The Hollister and San Juan Valleys are within the Gilroy-Hollister groundwater basin. That part of the groundwater basin underlying the valleys consists of three subbasins each of which contains two or more groundwater subunits. The subbasin and subunit boundaries are formed by known or postulated faults, folded sedimentary rocks, and igneous rocks. The principal water-bearing units are lenticular beds of sand and gravel interbedded with clay, silt, sand, and gravel, or their locally consolidated equivalents, which range from Pliocene to Holocene in age. Ground water occurs mainly under artesian or semiartesian conditions but also under unconfined (water-table) conditions in areas adjacent to most surface streams and, locally, under perched or semiperched conditions. In 1968 the depth to water in wells ranged from approximately 20 feet above land surface to more than 200 feet below land surface. Water-level differences in wells across the boundaries of adjacent subunits ranged from about 10 to more than 100 feet. 2 GROUNDWATER HYDROLOGY, HOLLISTER AND SAN JUAN VALLEYS, CALIF. Withdrawals of ground water for irrigation began in 1878. Since that time water levels in wells have declined more than 180 feet in the Hoilister Valley and more than 100 feet in the San Juan Valley. Serious declines in water levels probably did not begin, however, in most of the area until after 1945. Since 1945 large cones of depression have formed in each of the major subbasins. The centers of the cones are approximately one-half mile northeast of Hoilister in the Hollister subbasin, 1% miles northwest of Hollister in the Gilroy-Bolsa subbasin, and one-half mile east of San Juan Bautista in the San Juan subbasin. Groundwater movement beneath both valleys is now toward and into the cones. Ground water in the eastern part of the Hollister Valley locally contains objectionable concentrations of boron and chloride. However, available data indicate that significant changes in the distribution patterns of these constituents have not occurred since 1939. INTRODUCTION According to present plans, 273,000 acre-feet of water will be delivered annually through the U.S. Bureau of Reclamations San Felipe Division of the Central Valley Project to be apportioned to Hollister and San Juan Valleys in San Benito County, to the Pajaro Valley area of Santa Cruz and Monterey Counties, and to Santa Clara County. The Bureau's feasibility report of the San Felipe Division of the Central Valley Project, California, recommended that 46,000 acre-feet of this water be allocated to San Benito County for supplemental irrigation of approximately 33,000 acres of land (County of San Benito Imported Water Advisory Commission, 1968, p. 15). Most of this water will be used for irrigation and municipal supply; the imported water will constitute nearly one-third of the total estimated water requirement of the area under conditions of anticipated development. Some of the imported water may be percolated to recharge the groundwater basin.
Plates 1 and 2. Haps of Nassau County showing: 1. Location of public water-supply wells from 1920 to 1977 and boundaries of water-supply areas 2. Location of nonpublic water-supply wells that are required to report groundwater pumpage and other wells for which groundwater pumpage is available TABLES Explanation of columns and abbreviations in Tables 1 and 2.
Occurrence of ground water_________________________________________ General groundwater conditiOns m the Western Coal Field regiOn__ FluctuatiOn of water levels______________________________________ Water m the alluviUm__________________________________________ 18 Water m the bedrock__________________________________________ 21 Deterrnmmg the availability of ground water at a gtven site________ 23 SuggestiOns for further studies__________________________________ 25 Methods of obtammg ground water__________________________________
Purpose and scope of investigation_____________________________ 2 Acknowledgments _____________________________________________ 3 Location of the area.__________________________________________ 3 Surface-water supply and operational problems._____-___-__-_____ Well-numbering system________________________________________ Physical setting ___________________________________________________ 6 Surface features and drainage__________-_____-___-__-_-________ Climate ______________________________________________________ Volume and disposition of precipitation.____-_______-__-_-__-_-Influence of topography on local water supply___________________ Status of development on the reservation.________________________ Groundwater geology____________________________________________ Geologic features that affect the water supply.
Hydrogeology and Ground-Water Quality of theNorthern Part of the Town of Oyster Bay,
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.