United States Offi Environmental Protection Agency Superfund … · 2014. 3. 12. · Fisherville...
Transcript of United States Offi Environmental Protection Agency Superfund … · 2014. 3. 12. · Fisherville...
Offi ce of Solid Waste andEmergency Response(5201G)
Introduction to Groundwater Investigations
Superfund
United StatesEnvironmental ProtectionAgency
Student Manual
EPA-540-B-00-012OSWER 9285.9-47June 2006www.epa.gov/superfund
Course Introduction
Groundwater Investigations 1
INTRODUCTION TOGROUNDWATER INVESTIGATIONS
presented byTetra Tech, Inc.
for theU.S. Environmental Protection Agency's
Environmental Response Team
ENVIRONMENTAL RESPONSETRAINING PROGRAM (ERTP)
OSWER
U.S. EPA
Office of Solid Waste and Emergency Response (Superfund)
United States Environmental Protection Agency
Environmental Response TeamERT
Office of Superfund Remediationand Technical Innovation
OSRTI
• Are offered tuition-free for environmental and response personnel from federal, state, and local agencies
• Vary in length from one to five days• Are conducted at EPA Training Centers
and at other locations throughout the United States
ERTP TRAINING COURSES
Course Introduction
Groundwater Investigations 2
ERTP TRAINING COURSES
Course Descriptions, Class Schedules, and Registration Information are available at:
• www.trainex.org
• www.ertpvu.org
• Student Registration Card• Student Evaluation Form• Course Agenda• Disk with Course Materials• Student Workbook
COURSE MATERIALS
• Parking• Classroom• Restrooms• Water fountains, snacks, refreshments• Lunch• Telephones• Emergency telephone numbers• Alarms and emergency exits
FACILITY INFORMATION
Introduction to Groundwater Investigations
Groundwater Investigations 1
Introduction to Groundwater Investigations
Groundwater Hydrology"The science of hydrology would be relatively simple if water were unable to penetrate below the earth's surface."
Harold E. Thomas
Lecture Objectives
Define hydrogeology
Discuss the hydrologic cycle
Define basic aquifers
Identify common types of groundwater contamination
Present case study
Introduction to Groundwater Investigations
Groundwater Investigations 2
Groundwater Hydrology
"Ground-water hydrology is the subdivision of the science of hydrology that deals with the occurrence, movement, and quality of water beneath the earth’s surface.“
Ralph C. Heath
Hydrologic Cycle
Hydrologic Cycle
Introduction to Groundwater Investigations
Groundwater Investigations 3
Groundwater Discharge
Unconfined Aquifer
Confined Aquifer
Introduction to Groundwater Investigations
Groundwater Investigations 4
Perched Aquifer
Aquifer Properties
Groundwater AquifersPrimary Openings
Unconsolidated Aquifer MaterialPoorly sorted, stratified, sands and gravels
Introduction to Groundwater Investigations
Groundwater Investigations 5
Groundwater AquifersSecondary OpeningsGroundwater in Caverns
Limestone, Indiana
Fractured Sandstone
Groundwater AquifersSecondary Openings
Groundwater Contaminants
Introduction to Groundwater Investigations
Groundwater Investigations 6
Groundwater ContaminantsPetroleum products are a common groundwater contaminant. Referred to as a Light Non-aqueous Phase Liquid (LNAPL)
Groundwater Contaminants
Chlorinated solvents are another common groundwater contaminant. Referred to as a Dense Non-aqueous Phase Liquid (DNAPL)
Acid mine run off, Tinto River, Spain Photo Credit - Carol Stoker/NASA
Groundwater Contaminants
Introduction to Groundwater Investigations
Groundwater Investigations 7
Groundwater InvestigationCase Study
Fisherville Mill, Grafton, MA
Fisherville Mill Aerial Photograph
Image Courtesy of USGS
Blackstone River
Mill Building
Old Blackstone Canal
Rail Road
Blackstone Canal Bridge
Fisherville Mill Site Investigation
Image Courtesy of USGS
Site investigation initiated because of the discovery of oil in the former Blackstone Canal
Introduction to Groundwater Investigations
Groundwater Investigations 8
Fisherville Mill, Grafton, MAOil release discovered in Old Blackstone Canal
Looking north at Blackstone Canal Bridge
Looking south
Image Courtesy of USGS
Initial investigation for the source of the oil release discovered high concentrations of a chlorinated solvent (TCE)north of mill building
Boiler USTs
Boring with highTCE concentrations
Fisherville Mill Site Investigation
Initial TCE treatment system destroyed in 1990 fire
Fisherville Mill Site Investigation
Introduction to Groundwater Investigations
Groundwater Investigations 9
Image Courtesy of USGS
Position of TCE plume during thewinter months
Blackstone River
Fisherville Mill Site Investigation
Image Courtesy of USGS
Position of TCE plume during thesummer months
Fisherville Mill Site Investigation
Image Courtesy of USGS
TCE plume affected during the summer months by pumping of a municipal well (GP#3)
Pumping wellGP#3
Fisherville Mill Site Investigation
Introduction to Groundwater Investigations
Groundwater Investigations 10
Image Courtesy of USGS
A
A'
Fisherville Mill Site InvestigationCross Section A – A'
#3 SG-7
SG-6
Bend in section
276.6PA-1A277.20
MW-100 MW-31
300
290
280
270
277.43
260
250
240
277.40
220
6005004003002001000 feet
7/16/01-Ambient
278277
278.5
278
277.96277 277
277
277.5
277.20
277.34
277.34
278.52279.29
279.10
278.87
278.74
230
DP-4A
Water TablePotentiometric SurfaceGroundwater Flow
LEGEND
Groundwaterflow
Groundwater Discharge Point
Seep SW-2A
Fisherville Mill Site InvestigationCross Section A – A' Ambient Flow
Fisherville Mill Site InvestigationCross Section A – A' GP#3 Pumping
SG-7
SG-6
Bend in section
SW-2APZ-1A
MW-100 MW-31
300
290
280
270
260
250
240
220
6005004003002001000 feet
10/25/01 Pumping
276.38276.6
230
276.63
276.69
276.71
276.5276
276.32
275.5
275
276.55
271.39274.65
SW-4A
#3
Seepno flow
DP-4A
Groundwater flow
Water TablePotentiometric SurfaceGroundwater Flow
LEGEND
Introduction to Groundwater Investigations
Groundwater Investigations 11
Fisherville Case StudyTemporary dam built in stream to create a hydraulic head. The hydraulic head influenced the flow of groundwater to keep the TCE plume away from GP#3.
Temporary dam
Fisherville Remediation
Sodium Permanganate tanks (above) and injection well (left)
TCE source was degraded using an oxidation-reduction remediation method. The oxidizer was sodium permanganate.
Great Sand Dunes National Park, Colorado
Groundwater Regions
Groundwater Investigations 1
GroundwaterRegions
Groundwater Regions
Lecture Objectives:
Define the twelve general groundwater regions within the United States
Describe the aquifers within these groundwater regions
Describe the general movement of groundwater and contaminates within the aquifers of these regions
Alluvial Valleys
Northeast & Superior Region
Piedmont – Blue Ridge Region
Atlantic & Gulf Coast Region
Southeast Coastal Plain
Non-Glaciated Central Region
Groundwater Regions
Groundwater Regions
Groundwater Investigations 2
Glaciated Central Region
High Plains Region Western Mountain Range Alluvial Basins
Colorado Plateau & Wyoming Basins Columbia Lava Plateau
Groundwater Regions
Alluvial Valleys Groundwater Regions
STREAM HEADWATERS
MOUTHOF STREAM
OCEAN
Longitudinal Profileof Streams
Groundwater Regions
Groundwater Investigations 3
OCEAN
LARGE SMALL
Sediment Grain Size
POOR WELL
Sediment Sorting
OCEAN
ANGULAR ROUNDED
Sphericity of Sediment
OCEAN
Groundwater Regions
Groundwater Investigations 4
Alluvial Valleys
Thick sand and gravel deposits beneath floodplains and terraces of streams and rivers.
Meandering Stream
Characteristics ofMeandering Streams Depositional environments:
– Low gradients– Deep streams– Grain size variations
– Oxbow lakes– Levees and floodplains– Point bars and cut banks
Groundwater Regions
Groundwater Investigations 5
Groundwater Regions
Columbia Lava Plateau
Alluvial Basins Colorado
Plateau and
Wyoming Basin
Nonglaciated Central Region
Alluvial Basin
Western Mountain Ranges
Nonglaciated Central Region
Atlantic and Gulf Coastal
Plain
Nonglaciated Central Region
Glaciated Central Region
Northeast and
Superior Uplands Northeast
and Superior Uplands
Piedmont and Blue
Ridge
Southeast Coastal Plain
High Plains
High Plains
Nonglaciated Central Region
Glaciated Central Region
Non-glaciated Central Region
Western Mountain Ranges
Northeast & Superior Uplands Region
Glacial deposits over fractured crystalline rocks.
Northeast Region
Bedrock Map
Groundwater Regions
Groundwater Investigations 6
Superior Uplands Region
Groundwater Map
Northeast Region
Blackstone RiverGrafton, Massachusetts
Northeast Region
Blackstone River DepositsGrafton, Massachusetts
Groundwater Regions
Groundwater Investigations 7
Northeast Region
Metamorphic bedrock, Waterbury, VT
Superior Uplands Region
Lake Itasca, Lake Itasca State Park, Minnesota
Northeast CoastCape Cod, MAGlacial Moraine
Image courtesy of NASA
Groundwater Regions
Groundwater Investigations 8
NANTUCKET SOUND
CAPE COD BAY
SAGAMORE
PILGRIM PAMET
CHEQUESSET
NAUSET
MONOMOY
5 45
10
20
EASTWEST
Atla
ntic
Oce
an
WEST EAST
Freshwater Recharge AreaFor Cape Cod Aquifer
CAPE COD BAY ATLANTIC OCEAN
ZONE OF DIFFUSION
BEDROCK
FRESHWATERLENS
SALINEWATER
SALINEWATER
UNCONSOLIDATEDSEDIMENTS
Piedmont & Blue Ridge Region
Thick regolith over fractured crystalline and metamorphosed sedimentary rocks.
Groundwater Regions
Groundwater Investigations 9
Highland County, VA
Piedmont & Blue Ridge Region
Aquifers In Semi Consolidated and Consolidated Rocks
Groundwater Regions
Groundwater Investigations 10
Atlantic & Gulf Coast Region
Complexly interbedded sand, silt, and clay.
