Long-Term Monitoring at the Sunnyvale Permeable Reactive Barrier: Lessons Learned / Future Expectations

Transcription

1 Long-Term Monitoring at the Sunnyvale Permeable Reactive Barrier: Lessons Learned / Future Expectations Scott D. Warner, Bettina L. Longino Geomatrix Oakland, California Lisa A. Hamilton DKTM King of Prussia, Pennsylvania

2 Site Location Site N Sunnyvale, California

3 Site History 1983 VOCs detected at the site 1986 Source area excavated 1987 Groundwater Extraction System installed 1991 Zero-valent iron PRB concept identified 1992 Lab and pilot test studies for ZVI treatment 1993 PRB full scale design and regulatory approval 1994 PRB construction November 1995 GWS removed - February 1997 Hydrogen gas evaluation 1999 Five-year effectiveness evaluation completed 2000 Passive diffusion bag sampling implemented 2002 Hydrogen gas evaluation (2004 Ten-year effectiveness evaluation)

4 PRB Layout

5 PRB Design Wall Thickness Co C C in f MC L N t1/2 (µ g /L) (µ g /L) (- -) t 1/2 (h r) t R (hr) v (ft/d ) W (ft) VC c DCE TC E Cinf = influent concentration t 1/2 = half-life Nt 1/2 = number of half-life to achieve MCL tr= residence time v= groundwater velocity W= required barrier width

6 PRB Emplacement

7 PRB Emplacement Building Constraints and Media Placement

8 PRB Emplacement Treatment Section Treatment media 2 feet 4 feet 2 feet JEE, 1998

9 Monitoring Water Levels E7A, E14A off line E15A off line Final Remedy Installed Slurry Wall Damaged Slurry Wall Repaired A 25A 20A 11A Water Level Elevation (feet) Nov-93 May-94 Nov-94 May-95 Nov-95 May-96 Nov-96 May-97 Nov-97 May-98 Nov-98 May-99 Nov-99 May-00 Nov-00 May-01 Nov-01 May-02 Nov-02

10 Monitoring Organic Chemistry

11 Passive Diffusion Bag Sampler Pilot Test Methods

12 Passive Bag Sampler Pilot Test Results A A cdce tdce PCE TCE F113 VC TCFM cdce tdce TCE VC T E X Zero-valent iron Pea gravel A Pre PDB PDB Post PDB A cdce tdce 1 Purge 1 TCE F113 VC TCFM TCFM 12DCB cdce tdce PCE TCE F113 VC X DCDFM TCFM Downgradient Groundwater flow Direction Upgradient 3-casing volume purging Low flow purging

13 Monitoring Water Quality Parameters

14 Trend in ph Conditions ph Jan-95 Jan -96 Jan -97 Jan-98 Jan-99 Jan -00 Jan -01 Jan -02 Jan-03 E xplanation 19A 20A 21A 22A 26A 27A

15 Redox Conditions Eh (Volts) Fe(+2a) Fe - H2O - System at C Fe2O3 Fe Fe3O4 Ambient After 1 yr -1.0 After 5 yr File: C:\HSC\FE25.IEP ph After 8 yr

16 Monitoring Inorganic Chemistry

17 Dissolved Gas Monitoring Hydrogen and Methane gas 10A 480, , A 670, , A A A Nitrate reduction Fe (III) reduction Sulfate reduction Methanogenesis H 2 < 0.1nM 0.2 < H 2 <0.1nM 1< H 2 <4nM 5 < H 2 <15nM 2 NM NM 43A NM LEGEND 480,000 H ,000 H methane A H 2 collected via bubble strip method H 2 concentration in nm Methane concentration in ug/l H 2 Solubility = 1.6 ppm = 0.02 L/L= 800,000 nm

18 Economic Assessment Project Costs 1993-CURRENT Cost (Thousands of Dollars) S lurry W all and In-Situ T reatm ent W all C osts (A ctual) G roundw ater E xtraction and T reatm ent C osts (P rojected) S lurry W all and In-S itu T reatm ent W a ll C osts (P rojected) 500 * = capital costs assum ed zero since treatm ent plant already operational Year

19 Summary of Conditions Zero-valent iron PRB is successfully meeting site remediation goals PDB sampling provides representative results in Fe-PRB environment Hydrogen gas suggests continued reaction Methane gas suggests biological activity Inorganic data suggests mineralization in PG Hydraulic conditions are seasonal

20 What have we learned The PRB concept IS an economical remedy Hydraulics are key for design/performance H 2 may be useful for periodic monitoring The corrosion reaction appears long-lasting Mineralization does occur PDB sampling works and is representative Expect the unexpected

21 What do we anticipate The PRB will remain economical for years Treatment viable for several more years at least 10; next key period H 2 should decrease gradually (?) Mineralization should continue Season hydraulic variability - non-uniformity Continued drift in redox sensitivity?

22 Acknowledgements Miao Zhang - Geomatrix Dominique Sorel - SSPA EnviroMetal Technologies, Inc. University of Waterloo