A few different methods are commonly used to determine the acid-producing potential of sulfide bearing materials. In our lab in the CSES department at Virginia Tech, the Potential Peroxide Acidity (PPA) method is used. This method involves rapidly oxidizing a sample of soil with hydrogen peroxide and then measuring the amount of acidity produced. The results are expressed as a calcium carbonate equivalent: i.e. how much lime must be added to neutralize the acidity.