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Why Planners need to know about it

Today:

Basics of groundwater system

Land-use and groundwater

World Fresh Water Supply

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Why is groundwater important to Planners?

• Our largest readily available source of freshwater is groundwater– Approx. 20% of all fresh water on Earth

• In the U.S., 40% of all fresh water comes from groundwater– Nearly half the states obtaining half their water from groundwater

• Currently, groundwater supplies:– 50% of all water used for drinking

– 40% of water used for irrigation and crop growth

– 25% of fresh water demands for industtry

• Groundwater provides ~66% of the water to streams, lakes and wetlands

Urban water cycle• This graphic illustrates

the impact of human activity on groundwater. It shows that groundwater is obtained from periurban wellfields and urban wells, then used and disposed of as wastewater through pluvial drainage, piped sewage and on-site sanitation and industrial effluent disposal. It also shows that wastewater is treated and then reused for irrigation, with excess flows re-entering the aquifers.

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Hydrologic or Water Cycle

• Moves water back and forth between the earth’s surface (biosphere, hydrosphere and lithosphere) and the earth’s atmosphere

• 91,000 cubic miles of water evaporates into the atmosphere from the earth’s surface each year (84% from the oceans and 16% from land)

• 75% of atmospheric water falls to oceans and 25% falls to land

Hydrologic/Water cycle

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Groundwater recharge• GW recharge (or deep drainage) is a hydrologic process

that is part of the hydrologic cycle where water moves downward from surface water to groundwater

• Human activity can impede recharge due to development activities such as;– Paving (creating impervious surfaces)

– Logging

– Grading• All of which can decrease GW recharge and increase SW runoff

• GW recharge is related to other processes such as;– Evaporation

– Transpiration

– Infiltration

Infiltration - Definitions

• Infiltration – rain and snow melt entering the soil through the soil surface

– f : infiltration rate (in/hr)

– F : total infiltration amount over some time (in)

• Infiltration Capacity – maximum infiltration rate

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Infiltration - Dependencies

• Surface– Type of vegetative cover

– Type of landuse practice (compaction)

– Rainfall Intensity

• Subsurface– Soil type

– Moisture content

– Root systems

Infiltration - Measurement

• Ring Infiltrometer

• Sprinkling

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Percentage of total water use that is from groundwater and amount of groundwater used in PA, by county, 1990

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Average annual precipitation in Pennsylvania, inches

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oIndiana County receives the highest amount of rainfall per year

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Why does Indiana get so much precipitation? One reason is orographic lifting

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The Groundwater System

Aquifers• Are formations that contain enough water and have

sufficient permeability to be used as water supply sources

• An aquiclude (such as clay) us usually porous and may contain groundwater but transmits is slowly and is not a good source

• An aquifuge (such as rock) neither stores nor transmits water

• Aquicludes and aquifuges can serve as confining layers, known as aquitards

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The Groundwater System

Unconfined and confined aquifers• Unconfined, or free, aquifers have direct vertical contact with the

atmosphere through open pores in the soil, and recharge from the infiltration above– The top of an unconfined aquifer is the groundwater table

– Below the table is the saturated zone

– Above the table is the unsaturated zone, a.k.a. vadose zone

• Unconfined aquifers that are perched produce seeps and springs, where the underlying layers force water to spill out of the ground– Primary recharge usually occurs directly above the aquifer

– Secondary recharge occurs from runoff of nearby slopes to primary area

• Confined aquifers are overlain by some geologic layer which water cannot move– Recharge is influenced by stratigraphy and structure

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Recharge Zones (surface)A group of aquifers linked together in a large flow system is

called a ground water basin

Types of Recharge Zones

1. Topographic Depression (wetland)

2. Highly permeable surface material (alluvial fan)

3. Exposed Aquifer (escarpment)

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Unconfined Perched (hanging) Aquifers

• One of largest in the world (unconfined)

• 174,000 square miles

•Primarily sandstone

• Provides 30% of nations irrigation water

• Could dry up in 25 years??

Regional Aquifer (Ogallala)

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Storage of groundwater in consolidated rocks and in unconsolidated sediments

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Unconsolidated AquiferUnconsolidated aquifers in PA have significant porosity and permeability;

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Groundwater Protection

• It is important to recognize three critical areas of concern in regards to groundwater protection:

– Groundwater recharge areas• Rock outcrops, depressions, wetlands

– Groundwater emergent areas• Seeps and springs

– Aquifer material composition• Seeking no decrease in permeability

Groundwater vs. Surface water• Groundwater chemistry varies from location to location

– Due to the minerals with which the water comes in contact with, and

– How long (duration) the water is in the groundwater system

• As groundwater flows, it dissolves minerals in the soil and rock– Resulting in various amounts of dissolved solids, measured mg/L

