Field deployable radioanalytical platform for unattended near-well monitoring of radioactive groundwater plumes

Transcription

1 Field deployable radioanalytical platform for unattended near-well monitoring of radioactive groundwater plumes Matthew J. O Hara 1, Jay W. Grate 2, Scott R. Burge 3, Robert C. Harding 3 1 Energy & Environment Directorate, 2 Fundamental Science Directorate, Pacific Northwest National Lab., Richland, WA 3 Burge Environmental, Inc., Tempe, AZ

2 Presentation Outline Need for monitoring radionuclides in groundwater Radiochemical sensing Equilibrium-based mini-column sensors Sensor & detector hardware Sensor performance & behavior (focus on 99 Tc) Plug & Play analytical platform for field monitoring Operational scheme & primary components Field deployable formats: Pump & Treat process monitor ( 99 Tc) Remote autonomous instrumentation ( 90 Sr) Future path

3 Select U.S. Drinking Water Limits (DWLs) for radionuclides Radionuclide EPA Regulatory Limits (Max. Contaminant Level, MCL*) pci/l Bq/L µg/l Tc x 10-2 Uranium (nat l) ** 30 Sr x 10-8 I x 10-3 * Equivalent dose of 4 mrem/year for β-emitters ** Based on nat l U specific activity of 25,280 Bq/g

4 The Hanford Site & its Subsurface Contamination Hanford Area: ~1600 km 2 Original mission: Pu production; Current mission: Restoration! 1.7 T liters of radioactive waste water discharged to the ground Created 4 M m 3 of contaminated soil 1 B m 3 of groundwater exceeding Drinking Water Limits (DWL) for radionuclides Covering an area ~200 km 2 DOE Richland Operations Office Soils & Groundwater Remediation Project website:

5 Contaminant Plume Distribution Hartman, M.J., V.S. Richie, J.A. Rediker, Hanford Site Groundwater Monitoring for FY2008, March, 2009

6 Contaminant Plume Distribution Reactor disassembly/cocooning; Pump & treat; In-situ remediation; Facility D&D; Pump & treat Waste Vitrification Hartman, M.J., V.S. Richie, J.A. Rediker, Hanford Site Groundwater Monitoring for FY2008, March, 2009

7 RADIOCHEMICAL SENSING

8 Basic Radiochemical Sensor Dense homogeneous packing of sorbent & scintillating particles is ideal for moderate to high energy β-emissions Concentration of analyte places β-decay events within range of scintillator particles Column viewable by dual PMTs Using SENS-TECH PMTs w/ TTL output Coincidence counting logic reduces background ~15x Stainless Steel (SS) shielding reduces background ~10x

9 Equilibrium Sensing Approach Minicolumn equilibrium sensor: reagentless & reversible 1. Sorbent in equilibrium w/ GW 2. β-emitter/gw delivered to sensor column 3. Sorbent in chemical equilibrium w/ β-emitter/gw 4. Reversible analyte-sorbent interaction in GW 5. Sorbent in equilibrium w/ GW Response, cps Time, min

10 Equilibration Sensing Calibration; 99 Tc Calibration range ½ to 5x the Drinking Water Limit (0.033 Bq/mL) 150 ml each standard delivered at ~1 ml/min syringe flow rate Performed 60min. static counts Measurement Efficiency, E m = 16.6 cps/(bq/ml) Tc-99 DWL (0.033 Bq/mL) Count Rate, cps B B Count Rate, cps y = x R 2 = Time, min Tc-99 Activity, Bq/mL

11 Minimum Detectable Activity (MDA) of the Minicolumn Sensor: 99 Tc MDA allows one to determine the analytical limit of the sensor 1. Count time, t [Vary from <1 to 8 hours] 2. Background cnt rate, C b [0.47 cps] 3. Measurement Effic., E m [16.6 cps/(bq/ml)] L d = C b t * Tc DWL = Bq/mL MDA (Bq / ml ) = L d t E m 1 MDA, Bq/mL /10 th 99 Tc DWL = Bq/mL * L. A. Currie, Anal. Chem. 40, (1968) Count Time, hr

12 Equilibration Sensing Calibration; 90 Sr Change sorbent chemistry: crown ether Measurement Efficiency, E m = cps/(bq/l) Counts / Update Bq/L Time, min Sensor Response, cps y = x R² = Sr-90 Conc., Bq/L

13 Minimum Detectable Activity (MDA) of the Minicolumn Sensor: 90 Sr MDA allows one to determine the analytical limit of the sensor 1. Count time, t [Vary from 1 to 24 hours] 2. Background cnt rate, C b [0.27 cps] 3. Measurement Effic., E m [ cps/(bq/l)] L d = C b t MDA (Bq / ml ) = L d t E m 1 * L. A. Currie, Anal. Chem. 40, (1968). * MDA, Bq/L [Plume site typically runs ~70 120x greater than DWL] 90 Sr DWL = 0.3 Bq/L Count Time, hrs

14 Contamination Plume Data: Well 299-W Tc migration does not happen in isolation Other major anions that track 99 Tc migration: Nitrate Chloride Chromate Sensor must function in this dynamic environment! Concentration (µg/l) 100, , , Nitrate Sulfate Chloride Chromate Tc Sampling Date

15 Co-Contaminant Effects on 99 Tc Sensor ) Pristine groundwater + 99 Tc Anion E m = 16.5 cps/(bq/ml) Pristine GW Nitrate 1.7 Chloride 3.9 Sulfate 13.5 Chromate --- Elevated Anions Elevated Anions + Cr(VI) Count Rate, cps Bq/mL 0.5 Bq/mL 2 Blank Time, min

16 Co-Contaminant Effects: Chemical Selectivity Count Rate, cps ) Anionic co-contaminants in groundwater + 99 Tc E m = 11.8 cps/(bq/ml) (28.5% loss) Anion Pristine GW Elevated Anions Nitrate Chloride Sulfate Chromate Elevated Anions + Cr(VI) Time, min

17 Co-Contaminant Effects: Color Quench Count Rate, cps ) Anionic co-contaminants + color quench agent + 99 Tc E m = 7.9 cps/(bq/ml) (52.1% loss) Anion Pristine GW Elevated Anions Elevated Anions + Cr(VI) Nitrate Chloride Sulfate Chromate Time, min

18 Co-Contaminant Effects: Color Quench Count Rate, cps ) Anionic co-contaminants + color quench agent + 99 Tc E m = 7.9 cps/(bq/ml) (52.1% loss) Anion Pristine GW Elevated Anions Elevated Anions + Cr(VI) Nitrate Chloride Sulfate Chromate Time, min

19 Matrix Spike Addition Analysis Analysis of Hanford groundwater samples (HGW) with increasing levels of co-contaminants Use matrix spike addition to calibrate Count Rate, cps Anion Sulfate HGW a a HGW b b HGW c Time, min c HGW d Nitrate Chloride d

20 Matrix Spike Addition Analysis: Results 99 Tc in each sample = Bq/mL 99 Tc injected during spike run = Bq/mL Activity Conc. of sample: A = Sample R E eq m Where: E m R V ( s sp eq, sp eq Vs = A matrixsp = A spv sp A V matrixsp ) R And: V s Sample Sensor Response, Pre-Spike (cps) Sensor Response, Post-Spike (cps) Measured E m (cps/(bq/ml)) Calculated Activity, (Bq/mL) Actual Activity, (Bq/mL) % Bias HGW a % HGW b % HGW c %

21 PLUG & PLAY ANALYTICAL PLATFORM

22 Plug & Play Analytical Platform Schematic Purge Water Reagent & Spike Inlet Waste H 2 O Quality Sensors Sampling Chamber Detection Module Wells / Aquifer Tubes Syringe Pump Detection Module

23 Configuration 1: 99 Tc Platform for Pump & Treat Plant Panel configuration Dimensions 2.5 x 2 x 0.5 Conducive to wall-mount 4 sample input lines Multiple waste pathways

24 Configuration 1: 99 Tc Platform for Pump & Treat Plant Flat panel configuration Dimensions Computer boards; 2.5 x 2 x 0.5 Conducive to wall-mount fluid routing & peripheral sensors 4 sample input lines 3 waste water paths Communications: Platform Laptop via 2- way radio User Laptop via wireless internet Software: Laptop runs Visual Basic Platform has EEPROM chips onboard 4 Sample Inlet lines Sampling Chamber Syringe Pump Sensor & Shielding Reagent Calib. Std.

25 Configuration 1: 99 Tc Platform for Pump & Treat Plant Flat panel configuration Dimensions 2.5 x 2 x 0.5 Conducive to wall-mount 4 sample input lines 3 waste water paths Communications: Platform Laptop via 2- way radio User Laptop via wireless internet Software: Laptop runs Visual Basic Platform has EEPROM chips onboard

26 Hanford 200 West Area: ZP-1 Pump & Treat Plant CCl 4 extraction process CCl 4 -Bearing Extraction Wells 99 Tc present 99 Tc extraction process To Injection Well Post-CCl 4 Treatment Pre-CCl 4 Treatment < DWL Monitoring Location Column Breakthrough

27 Configuration 2: Field Deployable Remote Analytical System 90 Sr analytical system connected to well near Columbia River Support structure deployed; analytical system scheduled for June, 2010 deployment System capable of connecting to 4 well sources Design: Off-the-grid operation 365 day/yr operation Sr-90 Plume Apatite Barrier >5000 pci/l contour line

28 Evaluation of 2- and 3-Dimensional Computer Modeling Daily uploads of most recent analytical data would provide near-real time information: Plume movement Flux calculations across horizontal / vertical transects Remediation efficacy

29 Conclusions Need exists for remote groundwater monitoring of radioactive contamination plumes More resolved transport / migration data Low cost Analytical results interlinked to plume migration database Measurement of radionuclides is possible via the equilibrium sensing approach Detection modules for Tc-99; Sr-90; I-129 being developed currently (x-rays) (plus uranium via spectrophotometry) Versatile Plug & Play platform allows multiple detection scenarios on one chassis Substantially reduces platform development cost

30 Acknowledgements U.S. Department of Energy Office of Science Small Business Technology Transfer (STTR) program U.S. DOE s Environmental Management Science Program (EMSP) U.S. DOE s Environmental Remediation Science Program (ERSP) Further Reading O Hara, M.J., S.R. Burge, J.W. Grate, Anal Chem, 2009, 81(3): O Hara, M.J., S.R. Burge, J.W. Grate, Anal Chem, 2009, 81(3): Grate, J.W., O.B. Egorov, M.J. O Hara, T.A. DeVol, Chem Reviews, 2008, 108(2): Egorov, O.B., M.J. O Hara, J.W. Grate, Anal Chem, (15):