Public Works and Government Services Canada (PWGSC) — Pacific Environment Centre (PEC), West Vancouver, BC
Site Background
The PEC site was an industrial site located on a fluvial plain. In 2001, Treatment Wall A was installed with a cut and fill excavation method. A bio-degradable slurry was used to maintain excavation trench stability. The 2001 Treatment Wall installation was believed to have achieved the design dimensions. In 2020, Treatment Wall A was rejuvenated using a caisson excavation method. The Wall A media typically consists of unconsolidated pea gravel with trace amounts sand and reactive media (compost, limestone and zero valent iron).
II. Project Scope
Original specification were the following for the new wall construction
Hoganas/Chemco have proposed to the selected contractor the use of the CLEANER PRB sponge iron that would bring great advantages as the wall was to be constructed BY VOLUME. The use of the sponge iron media brings a large mass differential against the qualified original ZVI material that was using a regrind iron from Connelly-GPM or Peerless. In addition, the Hoganas CLEANER PRB media shows higher purity (98 % + iron content), slower passivation, increased reactivity, longevity and surface area for more efficient contaminant reduction. However, due to the inherent morphology of all CleanER media – it will have higher surface area and longer life span than any other ZVI in environmental market.
Hoganas Environment Solutions maintains a state of the art laboratory facilities for process and product development work and customer/project support. Specific laboratories include soil/groundwater, microbiology, water and wastewater, and general analytical testing.
These service capabilities were used to help the contractor to determine ZVI quality and dosage rate during the construction of the PRB.
Calculated ZVI saving estimate using the CLEANER PRB Sponge iron
Over a volume of 1485 m3 @ 4 % v/v iron for M-1 wall this loading would represent a 59.4 m3 ZVI loading (or 59.4 m3 x 1.45 kg/m3) = 86.13 MT of CLEANER PRB
For the Connelly-GPM material using a density of 2402 kg/m3 you would require 59.4 m3 x 2.402 kg/m3 = 142.7 MT of regrind ZVI
III. Conclusions
- Contractor was able to obtain significant budgetary and volume saving (media cost and freight) by using the CLEANER PRB sponge iron versus a typical regrind ZVI.
- Lower density of the CLEANER PRB allow the ZVI to be better mix with the other component as it behave like sand in the mixing equipment giving a more homogeneous mix at the end.
- Higher purity for the ZVI portion is providing the PRB with better longevity & reactivity.
