WRIA 16 Hydrogeologic Study

Client:
WRIA 16 Planning Unit

Location:
Jefferson & Mason Counties, WA

Project Background & Challenges

As population grows in the Brinnon area, groundwater withdrawals are expected to increase in response to higher water demands. Resource managers are concerned about impacts to the Dosewallips River because wells may intercept groundwater discharging to the river, reducing flows. Although impacts would be greatest during the summer and fall, when salmon spawn, these fish rely on adequate flows during other seasons to support various life-cycle processes. Because of insufficient hydrologic data and other factors, regulators have not set a minimum instream flow for the Dosewallips. In addition, seawater intrusion could impact water quality if groundwater development does not proceed in a technically sound manner.

Solution

Aspect worked with the WRIA 16 Planning Unit to design a hydrogeologic study that focuses on characterizing aquifer geometry, groundwater flow patterns, and hydraulic continuity between groundwater and surface water in the Brinnon vicinity. To characterize the aquifer system, we analyzed existing hydrogeologic and stratigraphic data, surveyed wells, measured groundwater levels, and developed water level maps and GIS coverages. We also collected samples for analysis of major ions and naturally occurring isotopes. A network of mini-piezometers facilitated the measurement of groundwater levels along four reaches of the lower Dosewallips River; we also gauged the river along these reaches. The information we collected will help resource managers make science-based decisions for this section of the watershed.