007 and is a Certified Erosion & Sediment Control Lead with Washington State.