United States Ofﬁ Environmental Protection Agency Superfund … · 2014. 3. 12. · Fisherville Case Study Temporary dam built in stream to create a hydraulic head. The hydraulic

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


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




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



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



Groundwater Discharge

Unconfined Aquifer

Confined Aquifer



Perched Aquifer

Aquifer Properties

Groundwater AquifersPrimary Openings

Unconsolidated Aquifer MaterialPoorly sorted, stratified, sands and gravels



Groundwater AquifersSecondary OpeningsGroundwater in Caverns

Limestone, Indiana

Fractured Sandstone

Groundwater AquifersSecondary Openings

Groundwater Contaminants



Groundwater ContaminantsPetroleum products are a common groundwater contaminant. Referred to as a Light Non-aqueous Phase Liquid (LNAPL)


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 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


Site investigation initiated because of the discovery of oil in the former Blackstone Canal



Fisherville Mill, Grafton, MAOil release discovered in Old Blackstone Canal

Looking north at Blackstone Canal Bridge

Looking south


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


Initial TCE treatment system destroyed in 1990 fire





Position of TCE plume during thewinter months

Blackstone River



Position of TCE plume during thesummer months



TCE plume affected during the summer months by pumping of a municipal well (GP#3)

Pumping wellGP#3





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



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


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


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


OCEAN

LARGE SMALL

Sediment Grain Size

POOR WELL

Sediment Sorting

OCEAN

ANGULAR ROUNDED

Sphericity of Sediment

OCEAN

Groundwater Regions


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 Regions

Columbia Lava Plateau

Alluvial Basins Colorado

Plateau and

Wyoming Basin

Nonglaciated Central Region

Alluvial Basin

Western Mountain Ranges


Atlantic and Gulf Coastal

Plain



Northeast and

Superior Uplands Northeast

and Superior Uplands

Piedmont and Blue

Ridge

Southeast Coastal Plain

High Plains

High Plains



Non-glaciated Central Region


Northeast & Superior Uplands Region

Glacial deposits over fractured crystalline rocks.

Northeast Region

Bedrock Map

Groundwater Regions


Superior Uplands Region

Groundwater Map

Northeast Region

Blackstone RiverGrafton, Massachusetts

Northeast Region

Blackstone River DepositsGrafton, Massachusetts

Groundwater Regions


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


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


Highland County, VA

Piedmont & Blue Ridge Region

Aquifers In Semi Consolidated and Consolidated Rocks

Groundwater Regions


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


Groundwater Regions



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


Southeast Coastal Plain Region

Thick layers of sand and clay over semi-consolidated carbonate rocks.

Southeast Region Aquifers

Cape Canaveral, FL


Groundwater Regions


Southeast Coastal Plain Region

Floridan Aquifer

Non-Glaciated Limestone Region

Thin regolith over limestone bedrock forming a Karst topography.

LimestoneCentral Kentucky

Groundwater Regions


Karst Topography


– 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


Red Penn SiteCarrollton, KY


Glacial deposits over fractured sedimentary rocks.

Glaciated Regions of United States

Groundwater Regions


Process of Glaciation

• Erosion

• Transportation• Deposition

Glacial GroovesTurnagain BasinCook Inlet, AK

Ruth GlacierDenali National Park, AK

Groundwater Regions


Glacial Deposits


– Outwash and till– Moraines– Drumlins

– Eskers– Kettle holes– Kames

Glacial OutwashSeward, AK

Glacial Outwash Southwest Ohio

Great Miami River, Hamilton, Ohio

Groundwater Regions


Mt. Spurr Ash, AK

Loess Deposit

Loess Deposit, Southwest Iowa

High Plains, Braided Stream Region

Thick alluvial deposits over fractured sedimentary rock.

Groundwater Regions


Braided StreamKnik Arm, Cook Inlet

Characteristics ofBraided Streams


– 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


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


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)


Fluvial deposits over fractured crystalline rocks.

