The D-aquifer, one of the main aquifers north of the Little Colorado River, occurs over about a 3,125 square-mile area (Figure 7). It is used for domestic supplies in the north-central parts of the Little Colorado River Plateau basin where the N and C-aquifers are too deep or have very poor-quality water. The D-aquifer is made up of the Dakota, Cow Springs, and the Entrada Sandstones. Recharge to the D-aquifer is from local precipitation and runoff from the Defiance Uplift to the east. Groundwater flows to the north, west, and south from the areas of recharge (Arizona Department of Water Resources, 1988). Some water is lost from the aquifer by downward leakage into the underlying N-aquifer. Water in the D-aquifer is of marginal- to- unsuitable chemical quality for domestic use. Eychaner (1981) reported dissolved-solids concentration in water from the D-aquifer as seven times greater than in the N-aquifer; chloride concentration was 11 times greater; and sulfate concentration was 30 times greater than water from the N-aquifer. Dissolved solids concentrations range from 190 to 4,410 milligrams per liter, generally exceeding the recommended secondary maximum contaminant level of 500 milligrams per liter for drinking water (Arizona Department of Water Resources, 1988).