Title Page Bioremediation of contaminated soil and groundwater at a service stationWaterloo, Ontario, Canada
Site The gas station at Phillip and Columbia Street was sold to a new company and any soil and groundwater contamination of the site due to its previous operation by Sunoco had to be removed.
The old gasoline tanks were removed and holes bored to detect gasoline and then a deeper excavation was done to the groundwater level to check for this contamination Excavation and Tank Removal The water surface showed visible signs of oil contamination.
Drilling The soil that was contaminated was excavated and removed to a secure landfill site To remove, or at least reduce, the contamination of the groundwater below the soil, holes were drilled and pipes were installed around the edge of the contaminated zone These pipes had perforated sections spanning the soil and groundwater regions and going a few feet below the water table The larger pipes surrounded the contaminated areas and were all then joined to the vacuum pumping systems
Pumping The pipes were joined together at the surface and pumps were attached to these pipes. The pumping systems pumped a mixture of groundwater, pure gasoline product floating on the surface of the groundwater and soluble products from gasoline that had entered the groundwater. These soluble products would have included benzene, ethylbenzene, toluene and xylenes. The mixture of gasoline, soluble products from gasoline products and water was pumped into a tanker truck on the property and disposed of after separation into the two phases of water and gasoline. The water would have contained the water-soluble components.
X-sectional Diagram To Separation and Collection Pump Excavation Soil Free gasoline product Groundwater Cross Sectional Diagram of excavation and wells
Final Operations • Pumping continued for some months until most of the free product and soluble components had been removed from the immediate vicinity of the site. Pumping also ensured that no more migration of the soluble components in the groundwater could occur. A negative gradient was established during pumping so that surrounding contaminated water flowed into the site and not away from it. • Pumping would have to have been continued for many years if ALL of the soluble components in the groundwater needed removal through this “pump & treat” methodology. • The residual soluble components were assumed to have been remediated through biological mechanisms in the groundwater. • In this particular case, bioremediation was used as a final cleanup operation, but the bulk of the materials were removed via the pump and treat method. This is often referred to as “polishing” – that is, removal of the residual, low levels of soluble components through bioremediation activities performed by indigenous microorganisms End