Typical Coastal Deposits
• Depositional environments:
– Barrier islands– Offshore bars– Deltas
– Spits– Tidal flats– Reefs/cays
Mississippi RiverDeltaic Environment
Image courtesy of NASA
Groundwater Regions
Groundwater Investigations 11
Image courtesy of NASA
Galveston Island
GULF OF MEXICO
GALVESTON BAYWEST BAY
SANLUISPASS
BOLIVARPASS
F'
F
Galveston Barrier Island
Barrier Island
EQUIPOTENTIALHIGH
WEST BAY
F F'
GULF OF MEXICO
Groundwater Regions
Groundwater Investigations 12
Southeast Coastal Plain Region
Thick layers of sand and clay over semi-consolidated carbonate rocks.
Southeast Region Aquifers
Cape Canaveral, FL
Image courtesy of NASA
Groundwater Regions
Groundwater Investigations 13
Southeast Coastal Plain Region
Floridan Aquifer
Non-Glaciated Limestone Region
Thin regolith over limestone bedrock forming a Karst topography.
LimestoneCentral Kentucky
Groundwater Regions
Groundwater Investigations 14
Karst Topography
• Depositional environments:
– Soluble rocks at or beneath surface (carbonates, sulfates, chlorides)
– Chemical solution of soluble rocks
– Closed depressions (sinkholes, swallets)– Little or no surface drainage– Caves, springs, disappearing streams
Sinkhole
CLAY
LIMESTONE
LIMESTONESHALE
Karst Conduits
Red Penn SiteCarrolton, KY
Groundwater Regions
Groundwater Investigations 15
Red Penn SiteCarrollton, KY
Glaciated Central Region
Glacial deposits over fractured sedimentary rocks.
Glaciated Regions of United States
Groundwater Regions
Groundwater Investigations 16
Process of Glaciation
• Erosion
• Transportation• Deposition
Glacial GroovesTurnagain BasinCook Inlet, AK
Ruth GlacierDenali National Park, AK
Groundwater Regions
Groundwater Investigations 17
Glacial Deposits
• Depositional environments:
– Outwash and till– Moraines– Drumlins
– Eskers– Kettle holes– Kames
Glacial OutwashSeward, AK
Glacial Outwash Southwest Ohio
Great Miami River, Hamilton, Ohio
Groundwater Regions
Groundwater Investigations 18
Mt. Spurr Ash, AK
Loess Deposit
Loess Deposit, Southwest Iowa
High Plains, Braided Stream Region
Thick alluvial deposits over fractured sedimentary rock.
Groundwater Regions
Groundwater Investigations 19
Braided StreamKnik Arm, Cook Inlet
Characteristics ofBraided Streams
• Depositional environments:
– Resembles braided hair– High to low gradients– Shallow streams
– Poor to medium sorting– Angular to subangular grains
Braided Stream Sediments
Salt RiverNear Phoenix, AZ
Groundwater Regions
Groundwater Investigations 20
Braided Stream Sediment
High Plains, Front Range Region
Eastward sloping aquifer sediments that range in elevation from 6,000 ft above sea level near the Rocky Mountains to 1,500 feet above sea level.
High Plains, Front Range Region
Morrison Formation, CO
Groundwater Regions
Groundwater Investigations 21
High Plains Aquifers
McGuire, V.L., 2011, Water-level changes in the High Plains Aquifer, predevelopment to 2009, 2007 – 08, and 2008 – 09, and change in water in storage, predevelopment to 2009: USGS Scientific Investigations Report 2011-5089
Water-level Changes in the
High Plains Aquifer
• Yellow, orange, and red colors indicate declining water-levels
• Greens and blues indicate rising water-levels
• Gray indicates no substantial changes (+/- 10 feet)
Western Mountain Ranges
Fluvial deposits over fractured crystalline rocks.
Groundwater Regions
Groundwater Investigations 22
Western Mountain Ranges
Mountain ValleyAlluvial Deposit
Grand Lake, CO
Western Mountain Ranges
Area of Alluvial Basins
Groundwater Regions
Groundwater Investigations 23
Alluvial Basin Region
Northwest of Lake Mead, NV
Alluvial Basin Region
Thick alluvial deposits in basins & valley bordered by mountains and locally of glacial origin
West of Lake Mead, NV
Groundwater Regions
Groundwater Investigations 24
Thick alluvial deposits in basins & valley bordered by mountains
Alluvial Basin Region
Death ValleyNational Park
Characteristics ofAlluvial Fans
• Depositional environments:
– Poor sorting and rounding– High gradients– Shallow and intermittent streams
– Hand-shaped
Groundwater Regions
Groundwater Investigations 25
Alluvial Fan: Death Valley
Image courtesy of NASA
Major Aquifers of
California
Colorado Plateau, Wyoming Basin
Groundwater Regions
Groundwater Investigations 26
Colorado Plateau, Wyoming Basin
Grand Canyon, AZ
Grand Canyon, AZ
Colorado Plateau, Wyoming Basin
Volcanic Rocks of the Northwest
Columbia Lava Plateau
Groundwater Regions
Groundwater Investigations 27
PNW Major Aquifers
Columbia Lava Plateau
Thick sequence of lava flows irregularly interbedded with thin unconsolidated deposits and overlain by thin soils.
Interflow sediments below
basalt flow
Columbia Lava Plateau
Groundwater Regions
Groundwater Investigations 28
Drilling Methods
Groundwater Investigations 1
DrillingMethods
Discuss basic drilling principles, sample collection methods, advantages and disadvantages of the following drilling methods: – Direct push technologies (DPT) – Hollow-stem auger drilling– Air rotary drilling – Rotosonic drilling
Define vertical profiling and list two examples List six considerations when selecting a
drilling method
Lecture Objectives
Utility Locations
Above and below ground surface
Drilling Methods
Groundwater Investigations 2
Hollow-stem auger Air rotary
– Roller bit with compressed air– Down hole hammer driven with
compressed air Direct-push technology Rotosonic
Drilling Methods
Hollow-StemAuger
Hollow-Stem Augers
Drilling Methods
Groundwater Investigations 3
Hollow-Stem Auger Drilling
Video
Hollow-Stem Auger Drilling
5 footsection
Split‐spoon sampler, advanced into undisturbed soil
Center rod removed, allowing split spoon to advance through open bottom
Lead auger with center rod in place
Cuttings
Surface
Split-Spoon Samplers
Shown above: assembled sampler (left), opened sampler, flex plug (orange), and drive shoe (right)Shown right: soil sample exposed after opening split-spoon.
Drilling Methods
Groundwater Investigations 4
Equipment Decontamination
Available and mobile No drilling fluid required Problems of hole caving minimized Rapid and continuous sample recovery,
especially at depths greater than 30 feet Good for monitoring well construction Allows for a variety of groundwater sample
collection techniques while drilling
Hollow-Stem Auger: Advantages
Consolidated formations require alternate drilling method
Limited depth capability Large volume of drill cuttings produced Issues in “heaving” sands Possible cross contamination
Hollow-Stem Auger: Disadvantages
Drilling Methods
Groundwater Investigations 5
Air Rotary
Air Rotary Drilling – Percussion Hammer
5 foot auger section
Steel casing
Hollow stem augers keep borehole open
Drilled rock cuttings blown up annular space
Compressed air
Drill bit hammers and rotates
Inter drive compressed‐air operated percussion hammer
Open at bottom
Surface
Bedrock
Second auger
Lead auger
Soil
Air Rotary Drilling
Down hole roller bit
Drilling Methods
Groundwater Investigations 6
Air Rotary Drilling
Air Rotary Drilling
This air rotary drilling rig is using a high capacity air compressor which creates issues with dust control, cuttings management, and noise.
Air Rotary Drilling
Drilling Methods
Groundwater Investigations 7
No liquid drilling fluid required Excellent drilling in hard rock Compatible with hollow-stem auger drilling Good depth capability Decent delineation of water-bearing zones Bedrock wells are compatible with packers that
allow sampling and testing
Air Rotary: Advantages
Difficult sample collection Casing may be required during drilling Cross contamination of different
formations possible Mobility may be limited Management of cuttings Collection of continuous cores expensive
Air Rotary: Disadvantages
Direct PushTechnology
(DPT)
Drilling Methods
Groundwater Investigations 8
Direct Push Technology (DPT)
DPT Platforms
Samples collected using DPT
Drilling Methods
Groundwater Investigations 9
DPT
Video
DPT Dual Tube Sampler
5 feet,depending on tools selected
New empty tube added and advanced
Soil
Steel inter‐rod
New outer casing added
Drive head
Outer tube remains open
Sample tube with soil sample is removed
Drive head is removed
Drive head
Drive head
Sample tube filled
Outer casing 3½” diameter
Open
Sample tube fills with soil as advanced downward
Two soil samples collected using the DPT dual tube system.
The tubes have been split for screening, samples description, and collection.
Drilling Methods
Groundwater Investigations 10
DPT Groundwater Samples
Additional information available on the Clu-In Web site:http://www.clu-in.org/characterization/technologies/dpgroundwater.cfm
DPT Soil Gas SamplesTwo general soil gas sampling methods include: Continuous
Sampling Tools Discrete
Sampling Tools
Additional information available on the Clu-In Web site:http://www.clu-in.org/characterization/technologies/dpgroundwater.cfm
DPT Soil Gas SamplesContinuous Sampling Tool
Continuous sampling tools are driven in “sniffing mode”; that is, vapor samples are collected as the tool is driven
Advantage: Continuous tools can quickly characterize a soil sequence.
Limitations: False positives may occur due to residual Volatile Organic Compounds (VOCs) in vapor transfer tubes.
Drilling Methods
Groundwater Investigations 11
DPT Soil Gas SamplesDiscrete Sampling Tool
Discrete sampling toolsare driven to the target depth, the rods are retracted to expose the soil, and the sample is collected using a vacuum pump.
Advantage: Discrete sampling tools more accurately locate the source of contamination.
Limitations: DPT depth limitation and difficulty advancing tools in densely compacted materials.
Generally faster sample collection and continuous sample collection.
Reduced Investigation Derived Waste (IDW) Smaller equipment profile Capable for ground water monitoring well
and temporary well placement
DPT Advantages
Limited depth capability Cannot penetrate bedrock or dense materials Sample volumes may be limited depending
on tools Limited groundwater sampling techniques
at depth Limited bore hole diameter for monitoring
well placement
DPT Disadvantages
Drilling Methods
Groundwater Investigations 12
Rotosonic
Rotosonic Drilling
Photo courtesy of Boart-Longyear, Inc.
