dation program was conducted on the soil recovered from Stockpiles 2 and 3. Upon completion of the remedial program, the excavated soil from Stockpile 1 was used for backfilling of the remedial excavation below a depth of 1.5 mbgs (criteria for stratified condition). REMEDIATION STATION LAYOUT The ex situ chemical oxidation remedial program was implemented using a trommel, two cement mixer trucks with a capacity of 9 m3 each, a mobile conveyer for loading soil and cement into mixers, a power generator to supply power to the conveyor, a large excavator, a skid steer loader, a stainless steel utility pump with the associated hosing for transferring chemicals to a cement mixer, and two plastic holding tanks for water. The program included the following stages: • Pumping water into the cement mixers. • Loading the water-filled cement mixers with the cyanide impacted soils from Stockpiles 2 and 3. • Adding sodium hydroxide and sodium
hypochlorite to the mix of water and soil. • Mixing of the resulting slurry from 30 to 45 minutes. • Adding cement to the treated slurry after the completion of the oxidation process to produce un-shrinkable fill. • Placement of un-shrinkable fill at the site.
produce un-shrinkable fill varied from 200 to 280 kg per mixer truck load. A treatment period was initially set up as 45 minutes, and then was adjusted to 30 minutes, based on the field observations.
SOIL CHEMICAL ANALYSIS A total of 41 soil samples of pretreated and treated soil were submitted CONCLUSIONS to an accredited laboratory for analyses. The ex situ chemical oxidation pro- This included free cyanide (29 samples), gram of the cyanide impacted soil was pH (four samples), free cyanide and pH conducted from November 20, 2008 to (three samples), free and total cyanides January 13, 2009. Field measurements (four samples), free/total cyanides and during the remediation program were pH (one sample). Selected samples were conducted using a portable meter HI analyzed for pH to confirm the required 9025 for measuring pH and ORP in the conditions for oxidation of the cyanide treated soil, and VRAE PGM-7800 gas impacted soil. All soil samples analyzed monitor for measuring hydrogen cya- for free cyanide were within the MECP Table 4 standard for surface soil. nide vapours in the ambient air. In total, 105 mixer truck loads or 1,345 tonnes of cyanide impacted soil Viktor Kopetskyy, PhD, P.Eng., is were treated with chemicals. 16,082.5 kg with Soil Engineers Ltd. Email: of 25% sodium hydroxide and 15,444 kg vkopet1661@rogers.com. Jim Phimister, of 12% sodium hypochlorite were used. P.Eng., P.Geo., was formerly with Cement adding to the treated soil to Barenco Inc.
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