Unconsolidated deposits on the Kitsap peninsula are of glacial and interglacial origin. These deposits were divided into three units on the basis of their lithology and hydraulic properties. Two of the three units are composed of layers of sand and gravel alternating with layers of silt and clay. The third unit consists of silt and clay and in most places separates the other two units. The thickness of the upper unit ranges from 200 to 600 feet and the middle unit from 10 to 260 feet. The thickness of the lower unit is believed to range from 2,000 to 3,000 feet.
The water-bearing strata in the upper unit are fairly continuous and average 15 feet in thickness. The lower water-bearing strata probably are not as continuous as those in the upper unit, but they yield larger quantities of water to wells. The silt-and-clay unit averages 70 feet in thickness, occurs generally near sea level, and is not known to contain any major water-bearing deposits.
The average annual ground-water recharge to streams on the Kitsap peninsula was estimated to be 17 times the 1975 annual ground-water pumpage for the peninsula. Some, hut an unknown amount, of this water is available for increased withdrawal by wells. Increased withdrawals cause decreased streamflow, declining water levels, and increased seawater contamination.
There appears to be no widespread seawater contamination of wells in the study area. Local areas where chloride concentrations in well water exceed 25 milligrams per liter are the southern part of the Longbranch peninsula, Horsehead Bay, Point Evans, Sinclair Inlet, Eagle Harbor, Fletcher Bay, the north end of Bainbridge Island, and the north tip of the Kitsap peninsula.
