Step 3: Identify and Prioritize All Potential Sources of Contaminants

Many drinking water contamination problems arise from people’s everyday activities. Contaminants can be introduced into ground water, rivers, lakes, and streams from a variety of sources: septic tanks and cesspools; surface impoundments; agricultural activities; landfills; lawn care and gardening; underground storage tanks; abandoned wells; accidents; storm water systems; illegal dumping; and highway de-icing are examples.

The Safe Drinking Water Act requires that all public water systems in the U.S. supply drinking water that complies with the primary and secondary Maximum Contaminant Levels (MCLs).  Understanding where contaminants come from, and preventing, reducing or managing them in source water areas can improve a system’s raw water, prevent future contamination, and reduce treatment costs.

A wide range of contaminants may be present in raw source water before it is treated, including:

  • Microbial contaminants, such as viruses and bacteria, which can come from sewage treatment plants, septic systems, agricultural livestock operations, and wildlife.
  • Inorganic contaminants, such as salts and metals, which can occur naturally or result from urban stormwater runoff, industrial or domestic wastewater discharges, oil and gas production, mining, or farming.
  • Pesticides and herbicides, which can come from a variety of sources such as agriculture, stormwater runoff, and residential uses.
  • Organic chemical contaminants, including synthetic and volatile organic chemicals, which are by-products of industrial processes and petroleum production and can also come from gas stations, urban stormwater runoff, and septic systems.
  • Radioactive contaminants, which can occur naturally or as the result of oil and gas production and mining activities.

It’s important to have a thorough inventory that takes into consideration all POTENTIAL SOURCES OF CONTAMINATION (PSOCs) that could affect the water system. PSOCs for public water systems are identified in DEP’s Source Water Assessments and Source Water Protection Plans. Each PSOC is ranked according to the level of risk it presents to the water supply (A=highest risk through F=lowest risk).

A finalized list of PSOCs sets priorities for strategic planning purposes by categorizing PSOCs and focusing effort on those which are high risk (ranked A and B) and found in Zones I and II (groundwater), and/or Zones A and B (surface water).

The more obvious potential sources of contamination are POINT SOURCES. LEARN More >>
In many areas, NONPOINT SOURCES pose an equal or greater risk. Learn MORE >>
GAS DRILLING in the MARCELLUS SHALE formation is an increasing area of concern.  MORE INFORMATION >>


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