A supply of fresh ground water for the Squaxin Island Indian Reservation exists in saturated deposits underlying the 3.09-square-mile island, whereas surface-water supplies are practically nonexistent. Four test wells tapped a water-hearing zone of sand and gravel and had yields ranging from 27 to 170 gallons per minute, with drawdowns of about 5 feet to about 65 feet. Except for high concentrations of iron and manganese (which can be treated and reduced for domestic use), the water quality is good. Conditions for drain-field waste disposal (such as from septic tanks) are probably good in at least the northern two-thirds of the island. The potential for seawater encroachment into the water-bearing zones underlying the island is unknown but may be great in places. The danger of inducing encroachment can be minimized by maintaining pumping levels above sea level, using a network of several wells pumped intermittently into a storage facility, and spacing these wells to spread out the effects cf pumping. Monitoring of the water quality in all wells would help indicate early signs cf increasing chloride content that warn of impending seawater encroachment.
In the northern half of the island, where ground-water conditions are the most favorable, wells 100 tc 200 feet deep may yield 25 to 100 gallons per minute with minimum chances of seawater encroachment. The southern half of the island has a smaller apparent potential for ground-water development and an increased possibility of seawater encroachment.
