Assessing Vulnerability

Public Water Systems using a surface water source could be impacted by HABs. These systems should assess the vulnerability of each surface water source, even if blooms have not yet been confirmed. The Division of Drinking Water is available to help with the assessment as needed. Appendix A has two tables; A1 and A2, that provide historical and more recent data on Utah surface water sources in which the presence of cyanobacteria have previously been confirmed. Table A2 contains the most current 2017 data DWQ has compiled and identified critical water bodies most at-risk to HABs. These water bodies either serve as drinking water sources, have high recreational value, or both.

A Public Water System first evaluates its surface water/UDI groundwater sources when assessing for vulnerability to HABs and cyanotoxin contamination.

Potential information to consider when conducting a source-specific evaluation:

Source Water Considerations

Evaluation of source waters at or near the intake:

  • Source Water Physical Characteristics (e.g., inlets, outlets, detention time, range of flow rates)
  • Source Water Physical Characteristics (e.g., inlets, outlets, detention time, range of flow rates)
  • Historical data (e.g., Appendix A, Table 1 and 2)
  • Climate and Weather Information
  • Land Uses in the Watershed
  • Intake elevation(s)
  • Limnology (ie., history of stratification and occurrence of turn-over)

Water Quality Parameters

Water quality parameters can help to determine if the source water has had a history of blooms. Parameters to look for include:

  • Secchi disc depth in source water reservoirs/lakes
  • Cyanobacterial cell counts (including dominant cyanobacterial species)
  • Nitrogen and phosphorus levels
  • Dissolved oxygen levels and stratification (historical patterns/potential)
  • Local phytoplankton levels
  • Chlorophyll-a levels • Phycocyanin levels
  • Presence of taste and odor causing compounds (e.g., MIB and geosmin)
  • Zebra mussel population
  • Fish kills due to hypoxia
  • Presence of blooms and scums on the water

* Useful resources include Source Water Assessments and Lake Management Plans, as well as Clean Water Act 303(d) and 305(b) Integrated Reports.