GSI helped the City of Florence collect information and develop a source water protection plan in order to protect the City’s drinking water source as well as habitat in the Siuslaw River Watershed.

Background

The City of Florence’s drinking water is derived from the shallow North Florence Dunal Aquifer, Oregon’s only EPA-designated Sole Source Aquifer. As a result of the shallow and sensitive nature of the aquifer and the City’s desire to have a sustainable drinking water source, they needed an aquifer-wide protection plan that included both their current and future wellfields.

GSI’s Solution

We helped the City prepare an EPA grant for a Siuslaw Estuary Partnership project with the objectives to protect and restore water quality and fish and wildlife habitat in the Siuslaw River Watershed and the North Florence Sole Source Dunal Aquifer. Under the grant, GSI monitored and evaluated groundwater and surface water quality starting in 2010 and concluding in 2012. This work included:

  • Identifying the connection between groundwater and surface water.
  • Determining the variation in groundwater composition over the study area.
  • Determining seasonal variation of surface water composition and flow rate.
  • Conducting the source water assessment.
  • Based on the conceptual model, the original groundwater flow model completed by the OHA’s Drinking Water Program was updated using a 3-D numerical model.

To help the City manage its Source Water Protection Program the GSI team:

  • Conducted an evaluation of the capacity of the current wellfield and provided recommendations for wellfield management and expansion.
  • Provided technical assistance with respect to the potential impact of septic effluent on shallow groundwater within the City’s northern Urban Growth Boundary (UGB).
  • Identified the locations of 15 monitoring wells for the purpose of monitoring groundwater levels and quality.
  • Determined the Drinking Water Protection Areas for the City’s primary and proposed wellfields.
  • Identified potential contaminant sources within the capture zones of the active and proposed wellfields, and evaluated the relative risks to groundwater.
  • Provided technical assistance to a Stakeholders Source Water Protection Committee for selecting the management strategies and designing an implementation strategy to revise the City’s Source Water Protection Plan. This included:
      • Determining seasonal variation of surface water composition and flow rate.
      • Conducting the source water assessment.
      • Updated the original groundwater flow model completed by the OHA’s Drinking Water Program.
      • GSI then helped the City prepare an application for the EPA Urban Waters Small Grants Program, including writing the Quality Assurance Project Plan for the assessment and monitoring phase of the project. The City was awarded $60,000 to continue the Siuslaw Estuary Partnership project. To assist the City in meeting the objectives and goals of the new grant, the GSI team:
  • Calibrated the City’s 3-D groundwater flow model (which GSI previous developed) based on new baseline data.
  • Conducted quarterly water quality and quantity monitoring events over a two year period for groundwater and surface water sources, reported results to the city, and incorporated new data into the flow model to inform source water protection measures.
  • Produced a series of Groundwater Flow Maps showing seasonal fluctuations in groundwater flow direction.
  • Determined the relationship between rainfall and depth to the aquifer.