One liter of gasoline can contaminate 1,000,000 litres of groundwater. Approximately 50% of the steel storage tanks that were installed underground in 1950s and 1960s starting leaking within 15 years of installation. We are talking about 65+ years worth of contamination that has likely travelled to neighbouring properties!
Remediation is expensive. We have heard stories from investors who have sold all their properties to remediate that one piece of contaminated land. Phase One Environmental Site Assessment will reduce your future liability.