Rotosonic Drilling
Drilling Methods
Groundwater Investigations 13
Rotosonic DrillingOSCILLATOR
COUNTER-ROTATING WEIGHTS
HIGH FREQUENCYSINUSOIDAL
FORCE STANDING HARMONIC
WAVE IN DRILL PIPE
DRILL BIT ROTATES AND
VIBRATES
Rotosonic Drilling Method
CoreBarrels
OverrideCasings
(shown semi-transparent for illustration only)
Drill Rods
Rotosonic Drilling Method
CoreBarrelsExtruded
Samples
Drill Rods
OverrideCasings
(shown semi-transparent for illustration only)
Drilling Methods
Groundwater Investigations 14
Rotosonic Drilling Method
CoreBarrels
OverrideCasings
(shown semi-transparent for illustration only)
Drill Rods
ExtrudedSamples
Rotosonic Drilling
Power Head
Photo Courtesy State of Washington, Department of Ecology
Rotosonic Samples
Drilling Methods
Groundwater Investigations 15
Rotosonic Mini-Track Mounted Rig
Courtesy State of Washington, Department of Ecology
Rotosonic Drilling Special Application
Photos courtesy State of Washington, Department of Ecology
Quality samples Faster drilling Good depth capacity Drills into consolidated materials,
unconsolidated materials, and challenging conditions
Minimal drilling fluids Fewer cuttings than HAS or air rotary Temporary casing can be set
Rotosonic: Advantages
Drilling Methods
Groundwater Investigations 16
Cost Heat generated by drilling may negatively
affect samples Management of circulating water returned
from borehole Sediment with large cobbles can cause
drilling and sampling problems
Rotosonic: Disadvantages
Vertical ProfilingDuring Drilling
Vertical Profiling
Vertical profiling is the collection of data during the advancement of the borehole. Date collected can include lithology, chemical, or hydrological data.
Two types of vertical profiling include: Groundwater sample collection Membrane interface probe (MIP)
Drilling Methods
Groundwater Investigations 17
Vertical Groundwater Profiling
Vertical groundwater profiling is the collection of groundwater chemical or hydrological data during the advancement of the borehole.
Shown in photo is a DPTexposed-screen groundwater sampler.
Photo courtesy of Ohio EPA
Vertical Profiling Using MIP
The membrane interface probe (MIP) is a semi-quantitative, field-screening device that can detect volatile organic compounds and lithology in both the saturated and unsaturated zones.
Membrane Interface Probe
The MIP tool heats the soil or groundwater to volatilize and mobilize contaminants for detection using photo-ionization (PID), flame ionization (FID), and electron capture (ECD/SXD) detectors. The MIP also records soil or pore water conductivity.
Drilling Methods
Groundwater Investigations 18
Membrane Interface Probe
MIP recording devices and carrier gas cylinders
Membrane Interface Probe
Vertical Profiling Advantages
Enhances the conceptual site model (CSM) which reduces uncertainty in project decisions
Real time mapping of contaminant fate and transport
Reasonable cost for data recovered
Drilling Methods
Groundwater Investigations 19
Vertical Profiling Disadvantages
Data is screening level MIP is only useful in unconsolidated zones Determining precise depth can be difficult Complex mixture of subsurface chemicals
problematic with MIP detectors MIP operator and DPT driller must
communicate and have compatible equipment
Drilling Method Selection Criteria
Sample Collection
Collection of defensible environmental samples
– Anticipated analysis – Sample yield
Drilling Methods
Groundwater Investigations 20
Well Construction
Monitoring and recovery well installation– Hollow-stem auger, rotosonic drilling,
and air rotary may be more suited for monitoring and recovery well construction, however, these drilling methods can create well development issues
– DPT boreholes cause less stress on the aquifer, however, the monitoring wells generally are smaller in diameter
Anticipated Depth
Anticipated depth, lithology, and surface access– Depth– Unconsolidated or consolidate
sediments– Surface obstructions
Anticipated Contaminant
Anticipated contaminant – Light Non-aqueous phase liquid
(LNAPL) – Dense Non-aqueous phase liquid
(DNAPL)– Volatile organic compounds
Drilling Methods
Groundwater Investigations 21
IDW
Investigative derived waste can add to the overall project costs – Hazardous versus non-hazardous
materials in subsurface – Hollow-stem auger versus DPT
or rotosonic
Drilling CostsDPT Hollow-
StemAir Rotary Rotosonic
Mobilization $250 to $500 $450 to $750 $2,500 $3,000 to $6,000
Drilling & sampling
$1,500 to $1,800 per day
$11.00/ft $32/ft. to$42.00/ft
$26/ft. to $32/ft
Well installation
$6.00/ft $12.00/ft $16.00/ft$55/ft*
$22/ft to $25/ft.
WellDevelopment
na na $145/hr $200/hr to $250/hr
Flush mount na $350/ea $350/ea $230/ea to 310/ea
Stand-by Included in day rate
$150/hr $150/hr $350/hr to $450/hr
na = not available * 6-in steel surface casing to seal upper water zone
Drilling Methods
Groundwater Investigations 22
Discuss basic drilling principles, sample collection methods, advantages and disadvantages of the following drilling methods: – Direct push technologies (DPT) – Hollow-stem auger drilling– Air rotary drilling – Rotosonic drilling
Define vertical profiling and list two examples List six considerations when selecting a
drilling method
Lecture Objectives
Hydrogeology
Groundwater Investigations 1
Hydrogeology
Hydrogeology
The study of interactions of geologic materials and processes with water, especially groundwater.
GROUNDWATERRECHARGE
GROUNDWATERDISCHARGE
SOILMOISTURE
PRECIPITATION
Hydrologic Cycle
RUNOFF
EVAPORATION
TRANSPIRATION
WATERTABLE
Hydrogeology
Groundwater Investigations 2
Stream Flow
Stream Flow
Q = Av
A (cross-sectional area)Q (discharge)
v (velocity)
Gaining Stream
DISCHARGE = 10 cfs
DISCHARGE = 8 cfs
Hydrogeology
Groundwater Investigations 3
Losing Stream
DISCHARGE = 8 cfs
DISCHARGE = 10 cfs
POROSITY(Nt)
The volumetric ratio between the void spaces (Vv) and total rock (Vt):
Nt = Vv
Vt
; Nt = Sy + Sr
Sy = specific yield
Sr = specific retention
VOID SPACE
SOLID PARTICLE
TOTAL VOLUME - VOLUME SOIL PARTICLES
TOTAL VOLUME x 100
PERCENTPOROSITY
=
Hydrogeology
Groundwater Investigations 4
Sediment and Water Capacity Relationships
Void Space Volume: Porosity
Water Saturation
Hydrogeology
Groundwater Investigations 5
Water Retained After Gravity Drainage
SPECIFIC YIELD
SPECIFIC RETENTION
Primary Porosity
Refers to voids formed at the time the rock or sediment formed.
Porosity
TOTAL POROSITY (Nt):
CLAY
SAND
GRAVEL
EFFECTIVE POROSITY (Ne):
40-85%
25-50%
25-45%
1-10%
10-30%
15-30%
Hydrogeology
Groundwater Investigations 6
Secondary Porosity
Refers to voids that were formed after the rock was formed.
Secondary Porosity
Fractured rock (grey) and solution weathered rock (blue)
18
Secondary Porosity
Solution Weathering Derived Secondary Porosity
Hydrogeology
Groundwater Investigations 7
Permeability
The ease with which liquid will move through a porous medium.
Hydraulic Conductivity
The capacity of a porous medium to transmit water.
Hydraulic Conductivity
Hydrogeology
Groundwater Investigations 8
Aquifer
A permeable geologic unit with the ability to store, transmit, and yield water in "usable quantities."
Usable Quantity?
Homogeneous
Having uniform sediment size and orientation throughout an aquifer.
Hydrogeology
Groundwater Investigations 9
Heterogeneous
Having a nonuniform sediment size and orientation throughout an aquifer.
Isotropic
Hydraulic conductivity is independent of the direction of measurement at a point in a geologic formation.
Anisotropic
Hydraulic conductivity varies with the direction of measurement at a point in a geologic formation.
Hydrogeology
Groundwater Investigations 10
HOMOGENEOUS HETEROGENEOUS
Aquitard
A layer of low permeability that can store and transmit groundwater from one aquifer to another.
Aquiclude
An impermeable confining layer.
The USGS refers to both Aquicludes and Aquitards as “confining layers” or “confining units”.
Hydrogeology
Groundwater Investigations 11
Total Head(ht)
Combination of elevation (z) and pressure head (hp)
Total head is the energy imparted to a column of water
ht = z + hp
GROUNDWATER LEVEL
PRESSUREHEAD
HYDRAULIC
OR
TOTALHEAD
ELEVATIONHEAD
DATUM(usually sea level)
POINT OFMEASUREMENT
(hp)
(ht)
(z)
Unconfined Aquifer: Water Table
A permeable geologic unit without a confining bed between the zone of saturation and the surface.
Hydrogeology
Groundwater Investigations 12
Unconfined Aquifer
VADOSEZONE
CONFINING UNIT -AQUITARD
WATERTABLE
VERTICAL EQUIPOTENTIAL
LINES
GROUNDWATERFLOW
UNCONFINED AQUIFER
GROUNDWATERFLOW
100 90 70 60 50 40
Confined Aquifer: Artesian
An aquifer – overlain by a confining layer – whose water is under sufficient pressure to rise above the base of the upper confining layer if it is perforated.
Confined Aquifer
CONFINED AQUIFER
CONFINING UNIT -AQUITARD
POTENTIOMETRICSURFACE
CONFINING UNIT
AQUITARD
BASE OF UPPER CONFINING UNIT
VADOSEZONE
Hydrogeology
Groundwater Investigations 13
Aquifers and Aquitards
VADOSEZONE
UNCONFINED AQUIFER
AQUITARD
AQUITARD
CONFINED AQUIFER
CONFINED AQUIFER
WATERTABLE
WATER TABLE
VADOSEZONERECHARGE
CONFINING LAYERS(AQUITARDS)
Potentiometric Surface
The level to which water will rise in an opening (well) if the upper confining layer of a confined aquifer is perforated.
