Capture, Containment, and Monitoring of TCE in Groundwater for Protection of a Municipal Water Supply Leslie T. Katz Errol L. Montgomery & Associates, Inc. Errol L. Montgomery & Associates, Inc. Arizona Hydrological Society Symposium 2000

Acknowledgments 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 1994 Detection at sentinel well Nov 1994 Begin Phased Construction Decision Process Cooperative agreement between PRPs and AAWC Outside of formal regulatory process Involvement from agencies Phase I Phase II 1997-Present Monitoring 1992 Migration beyond capture Sentinel wells installed Time Line Phased Construction Decision Process

Construction Decision Process On-going: Monitoring and verification Phase I Phase II Modeling analysisModel refinements MRTF designMRTF construction Installation of extraction wells Tie-in to treatment Data collectionAdditional data collection Decision meeting

Data Acquisition Programs Aquifer testing Zonal (interval-specific) testing Spinner logging/depth-sampling Enhanced WL and WQ monitoring Regional water level monitoring Regional 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 FLOW GENERAL HEAD

 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

Conclusions 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

Observations Rapid response Work outside of regulatory framework Cooperative relationships between parties Thorough data acquisition programs Comprehensive monitoring program Project success attributed to: