Zinc can be a particularly problematic compound on industrial sites because the source of zinc in stormwater discharges is often hard to determine. Industrial stormwater often contains a mix of metals, sediment, oil and grease, and other potential pollutants with many potential sources from your industrial site or your neighbor’s (or nearby non-industrial operations). Industrial General Permit (IGP) or Multi-Sector General Permits (MSGP) that require monitoring for zinc typically use total zinc concentration, which will include both the dissolved zinc and particulate zinc fractions in the analysis. This means that the zinc concentration you are reading on your facility’s laboratory report is potentially caused by more than one source. The best management practices (BMPs) a facility employs to reduce its zinc concentrations will need to correspond to their site-specific zinc source(s) and the fraction, particulate and/or dissolved, contributing to most of the exceedances of benchmarks. In addition, like most industrial stormwater situations, a site’s BMPs will consist of both structural (e.g. filter socks) and non-structural BMPs (e.g. site sweeping) to reduce zinc concentrations.