"No water woes, report saysThe island should have plenty, even at zoning buildout."
June 9, 2008 · Updated 3:33 PM
"Contrary to concerns that Bainbridge Island's growth is outstripping its water supply, a detailed new study shows that the island has an abundance of good-quality underground drinking water lying relatively close to the surface.We have our soggy climate to thank.The study, by consultant Richard Warren of the Seattle engineering firm of Kato and Warren, shows that rainfall is providing the water-bearing aquifers under the island with almost six times as much water annually as is being used.In terms of total available groundwater, it looks like the island can reach the goals it set for itself, Warren said.That means there is plenty of water to allow the island to reach its projected population growth. In fact, the study shows that at the present rate of use, there is enough water to support an island population of well over 100,000 people - a number nobody expects to see for a very long time indeed.This is a very well done study, city council member Michael Pollock said. It allays fears about water availability.Warren said that the island's water issues tend to be localized - spot shortages, wells drilled in the wrong place and distribution-system problems.The south end - south of Eagle Harbor - is more at risk of shortages, and at some point development will feel a pinch, he said. But the north and central portions of the island lie on top of several prolific aquifers, he said.The study produced a water budget that balanced supply and demand. It looked at weather data and determined that over the long term, the island receives an average annual rainfall of 35 inches. Calculations indicated that about 15 inches is lost to evaporation, and seven inches to runoff, leaving 13 inches to recharge the aquifers.Spreading 13 inches of water of the island's 17,600 acres yields an annual recharge of 19,000 acre feet, the study says.An acre-foot of water - the amount required to cover an acre with water one foot deep - is roughly 325,000 gallons, enough to satisfy the annual requirements of almost seven people, the study says. Current island population estimates range from about 20,000 to 25,000 people, which would indicate water use of 3,000 to 3,700 acre feet per year.And if all the buildable lots on the island were developed, the estimated population would be roughly 35,000 to 40,000 people, according to long-range planner Marti Stave. That number would still use less than 6,000 acre feet of water annually.With present zoning, water is not likely to be the limiting factor in growth, Warren said.Good to drinkWater quality is also excellent, the report says. Of the 983 wells that were examined - virtually all the wells on the island - only 13 showed above-background levels of chlorine, indicating that saltwater intrusion is a negligible problem. No well exceeded health standards for nitrates - a pollutant that comes from septic failure or fertilizer getting into the groundwater.A number of wells, mainly those drilled into very shallow aquifers, showed elevated quantities of iron and manganese. The report says those naturally occurring elements do not pose a health problem but only an esthetic problem - the water looks dirty.In general, the water problems that do exist stem from excessive reliance on very shallow sources of water, Warren said - those aquifers that lie above sea level.Pollock said use of the above-sea-level aquifers should also be discouraged because those are the sources of many island streams.The report said greater use should be made of two large and productive aquifers, the so-called Fletcher Bay Aquifer, which supplies most of the municipal water supply, and what is called the Sea Level Aquifer, a relatively shallow formation that underlies some 85 percent of the island.Warren also said that water-pressure problems, which can be an issue for firefighting, stem from inadequate distribution systems, not insufficient water.In some places you need bigger pipes, he said. Pollock said the report may have resolved the question of whether water supply is adequate, but it points out a policy issue that needs to be addressed, namely, whether to move to a more integrated water system and away from reliance on individual wells.In some areas of short supply, it may make more sense to take the water to the people through a better distribution system rather than have everybody dig their own well, he said.A summary is available on the city web site, with the full report available for review at city hall, and for purchase at Custom Printing and Sound Reprographics. "