Hydrogeology
Groundwater Investigations 14
Artesian Groundwater System
AQUITARDS
POTENTIOMETRIC SURFACERECHARGE AREARECHARGE AREA
AQUIFER
AQUITARDS
POTENTIOMETRIC SURFACE
FLOWINGARTESIAN
WELL
OVERBURDENPRESSURE
HYDRAULICPRESSURE
GWFLOW
Artesian Groundwater System
Q = discharge
K = hydraulic conductivity
I = hydraulic gradient
A = area
Darcy's LawQ = KIA
( ) dhdl
Hydrogeology
Groundwater Investigations 15
The flow rate through a porous material is proportional to the head loss and inversely proportional to the length of the flow path
Valid for laminar flow Assume homogeneous and
isotropic conditions
Darcy's Law
Hydraulic Conductivity(K)
The volume of flow through a unit cross section of an aquifer per unit decline of head.
Q
dh
dl
HYDRAULICCONDUCTIVITY
AQUITARD
CONFINEDAQUIFER
AQUITARD
Hydrogeology
Groundwater Investigations 16
K = hydraulic conductivity A = cross-sectional area Q = rate of flow I = hydraulic gradient
Hydraulic Conductivity
QQ = KIA
IAK =
( ) dhdl
Q
dh
dl
( )
Q
Q(Flow rate)
dh
dl(length offlow path)
A(area)
headloss
Darcy's Law
Decreasing the hydraulic head decreases the flow rate.
dl
dh1
dl
dh2
Q1 > Q2Q1
Q1
Q2
Q2
Hydrogeology
Groundwater Investigations 17
dh
dl1
dl2
Increasing the flow path length decreases the flow rate. Q1 > Q2
dh
Q1
Q1
Q2
Q2
Stream Flow
Q = Av
A (cross-sectional area)Q (discharge)
v (velocity)
Darcy's Law Q = KIA or = Kl QA
Groundwater Velocity
Velocity equation Q = Av or = v
v = KI Darcian velocity By combining, obtain:
QA
Hydrogeology
Groundwater Investigations 18
Because water moves only through pore spaces that are connected, porosity is a factor.
Nt = or Nt = Sr + SyVvVt
ne = Sy = Nt - Sr ~ effective porosity
seepage velocityKlne
vs =
Groundwater Velocity
Transmissivity
The capacity of the entire thickness of an aquifer to transmit water
T = transmissivity
K = hydraulic conductivity
b = aquifer thickness
T = Kb
AQUITARD
AQUITARD
dh
dl
GW FLOW
K = 20 m/d
Transmissivity
b = 100m
Hydrogeology
Groundwater Investigations 19
Transmissivity
T = Kb
T = (20 m/d) (100 m)
T = 2000 m2 /d
Storativity
The amount of water available for "use" in an aquifer (storage coefficient)
"Specific yield" in an unconfined aquifer
Well Installation
Groundwater Investigations 1
Well Installation Lectureand
Filter Pack and Well Screen Selection
Exercise
List well design considerations and basic well construction materials.
Differentiate between unconfined aquifer and confined aquifer monitoring well designs.
Define a well cluster and a nested well.Discuss the purpose, basic principles and methods for well development. List the advantages and disadvantages of temporary monitoring wells and describe the different well construction methods.Describe well abandonment purpose and procedures.
Determine the filter pack and well screen slot size given a sieve analysis of aquifer material surrounding a well.
Lecture Objectives
Well Design Considerations
The following should be considered when designing a groundwater monitoring well:
● Purpose of the well● Project duration● Contaminant characteristics● Aquifer properties● Well depth● Surface considerations● Potential negative environmental impacts
Well Installation
Groundwater Investigations 2
Well Installation
Well Construction Materials
Simple Monitoring Well Design Construction
Weep hole
Bottom cap
maximum frost line
Outer locking cap
Surface seal
Inner cap
Protective surface casing
Bollards
Well pad
Well casing
Annular area
Grout seal
Bentonite seal
Filter pack
Well screen
Well Screen and Casing Materials
Material Polyvinyl chloride (PVC)
StainlessSteel
Steel andGalvanizedPipe
Advantage Low cost
Light weight Easy to use
Medium cost
Non-reactiveHigh ductile strength
Low cost
High ductile strength
Disadvantage May react with chemicals
Limited depth due to low ductile strength
Brittle, can be difficult to work with
Not acceptable because of corrosionpotential
Materials types, advantages and disadvantages
Well Installation
Groundwater Investigations 3
Well Screen and Casing MaterialsPVC
Well ScreenStainless Steel
Continuous wrapWell Screen
Pre-Packed Well Screen
Direct Push Technology pre-packed screenPhoto courtesy of Ohio EPA
Generic pre-packed well screen design
Setting the Wellwith Centralizer
Well Installation
Groundwater Investigations 4
The purpose of filter pack is to allow the groundwater to freely flow into the well and to minimize the entrance of fine-grained materials.
Two types:Natural – less commonArtificial – more common
Well Installation – Filter Pack
A natural filter pack is where the formation material is allowed to collapse around the well screen.Acceptable in:
Coarse-grained, permeable materials, uniform in grain size
Not acceptable in:Fine grained or non-uniform materials
Natural Filter Pack
Artificial filter pack allows the use of a larger screen slot size than if natural material is used. Recommended if: ● Formation is poorly sorted● Formation is uniform fine sand, silt or clay● Well screen spans thinly stratified materials,
poorly cemented sandstones, shales and coal seams that contribute to turbidly, and
● If the borehole diameter is significantly larger than the screen diameter.
Artificial Filter Pack
Well Installation
Groundwater Investigations 5
Installing Filter Pack Material
Bentonite and Grout
Bentonite pellets, chips, and powder shown above
WellRiser Pipe
Well Installation
Groundwater Investigations 6
Finished Well Pad vs. Unfinished Well Pad
Flush MountedWells
Photo courtesy of Ohio EPA
Well Installation
Well Construction Designs for:
Unconfined Aquifers andConfined Aquifer
Well Installation
Groundwater Investigations 7
Monitoring Well Installation: Unconfined Aquifer
Weep hole
Bottom cap
Maximum frost line
Outer locking cap
Surface seal
Inner cap
Protective surface casing
Bollards
Well pad
Well casing
Annular area
Grout seal
Bentonite seal
Filter pack Well screen Unconfined
aquifer surface
(Equipotentialsurface)
Monitoring Well Installation: Confined Aquifer
Weep hole
Bottom cap
Maximum frost line
Steel casing
Inner capBollards
Well pad
Well casingGrout
seal
Bentonite seal
Filter pack
Well screen
Unconfined aquifer
Confininglayer
Confined aquifer
Potentiometric surface
Confined aquifer
Large diameter boring
Grout
Protective casing with lock
Well Installation
Well Cluster versus Nested Well
Well Installation
Groundwater Investigations 8
Well Cluster
Well clusters are two or more adjacent monitoring wells each representing a different groundwater interval or zone.
Unconfined sand & gravel aquifer
Surface
20’
10’
25’
35’
45’
55’10’
0’
Scale
Well Cluster
Two of three monitoring wells in a cluster
A nested well is constructed to monitor different groundwater intervals or zones within the same borehole.
24
Nested Well
Confined aquifer
Open from 70’ to 80’ and from 105’ to 115’ below surface
80’
70’
105’
115’
Grout to surface
Bentonite
Filter pack
Grout
Bentonite
Filter packSingle large‐diameter borehole
Well Installation
Groundwater Investigations 9
Well Installation
Well Development
The purpose for well development is to ensure good hydraulic communication between the well and surrounding formation so that the water in the well represents the current groundwater conditions.
Well Development
Proper well development facilitates the collection of low-turbidity groundwater samples and better represents the hydraulic properties of the water bearing zone.
Sample filtration is not a substitute for proper well development.
Well Development
Well Installation
Groundwater Investigations 10
A properly developed well develops a graded filter pack around the well screen.
Small amount of sediment in well
Well Development
The well development process creates a layer of coarse particles against the well screen with progressively fine grain particles away from the screen.
Well Development
Monitoring wells installed in unconsolidated, fine grained sediments are the most difficult to develop because of:
● Low yield● Difficult to create a graded filter pack● Generation of excessive silt and clay
may damage filter pack
Well development should not begin until the grout seal has cured and settled.
Well development should continue until the well water is free of visible sediment, and the pH, temperature, turbidity and specific conductivity have stabilized.
Well Development
Well Installation
Groundwater Investigations 11
Well Development Methods
The well development method should match the formation material, using:● Surging and pumping
● Over pumping
● Bailing
The most effective approach may be a combination of methods that allows for water movement in both directions through the screen to minimize filter pack bridging.
Surging and Pumping
Surging is the pushing and pulling of water into and out of the well.
Pumping removes the sediment.
Recommended for sand, gravel and bedrock aquifers.
Drawing not to scale
Surge block
Over PumpingTwo methods:● Repeatedly pumping at a
high rate to induce quick drawdown and then allowing the well to recover
● Raising and lowering an operating pump over the length of the screened interval without excessive surging
Acceptable for wells installed in clay and silt water-bearing zones.
Hose
Power cableWire line
Drawing not to scale
Pump
Well Installation
Groundwater Investigations 12
Bailing
Lowering and lifting a bailer through the water column acts as a surge block and removes the turbid water.
Effective in removing sediment from well bottom.
Drawing not to scale
Bailer
Well Installation
Temporary Wells
Temporary Wells
If temporary monitoring or remediation wells are installed, they must be compliant with the regulatory agencies.Temporary wells can be constructed with:● No filter pack
● Traditional filter pack
● Pre-packed or double filter pack
Well Installation
Groundwater Investigations 13
Temporary Injection Wells
Temporary wells for in-situ injection pilot study.
Water was injected to determine radius of influence.
Temporary Monitoring WellsNo Filter Pack
Well screen is placed inside the drive probe with a sacrificial drive point. As the drive casing is removed, the well bore either remains open or collapses around the well screen.
Temporary Monitoring WellsNo Filter Pack
Stainless steel well screen which is placed inside the drive probe with a sacrificial drive point
Photo courtesy of Ohio EPA
Well Installation
Groundwater Investigations 14
Temporary Monitoring WellsConventional Filter Pack
A temporary well may also be set like a conventional monitoring well with filter pack placed around the well screen.
Grout may or may not be used.
Photo courtesy of Ohio EPA
Temporary Monitoring WellsPre-Pack Well Screen
Pre-packed well screen eliminates the problem of placing of filter pack in a small diameter bore hole.