Groundwater Regions



Mountain ValleyAlluvial Deposit

Grand Lake, CO


Area of Alluvial Basins

Groundwater Regions


Alluvial Basin Region

Northwest of Lake Mead, NV


Thick alluvial deposits in basins & valley bordered by mountains and locally of glacial origin

West of Lake Mead, NV

Groundwater Regions


Thick alluvial deposits in basins & valley bordered by mountains


Death ValleyNational Park

Characteristics ofAlluvial Fans


– Poor sorting and rounding– High gradients– Shallow and intermittent streams

– Hand-shaped

Groundwater Regions


Alluvial Fan: Death Valley


Major Aquifers of

California

Colorado Plateau, Wyoming Basin

Groundwater Regions



Grand Canyon, AZ

Grand Canyon, AZ


Volcanic Rocks of the Northwest


Groundwater Regions


PNW Major Aquifers


Thick sequence of lava flows irregularly interbedded with thin unconsolidated deposits and overlain by thin soils.

Interflow sediments below

basalt flow


Groundwater Regions


Drilling Methods


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


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


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


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


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


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


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


Direct Push Technology (DPT)

DPT Platforms

Samples collected using DPT

Drilling Methods


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


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


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


Rotosonic

Rotosonic Drilling

Photo courtesy of Boart-Longyear, Inc.

Rotosonic Drilling

Drilling Methods


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


CoreBarrelsExtruded

Samples

Drill Rods

OverrideCasings


Drilling Methods



CoreBarrels

OverrideCasings


Drill Rods

ExtrudedSamples

Rotosonic Drilling

Power Head

Photo Courtesy State of Washington, Department of Ecology

Rotosonic Samples

Drilling Methods


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


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


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



MIP recording devices and carrier gas cylinders


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


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


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


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


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


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


Stream Flow

Stream Flow

Q = Av

A (cross-sectional area)Q (discharge)

v (velocity)

Gaining Stream

DISCHARGE = 10 cfs

DISCHARGE = 8 cfs

Hydrogeology


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


Sediment and Water Capacity Relationships

Void Space Volume: Porosity

Water Saturation

Hydrogeology


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


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


Permeability

The ease with which liquid will move through a porous medium.

Hydraulic Conductivity

The capacity of a porous medium to transmit water.


Hydrogeology


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


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


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


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


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


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


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


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


K = hydraulic conductivity A = cross-sectional area Q = rate of flow I = hydraulic gradient


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


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


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


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


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


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


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


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


Installing Filter Pack Material

Bentonite and Grout

Bentonite pellets, chips, and powder shown above

WellRiser Pipe

Well Installation


Finished Well Pad vs. Unfinished Well Pad

Flush MountedWells


Well Installation

Well Construction Designs for:

Unconfined Aquifers andConfined Aquifer

Well Installation


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


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


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


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


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


Pump

Well Installation


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.


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


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


Well Installation


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.


Temporary Monitoring WellsPre-Pack Well Screen

Pre-packed well screen eliminates the problem of placing of filter pack in a small diameter bore hole.


Pre-Pack Well Screen

Photos courtesy of Ohio EPA

Well Installation


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


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


● 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


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


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

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AQUIFERSIEVE ANALYSIS

Well Installation


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

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AQUIFERSIEVE ANALYSIS

20

100

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Well Installation


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

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#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


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



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 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



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



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



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



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



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



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


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


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


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


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.


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).


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


Unsaturated Flow, Un-Stratified Bed


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.


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


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


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


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


Vapor Intrusion


TCE Chemical Spill

Groundwater TCE = 20,000 ppb

MW033s TCE = 3,800 ppb



Groundwater Data2003-2006

MW029s TCE = 16,000 ppb

Groundwater TCE concentrations near

houses.

Vapor Intrusion


TCE Chemical Spill

Groundwater TCE = 16,000 ppbGroundwater TCE

= 20,000 ppb

Unsaturated Zone


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


TCE Chemical Spill


Soil Gas TCE = 160,000 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


Sub-Slab Sampling


TCE Chemical Spill



Sub-Slab sampling conducted. TCE screening level = 4 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


Vapor Intrusion


TCE Chemical Spill



Sub-slab TCE = 62,000 ppb


Indoor Air Sampling


TCE Chemical Spill



If Indoor Air Sample >0.4 ppb, mitigation required



Pre-Sample Residential Checklist

Screen indoor airprior to indoor airsampling to identifyresidential interferences

Unsaturated Zone


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


TCE Chemical Spill




Indoor Air TCE = 260 ppb

ATSDR & ODH:Completed ExposurePathway


Vapor Abatement Mitigation System(Sub-Slab Depressurization System or SSDS)

Radius of Influence?Least amount of vacuum?

Unsaturated Zone


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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)


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.


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


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.

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