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Groundwater 101

Fundamentalsof

Hydrogeologyand

a few Texas aquifers

TAGD Training November 16

2017

Dr. Joe

Dr. Joe?

Hydrogeologist

Baylor University

Dr. Joe

Hydrogeologist

Baylor University

Texas land owner

wells (registered)

Dr. Joe

Hydrogeologist

Baylor University

Texas land owner

wells (registered)

springs

Dr. Joe

Hydrogeologist

Baylor University

Texas land owner

wells (registered)

springs

rivers/streams

Grandparent

OutlineA. What is Hydrogeology?

B. What is Groundwater?

C. How does GW flow?

D. Basic GW concepts

E. GW-ABCs (Terminology)

F. Affects of wells

G. Water Chemistry

H. A few Texas aquifers

I. Management challenges

A. What is Hydrogeology?

The study of groundwater

• Hydrology– Surface water

• Geohydrology– Engineer?

• Subsurface hydrology– Engineer?

• Hydrogeology

– Geologist

Complex and Difficult

Rocks are different in places

Groundwater flow changes And you can’t see it!

Hydrogeology

Complex and difficult

not secret and occult

Hydro and geology

The

study

of

Groundwater

B. What is Groundwater?the saturated zone

The Earth’s Water• Oceans and Inland Seas 97.208%• Ice (mostly Greenland and Antarctica) 2.15 %• Groundwater 0.62% 97.5%• Surface water 0.0091%

– Lakes 0.009%– Rivers and Streams 0.0001%

• Other 0.00604%– Soil water 0.005%– Atmosphere 0.001%– Biosphere 0.00004%

C. How does groundwater flow?• the Ohio Supreme Court in Frazier v. Brown:48 (1861)

• In the absence of express contract and a positive authorized legislation, as between proprietors of adjoining land, the law recognizes no correlative rights in respect to underground waters percolating, oozing, or filtrating through the earth; and this mainly from considerations of public policy: (1) Because the existence, origin, movement, and course of such waters, and the causes which govern and direct their movements, are so secret, occult, and concealed that an attempt to administer any set of legal rules in respect to them would be involved in hopeless uncertainty, and would, therefore, be practically impossible.

Darcy’s Law1856

Q = KIA

Darcy’s Law

Darcy’s LawQ = KIA

Groundwater flows from higher to lower head

Groundwater contour maps and flow directions

Our activities affect our wells

Darcy’s Law1856

Q = KIA

D. 2 Groundwater concepts

1. Aquifer– Material that can

store and transmit water easily

2. Flow system– Recharge to

discharge

Aquifer concept

• Aquifer - material that can store and transmit water easily

• Aquitard – material that retards groundwater flow (also – Confining Bed)

Aquifer (sand)

Confining bed (shale)

Aquifer concept

1. Unconfined (water table) aquifer – an aquifer that has a free water surface (water table) on the top.

2. Confined (artesian) aquifer – an aquifer where the water rises above the top of the aquifer or above the bottom of the overlying confining bed.

Aquifer concept1. Unconfined (water table) aquifer –

an aquifer that has a free water surface (water table) on the top.

Aquifer concept

2. Confined (artesian) aquifer – an aquifer where the water rises above the top of the aquifer or above the bottom of the overlying confining bed.

Confined aquifer

Unconfined and Confined aquifers

2 Groundwater concepts

1. Aquifer– Material that can

store and transmit water easily

2. Flow system– Recharge to

discharge

Groundwater flow systemsrecharge to discharge

Local, Intermediate, and Regional flow systems

E. GW – ABCs: terminology• Porosity

• Hydraulic conductivity Q=KIA– Similar to permeability

• Transmissivity T = K x b

Hydrogeological terminology

• Storativity or Storage Coefficient S

• Specific Yield Sy

Hydrogeological terminology

Homogeneous (Homogeneity)– The same everywhere

Heterogeneous (Heterogeneity)

Isotropic (Isotropy)– The same in all directions

Anisotropic (Anisotropy)

F. Groundwater and Wells

Flow to wells

Overlapping cones of depression

G. Water chemistry

• H2O

– H180 O90

• Dipolar • The universal solvent

Water - the universal solvent

Electrical ConductanceCharged ionic species increase conductance therefore, Ec = TDS?

TDS = A x (Ec) where A = .55 to .75 or about .67

Chemistry changes with depth

H. A few Texas aquifers

Ogallala

OgallalaAeolian

wind

Fluvial

water

A few Texas aquifers

Trinity aquifer

Major aquifer

unconfinedoutcrop

confineddowndip

Sandclay and Ls

Discovery, Value, and Problem

– The first artesian well drilled in Waco in 1889 • 1830 ft deep•

• Flowed at the surface

• ~400,000 gal/d

– Waco advertized as “Geyser City”

– by 1894, some wells ceased flowing at the surface

?

A few Texas aquifers

Edwards BFZ

Northern Segment

Barton Springs Segment

San Antonio Segment

The Edwards BFZ aquifer

48

SALADO

SAN ANTONIO

AUSTIN

(I-35 CAC, 2011)

Northern Segment of the Edwards BFZ aquifer, Central Texas

(Jones, 2003)

fractures

cave

losing stream

sink hole

Fractures and dye tracing

N

Linear features

52

• Lineation is directly in line with Big Boiling

• Desktop measurement: 213°

• Field measurement: 220°

I. Management challenges

UnderflowTCEQ’s definition at 30 Tex. Admin. Code § 297.1(56)

• (56) Underflow of a stream--Water in sand, soil, and gravel below the bed of the watercourse, together with the water in the lateral extensions of the water-bearing material on each side of the surface channel, such that the surface flows are in contact with the subsurface flows, the latter flows being confined within a space reasonably defined and having a direction corresponding to that of the surface flow.

Hyporheic Zone

Underflow

• (56) Underflow of a stream--Water in sand, soil, and gravel below the bed of the watercourse, together with the water in the lateral extensions of the water-bearing material on each side of the surface channel, such that the surface flows are in contact with the subsurface flows, the latter flows being confined within a space reasonably defined and having a direction corresponding to that of the surface flow.

Underflow

Underflow

Models

Uncertainty

Often quoted:“All models are wrong, but some are useful”

Box and Draper (1987)

Uncertainty

Often quoted:“All models are wrong, but some are useful”

Box and Draper (1987)

The second half:

“...the practical question is how wrong do they have to be to not be useful.”

Questions?