Photo courtesy of Ohio EPA
Pre-Pack Well Screen
Photos courtesy of Ohio EPA
Well Installation
Groundwater Investigations 15
Temporary Monitoring WellsAdvantages
● Temporary monitoring wells allow purging prior to sampling and does not idle the drilling rig from further sample collection
● Allows a quick and efficient hydrogeology delineation
● Uses less well material● Optimizes permanent well locations● Useful if permanent monitoring wells are
not permitted
Temporary Monitoring WellsDisadvantages
● Contaminated water bearing zones may be missed because of shorter screen intervals
● Well development may be insufficient and allow possible turbidity issues
● Possible loss of VOCs if no grout is present● No long term groundwater monitoring
trend results● Setting small diameter casing can be
challenging
Well Installation
Well Abandonment
Well Installation
Groundwater Investigations 16
Monitoring wells no longer in service should be properly sealed to:● Prevent cross contamination between water
bearing zones or contamination from a surface source
● Restore the aquifer to as close to its original condition as possible
● Remove physical surface hazards
● Reduce potential future liability
Well Abandonment
Prior to abandonment:● Review the well log if available ● Inspect the well● Remove all downhole equipment and debris
– and –● Disinfect the well if microbiological growth
is present
Well Abandonment
The most effective well abandonmentmethod is to remove the well casing, well screen, filter pack, and annular seal by over drilling the borehole.
The borehole should then be pressure grouted using a tremie pipe in one continuous procedure.
Well Abandonment
Well Installation
Groundwater Investigations 17
● Inspect grout plug after 24 hours to check for settling
● Add additional grout if needed● Return well surface location to be
compatible with site● Document abandonment procedure
and provide a report to the regulatory agency
Well Abandonment
In some cases monitoring wells may be sealed in-place. This is possible if:● The well construction details are known● The annular seal is intact
– and –● The filter pack does not cross more than one
water bearing zone
When wells are sealed in-place, the well casing should be grouted to 2 or 3 feet below surface and the casing cut and capped.
Well Abandonment
However, wells should not be sealed in-place if:● The annular seal is inadequate● The filter pack connects two or more water bearing zones● Water is flowing from around the outside casing
– or –● The well construction detail is not known
In these cases, the well casing, screen, annular seal and filter pack should be removed.
Well Abandonment
Well Installation
Groundwater Investigations 18
Well Abandonment
In the event the well screen cannot be removed,the well screen can be filled with clean sand to 1 foot above the screen and a 1-foot bentonite seal placed above the screen.
If the well casing cannot be removed, the casing should be split vertically or perforated at 2-foot intervals beginning 1 foot above the well screen bentonite seal and the well sealed with bentonite.
Selection of Filter Pack and Well Screen
Exercise
FINE SAND SIEVE ANALYSISSIEVE OPENING
(thousandthsof an inch)
PERCENTRETAINED
CUMULATIVEPERCENTRETAINED
16 (.016")
20 (.020")
24 (.024")
28 (.028")
18%32%20%12%
90%72%40%20%
Sediment Analysis
TABLE 1
34 (.034") 8% 8%
Well Installation
Groundwater Investigations 19
100
90
80
70
60
50
40
20
30
10
00 10 3020 6040 50 70 80 90 100 110 120 130 INCH
SIEVE or GRAIN SIZE IN THOUSANDTHS OF AN INCH
CU
MU
LATI
VE P
ERC
ENT
RET
AIN
ED
#4#5
100
90
80
70
60
50
40
20
30
10
00 10 3020 6040 50 70 80 90 100 110 120 130 INCH
SIEVE or GRAIN SIZE IN THOUSANDTHS OF AN INCH
CU
MU
LATI
VE P
ERC
ENT
RET
AIN
ED
#4#5
100
90
80
70
60
50
40
20
30
10
00 10 3020 6040 50 70 80 90 100 110 120 130 INCH
SIEVE or GRAIN SIZE IN THOUSANDTHS OF AN INCH
CU
MU
LATI
VE P
ERC
ENT
RET
AIN
ED
#4#5
AQUIFERSIEVE ANALYSIS
Well Installation
Groundwater Investigations 20
By convention, the filter pack size is determined by multiplying the value of the formation grain size shown at the 70-percent retained by 4 or 6.
Four if the formation is fine-grained and uniformSix if the formation is coarse-grained and non-uniform
Filter Pack: Selection
100
90
80
70
60
50
40
20
30
10
00 10 3020 6040 50 70 80 90 100 110 120 130 INCH
SIEVE or GRAIN SIZE IN THOUSANDTHS OF AN INCH
CU
MU
LATI
VE P
ERC
ENT
RET
AIN
ED
#4#5
AQUIFERSIEVE ANALYSIS
20
100
90
80
70
60
50
40
20
30
10
00 10 3020 6040 50 70 80 90 100 110 120 130 INCH
SIEVE or GRAIN SIZE IN THOUSANDTHS OF AN INCH
CU
MU
LATI
VE P
ERC
ENT
RET
AIN
ED
#4#5
20 80
Well Installation
Groundwater Investigations 21
Well Screen: Selection
By convention, the well screen opening size is determined by the sieve opening value at the 90% retained value of the selected filter pack material.
100
90
80
70
60
50
40
20
30
10
00 10 3020 6040 50 70 80 90 100 110 120 130 INCH
SIEVE or GRAIN SIZE IN THOUSANDTHS OF AN INCH
CU
MU
LATI
VE P
ERC
ENT
RET
AIN
ED
#4#5
8070
List well design considerations and basic well construction materials.
Differentiate between unconfined aquifer and confined aquifer monitoring well designs.
Define a well cluster and a nested well.Discuss the purpose, basic principles and methods for well development. List the advantages and disadvantages of temporary monitoring wells and describe the different well construction methods.Discuss well abandonment purpose and procedures.
Conduct well screen and filter pack selection exercise.
Lecture Objectives
Aquifer Stress Tests
Groundwater Investigations 1
AQUIFER STRESS TESTS
Aquifer Stress Test
Information collected from aquifer tests includes: Transmissivity and
storage coefficient Position and nature of
aquifer boundaries Groundwater available
for withdrawal
AQUICLUDE
Unconfined Aquifer"Non-Pumping"
WATERTABLE
SURFACE
LANDSURFACE
GROUNDWATERFLOW
Aquifer Stress Tests
Groundwater Investigations 2
LAND SURFACE
FLOWLINES WATER
LIMITS OFCONE OF
DEPRESSION
CONE OFDEPRESSION
AQUICLUDE
Q
TABLE
Unconfined Aquifer
CONE OFDEPRESSION
DRAWDOWN
Q
LAND SURFACE
LIMITS OFCONE OF
DEPRESSION
AQUICLUDE
AQUICLUDE
Potentiometric Surface
Confined Aquifer
CONFINED AQUIFER
AQUICLUDE
CONE OFDEPRESSION
POTENTIOMETRIC SURFACE
LANDSURFACE
Rr
DRAWDOWN
AQUICLUDE
0(h -h)
hh0
Q
Confined Aquifer
Aquifer Stress Tests
Groundwater Investigations 3
Aquifer Response
Rate of expansion of the cone of depression relates to the transmissivity of the aquifer.
Equilibrium vs. Non-equilibrium
Initial pumping causes a non-equilibrium cone of depression
Eventually the cone expands away from the pumping well as partly steady shape and partly unsteady shapes
Non-Pumping
CONFINEDAQUIFER
CONFININGLAYER
LAND SURFACE RIVER
CONFINING LAYER
Aquifer Stress Tests
Groundwater Investigations 4
Non-Equilibrium
CONFINEDAQUIFER
CONFININGLAYER
RIVER
AQUICLUDE
Q LAND SURFACE
CONE OF DEPRESSION(unsteady shape)
LAND SURFACE RIVERQ
AQUICLUDE
AQUICLUDE
unsteadyshape
steady shape
Non-Equilibrium
Equilibrium
LAND SURFACE RIVERQ
steady statesteady state
AQUICLUDE
AQUICLUDE
Aquifer Stress Tests
Groundwater Investigations 5
A. Equilibrium Method• Theim Test
B. Non Equilibrium Methods• Time-drawdown tests• Slug tests
Aquifer Test Methods
Gustav Theim in 1906 developed the mathematical relationship between Darcy's Law and distance-draw down data.
Theim's test required pumping from the well until the expanding cone of depression ceased to move, reaching a steady state and equilibrium
Equilibrium Method Theim's Method
Theim's Method
Disadvantages Time consuming, many days or weeks to
achieve this equilibrium During that time could produce large quantities
of water especially contaminated water Requires multiple wells to observe the growth
of the cone of depression ExpensiveAdvantages Enough time to see satellite boundaries
Aquifer Stress Tests
Groundwater Investigations 6
Non-Equilibrium Method Theis Method
Developed in 1935 by Charles Theisand was a major advancement in aquifer testing
First formula for nonsteady-state flow Groundwater flow derived from analogy
of heat flow
Non-Equilibrium Test Methods
Theis Cooper-Jacob Slug Test
Cooper–Jacob Test Method
Somewhat more convenient than Theis's method
Semilogarithmic paper straight line plot Eliminates need to solve
well function W(u) No curve matching required
Aquifer Stress Tests
Groundwater Investigations 7
Cooper–Jacobs Formulas
T = transmissivity feet squared per day (ft /day)Q = pump rate (gpm)∆s= change in drawdown (ft/log cycle)K = hydraulic conductivity ft /dayb = aquifer thickness (feet)
T = TbK =
2
35 Q∆s
Cooper–Jacobs Semi Log Plot
Cooper - Jacobs Method
Advantages Less time to perform test; consider
straight-line drawdown over one log cycle on the semi log graphical plot
Only one well required Tests larger aquifer volume than slug
test
Aquifer Stress Tests
Groundwater Investigations 8
Cooper - Jacobs Method
Disadvantages Requires conductivities >10-2 cm/s Tests smaller portion of the aquifer
volume than multiple-well tests Must handle discharge water
Perform on low-yielding aquifers (between 10-7 to 10-2 cm/s)
Water level is abruptly raised or lowered using a slug or volume of water
Water level changes are recorded, and a ratio of these changes (h) to the initial change in head (h0) measurement is calculated and plotted against the time when these changes occurred
Slug Tests
The graph allows one to determine the "hydrostatic time lag" (T0), i.e., the amount of time necessary to obtain pressure equalization between the measuring device and the aquifer
This time lag accounts for some of the error encountered in performing this type of test
Slug Tests
Aquifer Stress Tests
Groundwater Investigations 9
Slug Tests
o.63
Slug Tests
Advantages Can use small-diameter well No pumping no discharge Inexpensive less equipment required Estimate made in situ Interpretation/reporting time is shortened
Disadvantages Very small volume of aquifer tested Only apply to low conductivities Transmissivity and conductivity
only estimates Not applicable to large-diameter wells Large errors if well not properly
developed
Slug Tests
Unsaturated Zone
Groundwater Investigations 1
Unsaturated Zone
Lecture Objectives
Discuss water movement within the unsaturated zone
Discuss principals of vapor intrusion Present vapor intrusion case study
Sandy silt
Water table
Loam
Sand and gravel
Sand
Bedrock
Unsaturated Zone
Unsaturated Zone
Groundwater Investigations 2
Why Discuss Unsaturated Zone?
Recharge of groundwater zones often occurs with the percolation of surface water or contaminants flowing through the unsaturated zone.
Flow can be influenced by physical and chemical properties of the unsaturated zone
Unsaturated Flow
Defined as the movement of water through the unsaturated zone.
Water flow in the unsaturated zone is controlled by the combination of gravitational and capillary forces.
Gravitational and Capillary Forces
Gravitational force is the downward pull on water and encourages infiltration.Capillarity force is the combination of: Cohesion, the mutual attraction between
water molecules Adhesion, the molecular attraction
between water and different solid materials
Unsaturated Zone
Groundwater Investigations 3
Capillarity
As a result of capillary forces, water will rise in the pore throats of a porous media above the water table or a water surface.
Figure from USGS Water-Supply Paper 2220
Unsaturated FlowThe steady state of water flow in the unsaturated zone is determined by a modified Darcy's law:
Q = Ke A (hc-z)/z ± (dh/dl)Q = Quantity of water A = Area of flowKe = Effective hydraulic conductivity under the degree of
water saturation existing in the unsaturated zone(hc-z)/z = gradient due to capillary force±dh/dl = gradient due to gravity. The plus or minus sign is
related to the direction of movement-plus for downward and minus for upward.
The variables in the modified Darcy's law are:
Q = Ke A (hc-z)/z ± (dh/dl)
Effective hydraulic conductivity (Ke) and Capillary force (hc-z)/z
Unsaturated Flow
Unsaturated Zone
Groundwater Investigations 4
Unsaturated Flow
Effective hydraulic conductivity (Ke) is the hydraulic conductivity of the material that is not completely saturated.
The value can change based on the water content of the unsaturated zone.
Figure from USGS Water-Supply Paper 2220
The capillary forces (hc-z)/z can change based on the length of the capillary water column (z) in relation to the maximum possible height of capillary rise (hc).
Figure from USGS Water-Supply Paper 2220
Unsaturated Flow
Because most unconsolidated sediments are deposited in stratified layers, the water or contaminants must percolate vertically through horizontal layers.
Each layer may have a different effective hydraulic conductivity and capillary force.
Unsaturated Flow
Unsaturated Zone
Groundwater Investigations 5
Unsaturated Flow, Un-Stratified Bed
Figure from USGS Water-Supply Paper 2220
Model filled with consistent sized medium-sand glass beads (diameters of 0.47 mm) having a capillary height of about 250 mm and a hydraulic conductivity of 82 m/day.
Figure from USGS Water-Supply Paper 2220
The water in Beds A and C spread horizontally because of the strong capillary force and the low hydraulic conductivity. Because the hydraulic conductivity of Beds B and D is 100 times greater than Bed A and C, the water moved vertically downward.
Unsaturated Flow, Stratified Bed
Vapor Intrusion
Image from ITRC (Interstate Technology & Regulatory Council). 2007. Vapor Intrusion Pathway: A Practical Guideline. VI-1. Washington, D.C.: Interstate Technology & Regulatory Council, Vapor Intrusion Team. www.itrcweb.org.
Unsaturated Zone
Groundwater Investigations 6
Vapor Intrusion
Source of vapors are either from vapors in the unsaturated zone or a migrating plume dispensing vapors into the unsaturated zone.
Vapor IntrusionVapors move through the unsaturated zone by: Diffusion - the expansion of gases
from high concentrations to lower concentrations
Advection - the movement of gases through pressure changes (in vapor intrusion issues this may occur near buildings)
Vapor IntrusionThe movement of the vapors from the subsurface into a structure depend on: Depth to groundwater (if source is from
groundwater contamination) Soil and unconsolidated material types
below the structure Chemical properties of the contaminant Structure design and condition Pressure differential
Unsaturated Zone
Groundwater Investigations 7
Vapor Intrusion
Image from ITRC (Interstate Technology & Regulatory Council). 2007. Vapor Intrusion Pathway: A Practical Guideline
This ITRC graphic shows vapors entering the structure through advection.
This can be caused by stack effect, exhaust fans, wind effects, thermal currents, and barometric pressure changes.
Behr VOC SiteDayton, Ohio
Vapor Intrusion Case Study
Common Characteristics of Vapor Intrusion Sites in Southwest Ohio
Shallow groundwater (<25’) Sand & Gravel Aquifer VOC or petroleum
groundwater contamination VOCs in GW > 200ppb Residential area over
groundwater plume 1940s industrial
complex…plant surrounded by houses
Residential homes with basements (biggest variable)
Unsaturated Zone
Groundwater Investigations 8
What is Vapor Intrusion?
Groundwater Contamination
Chemical Spill-Trichloroethylene (TCE)
Groundwater contamination . . . inhalation?
Connects groundwater, soil gas, sub slab gas, and indoor air.
What are Screening Levels?
Chemical Spill-TCE
Screening levels provided by ODH and ATSDR. For TCE (residential):• Sub-Slab Screening Level = 4 ppb• Indoor Air Screening Level = 0.4 ppb
2003 Ohio EPA Ground-
water Results
Source Area =20,000 ppb
Unsaturated Zone
Groundwater Investigations 9
Vapor Intrusion
Groundwater Contamination
TCE Chemical Spill
Groundwater TCE = 20,000 ppb
MW033s TCE = 3,800 ppb
MW028s TCE = 3,900 ppb
MW038s TCE = 3,900 ppb
Groundwater Data2003-2006
MW029s TCE = 16,000 ppb
Groundwater TCE concentrations near
houses.
Vapor Intrusion
Groundwater Contamination
TCE Chemical Spill
Groundwater TCE = 16,000 ppbGroundwater TCE
= 20,000 ppb
Unsaturated Zone
Groundwater Investigations 10
Soil Gas Sampling Results
Oct 24, 2006
7 Locations sampledutilizing Geoprobe
Location TCE (ppbv)SG-01 120,000 SG-02 70,000SG-03 160,000SG-04 140,000 SG-05 13,000SG-06 16,000 SG-07 12,000
Vapor Intrusion
Groundwater Contamination
TCE Chemical Spill
Groundwater TCE = 16,000 ppb
Soil Gas TCE = 160,000 ppb
Groundwater TCE = 20,000 ppb
Request for Assistance
Ohio EPA requested assistance from U.S. EPA on November 6, 2006
Noted elevated levels of TCE present in soil gas and groundwater.
Evaluate potential for Vapor Intrusion into occupied structures.
Unsaturated Zone
Groundwater Investigations 11
Sub-Slab Sampling
Groundwater Contamination
TCE Chemical Spill
Groundwater TCE = 16,000 ppb
Soil Gas TCE = 160,000 ppb
Sub-Slab sampling conducted. TCE screening level = 4 ppb
Groundwater TCE = 20,000 ppb
Sub Slab Air Sampling
EPA sampled sub-slab air in 8 residences in November 2006.
Location TCE (ppb)
EPA-01 980EPA-02 18,000EPA-03 16,000EPA-04 260EPA-05 62,000EPA-06 3,700 EPA-07 49 EPA-08 62,000
ATSDR & ODH Sub-Slab Screening Level = 4 ppb
EPA Sub-SlabSample ResultsNovember 2006
Unsaturated Zone
Groundwater Investigations 12
Vapor Intrusion
Groundwater Contamination
TCE Chemical Spill
Groundwater TCE = 16,000 ppb
Soil Gas TCE = 160,000 ppb
Sub-slab TCE = 62,000 ppb
Groundwater TCE = 20,000 ppb
Indoor Air Sampling
Groundwater Contamination
TCE Chemical Spill
Groundwater TCE = 16,000 ppb
Soil Gas TCE = 160,000 ppb
If Indoor Air Sample >0.4 ppb, mitigation required
Sub-slab TCE = 62,000 ppb
Groundwater TCE = 20,000 ppb
Pre-Sample Residential Checklist
Screen indoor airprior to indoor airsampling to identifyresidential interferences
Unsaturated Zone
Groundwater Investigations 13
Location TCE (ppb)
EPA-01 1.9 EPA-02 180 EPA-03 130EPA-04 13EPA-05 260EPA-06 7.5EPA-07 0.4EPA-08 49
ATSDR & ODH Indoor Air Screening Level = 0.4 ppb
EPA Indoor AirSample ResultsNovember 2006
Vapor Intrusion
Groundwater Contamination
TCE Chemical Spill
Groundwater TCE = 16,000 ppb
Soil Gas TCE = 160,000 ppb
Sub-slab TCE = 62,000 ppb
Indoor Air TCE = 260 ppb
ATSDR & ODH:Completed ExposurePathway
Groundwater TCE = 20,000 ppb
Vapor Abatement Mitigation System(Sub-Slab Depressurization System or SSDS)
Radius of Influence?Least amount of vacuum?
Unsaturated Zone
Groundwater Investigations 14
Vapor Abatement System InstallationExtraction Pipe into Slab
Based on radius of influence testing, multiple extraction points may be necessary.Note: Looking for entire slab to be under vacuum
Fan installed with electric on/off switchin a lockbox. Key provided to owner
VAS $ = average $1,500 installation
Vapor Abatement System InstallationOutside Fan and Vent
Vapor Abatement System InstallationRadius of Influence Testing
Radius of Influence testing = 96% successrate on initial installation at the Behr Site
Success = 30 & 90 day samples < IA screening level
Unsaturated Zone
Groundwater Investigations 15
Vapor Abatement System InstallationCrawl Space Application
Vapor Abatement System InstallationDirt Basement (Test Case)
Vapor Abatement System InstallationDirt Basement
Plastic netting applied under concreteto increase air flow to extraction pipe
Concrete creates impervious layer
Unsaturated Zone
Groundwater Investigations 16
Highest vacuum achieved based on radius of influence testing.
Vapor Abatement System InstallationDirt Basement
Vapor Abatement System InstallationU Tube Manometer on Extraction Pipe
1"- 2" vacuum applied to extraction point
30 & 90 Day Performance Sampling
30 & 90 day sampling performed to confirm ATSDR screening levelshave been achieved. 180 day sampling completed per HD request.
Geophysical Methods
Groundwater Investigations 1
GeophysicalMethods
Geophysics Nonintrusive, investigative tool Methods specific to site Professional interpretation Interpretation needs to be
ground-truthed
Relative Site Coverage
VOLUME OF TYPICAL GEOPHYSICAL MEASUREMENT
VOLUME OF DRILLING OR WATER SAMPLING
Geophysical Methods
Groundwater Investigations 2
Anomaly
Significant variationfrom background
Interpretations are non-unique
Geophysical Techniques Magnetics Electromagnetics (EM) Electrical resistivity Seismic refraction/reflection Ground-penetrating radar Borehole geophysics
Magnetics Measurement of magnetic field strength
in units of nanoTeslas Anomalies are variations in magnetic
field strength from the ambient field Anomalies can be positive or negative
Geophysical Methods
Groundwater Investigations 3
Magnetometer
RECORDER
Magnetic Field Sensors
FERROUS MATERIAL ALTERING EARTH'S
MAGNETIC FIELD
40
100
80
60
0
20
CH
ANG
E IN M
AGN
ETIC FIELD
(Nano-Tesla)
GROUND SURFACE
Cesium magnetometer –Gradiometer configuration
Geophysical Methods
Groundwater Investigations 4
Magnetics: Advantages
Relatively low cost for area covered Short time frame required Little site preparation needed Relatively simple line locations are sufficient
Magnetics: Limitations Cultural noise limitations Difficulty in differentiating between objects
(i.e., 55-gallon drums and a refrigerator) Only iron or steel objects are detected Depth determination difficult
Electromagnetics: EM-31
Measures bulk conductivity
Geophysical Methods
Groundwater Investigations 5
Electromagnetics: EM-31 Based on physical principles of
inducing and detecting electrical flow within geologic strata
Measures bulk conductivity beneath the transmitter and receiver coils
EM-31 is a frequency domain instrument
Electromagnetics: EM-61 EM-61 is basically a metal detector It also uses electric fields but in the
time domain It is very good at locating drums
and tanks No geologic data
is obtained
Rapid data collection with minimum personnel
Lightweight, portable equipment Commonly used in groundwater
pollution investigations for determining plume flow direction (EM-31 and 34)
Electromagnetics: Advantages
Geophysical Methods
Groundwater Investigations 6
Cultural noise limitations, – Sometimes there is difficulty
operating near buildings, fences, etc
Limitations in areas where geology varies laterally– Anomalies can be misinterpreted
as plumes
Depth of penetration limited by coil spacing (EM-31, EM-34)
Electromagnetics: Limitations
ResistivitySurvey
Resistivity Survey Setup
STING Resistivity Unit
Electrodes
Wires for electrodes
Tape measures for laying out wires
Geophysical Methods
Groundwater Investigations 7
Electrical Resistivity
Measures the bulk resistivity of the subsurface in ohm-meter units
Current is injected into the ground through surface electrodes
Electrical ResistivityWenner Array
CurrentPotential
Current Source Ammeter
Volt Meter
SURFACE
Current FlowThrough the Earth
C1 C2P2P1
Depth of investigation is equal to one-fourth to one-third of the distance
between electrodes
Electrical Resistivities of Geologic Materials
Media Porosity Permeability Water saturation Concentration of dissolved solids
in pore fluids
Function of:
Geophysical Methods
Groundwater Investigations 8
Electrical Resistivity Data
INVERSE MODEL RESISTIVITY SECTION
0.5
6.5
2.9
9.0
12.2
16.1
44.0 82.2 536154 287 1001 1869 3491Unit electrode spacing 3.0 m.Resistivity in ohm.m
LIMESTONECAVERN
SOIL3.06.0
9.0
Qualitative modeling of data is feasible Models can be used to estimate depths,
thicknesses, and resistivities of subsurface layers
These resistivities are somewhat indicative of the material observed
Electrical Resistivity: Advantages
Layer resistivities can be used to estimate resistivity of saturating fluid
Extent of groundwater plume can be approximated
Electrical Resistivity: Advantages
Geophysical Methods
Groundwater Investigations 9
Cultural noise limitations– Fences, buildings, piping
Large area free from grounded metallic structures required
May require a significant level of effort and/or number of trained personnel– Newer units require fewer, better
trained people
Electrical Resistivity: Limitations
SEISMICSOURCE
GEOPHONES
REFLECTED WAVE
SEISMIC WAVE PATHS
2500fps
sand
5000fps
saturatedsand
REFRACTED WAVE
Seismic Refraction
Seismic Refraction Measures travel time of acoustic
wave refracted along an interface Most commonly used at sites where
bedrock is less than 500 feet below ground surface
Geophysical Methods
Groundwater Investigations 10
BEDROCK
GEOPHONE ARRAYTRIGGER
CABLE
SEISMOGRAPHHAMMERSOURCE
Seismograph Field Layout Showing Direct and Refracted Waves
FIRST ARRIVAL WAVE FRONTSSECOND ARRIVAL WAVE FRONTS
SOIL
DIRECTWAVES
Seismometer Setup
Computer with seismic program
Geophone cable connection box
Seismic SurveyPlanting the geophones
Geophysical Methods
Groundwater Investigations 11
Wave Signatures
0102030405060708090
100110120
10 9080706050403020
DIS
TAN
CE
FRO
M S
OU
RC
ETIME
Seismic Refraction:Assumptions
Velocities of layers increase with depth Velocity contrast between layers is
sufficient to resolve interface Geometry of geophones in relation to
refracting layers will permit detection of thin layers
Seismic Refraction:Advantages
Layer velocities indicative of material Calculate estimates of depths to
different rock or groundwater interfaces Obtain subsurface information
between boreholes Determine depth to water table
Geophysical Methods
Groundwater Investigations 12
Seismic Refraction:Limitations
There is an assumption that the material velocity always increases with each layer
That each layer is thick enough to be detected
There is no way to test these other than a seismic reflection survey or drilling
Depth is related to spread length
Ground-Penetrating Radar
An antenna transmits high-frequency electromagnetic energy into the subsurface. This energy is reflected back to the receiving antenna from material interfaces and recorded.
Ground-Penetrating Radar
Data Display
Antenna
GPS unit
Data Display
Geophysical Methods
Groundwater Investigations 13
Ground-Penetrating Radar: Advantages
Continuous display of data Highest resolution data under favorable
site conditions Real-time site evaluation possible Very good water table and
sediment layer determination possible
Depth of penetration adversely affected by high clay content
Fairly shallow (100 feet) even with excellent conditions
Site preparation may be necessary for survey
Quality of data can be degraded by cultural noise, surface conditions and uneven ground surface
Ground-Penetrating Radar: Limitations
BoreholeGeophysics
Geophysical Methods
Groundwater Investigations 14
Resistivity Log
UNSATURATED SANDY CLAY
UNSATURATED SILTY SAND
CLAY
SATURATED SILTY SAND
SATURATED SANDY
GRAVEL
FRACTUREDGRANITE
0
50
150
100
200
API UNITS0 15050
-50
150 OHMS
NATURAL GAMMA SINGLE POINT RESISTANCEMILLI VOLTS 0 OHM METER 200+50
SP
-50SINGLE POINT RESISTANCE
64" NORMAL RESISTIVITY0 OHM METER 200
16" NORMAL RESISTIVITY
GAMMA
64"BACKUP
RESISTANCE16"
16"64"
Borehole Geophysics Normal resistivity Natural-gamma Gamma-gamma Electromagnetic Induction Neutron Caliper Temperature Full Wave Sonic Down hole camera
Geophysical Methods
Groundwater Investigations 15
Resistivity Measures apparent resistivity of a
volume of rock or soil surrounding the borehole
Radius of investigation is generally equal to the distance between the borehole current and measuring electrodes
Can only be run in open, fluid-filled boreholes
Natural Gamma Measures the amount of
natural-gamma radiation emitted by rocks or soils (Potassium-40)
Primary use is identification of lithology and stratigraphic correlation
Can be run in open or cased and fluid- or air-filled boreholes
Density Probe Measures the intensity of gamma
radiation from a source in the probe after it is backscattered and attenuated in the rocks or soils surrounding the borehole
Also known as gamma-gamma tool
Geophysical Methods
Groundwater Investigations 16
Primary use is identification of lithology and measurement of bulk density and porosity of rocks or soils
Can be run in open or cased and fluid- or air-filled boreholes
Density Probe
Electromagnetic Induction Measures the conductivity of the rock Measures the conductivity of the pore fluid Useful for correlating lithology and
conductive plumes Technique the same as surface frequency
domain EM (EM-31)
Neutron Measures moisture content in the
vadose zone and total porosity in sediments and rocks
Neutron sources and detector are arranged in logging device so that output is mainly a function of water within the borehole walls
Can be run in open or cased and fluid-or air-filled boreholes
Geophysical Methods
Groundwater Investigations 17
Caliper Records borehole
diameter and provides information on fracturing, bedding plane partings, or openings that may affect fluid transport
Can be run in open or cased and fluid-or air-filled boreholes
Temperature A continuous record of the temperature
of the environment immediately surrounding the borehole
Information can be obtained on the source and movement of water and the thermal conductivity of rocks
Can be run in open or cased, fluid-filled boreholes
Full Wave Sonic Acoustic wave form is recorded by one
or two sensors Compressional, Shear and Stoneley
waves are recorded and analyzed Porosity, permeability, bulk modulus,
shear modulus and Poisson’s ratio can be calculated
Used in fluid filled open holes
Geophysical Methods
Groundwater Investigations 18
Borehole Video LoggingBorehole video logging provides a visual picture of borehole conditions.
Useful in identifying fractures, voids, cascading water, well/boring blockage and other downhole trouble shooting.
