§ 96.1. Definitions.
The following words and terms, when used in this chapter, have the following meanings, unless the context clearly indicates otherwise:
Concentration—The amount of a substance, expressed in mass units, in a unit volume of water or wastewater.
Conservative substance—A pollutant that undergoes no or minimal transformation or decay in a water system, except by dilution.
Cumulative loading—The sum of pollutant loadings from individual pollutant sources.
Factor of safety—A margin to take into account uncertainty concerning the relationships between effluent limitations and water quality.
Harmonic mean flow—The flow that is determined by taking the reciprocal of the arithmetic mean of reciprocals of daily flow values.
LA—Load allocation—The portion of a surface water’s loading capacity that is assigned or allocated to existing and future nonpoint sources and natural quality.
Lake, pond or impoundment—A surface water with a hydraulic residence time of 14 days or more based on average annual daily stream flow. Residence time shall be determined at average annual daily stream flow and normal pool volume. In the absence of actual records, an average annual daily discharge rate of 1.5 CFS per square mile shall be used.
Loading capacity—The greatest amount of loading that a surface water can receive without violating a water quality standard.
Margin of safety—The portion of a surface water’s loading capacity that is set aside to account for uncertainty about the relationship between pollutant loadings and resulting surface water quality, including any uncertainty or imprecision in mathematical models used to determine these relationships. For nonconservative substances, any imprecision or uncertainty concerning the mechanisms by which the substance decays or is transformed shall be considered.
Mass load—The pollutant loading expressed in units of mass per unit time.
NPDES or National Pollutant Discharge Elimination System Permit—A permit issued under Chapter 92 (relating to National Pollutant Discharge Elimination System permitting, monitoring and compliance) for the discharge or potential discharge of pollutants from a point source to surface waters.
Natural quality—The water quality conditions that exist or that would reasonably be expected to exist in the absence of human related activity.
Nonconservative substance—A pollutant whose concentration in the water column changes as a result of volatilization, photolysis, hydrolysis, biodegradation, transformation, or other processes, except dilution.
Nonpoint source—A pollutant source which is not a point source discharge.
Nonpoint source restoration plan—A nonpoint source management plan which describes needed actions to restore and improve water quality in a watershed or stream.
Point source discharge—A pollutant source regulated under the NPDES permit system as defined in § 92.1 (relating to definitions).
Pollutant—Any contaminant or other alteration of the physical, chemical, biological, or radiological integrity of surface water which causes or has the potential to cause pollution as defined in section 1 of The Clean Streams Law (35 P. S. § 691.1).
Potable water supply—A water source that is used by humans after conventional treatment for drinking, culinary and other purposes such as inclusion in food products.
Q7-10 flow—The actual or estimated lowest 7 consecutive-day average flow that occurs once in 10 years for a stream with unregulated flow, or the estimated minimum flow for a stream with regulated flow.
Q30-10 flow—The actual or estimated lowest 30 consecutive-day average flow that occurs once in 10 years for a stream with unregulated flow, or the estimated 30 day average minimum flow for a stream with regulated flow.
Reserve factor—A portion of the effluent flow held to provide for projected future wasteloads.
Surface waters—Perennial and intermittent streams, rivers, lakes, reservoirs, ponds, wetlands, springs, natural seeps and estuaries, excluding water at facilities approved for wastewater treatment such as wastewater treatment impoundments, cooling water ponds, and constructed wetlands used as part of a wastewater treatment process.
TMDL—Total maximum daily load—The sum of individual waste load allocations for point sources, load allocations for nonpoint sources and natural quality and a margin of safety expressed in terms of mass per time, toxicity or other appropriate measures.
WLA—Wasteload allocation—The portion of a surface water’s loading capacity that is allocated to existing and future point source discharges.
WQBEL—Water quality based effluent limitation—An effluent limitation based on the need to attain or maintain the water quality criteria and to assure protection of existing and designated uses.
Water quality criteria duration—The averaging period associated with a water quality criterion.
Water quality standards—The combination of water uses to be protected and the water quality criteria necessary to protect those uses.
Wetlands—Areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions, including swamps, marshes, bogs and similar areas.
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