Hydrogeology 101

W. Richard Laton, Ph.D., PG, CPGAssociate Professor of HydrogeologyCalifornia State University, FullertonDepartment of Geological Sciences

Hydrogeology 101

The objective is to obtain a better understanding of the principles of groundwater, hydrologic cycle and water budgets. The lecture will also cover various types of aquifers and general groundwater quality. 

Objective

To understand Basic definitions Hydrologic Cycle Groundwater Aquifers How water flows Water Budgets Wells Water Quality Contamination Investigation Tools

Definitions

Water on Earth Hydrologic Cycle Meteorology

weather Hydrology

Surface water Hydrogeology

Groundwater

Unsaturated Zone Vadose Zone

Aquifers Water Table Unconfined Confined

Darcy’s Law Safe Yield Water Chemistry

Distribution of H2O

on Earth

Hydrologic Cycle

Meteorology

Climate Precipitation

Rain Snow

Temperature Other factors

Location Altitude

Rain Shadow Deserts

Surface Water

Ocean, Lake, Pond River, Stream Spring, Wetland

Surface Water Flow

Discharge Baseflow Flood Stage Gaining Stream Losing Stream

Gaining - Losing

Groundwater

Water contained in spaces within soil and bedrock

Less than 1% of all H2O on Earth

40 times more abundant than water found in lakes and streams

Groundwater

zone of aeration:  portion of soil and rock near the surface in which open spaces are filled primarily with air (a.k.avadose zone, unsaturated zone) 

saturated zone: zone in which pore spaces are filled with water

water table:   boundary between zone of aeration and saturated zone

Groundwater terms

aquifer:  body of rock that is sufficiently water permeable to yield economically significant quantities to wells and springs

Unconfined vs Confined  aquitard:  body of rock that retards but does not prevent flow of water to or from an adjacent aquifer

aquiclude:  body of relatively impermeable rock that is capable of absorbing water slowly but does not transmit it rapidly enough to supply a well or spring

More groundwater terms

Impacts of Faults on Groundwater Flow

Barriers to Groundwater Flow

Conduits of Flow

Perched Water Table

Confined Aquifer

Aquifers

Vadose Zone

Unconfined Aquifer

Aquitard

Confined Aquifer

Water Table 

Isotropy/AnisotropyHomogeneous/Heterogeneous

Isotropy – The condition in which hydraulic properties of the aquifer are equal in all directions.

Anisotropy – The condition under which one or more of the hydraulic properties of an aquifer vary according to the direction of flow.

Homogeneous – A geologic unit that has the same properties at all locations. 

Heterogeneous – Hydraulic properties vary spatially.

porosity:  portion of volume of a material that consists of open spaces

permeability:  measure of the speed at which fluid can travel through a porous medium

Imagine two vertical pipes, one filled with gravel, one with sand.  Out of which one will the water flow faster? 

Soils and rocks are not completely solid

Poorly‐sorted Sandstone

Well‐sorted Sandstone

Fractured / Unfractured Shale

Porosity and PermeabilityPrimary and Secondary Porosity

Hydraulic ConductivityTransmissivity

Slow to very slow (depending on permeability)

Generally within the range of 10 to 100 cm per day

Rates of groundwater movement

Q = discharge (m3/sec)A = cross-sectional area (m2)K = coefficient of permeability (m/sec)h1 = beginning height (m)h2 = ending height (m)l = length of flow (m)

Darcy’s Law

Q = AK(h1– h2)l

Groundwater Movement in Temperate Regions

Wet Period

Dry Period

In = Out ± change in storage

Simple in concept Data driven Difficult in practice

Water Budgets

How and where is the water coming from; Recharge Return flow

How and where is the water going; Pumping Surface water Evapotranspiration

Assumptions – Water Budget

Variables

Inputs Precipitation Return flow Overland Flow

Streams Springs

Groundwater

Outputs Pumping Evapotranspiration Overland Flow Groundwater

Example Water Budget

Annual Average(acre-ft) DWR [1967] Goodrich [1978]1 Brose [1987]

Total Input 1,744 1,050 1,750

Total Output 4,640 10,145 7,725

Total Water Budget -2,896 -9,095 -6,475

Annual Average (acre-ft) DWR [1967] Goodrich [1978]2 Brose [1987]

Surface Inflow 1,0501 1,0501 1,0501

Subsurface Inflow - - -

Precipitation 694 - 700

Imported Water - - -

Total 1,744 1,050 1,750

Annual Average (acre-ft) DWR [1967] Goodrich [1978]1 Brose [1987]Stamos and Predmore

[1995]

Surface Outflow - - - -

Subsurface Outflow 100 100 500 300 - 600

Consumptive Use 4,540 10,045 7,725 -

Total 4,640 10,145 8,225 -

The amount of naturally occurring groundwater that can be economically and legally withdrawn from an aquifer on a sustained basis without impairing the native groundwater quality or creating an undesirable effect such as environmental damage. It cannot exceed the increase in recharge or leakage from adjacent strata plus the reduction in discharge, which is due to the decline in head caused by pumping.