Plas
tic R
iser
Plas
ticSc
reen Au
ger F
light
Screened Auger
CaliperNatural GammaNeutronGamma-GammaFlowmeterAcoustic TomographyTemperatureFluid ResistivityVideoDeviation
Same As Above +Single Point-Resistivity
CaliperNatural GammaNeutronGamma-GammaFlowmeterFluid ResistivityVideo
CaliperNatural Gamma
NeutronGamma-Gamma
FlowmeterTemperature
Fluid ResistivityVideo
Same As Above
CaliperNatural Gamma
NeutronGamma-Gamma
FlowmeterTemperature
Fluid ResistivityVideo
6 Various Casing Conditions
Log ApplicationGuide
Metal R
iserM
etalScreen
Geophysical Methods
Groundwater Investigations 19
InstrumentsSurface Geophysics
EM – Geonics, www.geonics.com– Dualem, www.dualem.com– Geophex, www.aeroquestsensortech.com
Radar – Sensors and Software, www.sensoft.ca– GSSI, www.geophysical.com
Magnetics– Geometrics, www.geometrics.com– Gem Systems, www.gemsys.ca
InstrumentsSurface Geophysics
Resistivity– ABEM, www.abem.se– Advanced Geosciences Inc., www.agiusa.com
Seismic– Geometrics, www.geometrics.com– Seistronix, www.seistronix.com
Geophysical logging– Mount Sopris Instruments, www.mountsopris.com
References / SourcesBorehole Geophysics
Applications of Borehole Geophysics to Water-Resources Investigations, USGS– http://pubs.usgs.gov/twri– http://ny.water.usgs.gov/projects/bgag/intro.text.html
Introduction to Groundwater Investigations
GLOSSARY AND ACRONYMS
acre-foot enough water to cover 1 acre to a depth of 1 foot; equal to 43,560 cubic feet or 325,851 gallons adsorption the attraction and adhesion of a layer of ions from an aqueous solution to the solid mineral surfaces with which it is in contact advection the process by which solutes is transported by the bulk motion
of the flowing groundwater alluvium a general term for clay, silt, sand, gravel, or similar unconsolidated material deposited during comparatively
recent geologic time by a stream or other body of running water as sorted or semisorted sediment in the bed of the stream or on its floodplain or delta, or as a cone or fan at the base of a mountain slope
anisotropic hydraulic conductivity (“K”), differing with direction aquifer a geologic formation, group of formations, or a part of a
formation that contains sufficient permeable material to yield significant quantities of groundwater to wells and springs. Use of the term should be restricted to classifying water bodies in accordance with stratigraphy or rock types. In describing hydraulic characteristics such as transmissivity and storage coefficient, be careful to refer those parameters to the saturated part of the aquifer only.
aquifer test a test involving the withdrawal of measured quantities of water
from, or the addition of water to, a well (or wells) and the measurement of resulting changes in head (water level) in the aquifer both during and after the period of discharge or addition
aquitard a saturated, but poorly permeable bed, formation, or group of
formations that does not yield water freely to a well or spring artesian confined; under pressure sufficient to raise the water level in a
well above the top of the aquifer artesian aquifer see confined aquifer artificial recharge recharge at a rate greater than natural, resulting from
deliberate or incidental actions of man
Introduction to Groundwater Investigations
BTEX benzene, toluene, ethylbenzene, and xylenes capillary zone negative pressure zone just above the water table where
water is drawn up from saturated zone into matrix pores due to cohesion of water molecules and adhesion of these molecules to matrix particles. Zone thickness may be several inches to several feet depending on porosity and pore size.
capture the decrease in water discharge naturally from a ground-water reservoir plus any increase in water recharged to the reservoir
resulting from pumping coefficient of storage the volume of water an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in head cone of depression depression of heads surrounding a well caused by withdrawal
of water (larger cone for confined aquifer than for unconfined) confined aquifer geological formation capable of storing and transmitting water in usable quantities overlain by a less permeable or impermeable formation (confining layer) placing the aquifer under pressure confining bed a body of “impermeable” material stratigraphically adjacent to one or more aquifers diffusion the process whereby particles of liquids, gases, or solids intermingle as a result of their spontaneous movement caused by thermal agitation discharge velocity an apparent velocity, calculated from Darcy’s law, which
represents the flow rate at which water would move through the aquifer if it were an open conduit (also called specific discharge)
discharge area an area in which subsurface water, including both groundwater and water in the unsaturated zone, is discharged to the land surface, to surface water, or to the atmosphere
dispersion the spreading and mixing of chemical constituents in
groundwater caused by diffusion and by mixing due to microscopic variations in velocities within and between pores
Introduction to Groundwater Investigations
DNAPL dense, non-aqueous phase liquid drawdown the vertical distance through which the water level in a well is
lowered by pumping from the well or nearby well effective porosity the amount of interconnected pore space through which fluids
can pass, expressed as a percent of bulk volume. Part of the total porosity will be occupied by static fluid being held to the mineral surface by surface tension, so effective porosity will be less than total porosity.
evapotranspiration the combined loss of water from direct evaporation and
through the use of water by vegetation (transpiration) flow line the path that a particle of water follows in its movement
through saturated, permeable materials gaining stream a steam or reach of a stream whose flow is being increased by
inflow of groundwater (also called an effluent stream) gpm gallons per minute groundwater reservoir all rocks in the zone of saturation (see also aquifer) groundwater divide a ridge in the water table or other potentiometric surface from which groundwater moves away in both directions normal to
the ridge line groundwater system a groundwater reservoir and its contained water; includes
hydraulic and geochemical features groundwater model simulated representation of a groundwater system to aid
definition of behavior and decision-making groundwater water in the zone of saturation head combination of elevation above datum and pressure energy
imparted to a column of water (velocity energy is ignored because of low velocities of groundwater). Measured in length units (i.e., feet or meters).
heterogeneous geological characteristics varying aerially or vertically in a
given system homogeneous geology of the aquifer is consistent; not changing with
direction or depth
Introduction to Groundwater Investigations
hydraulic conductivity volume flow through a unit cross-section area per unit decline
in head hydraulic gradient change of head values over a distance H1 – H2 L where: H = head L = distance between head measurement points hydrogeology the study of interactions of geologic materials and processes
with water, especially groundwater hydrograph graph that shows some property of groundwater or surface
water as a function of time impermeable having a texture that does not permit water to move through it
perceptibly under the head difference that commonly occurs in nature
infiltration the flow of movement of water through the land surface into
the ground interface in hydrology, the contact zone between two different fluids intrinsic permeability pertaining to the relative ease with which a porous medium
can transmit a liquid under a hydrostatic or potential gradient. It is a property of the porous medium and is independent of the nature of the liquid or the potential field.
isotropic hydraulic conductivity (“K”) is the same regardless of direction K hydraulic conductivity (measured in velocity units and
dependent on formation characteristics and fluid characteristics)
laminar flow low velocity flow with no mixing (i.e., no turbulence) LNAPL light, non-aqueous phase liquid losing stream a stream or reach of a stream that is losing water to the
subsurface (also called an influent stream)
Introduction to Groundwater Investigations
mining in reference to groundwater, withdrawals in excess of natural replenishment and capture. Commonly applied to heavily pumped areas in semiarid and arid regions, where opportunity for natural replenishment and capture is small. The term is hydrologic and excludes any connotation of unsatisfactory water-management practice
MSL mean sea level non-steady state (also called non-steady shape or unsteady shape) the
condition when non-steady shape the rate of flow through the aquifer is changing and water levels are declining. It exists during the early stage of withdrawal when the water level throughout the cone of depression is declining and the shape of the cone is changing at a relatively rapid rate.
steady state (also called steady shape) is the condition that exists during
the intermediate stage of withdrawals when the water level is still declining but the shape of the central part of the cone is essentially constant
optimum yield the best use of groundwater that can be made under the
circumstances; a use dependent not only on hydrologic factors but also on legal, social, and economic factors
overdraft withdrawals of groundwater at rates perceived to be excessive
and, therefore, an unsatisfactory water-management practice (see also mining)
perched aquifer a zone of saturation in a formation that is discontinuous from
the water table and the unsaturated zones surrounding this formation. Some regulatory agencies include an upper limit on the hydraulic conductivity of the perched aquifer
permeability the property of the aquifer allowing for transmission of fluid
through pores (i.e., connection of pores) permeameter a laboratory device used to measure the intrinsic permeability
and hydraulic conductivity of a soil or rock sample piezometer a non-pumping well, generally of small diameter, that is used
to measure the elevation of the water table or potentiometric surface. A piezometer generally has a short well screen through which water can enter.
Introduction to Groundwater Investigations
porosity the ratio of the volume of the interstices or voids in a rock or soil to the total volume
potentiometric surface imaginary saturated surface (potential head of confined
aquifer); a surface that represents the static head; the levels to which water will rise in tightly cased wells
recharge the processes of addition of water to the zone of saturation recharge area an area in which water that enters the subsurface eventually
reaches the zone of saturation safe yield magnitude of yield that can be relied upon over a long period
of time (similar to sustained yield) saturated zone zone in which all voids are filled with water (the water table is
the proper limit) slug-test an aquifer test made by either pouring a small instantaneous
charge of water into a well or by withdrawing a slug of water from the well (when a slug of water is removed from the well, it is also called a bail-down test)
specific yield ratio of volume of water released under gravity to total volume
of saturated rock specific capacity the rate of discharge from a well divided by the drawdown in it.
The rate varies slowly with the duration of pumping, which should be stated when known.
steady-state the condition when the rate of flow is steady and water levels
have ceased to decline. It exists in the final stage of withdrawals when neither the water level nor the shape of the cone is changing.
storage coefficient “S” volume of water taken into or released from aquifer storage
per unit surface area per unit change in head (dimensionless) (for confined, S = 0.0001 to 0.001; for unconfined, equal to porosity)
storage in groundwater hydrology, refers to 1) water naturally detained
in a groundwater reservoir, 2) artificial impoundment of water in groundwater reservoirs, and 3) the water so impounded
Introduction to Groundwater Investigations
storativity the volume of water an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in head (also called coefficient of storage)
sustained yield continuous long-term groundwater production without
progressive storage depletion (see also safe yield) transmissivity the rate at which water is transmitted through a unit width of
an aquifer under a unit hydraulic gradient unsaturated zone the zone containing water under pressure less than that of the (vadose zone) atmosphere, including soil water, intermediate unsaturated
(vadose) water, and capillary water. Some references include the capillary water in the saturated zone. This upper limit of this zone is the land surface and the lower limit is the surface of the zone of saturation (i.e., the water table).
water table surface of saturated zone area at atmospheric pressure; that
surface in an unconfined water body at which the pressure is atmospheric. Defined by the levels at which water stands in wells that penetrate the water body just far enough to hold standing water.