Aquifer Recharge Area Study of Guemes Island

Science Center Objects

The Issue: Guemes Island is an 8.2-square-mile island in the northern part of Puget Sound in western Washington State. The population of the island is increasing, as is the demand for groundwater, which is the island's sole source of freshwater. Continued growth and development of the island, particularly in nearshore areas, has led to the increasing failure of nearshore wells due to seawater intrusion. The degradation of the island’s groundwater has led to a renewed urgency to better understand and protect the fragile groundwater system of the island. 

How USGS will help: To help the Guemes Island Planning Advisory Committee better understand the island's water resources, the USGS will conduct an evaluation that will include Guemes Island's aquifer recharge to its groundwater system, water use, and current groundwater conditions. 

Guemes Island

Guemes Island shoreline

(Public domain.)

Problem: Guemes Island is an 8.2-square-mile island in the northern part of Puget Sound in western Washington State. The population of the island is increasing, as is the demand for groundwater, which is the island's sole source of freshwater. Continued growth and development of the island, particularly in nearshore areas, has led to the increasing failure of nearshore wells due to seawater intrusion. The degradation of the island’s groundwater has led to a renewed urgency to better understand and protect the fragile groundwater system of the island. 

Objectives: To sustainably manage the island’s groundwater resources, an analysis of water budget components is an important next step in characterizing the availability of good-quality groundwater for island residents.  The specific objectives of this study are to describe aquifer recharge areas, provide better estimates of rates of recharge to the groundwater system, provide updated water use and water balance information for the island, and evaluate current groundwater conditions. 

Relevance and Benefits: Completion of the proposed work will provide information about the aquifer recharge areas and water budget components of Guemes Island and lay the groundwork for potential future studies to describe the groundwater flow system of the island. These data will also add to the USGS national database and will assist in understanding and describing the Nation’s water resources. The study will generate a published report and data sets that will be publicly accessible online. This proposed study also addresses the USGS Water Mission Area priorities of (1) expanding and enhancing water-resource monitoring networks, (2) delivering water data and analyses to the Nation, and (3) conducting integrated watershed assessment, research, and modeling (Evenson and others, 2013). 

Approach: To meet the objectives of this study, the following tasks will be completed: (1) make an island wide recharge estimation using the USGS Soil-Water-Balance (SWB) model; (2) compile or estimate groundwater withdrawals by water-use category and describe a water balance for the island and the fate of precipitation (surface runoff, evapotranspiration, groundwater recharge, interception, and change in soil moisture); and (3) evaluate current (2021) groundwater conditions by characterizing groundwater flow directions and gradients.