C.W. Fetter, 1994.

Safe Yield (sustainability)

Groundwater Hydrographs

Common Typically easy to interpret

Este Hydrologic Sub-basin(05N01E17D01)

1954-2002

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1701954 1957 1960 1963 1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999 2002

Measure Date

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Long-term monitoring Frequent monitoring Quality data you can trust

Assumptions - Hydrographs

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Este Hydrologic Sub-basinLucerne Valley Sub-Basin

Big Bear Lake Big Bear Dam Lake Arrowhead 06N01W27B001S 06N01W35A001S05N01E06C001S 05N01W01C001S 05N01W01L001S 05N01W01R003S 05N01E08N004S05N01E17D001S 05N01E20F001S 05N01E27H001S 05N01W25G001S 05N01W36F001S

What do the hydrographs say?

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Jan-94M

ay-94Jul-94O

ct-94Jan-95A

pr-95Jul-95O

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ct-96Jan-97A

pr-97Jul-97O

ct-97Jan-98A

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ct-99D

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ar-00Jun-00S

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ar-02Jun-02S

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ar-03Jun-03S

ep-03D

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ep-04D

ec-04

Dep

th to

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undw

ater

(Fee

t)

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ipita

tion

(Inch

es)

Este Hydrologic Sub-basinLucerne Valley Sub-Basin

Big Bear Lake Big Bear Dam Lake Arrowhead 06N01W27B001S 06N01W35A001S 05N01E06C001S

05N01W01C001S 05N01W01L001S 05N01W01R003S 05N01E08N004S 05N01E17D001S 05N01E20F001S

05N01E27H001S 05N01W25G001S 05N01W36F001S 04N01E06R001S 04N01E05P002S 04N01E12P001S

04N01W13R001S 04N01E23K001S 04N01E13M001S

Hydrographs – groundwater levels drive the analysis Decline in water levels Increased water levels No change

Balancing act

Analysis

z1

z2

z3

Groundwater and Wells

Drawdown Cone of depression Capture zone

Groundwater Withdrawal

Potable (municipal and private) Irrigation Industrial

Drawdown Due to Pumping

Water in aquifers is replenished primarily by infiltration of surface water (groundwater recharge).

Groundwater flows from areas of high pressure (or hydraulic head) to areas of low pressure. In unconfined aquifers, hydraulic head is given by the height of the water table above some reference level.

Left to itself, groundwater flow may intercept a surface water body, and flow into that body (natural groundwater discharge, Q).

Alternatively, it may be removed through wells for human consumption (artificial groundwater discharge). 

dischargeto stream

impermeable layer

flow lines

water table

dischargeto well

Q1

Q2

Water flowing underground

Mans Interaction

Groundwater Withdrawal Pollutants/Contamination

James W. Borchers/USGS

Fissures, Depressions and Land SubsidenceCaused by Over Pumping

Water quality can be thought of as a measure of the suitability of water for a particular use based on selected physical, chemical, and biological characteristics. To determine water quality, scientist’s first measure and analyze characteristics of the water such as temperature, dissolved mineral content, and number of bacteria. Selected characteristics are then compared to numeric standards and guidelines to decide if the water is suitable for a particular use.

Some aspects of water quality can be determined right in the stream or at the well. These include temperature, acidity (pH), dissolved oxygen, and electrical conductance (an indirect indicator of dissolved minerals in the water). Analyses of individual chemicals generally are done at a laboratory.

USGS, 2009

Water Quality

Water Quality and Groundwater Movement

Sources of Contamination

Groundwater Contamination

Investigation tools!

Remote Sensing Geophysics Subsurface Investigations 

(monitoring wells, soil and rock borings, etc.)

Aquifer Testing Water level monitoring Water Chemistry Computer Modeling

Conclusion

Basic definitions Hydrologic Cycle Groundwater Aquifers How water flows Water Budgets Wells Water Quality Contamination

Thank you

Questions?