• Most of the springs in PA have only flowed through

weathered rock where minerals have already leached

• Spring water in PA, therefore, is not much

different from surface water

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Groundwater flow rates

• Changing the composition of soil material will affect groundwater flow and, eventually, supply

• Protection of groundwater permeability can be regulated via ordinances

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Pore sizes affect groundwater flow rates

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Waltham A. C. and Fookes P. G. 2005

Karst• Karst landscapes are shaped

by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite

• Due to subterranean drainage, surface water is limited or absent

• Thus, protection of groundwater resources is even more crucial

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Karstclass

Locations Sinkholes Rockhead Fissuring CavesGroundinvestigation

Foundations

kI Juvenile Only in deserts and periglacial zones, or on impure carbonates

RareNSH <0.001

Almost uniform;minor fissures

Minimal;low secondary permeability

Rare and small;some isolated relict features

Conventional Conventional

kII Youthful The minimum in temperate regions

Small suffusion or dropout sinkholes;Open stream sinksNSH 0.001-0.05

Many small fissures

Widespread in the few metres nearest surface

Many small caves; most <3m across

Mainly conventional,probe rock to 3 m,check fissures in rockhead

Grout open fissures;control drainage

kIII Mature Common in temperate regions; the minimum in the wet tropics

Many suffosion and dropout sinkholes;large dissolution sinkholes;small collapse and buried sinkholesNSH 0.05 - 1.0

Extensive fissuring;relief of <5m;loose blocks in cover soil

Extensive secondary opening of most fissures

Many <5m acrossat multiple levels

Probe to rockhead,probe rock to 4m,microgravity survey

Rafts or ground beams,consider geogrids,driven piles to rockhead;control drainage

kIV Complex Localized in temperate regions;normal intropical regions

Many large dissolution sinkholes; numerous subsidence sinkholes; scattered collapse and& buried sinkholesNSH 0.5 – 2.0

Pinnacled;relief of 5-20m;loose pillars

Extensive large dissolutional openings, on and away from major fissures

Many >5m acrossat multiple levels

Probe to rockhead,Prove rock to 5mwith splayed probes,microgravity survey

Bored piles to rockhead,or cap grouting at rockhead;control drainage and abstraction

kV Extreme Only in wet tropics

Very large sinkholesof all types; remanent arches;soil compaction in buried sinkholesNSH >>1

Tall pinnacles;relief of >20m;loose pillarsundercut between deep soil fissures

Abundant and very complex dissolution cavities

Numerous complex 3-D cave systems; galleriesand chambers>15m across

Make individualground investigationfor everypile site

Bear in soils with geogrid, load on proven pinnacles,or on deep bored piles;control all drainageand control abstractionWaltham A. C. and Fookes P. G. 2005

Sinkholes

Occur naturally in karst landscapes

Sinkholes occur outside of karst areas when water weathers, or dissolves, minerals in the underlying rock structure

Human activity, however, will cause sinkholes to develop due to poor surface water management and/or permitting of land-uses unsuitable for soil conditions

PA DEP

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Human activity that can lead to sinkhole formation

• Any change to the hydrologic system can cause sinkholes. Some common activities that lead to sinkholes are:– Decline of water levels

• drought, groundwater pumping (wells, quarries, mines)

– Disturbance of the soil• digging through soil layers, soil removal, drilling

– Point-source of water• leaking water/sewer pipes, injection of water

– Concentration of water flow• Improperly sited stormwater drains, swales, etc.

– Water impoundments• basins, ponds, dams

– Heavy loads on the surface• structures, equipment

– Vibration• traffic, blasting

PA DEP

Abandoned deep wells affect on groundwater

The EPA defines an abandoned well as:– A well whose use has been permanently

discontinued or which is in a state of such disrepair that it cannot be used for its intended purpose

Unplugged, abandoned oil and gas wells provide pathways for oil, natural gas, and salty groundwater to migrate into the fresh groundwater flow system, and vice versa

All abandoned wells (water, oil, or gas) should be plugged (filled) with impermeable material

Shallow Oil and Gas Fields of PA

Migration of groundwater throughan abandoned, unplugged well

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Cones of Depression

• Cones of depression, which result from the tapping of wells near surface waters, can turn a gaining stream – a stream gaining water

from groundwater

to a losing stream– a stream losing

groundwater and surface water subterraineanly

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Delineation of Wellhead Protection Areas (WHPA)

Must determine 2 zones (sometimes 3)

Zone of Influence – the surface projection of the boundaries of the cone of depression around the well

Zone of Contribution – the surface projection of the boundaries of the portion of the aquifer recharge area that contributes to the well

- this normally extends up the upflow side and to a portion of the CofD on the downflow side

In PA, a 3rd zone is required, and is the area beyond Zone II that contributes recharge to the aquifer within the capture zone

ZOI ZOC

Groundwaterdivide

Direction of groundwater flow

A

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PROFILE VIEW

PLAN VIEW

Cone ofdepression