Chemical Changes in Groundwater of Northern Utah Valley, Utah

Northern Utah Valley is one of the fastest growing areas of Utah and has increasing needs for domestic, industrial, and agricultural water. To meet these needs, groundwater and surface water systems must be understood to maximize their use. Chemical studies of the sediment mineralogy and related water-chemistry give insight to the movement of the water. There are three major aquifers present in the valley: shallow Pleistocene; deep Pleistocene; and Tertiary. They are composed of sands and gravels and are separated by confining layers (aquitards) composed mostly of clay. Along the flanks of the bordering mountains there are undifferentiated aquifers which act as conduits supplying water for aquifers in the valley. Sediment samples from aquifers and confining layers were obtained by rotary and cable-tool drilling. X-ray diffraction analyses showed that the aquifers are mainly composed of quartz, calcite, and dolomite, whereas the con fining layers contain illite and montmorillonite with some kaolinite, quart z and calcite. One hundred nine water samples were collected in this study from s ur face water, spring water, undifferentiated aquifer water, shallow Pleistocene aquifer water, deep Pleistocene aquifer water and Tertiary aquifer water. Results show that the ground water system has several geochemical cells in each aquifer, due to diverse areas of recharge. Three major water types can be identified in different areas of the shallow Pleistocene aquifer, three in different areas of the Tertiary aquifer, and four in different areas of the deep Pleistocene aquifer. The differences in these water types are related to the composition of the mountain recharge areas and positions of faults within the valleys. The aquifer composition exerts relatively little influence on the chemistry of the ground water. Mountains of predominantly carbonate rocks produce recharge waters rich in calcium and bicarbonate. Mountains of predominantly granitic rocks produce recharge water low in mineral content. Valley sediments near major faults produce highly mineralized waters