Ground-water hydrology of the Lower Milliken-Sarco-Tulucay Creeks area, Napa County, California

Water-Resources Investigations Report 77-82



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The Sonoma Volcanics are the principal water-bearing materials in the lower Milliken-Sarco-Tulucay Creeks area, which occupies about 15 square miles in and east of Napa, Calif. The distribution and composition of these volcanic units are highly variable and complex. Annual pumpage of 3,000 acre-feet, mostly from the Sonoma tuffs, represents a significant portion of the ground-water discharge. The seasonal change in ground-water storage was about 6,600 acre-feet in 1975. Water-level data from the area reflect the seasonal change in ground-water storage, with fluctuations of 3 to 60 feet. The storage capacity to a depth of 500 feet may be as much as 196,000 acre-feet in the study area, but physical and economic factors may restrict the usable capacity to about 20,000 acre-feet. Recharge is generally inadequate to marginal under 1975 demand. There is insufficient recharge in the Milliken and Sarco Creeks area to support 1975 pumpage. Long-term changes in the seasonal peak water levels indicate an average decline of 1.5 feet per year. By 1975 annual pumpage was not exceeding recharge in the Tulucay Creek area. Although a downward trend in water levels was noted in the western part of this basin in the late 1940's, the pumping distribution and its stress on the ground-water system have since changed, and no overall downward trend was evident in the Tulucay Creek area in 1975. (Woodard-USGS)

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USGS Numbered Series
Ground-water hydrology of the Lower Milliken-Sarco-Tulucay Creeks area, Napa County, California
Series title:
Water-Resources Investigations Report
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U.S. Geological Survey, Water Resources Division,
v, 40 p. :ill., maps (some fold. in pocket) ;27 cm. --