Capture, Containment, and Monitoring ofCapture, Containment, and Monitoring of TCE in Groundwater for TCE in Groundwater for

Protection of a Municipal Water SupplyProtection of a Municipal Water Supply

Leslie T. KatzLeslie T. Katz

Errol L. Montgomery & Associates, Inc.Errol L. Montgomery & Associates, Inc.

Arizona Hydrological SocietyArizona Hydrological Society

Symposium 2000Symposium 2000

AcknowledgmentsAcknowledgments Montgomery & Associates

– Ronald DeWitt

– Elizabeth Lyons

– Janis Blainer-Fleming

Motorola– Dennis Shirley

Arizona-American Water Company– James McVeigh

– James Campbell

North Indian Bend Wash Area

Hydrogeology

Arizona-American Water Company

~ 5,000 customers 7 wells 3 wells tied into MRTF > 8,000 gpm annual average Predominantly LAU Down-gradient from NIBW

#15

#14

PCX-1

COS75A

MRTF

Regional Cone

Of Depression

In LAU

1996 CONDITIONS

TCE

1995

TCE

1994

Jan 1994Detection at sentinel well

Nov 1994 Begin Phased Construction

Decision Process Cooperative agreement between PRPs and AAWC Outside of formal regulatory process Involvement from agencies

1995-1996 Phase I

1996-1997 Phase II

1997-Present Monitoring

1992 Migration beyond capture Sentinel wells installed

Time Line

Phased Construction Decision Process

Construction Decision ProcessConstruction Decision Process

On-going:Monitoring and verification

Phase I Phase II

Modeling analysis Model refinementsMRTF design MRTF constructionInstallation of extraction wells Tie-in to treatment

Data collection Additional data collection

Decision meeting Decision meeting

Data Acquisition ProgramsData Acquisition Programs

Aquifer testingZonal (interval-specific) testingSpinner logging/depth-sampling Enhanced WL and WQ monitoring Regional water level monitoringRegional inorganic sampling

Generally coarse-grained with fine-grained interbeds Increasing lithification and consolidation with depth Decreasing permeability and yield with depth Convergent flow toward PVWC wellfield Larger concentrations and more rapid transport in upper LAU

LAU Conceptual Model

MODELING

Groundwater Flow• MODFLOW • 3D steady state • 12 sq. mile area• 2 layers, LAU only

Particle Tracking • PATH3D

Range of Pumping Conditions Simulated

NO

FL

OW

GENERAL HEAD

GENERAL HEAD

GE

NE

RA

L H

EA

D

TCE not projected to arrive at wellfield in advance of:

• MRTF completion • Tie-in of 3 wells

Contamination not projected to migrate north to wells not tied into treatment

PHASE I / II RESULTS

PHASE I / II DECISIONS

1. Provide treatment for PCX-1, #14, and #15

2. Provide blending for water from #14 and #15

3. Defer decision regarding additional extraction and treatment indefinitely 4. Design and implement WL and WQ monitoring program to verify containment

Continuous water level monitoring at 12 monitor wells and 6 production wells

Enhanced sampling frequency

at 7 monitor wells and 7 production wells

Tracking of wellfield pumping patterns

TCE

2000

MONITORING PROGRAM

Before Pumping

At PCX-1

(April 1997)

After Pumping At

PCX-1

(April 1999)

Recent

Conditions

(April 2000)

Estimated

Hydraulic

Capture FSA

Model

ConclusionsConclusions

Water level data– hydraulic gradients toward extraction wells

Water quality data– no TCE detected north of well #15

Containment of plume projected based on:– monitoring data

– particle tracking model

– FSA groundwater flow model

ObservationsObservations

Rapid responseWork outside of regulatory frameworkCooperative relationships between parties Thorough data acquisition programsComprehensive monitoring program

Project success attributed to: