Groundwater Remediation Thanks to Phil deBlanc, Groundwater Services, Inc.

Groundwater Remediation

• Thanks to Phil deBlanc, Groundwater Services, Inc.

Corrective Action Process

RESULTS:SITE-SPECIFIC EVALUATION

Release Assessment

Conceptual Exposure Model

Risk-Based Target Limits

Remedial Action

No Further Action

Provides site-specific classification, risk-based evaluation, remedy selection, and cost projection.

Compliance Monitoring

Conceptual Exposure Model: Key Questions

Waste or contaminant “hot spots”

RECEPTORSOURCE Migration in air or water Humans,

ecological species

Transport

Conceptual Model Development

KEY POINT:

Must have YES to all 3 questions to have complete exposure pathway.

SOURCE: Is it toxic, flammable, explosive, or otherwise harmful?

TRANSPORT: Is it in unsafe location or could it move to unsafe location?

RECEPTOR: Could humans or ecological receptors be exposed to hazardous chemicals?

?

?

?

Risk is a function of exposure concentration, intake, and toxicity.

KEY POINT:

X X =Exposure

Factors Toxicity Health RiskExposure Concentration

Corrective Action Fundamentals

Source POE

Risk-Based Approach: General Procedure

Calculation of Target Levels

Calculation

ExposureConcentration x

ExposureFactors = Health Riskx Toxicity

Safe cleanup limits at source are back-calculated based on allowable risk level at receptor.

KEY POINT:

POE = Point of Exposure

Corrective Action Process Overview

StartEnd

Source POE

Corrective Action Process

RESULTS:SITE-SPECIFIC EVALUATION

Release Assessment

Conceptual Exposure Model

Risk-Based Target Limits

Remedial Action

No Further Action

Provides site-specific classification, risk-based evaluation, remedy selection, and cost projection.

Compliance Monitoring

Remedy Selection Guidelines

Remediation Options

Natural Attenuationconfirm stable /

diminishing condition

KEY POINT:

Remedy should serve to prevent risk by controlling exposure.

Removal/Treatment:remediate source

RECEPTORSOURCE

Containment:prevent transport

Institutional Controls:control exposure activity

Transport

Soil Excavation at PST site

Remedial Action: Soils

PST = Petroleum Storage Tank

Excavation and Disposal / Treatment

On-Site or Off-Site

Thermal Treatment

On-Site Physical / Biological Treatment

Haul To Off-Site Landfill

Active Engineered Remedies

TREATMENT / DISPOSAL OPTIONS

Soil Vapor Extraction

Blower or Vacuum Pump

Vapor Treatment System (Where Required)

Air / VaporManifold

Clay

Grout Seal

Sand Pack

Affected Soils

Water Table

Screen


Air vacuum extracts volatile contaminants from affected soil.

Soil Vapor Extraction: Applicability

Likelihood ofSuccess

104

103

102

101

100

10-1

10-2

10-3

10-4

Source: CDM, 1988

COCVapor Pressure

(mm Hg)

Butane

Benzene

Xylene

Aldicarb

Soil AirPermeability

HIGH(Coarse Sand /Gravel)

MEDIUM(Fine Sand)

LOW(Clay or Silt)


VeryLikely

SomewhatLikely

LessLikely

Soil Vapor Extraction (SVE) System at Former Gasoline Station

Remedial Action: Soils

SVE Wells and

Collection Headers

Vapor Treatment

System

REMOVAL / TREATMENT OPTIONS

GW Remediation Options

GW Pump & Treat Air Sparging Dual Phase Extraction

Hydraulic Containment (pumping)

Barrier Walls

CONTAINMENT OPTIONS

Affected Soil

GW INGESTION

Affected Groundwater

Active Remediation Technologies

Use continuous GW extraction to reduce COC concentrations in GW to applicable target levels.

GOAL

APPLICABILITY

GW Extraction:Recovery wells / submersible pumps; wellpoint systems.

GW Treatment:GAC, air stripper, biological, etc.

Moderate-to-high permeability groundwater units (K > 10-4 cm/s), low COC concentrations (CRF < 100), and no NAPL plume.

GW Pump & Treat: Overview

DESIGNOPTIONS

NAPL

CRF = COC Reduction Factor = (Current COC Conc./Target Level); K = Hydraulic Conductivity (cm/s)


COC = Chemical of Concern

GW Pump & Treat: Well Installation


Recovery Well Installation

Well Screen

Centralizer

Driller’s Knee

Driller’s Helper

Sand-Gravel Filter Pack

Wire-Wrapped Well Screen

Material: Corrosion & contaminant resistant. Options = PVC, SS, teflon, FRP.

Large enough to fit pump, usually 4-in or 6-in.

GW Pump & Treat: Recovery Well Design

FRP = Fiberglass reinforced plastic PVC = Polyvinyl chlorideSS = Stainless steel

CasingProtective casingConcrete surface pad

Bentonite pellet seal

Cement/bentonite grout

Select sand backfill

Casing

Well screenŠ10 ft

Varies

Š 3 ft

10 in

2 ft

Š1 ftSump with plug

To collection pipe

Centralizer

Centralizer


GW Pump & Treat: Recovery Well Design

PVC = Polyvinyl chlorideSS = Stainless steel

Material: Typically same as casing. May use SS screen with PVC casing to economize.

Length: 30-50% of saturated thickness for unconfined unit; 70-80% of saturated thickness for confined unit

Placement: Adjust to match plume thickness, floating or sinking plume.

Diameter: Prevent excessive head loss through screen by evaluating screen open area and pumping rate.

Slot Size: Retain 90% of sand pack, slot size ≥ D10 of sand pack.

Well ScreenProtective casingConcrete surface pad




Casing

Well screenŠ10 ft

Varies

Š 3 ft

10 in

2 ft


To collection pipe

Centralizer

Centralizer


Purpose: Stabilize formation, minimize fines in well, & maximize screen slot size.

Thickness: 3-8 in thickness between well screen and borehole wall.

Material: Clean, uniform, silica sand/gravel.

Sand PackProtective casingConcrete surface pad




Casing

Well screenŠ10 ft

Varies

Š 3 ft

10 in

2 ft


To collection pipe

Centralizer

Centralizer

Material: Portland cement/bentonite mix.

Configuration: At ground surface, sloped to drain rainwater away from well casing.

Grout Seal

GW Pump & Treat: Recovery Well DesignGW Remediation Options

Groundwater P&T: The Bad News

CO

C C

on

c. i

n G

W

Time

?Cleanup Standard

KEY POINT: USEPA study shows that GW P&T cannot cleanup to DW standard at most sites.

WHY NOT? Complex hydrogeology, design flaws, and NAPL.


GW Pump & Treat: Tailing and Rebound

Source:From W, R, N, & W.

Regulatory Cleanup Level

C

t

C

t

Regulatory Cleanup Level

Pump Shut-Off

T

Continuous Pump and Treat Resulting in Tailing

Rebound After Pump and Treat System Shut-Off


GW Pump & Treat: Wrap-Up

• Capable of providing hydraulic containment

• May be required tosatisfy regulators

• Incapable of attaining drinking water standards

• Must treat or dispose of recovered GW

• Long-term commitment

10

PRO CON


Use aquifer dewatering and soil venting to reduce COC concentrations in GW to applicable target levels.GOAL

APPLICABILITY

GW Extraction:Recovery wells / submersible pumps; wellpoint systems.

Vapor Extraction: Blower, dual phase wellpoint pump.

Water Treatment: GAC, airstripper, biological

Vapor Treatment, GAC, catalytic furnace.

Low to moderate permeability groundwater units (K = 10-5 to 10-3 cm/s)

Dual-Phase Extraction: Overview

DESIGNOPTIONS

vapor

PumpGW

vapor

GW


Dual-Phase Extraction: Design Options

Separate Air & Water Headers:Equip each well with submersible pump. Run SVE vacuum header to each wellhead.

Combined Air/ Water Header:Use dual-phase air/water vacuum pump and run single suction header to each wellhead with drop tube to water.

Dual-phase pump extracts both air

and water

Air

GW


Inject air to volatilize organics and promote in-situ biodegradation, as needed to reduce COCs in GW to applicable target levels.

GOAL

APPLICABILITY

Air Injection:Air compressor with multiple small injection points.

Vapor Recovery: If needed, use SVE wells to recover and treat vapors.

Moderate to high-permeability GW units (K > 10-4 cm/s)

Air Sparging: Overview

DESIGNOPTIONS

Air


• Well Configuration– Injection Points: 1-2 inch diam.

PVC Wells, 2-5 ft Screen length– Typical Spacing: 5 - 20 ft centers

• Injection Pressure: 1-10 psig• Air Flowrates

– < 10 SCFM per well– Helps to Cycle injection periods (Hours, Not

Days)

Air Sparging: Design Issues

Air Injection

Points


Limitations

Air Sparging: Process Review

Air

Remediation Processes


Volatilization of NAPLs

Air Stripping of Dissolved Organics

Oxygenation of Water Enhances In-Situ Biodegradation

Effectiveness may be reduced if a few small channels are formed

Very sensitive to heterogeneities

If air flow from top of screen only, entire groundwater bearing unit not treated


In-Situ Biodegradation: Overview

Solid magnesium peroxide compound activated by moisture to slowly release O2 to GW. Can achieve higher dissolved O2 levels than air sparging, theoretically.

Inject ORC into aquifer or place in monitoring wells. Requires moderate GW pHlevels (e.g., pH 6-9).

Applicable if GW plume notexpanding & aggressivetreatment not needed tomeet remediation goals.

WHAT

HOW

WHEN O2 O2 O2

Oxygen Release Compound (ORC)

Use physical or hydraulic barrier system to prevent migration of affected GW to point of exposure.

GOAL

APPLICABILITY

Physical Barrier:Slurry wall, asphalt wall

Hydraulic Barrier:GW P&T system, cut-off trench

Applicable to all GW units and COCs. Physical barrier walls limited to 100 ft depth. Hydraulic containment (P&T) limited by water treatment requirements.

GW Containment: Overview

DESIGNOPTIONS

slurry wall

Affected GW zone


GW Containment: Hydraulic Containment

GW Pumping Well

Streamlines

Plume

Hydraulic Capture Zone

PLAN VIEW

n Design Methods- Javendahl Capture Zone Curves

n Computer Models

n Operational Factors- Well Efficiency - Seasonal / Annual Effects- Produced Water Treatment

GW Flow


GW Containment: Physical Barriers

• Purpose– Prevent Migration of COCs

from Affected Zone– Reduce Inflow of Clean Groundwater

• Design– Partial vs. Complete Enclosures– Can be Keyed Into Underlining

Confining Unit• Construction

– Routinely Installed Down to 50 feet– Cost: ~ $ 5 per sq. ft. for Slurry Wall

slurry wall

Affected GW zone


GW Containment: Physical Barrier

0’

35’

70’

DNAPLDrinking WaterAquifer

Unfract. Clay

Frac. Clay

Aquifers

Slurry Wall

Slurry WallWell

tPi s


Hydraulic Containment by Slurry Wall

Installation of Bentonite-

Slurry Barrier Wall

Remedial Action: Groundwater

Permeable Reaction Walls

Ref: Gillham

Funnels Dissolved Organics Through Reaction Wall

Funnel:ImpermeableBarrier Wall

Gate: Permeable Reaction Wall - Fill With Iron

FilingsFunnel:ImpermeableBarrier Wall

Installation of Permeable Treatment Trench


– Dispersion

– Sorption kd = (Koc)*(foc)

NON-DESTRUCTIVE PROCESSES

– Biodegradation

– Volatilization

– Dilution

DESTRUCTIVE PROCESSES

Reduction in contaminant mass or concentration in groundwater over time or distance due to natural processes:

– Abiotic Reactions (hydrolysis)

O2 Fe +2

NO

3

CH

4

CO

2HydrocarbonSO

4

Natural Shrinking of GW Plume Over Time

What is “Natural Attenuation”?

Common Applications of MNA

A. SHRINKING PLUME

GW POE

B. STABLE PLUME

GW POE

MOST COMMON USE:

Affected GW plume is stable or shrinking with no impacted groundwater receptors.

Therefore, no risk of exposure.

No risk to

existing user.

No risk to

existing user.

MNA= Monitored Natural Attenuation

Today’s Focus

Soil Excavation SVE

Soil Excavation (smear zone)

Continuous Recovery

Periodic Recovery (bailing, High-Vac)

Air Sparging

NAPL IN UNSAT. SOIL ZONE

NAPL IN GW ZONE

NAPL Removal Options


NAPL in Soil

NAPL in GW

Dissolved GW Plume

NAPL Removal Options: Key Factors

Soil Remediation Options

n Vertical distribution of NAPL

n Permeability of soil to NAPL

n Relative soil permeability to water & NAPL

Key Factors Influencing NAPL Removal

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Hydrocarbon Saturations

0

100

200

300

400

500

600

700

Ele

vati

on

Ab

ov e

Oil

/ Wat

er

Inte

rfac

e (c

m)

NAPL

Well

H2O

KEY POINT:

NAPL concentrates in “smear zone” atop GW table.


NAPL Removal Options: Vertical NAPL Distribution

NAPL = Non-aqueous phase liquid.

NAPL = Non-aqueous phase liquid. Source: Beckett & Huntley, 1999

10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102

Hydraulic Conductivity of Soil to NAPL (m/day)

0

100

200

300

400

500

Ele

va

tio

n A

bo

ve

Oil

/Wa

ter

Inte

rfa

ce

(c

m)

Fine/Med Sand (Ksat = 4 m/d)Silty Sand (Ksat = 0.4 m/d)Silt (Ksat = 0.1 m/d)

Coarse Sand (Ksat = 43 m/d)

KEY POINT:

NAPL easier to remove in coarse-grained dry soils.Hard to remove in fine-grained wet soils.


