capture, containment, and monitoring of tce in groundwater for protection of a municipal water...
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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:
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