Introduction to HydrogeologyJanuary 26, 2011

Thomas Seckington, P.G., C.HG.Senior Engineering Geologist

California Environmental Protection AgencyDepartment of Toxic Substances Control

tseckington@dtsc.ca.gov714-484-5424

GROUNDWATER

• Groundwater is one of the nation’s most valuable resources

• 14 percent of all freshwater is groundwater

• If only water is considered (omitting ice in glaciers), 94 percent of all freshwater is groundwater

• Groundwater exists nearly everywhere

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• Most rock near the Earth’s surface are composed of both solids and voids

• Consolidated rocks consist of soil, sand, and/or mineral particles welded by heat and pressure or cemented by chemical reactions

• Unconsolidated deposits consist of loose soil, sand, and/or minerals

ROCKS AND WATER3

• Voids formed at the same time as the rock are referred to as primaryExample: pores in sand and gravel

• Voids formed after the rock was formed are referred to as secondaryExample: fractures and caverns

• Sandstones have both primary and secondary openings

Secondary

Primary

THE VOIDS4

• Ratio of voids to the total volume of the rock is its porosity

POROSITY AND WATER5

WATER UNDERGROUND

• Water occurs in two different zones: unsaturated and saturated• Unsaturated zone: openings have both air and water• Saturated zone: all interconnected openings full of water

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AQUIFERS AND CONFINING BEDS

• An aquifer is a rock unit that will produce water • A confining bed is a rock unit that restricts the movement of

groundwater

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FAULTS

• Fault zones can act either as barriers OR conduits to groundwater flow

• Depends on the nature of the fault zone materials; grounded to a powder ORbroken up and fractured

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GROUNDWATER SYSTEMS9

GROUNDWATER VELOCITY

• Groundwater velocities are generally slow; feet to thousands of feet per year

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GROUNDWATER CONTAMINATION

PLEASE NOTE: The areas with wells containing detected concentrations and/or concentration over a regulatory threshold are shaded with a corresponding color for better visual presentation. The shaded areas should not be considered interpretations on the distribution and extent of these contaminants in the groundwater

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UPCOMING MEETINGS• General Hydrogeology

Dr. Richard Laton, CSUFMarch 8, 2011

• Contaminant Fate and TransportDr. Matt Becker, CSULBMarch 15, 2011

• Groundwater CleanupDr. Allen Shapiro, USGSApril 5, 2011

• SSFL Groundwater Flow, Contaminant Sources, Fate of ContaminantsDr. John Cherry, Dr. Beth Parker, and Dr. Dave McWhorterApril 28, 2011; May 5, 2011; and May 19, 2011

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Discussion/Questions13