Surface Water Sources

Delineation of contributing areas for surface water is more straightforward than for groundwater. EPA (1997) has identified three primary methods for source water protection area (SWPA) delineation:

  • Topographic boundary delineation (watershed)
  • Buffer zone/setback
  • Time-of-travel calculation
Although it is useful to know the limits of the entire drainage basin or catchment, it may be unrealistic to expect that a large basin could be managed for SWP purposes. Consequently, segmentation of basins into smaller sub-units allows the focusing of resources on critical areas for contaminant source identification and subsequent management.

Pennsylvania also employs a three-tiered approach to SWPA’s for surface water sources and is modeled after that used by the Ohio River Valley Sanitation Commission (ORSANCO). Zone A is a 1/4 mile buffer on either side of the river or stream extending from the area 1/4 mile downstream of the intake upstream to the five hour time-of-travel (TOT). Zone B is a two-mile buffer on either side of the water body extending from the area 1/4 mile downstream of the intake upstream to the 25 hour TOT. Zone C constitutes the remainder of the basin. The illustration shows the approach.

Illustration: Three-tiered approach to SWPA delineation for large drainage basin used by surface-water source.