OIL CONTAMINATED SITE CLEAN UP – COLWOOD CORNERS
CASE STUDY N°.: 4
Colwood, a Municipality in Greater Victoria, Vancouver Island, BC carried out a major renovation of a shopping mall called Colwood Corners in 2012.
The major problem was the fact that Colwood Corners was a site contaminated by dry cleaning fluids and the Capital Region District (CRD) would only give planning permission for the disposal of any water into sewer drains if the water was cleaned of any contaminant chemicals and met the standards set by CRD for such disposal.
Petro Barrier Systems Inc. (PBS) was approached by the main contractor Farmer Construction for a solution to the problem.
PBS designed a filtration system to remove hydrocarbon oils and the known contaminants including chlorinated solvents such as perchloroethylene, a dry cleaning liquid from a dry cleaning commercial operation nearly 50 years ago.
Over that period of time, rain water washed these dry cleaning fluids down through the soil and into the aquifer.
When the construction company was digging holes for foundations of buildings, contaminated water from the aquifer filed these holes and this water had to be removed and sent to existing sewer drains.
The Capital Region District, the authority issuing disposal permits, require that any water being disposed into storm and sewer drains must not exceed concentration levels as outlined in bylaw 2922.
Tetrachloroethylene – 10 mg/litre
Suspended solids – 350 mg/litre
The proposed clean-up system was submitted to the appropriate engineering department of the CRD, together with analytical results for water before and after treatment, which results demonstrated the effectiveness of the proposed treatment.
As a result, the CRD issued the necessary permits for disposal the treated water. This certificate did specify that the PBS process was an approved system which was required to be used (see Exhibit 1).
The only problem which was encountered was the suspended solids which were small and fine particles which were difficult to sink to the bottom of the water holding tank into which the dirty water slurry was pumped, prior to treatment.
To overcome this problem, a measured amount of a flocculating agent was fed into the dirty water.
This flocculant, which is a mixture of a number of chemicals has the effect of agglomerating the finely divided solid particles into much larger solids thereby increasing the speed of separation from the water.
In addition, it was possible to precipitate any dissolved chemicals which became agglomerated with the suspended solids.
Finally, to rapidly remove these solids from the water, this slurry was pumped through two hydrocyclones where the design of these devices (cone shaped) continuously separates the solids from the water.
The water continues from the hydrocyclones to polishing filters (36” long and 8” i.d.) filled with activated charcoal where the chemical contaminants are removed by adsorption and cleaning the water to contaminant levels below the permissible levels of the CRD bylaw 2922.
In the initial stage the water before and after treatment was sampled and tested daily, and after a month, the testing was weekly and finally monthly.
On many occasions, the total system operated 24 hours per day, 7 days a week, and was pumped at a rate of 100-120 gallons/minute,
When the system was handed over to the main contractor after 3 months of operation, volumes of more than 1 million gallons of water were treated and disposed down into the sewers.
The CRD designated that a totalising water flow meter be installed in the lines to measure both the water flow rate and the total volumes of water passing the sewer.
By this means, the CRD were able to calculate the volumes discharged from which the charged disposal fees were calculated.
It should be noted that this system which cost the contractors $50,000.00, saved the project at least 1 million dollars which would have been the amount for removing the waste water by trucking and disposal off-site.
No analytical testing of the treated water ever showed results below the CRD specifications and the only operating problem was the need to replace the activated charcoal which became partially blocked by minute solids which the hydrocyclones di not remove.
This replacement occurred about once every 2 to 3 weeks of operation.