Is Bainbridge running out of water?
We frequently hear at local meetings and in Bainbridge social media that Bainbridge is running out of water. As most people know, the current domestic water supply on Bainbridge is from groundwater. What is the status of that groundwater resource? To begin to answer this complex question the City of Bainbridge Island in 2006 partnered with the United States Geological Survey (USGS) to develop a model of ground water recharge and withdrawal on the Island with the goal to predict impacts of both past and future development. The report for this project was published in 2011. The report identified 11 hydrologic units within the Bainbridge aquifer system: five relatively permeable layers (aquifers) and six relatively non-permeable (confining) layers. The report described the construction of a numerical (computer) model of this aquifer system and its assumptions about precipitation, recharge, withdrawal rates and sea level.
The model was used to predict impacts on ground water levels in 2035 based on three different assumptions for population growth and recharge:
1) Minimal impact (26,000 population by 2035, higher than expected recharge),
2) Expected impact (32,000 population by 2035, expected recharge) and
3) Maximum impact scenario (50,000 population by 2030, approximately 60,000 by 3025, less than expected recharge).
Water levels were predicted in each of the five major aquifer units for each scenario. The findings of the study were that ground water levels were expected to decline by zero to five feet in most aquifers but there could be isolated declines up to 25 feet. For the minimal scenario level declines were less and for the maximal impact scenario somewhat higher, but no saltwater intrusion was predicted in any scenario except that in the maximum impact scenario the report said that “saltwater intrusion likely would occur in that aquifer unit (the deep aquifer) along the northern and eastern coastlines at a future date under continued exposure to these conditions.”
So, is Bainbridge running out of water? The USGS study shows that to manage water demands from greater than 50,000 persons on Bainbridge Island we will need to make changes in our water supply system. BREAK What are some policy and technical changes that could be made to manage our water supply differently in the future?
We could institute Island-wide conservation policies to minimize water use.
We could use alternative surface water sources on the Island with appropriate treatment. Since approximately two thirds of the Island’s commercial water customers are customers of the Kitsap Public Utility District, the KPUD could implement a water transfer from other sources in Kitsap County.
The Town of Port Gamble recently installed a wastewater treatment and recharge system to replace the old wastewater treatment plant that discharged to the harbor. This system removes pollutants including nitrates and recharges to groundwater using a drain field system. Similar systems could be used in future on Bainbridge.
Perhaps a better way to look at this is that while it is up to us to manage our growth sustainably for the generations that will follow us, there are solutions to water supply challenges. We just need to pay attention to both the management and the solutions.
The City is actively monitoring water levels and salt water intrusion. We will discuss that in an upcoming post.