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Groundwater Rule Background Information
General Background and How to Obtain Additional Information
  • We used the information found in Source Water Assessment Reports (i.e., SWA Rpts) to identify which water systems should be conducting 12-months of Source Assessment Monitoring. Water system regulators (i.e., Oregon Drinking Water Services (DWS), County, and Oregon Department of Agriculture) may not have a complete set of SWA Rpts in their files. The DWS Springfield Office can provide SWA Rpts to water system regulators or to the water system itself. Most of these reports are already scanned as electronic files.
  • Water system regulators should contact the DWS Hydrogeologist for the region if there are questions regarding a particular water system on the list, or contact the DWS Groundwater Coordinator about the process we used to identify the systems on the list. Contact information for the above individuals is listed below:
    Regional Hydrologist or Groundwater Coordinator
    Oregon Drinking Water Services
    444 "A" St
    Springfield, ORĀ  97477
    ph. 541-726-2587
    fax. 541-726-2596

Susceptibility Criteria
  • Some viruses are believed to survive as long as two years in groundwater. Since fecally derived viruses are of most concern (because they can cause acute illness), our Assessment Monitoring list consists of water systems identified as being susceptible to fecal contaminant sources located within their two-year water supply zone.
  • If a water system is identified as susceptible, both of the following conditions are true:
    • DWS believes the aquifer and/or well/spring construction is sensitive to contamination, and
    • There has been a fecal contamination source identified within the 2-year "Time-of-Travel," "Outreach Area," or Zone 1 (see Glossary below for definitions).
  • Aquifer sensitivity is based on several factors (e.g., water depth, aquifer material, historical monitoring results) that are addressed in the SWA Rpt for the water system. Well and spring construction sensitivity (also addressed in SWA Rpt) is evaluated based on the Oregon Department of Water Resources and DWS construction standards. If the well or spring is inadequately constructed (or there is no information on file regarding the construction) it is considered sensitive to contamination. Should a water system have a question regarding why they are considered susceptible to viral contamination, water system regulators can consult either the SWA Rpt for the water system or consult with the DWS Regional Hydrogeologist (see contact information above).

Glossary and Useful Definitions
  • 2-year Time-of-Travel Zone: Refers exclusively to C and NTNC water systems that have wells. It identifies the 2-year water supply around the well(s) and is represented on the delineation map included in the SWA Rpt for the Water System (typically as Figure 1). On the delineation map for these water systems, there are multiple Time-of-Travel Zones identified that represent a 1-year, 2-year, 5-year, and a 10/15-year water supply. Contaminant inventory results for the 2-year Time-of-Travel Zone are given on the Potential Contaminant Source (PCS) Inventory Map and in the Appendix materials at the back of the report (note that surface water is also considered a fecal contaminant source, but may not always show up in the potential contaminant source inventory, so you may have to review the map). Note that PCSs are number-coded on the map and in the report appendix.
  • Outreach Area: Refers exclusively to TNC water systems. It is an approximation of the 2-year water supply around the well(s)/spring(s) and is identified on the delineation map included in the SWA Rpt for the water system. Unlike the 2-year Time-of-Travel Zone (see above), it is the only area identified on the delineation map. Multiple Time-of-Travel Zones are not identified for these water systems because under the Groundwater Rule, we are only concerned about acute illness threats which are typically associated with fecal contaminant sources. Until there is evidence to disprove our current understanding, we do not consider those same acute illness threats to be viable outside the Outreach Area.
  • Recharge Zones (i.e., Zone 1): Refers to C and NTNC water systems that have springs. It identifies the portion of the watershed most likely to be contributing near-term groundwater to the spring (i.e., the travel time from the point of recharge, through the aquifer, to the spring is less than 2 years). It is our best estimate of what would likely be a 2-year Time-of-Travel Zone. Other zones (Zone 2, Zone 3.....) may also occur on the delineation map.