of concentrations below which adverse effects (relatively) rarely occur. The 50th percentile of the ranked data is identified as the ERM, and is indicative of concentrations above which adverse effects (relatively) frequently occur. Government agency use Sediment Quality Guidelines (SQGs) are used by US federal agencies, state agencies, and environmental consulting firms to characterize toxic levels of chemicals in marine and freshwater sediment. Following here is a summary of how the ERL/ERM guidelines are used by the National Oceanic and Atmospheric Administration, United States Geological Survey (USGS), and the United States Environmental Protection Agency (EPA). NOAA NOAA scientists use SQGs as a way to estimate if a concentration of contaminant in a sediment sample may have toxicological effects. The original intent of using SQGs was to rank order areas that may need further toxicological testing and potential chemicals of concern. Across the United States, NOAA has used these guidelines in regional surveys to determine the degree of contamination relative to other areas, and to identify if the concentration of a chemical exceeded guidelines, indicating a possible adverse effect. NOAA also reports ERLs and ERMs, along with other guidelines, on tables known as Screening Quick Reference Tables (SQuiRT) cards. These tables offer values that may be used in the preliminary screening of sediment or other media for toxic hazards. USGS The USGS makes use of both ERL and ERM on a case-by-case basis. During a study involving the concentration of heavy metals, pesticides, and semi-volatile organic compounds in stream sediments from the Schuylkill River within the Valley Forge National Historical Park, the USGS used the ERL and ERM to determine locations that could potentially pose a threat to living organisms. The USGS has also integrated ERL and ERM values into an Alert Range Table, a table that provides ranges of contaminant concentrations that predict the likelihood of adverse effects occurring in benthic organisms for the Lake Pontchartrain Basin in Louisiana. Both the ERL and ERM have proven to be useful guideline values for predicting toxicity during studies conducted by the USGS. EPA The EPA uses ERL and ERM values as a type of sediment “benchmark”. They define a benchmark as a concentration that, when exceeded, has the potential to cause harm or significant risk to humans or animals in the environment. The EPA has also used ERL and ERM values for sediment contamination studies. Assessment categories defining the condition of sampled