A large petrol station located along one of the busiest motorways in northern Italy was undergoing extensive reconstruction, including the demolition of existing buildings, removal of above- and below-ground structures; as well as remediation. The existing underground fuel tanks (USTs) were removed and the contaminated soil surrounding the USTs was excavated to a depth of 5m BGL.
The geology consists of a highly permeable soil comprising sand and gravel to approx. 40m BGL. The average groundwater level is at approximately 4m to 6m BGL, where an extensive contaminant smear zone was observed.
The main excavation was approx. 1,100m2 and 5m deep, with the extent and depth limited by the proximity of the motorway (as well as the presence of groundwater).
The soil at the bottom of the excavation was highly impacted with Total Petroleum Hydrocarbons (TPHs) and BTEX compounds, with concentrations of up to 10,000mg/kg. The groundwater inside the excavation was highly contaminated, with evidence of Light Non Aqueous Phase Liquid (LNAPL) and average concentrations in the range of 500,000μg/L.
For any treatment approach on this site, to be effective in improving the groundwater quality, it would have to be able to address this secondary source in addition to treating the residual dissolved contamination. The remedial approach also needed to be rapid and effective, in order to allow for immediate back filling. This was because a delay in the construction program would result in a loss of income if the petrol station was not opened on time.
REGENESIS and the Environmental Consultant created an intelligent treatment strategy that took these challenges on board. The remediation approach comprised:
PetroCleanze has been developed by REGENESIS to enhance the desorption of contaminants from soil, so that these can be recovered by physical treatment systems. It provides a cost-effective solution for the in-situ treatment of saturated contamination and smear zones. This allows physical treatment systems to be more effective over a shorter period of time, lowering asymptotes and reducing rebound due to ongoing desorption from the smear zone.
When applied in excavation areas, application is quick and desorbed contaminants can be recovered really easily. Usually two to three application and abstraction rounds are required to remove the bulk of the contamination. PetroCleanze is an inorganic technology and therefore avoids introducing a large oxygen demand (as occurs with using surfactants) and promotes enhanced biological degradation of the residual contamination.
ORC Advanced is a calcium oxy-hydroxide based product that, when hydrated, provides a controlled-release of molecular oxygen (17% by weight) for a period up to 12 months from a single application. This product contains an orthophosphates group (patented technology) that allows for controlled release along the 12 months period.
It is typically used to create and maintain favourable aerobic condition for the biodegradation of aliphatic and aromatic contaminants present as residual mass in the dissolved phase.
Phase I Application: Enhanced Desorption and Extraction using PetroCleanze
Following the initial excavation and enhanced desorption treatment, an ORC Advanced application was completed. This targeted the residual dissolved phase contamination. The ORC Advanced provided a controlled release of dissolved oxygen in order to stimulate and maintain enhanced aerobic biological degradation of the groundwater contamination for 9-12 months from the single application. This meant that the excavation could be immediately back filled and the construction continued. The remediation of the dissolved phase contamination therefore continued in situ, with no further operational costs and no disruption to the build programme.
To optimise the application process onsite, a pelletised version of ORC Advanced was chosen. This is because they can be applied directly in the excavation without the need for pre-mixing with water. The Pellets also minimise dust formation during application. The pit application was cost-effective, as it did not require additional equipment to be used on site and the application and mixing was safe, quick and straightforward.
Phase II Application of ORC Advanced Pellets
Petroleum hydrocarbon concentrations for each sub-area before, during and after treatment