NAPL Removal Options: Effects of Soil Type

Soil Type vs. Permeability of Soil to NAPL

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

Water Saturation of Soil

Irreducible Water Saturation


NAPL Removal Options: Relative Permeabilities

KEY POINT:Soil saturated with waterhas low permeability for NAPL, so NAPL easierto removefrom dry soil.

Re

lati

ve

Pe

rmea

bili

ty

Relative Permeabilities of Soil to Water & NAPL

Soil K for NAPL

Soil K for Water

Continuously recover NAPL to reduce source mass, stabilize NAPL plume (e.g., daily operation).

GOAL

APPLICABILITY

DESIGNOPTIONS

Recovery wells & skimmer pumps

Interceptor trench &skimmer pump

Multi-phase recovery system

Sites with significant mobile NAPL plume atop GW (e.g., >> 1 ft thick).

Continuous NAPL Recovery Methods

NAPL

Pump

NAPL


Multi-Phase NAPL Recovery

Groundwater and NAPL

Soil Vapor

Smear Zone Dewatered Remediated Through Air Flow


Multi-Phase Recovery: Wrap-Up

• May be effective in low to moderate permeability settings.

• Fast where It works: 2 months to 2 years.

• Vapor and GW treatment can be very expensive.

• Will not achieve low cleanup levels in groundwater.

• Can be impossible to dewater smear zone in certain hydrogeologic setting


PRO CON

Remove periodic accumulation of NAPL from observation wells to reduce NAPL mass and mobility (e.g., weekly to quarterly operation).

GOAL

APPLICABILITY

Periodic bailing of wells

Periodic skimmer pump operation in wells or trench.

Periodic High-Vac recovery

Sites with minor NAPL accumulations and/or non-mobile NAPL plumes.

Periodic NAPL Recovery Methods

DESIGNOPTIONS

Bailer

NAPL


AtmosphericAir Bleed Valve

Periodic NAPL Recovery: High-Vacuum

VacuumGauge

Two-PhaseFlow

NAPL / GW Collection

Operational Water Table

Saturated Zone

Soil VaporFlow

Suction Pipe

GW and NAPL Flow

Vacuum Truck

Vapor Treatment

discharge

clean air

Conduct periodic vacuum extraction to recover NAPL (e.g., monthly or quarterly for 8-hour episode).


Groundwater /NAPL P&T System

Vacuum Pump

Recovery Well

Control Panel

Vapor Control System

Fluid Separation

Tank


Remove NAPL smear zone by means of in-situ “air stripping.”GOAL

APPLICABILITY

Air Sparging:Periodically inject air to volatilize NAPL.

Sites with minor NAPL accumulations of volatile NAPL material in coarse-grained soils.

Air Sparging of NAPL Plume

DESIGNOPTIONS

Air

NAPL


Air Sparging System

Volatilizes Organics and Promotes In-Situ Biodeg.


Air Compressor

Blower

Vapor Treatment

Tiny Bubbles

Affected GW zone

SVE Well(Optional)

Air Sparging of NAPL Plume

NAPL Recovery Options

Silt

Smear Zone

Air Channels

Water Table

KEYPOINT:

Air pathways affected by subsurface heterogeneities. Can result in inconsistent removal.

Air Sparging: Wrap-Up

• Has the potential to remove NAPL from the saturated zone without dewatering

• Less expensive than many alternatives

• Not applicable in many hydrogeologic settings

• Requires closely spaced wells• Often requires concurrent SVE• No reliable pilot test criteria


PRO CON

NAPL Removal: Is It Worthwhile?

• May help abate further spreading of NAPL plume

• Initially, the lowest $/lb. recovered

• May not significantly reduce source longevity

• Large fraction of NAPL left behind

• Slow• Often requires groundwater

pumping


MAYBE MAYBE NOT

You can

switch to

RNA if:

Remedy Completion: When is “Enough” Enough?

No Impacts: No current or potential receptor impacts.

Stable Plume: Affected GW plume stable or shrinking.

Not Time Critical: No rush to meet final COC target levels.

No Benefit: Further active remediation not likely to significantly reduce COC levels.

RNA = Remediation by Natural Attenuation


No Further

Action

Required If:

Target Levels Achieved: COC levels reduced to applicable target levels in all media.

Compliance Monitoring: Follow-up monitoring (if needed) confirms remedy completion.

Institutional Controls: If needed. institutional controls in place. No COCs > target

levels

Remedy Completion: When is “Enough” Enough?


Groundwater Remediation Thanks to Phil deBlanc, Groundwater Services, Inc.

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Transcript of Groundwater Remediation Thanks to Phil deBlanc, Groundwater Services, Inc.