Groundwater Management Plan

Plan Overview

In 2023 the City hired a consulting firm, EA Engineering to continue the development of the Groundwater Management Plan. EA has been working with City staff and the Groundwater Management Sub-Committee (made up of members of the Utility Advisory Committee, the Environmental Technical Advisory Committee, and Climate Change Action Committee) to advance work on the plan.

Development of the plan can be broken up into three phases: documentation of existing conditions (complete); groundwater modeling scenarios (in process); and, plan development (started). The groundwater modeling phase of work is currently underway, and the project team is working to calibrate and improve the model for reliability, and also develop the parameters of the modeling scenario (see the 2/20/24 Council presentation link for more information). Input on the scenarios will be provided by the sub-committee and the City Council. Results and analysis from the scenarios are anticipated to be available in May 2024.

Groundwater Management Plan - Peer Review

The Groundwater Management Plan (GWMP) peer review is now available for informal public review. All related documents can be found on the Groundwater Management Plan Engage Bainbridge website.

A formal public engagement process, including an opportunity to provide written comments on all the documents - including the peer review - will be held in the first quarter of 2026.

Project Overview

Bainbridge Island residents, workers and visitors rely on groundwater for all water supply needs, from drinking water and dishwashers to toilets and garden watering. Groundwater also plays a vital role in supporting healthy streams and wetlands.

The City is developing a Groundwater Management Plan (GWMP) that will take an Island wide approach to managing our precious groundwater resource and will serve as a document that can be adapted as our needs change. The plan will include a summary of what we know about the island’s geology; groundwater systems; streams, lakes, and wetlands; climate and climate change projections; land use; and population projections.

What is groundwater?

Groundwater is water in saturated ground (bedrock or sediments) that flows from recharge areas to discharge into springs, seeps, shoreline or wells or deeper into the subsurface. If you were able to take a giant knife and slice through the water-filled layers of sediment (mixtures of clay, silt, sand, and gravel) underlying Bainbridge Island, you would see four major aquifers.

Most of the island’s residents and businesses take water from those four aquifers which can be as deep as 1,000 or more feet below the ground.

COBI Groundwater Management Program

Island Water Resources

The U.S. Environmental Protection Agency (EPA) has designated Bainbridge Island a sole source aquifer, meaning there is no other water supply source for the Island. The Washington Department of Ecology has designated the entire island a Critical Aquifer Recharge Area, which the City of Bainbridge Island requires to be protected by plans incorporated into all new development.

EPA: Support Documentation for Sole Source Aquifer Design of the Bainbridge Island Aquifer System - 2013 (PDF)

The vulnerabilities facing the City’s groundwater distribution are the mechanical systems and pipes that pump water from the ground and distribute it to homes and businesses. The City will be developing water conservation messaging and plans that will help relieve stress on systems during extreme weather events. The City is also planning for implementing water system resiliency projects and emergency measures.