The federal Clean Water Act was established to restore and maintain the chemical, physical, and biological integrity of the nation's waters. Water quality standards have been established by federal and state governments to ensure that waterbodies attain their designated uses. Designated uses include human uses and ecological conditions: general aquatic life, trout, recreation, drinking water supply, industrial water supply, agricultural water supply, shellfish harvesting, and fish consumption.
As mandated by the Clean Water Act, surface water quality in all states is monitored and assessed every two years. During this time, government-employed scientists take samples of water at various waterbody sites and test them to determine whether or not that waterbody has attained its designated use(s). The designated use of general aquatic life is the most indicative of overall surface water quality and is the most comprehensively monitored across the region. Therefore, aquatic life is used as the indicator of regional water quality.
Water quality in Pennsylvania is assessed based on stream segments. Attainment (or lack of attainment) is determined by analyzing the health of aquatic macroinvertebrates (i.e. insect larvae, crayfish, clams, snails, worms) present in the stream. Pennsylvania's Department of Environmental Protection's (PADEP) assessment plan covers the entire state in 10-year increments. Interim evaluations are performed using targeted sampling in each of the state's major subwatersheds every two years. New Jersey Department of Environmental Protection (NJDEP), on the other hand, assigns attainment or lack of attainment to entire subwatersheds (land area). Similar to PADEP, this determination is based on in-stream sampling of macroinvertebrates. New Jersey's most recent report for 2014 is based on data collected between 2008 and 2012.
Since the two states do not report water quality data using the same criteria (stream miles in Pennsylvania versus acres of subwatershed in New Jersey), the percentage of non-attaining water(s) in each state is taken according to its preferred unit, and then the two percentages are averaged together to obtain a regional value.