Step 2: Map/Delineate Protection Zones

This scientific, technical portion of the SWP answers the critical question: WHERE DOES YOUR WATER COME FROM?

Delineation is the process used to identify and map the area around a pumping well that supplies water to the well or spring, or to identify and map the drainage basin that supplies water to a surface water intake. The size and shape of the area depends on the characteristics of the aquifer and the well, or the watershed.

Delineation considers the characteristics of water flow in the aquifer or drainage basin and then narrows the focus to show areas where potential releases of certain contaminants would be most likely to end up in the community’s water supply. In Pennsylvania, the delineated source water protection area is further divided into regions called ZONES to enable a water system to adopt different management strategies based on separation distances between a potential contaminant source and the well or intake.

Three Zones for Surface Water Sources

There are 115 watersheds in Pennsylvania with an area of more than 100 square miles that provide source water for public water systems. For non-point source and microbiological contaminants of concern, a critical area analysis is conducted for each surface water intake, based on existing water quality data and the physical characteristics of the watershed; the analysis includes critical areas for nitrate, pathogens, sediment loading and metals. When available, assessments for stream impairment and TMDL determinations are used to delineate critical areas.

For these large watersheds (area > 100 square miles), a three Zone approach is used.

Zone A is an area ¼ mile wide on either side of the river or stream. It extends from an area ¼ mile downstream of the intake to an area that is 5-hour time of travel (TOT) upstream (based on the 3 year average, using maximum local river velocities).

Zone B is a two mile wide area on either side of the river or stream, extending upstream to a 25-hour TOT (based on the 3 year average, using maximum local river velocities from February 1995 to February 1998).

Zone C is the remainder of the watershed, but can be refined by consideration of river hydraulics to determine channeled flow and critical contributing tributaries. Critical contributing tributaries are tributaries that contribute significant flow to the surface water intake, and therefore, have the potential to contribute significant contaminant loads.

For watersheds with an area less than 100 square miles, a Zone A is delineated. The remainder of the watershed is inventoried as a Zone B.


To learn how Groundwater Sources are mapped, click here>>
Sounds complicated–but DON’T WORRY: YOU’RE NOT IN THIS ALONE!

The 1996 SDWA amendments require states to develop a Source Water Assessment and Protection (SWAP) program. Under Pennsylvania’s SWAP, source water assessments have been conducted for 98% of PA public water systems; the assessments include delineation of the boundaries of the areas providing source waters and the identification (to the extent practicable) of the origins of regulated and certain unregulated contaminants in the delineated area to determine the susceptibility of the water sources to such contaminants. These assessments offer a good starting point for a system looking to better understand potential threats to its sources and seeking to begin developing protection strategies.

The Source Water Protection Technical Assistance Program (SWPTAP) provides NO COST ASSISTANCE for public water systems looking to conduct a more rigorous delineation and develop and implement a customized, community-specific Source Water Protection plan.  LEARN MORE >>

Why are some public water supply wells more vulnerable to contamination? Check out the USGS Resources here>>

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