into the surrounding area. Unlike septic tanks, cesspools provide very little treatment to sewage before releasing it to the environment, and unlike holding tanks, cesspools do not retain sewage for treatment elsewhere.

Chemical stressors

Chemicals released to the environment through industrial waste, auto emissions, pesticides, and other human activity that can cause illness and even death in plants and animals.


The application of chlorine to drinking water, sewage, or industrial waste to disinfect or oxidize undesirable compounds.


Small tank or storage facility used to store water for a home or farm; often used to store rainwater.


Clearing action that occurs during wastewater treatment when solids settle out, it is often aided by centrifugal action and chemically induced coagulation in wastewater.

Cluster OSTDS

An on-site sewage treatment and disposal system under some form of common ownership and management that provides treatment and dispersal or discharge of wastewater from two or more homes or buildings but less than an entire community. (See On-site sewage treatment and disposal system)

Coliform index

A rating of water purity based on a count of fecal bacteria.

Coliform organism

Microorganisms found in the intestinal tract of humans and animals, their presence in water indicates fecal pollution and potentially adverse contamination by pathogens.

Collector sewers

Pipes used to collect and carry wastewater from individual sources to an interceptor sewer that will carry it to a treatment facility.

Combined sewer overflows

Discharge of a mixture of stormwater and domestic waste when the flow capacity of a sewer system is exceeded during rainstorms.

Combined sewers

A sewer system that carries both sewage and stormwater runoff. Normally, its entire flow goes to a waste treatment plant, but during a heavy storm, the volume of water may be so great as to cause overflows of untreated mixtures of stormwater and sewage into receiving waters. Stormwater runoff may also carry toxic chemicals from industrial areas or streets into the sewer system.

Community water system

A public water system that serves at least 15 service connections used by year-round residents or regularly serves at least 25 year-round residents.

Consent order

A legal document, also known as a consent decree, signed by the U.S. Environmental Protection Agency (EPA) and an individual, business, or other entity, committing that entity to take corrective action or refrain from an activity. The consent order describes the actions to be taken and can be enforced in court.


Any physical, chemical, biological, or radiological substance or matter that has an adverse effect on air, water, or soil. (See also pollutant, these two terms are used interchangeably in this report.)

Conventional pollutants

Statutorily listed pollutants that are well understood by scientists. These may be in the form of organic waste, sediment, acid, bacteria, viruses, nutrients, oil and grease, or heat.

Conventional sewage system

System employing the use of demonstrated on-site sewage treatment and disposal technology in a manner specifically recognized by 25 PA Code § 73; includes septic tank or gravity absorption trenches, in-ground seepage bed, aerobic treatment system, pressure distribution absorption system, subsurface sand filter, elevated sand mound, and recycling-incinerating-composting toilets.

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