Presentation to the on Former Orion Park Housing Area (OPHA) Supplemental Site Investigation (SSI) for Groundwater Project Update February 9, 2012

1. Former Orion Park Housing Area
(OPHA)
Supplemental Site Investigation
(SSI)
for Groundwater
Restoration Advisory Board Project
Update
February 9, 2012

2. Supplemental Site Investigation
(SSI) Topics
• Background
o Historical site use
o Trichloroethene (TCE) plume in groundwater
• SSI Investigation
o Purpose
o Investigation Methods
o Results
• Questions

3. OPHA Site Location
SF BAY
OPHA

4. OPHA Historical Aerial
Stevens Creek

5. Meandering Stream –
Typical Geology
Clay
Silt and Clay
Silt
Fine Sand
Sand
Gravel
Surface Water

6. Historical Site Use
Groundwater Flow

7. TCE Plume in Groundwater
Upper A1 Aquifer Lower A2 Aquifer
(≈ 0 to 25 feet bgs) (≈ 27 to 65 feet bgs)
Note: General flow directions are based on measurements from August 2005.
Source of TCE contours: Tetra Tech EC. 2007. Groundwater Monitoring Well Installation and Sampling Report for Orion
Park Housing Area. September.

8. Previous Investigations
Investigation Title Year Investigator Report Conclusions
Federal Facilities 1989 EPA, Navy NA
Agreement
Soil and Groundwater 1999 NASA Detected TCE on-site at downgradient
Investigation boundary
Groundwater Investigation 2000 Navy Detected TCE on-site at upgradient and
downgradient boundaries
Site Characterization 2002 Navy No on-site sources identified
Off-Site Investigation 2003 Army Detected TCE off-site upgradient
Off-Site Investigation 2005 EPA Detected TCE off-site upgradient
Groundwater Investigation 2007 Navy No on-site sources identified
and Monitoring Well
Installation
Septic Tank and Drain Field 2009 Army Septic tank and drain field not a source
Investigation

9. Supplemental Site Investigation
(SSI)
• Voluntary investigation by Army
• Work Plan approved by EPA and Water Board
• SSI Purpose
o Investigate locations of concern (LOCs) previously identified with input from
EPA and Water Board

10. Investigation Overview
• Verified Previous Groundwater Data (2010/2011)
o Flow direction –Water Levels
o TCE (and other VOCs) – Chemical analysis
• Measured (2011)
o Soil Lithology – cone penetrometer technology (CPT)
o VOCs (≈ TCE) in soil and groundwater - membrane interface probe (MIP)
o TCE in groundwater – direct push technology (DPT)

11. Investigation Methods
= electron
capture
detector
(ECD)
VOCs
-
Groundwater
Soil lithology VOCs TCE
CPT (cone MIP (membrane DPT (direct push
penetrometer interface probe) technology)
technology)

12. CPT/MIP Investigation
in Upper A1 Aquifer
• 5 LOCs
o 14 CPT/MIPs
• Upgradient TCE plume
preferential pathways
o 6 CPT/MIPs

13. CPT/MIP Investigation
in Lower A2 Aquifer
• 4 LOCs
o 13 CPT/MIPs
• Upgradient TCE plume
preferential pathways
o 5 CPT/MIPs

14. Screening Criteria to Identify
Potential On-Site Source
Criterion
Primary Characteristics:
ECDmax in capillary fringe?
If 1 of 2 = Yes
ECDmax ≥ 7e+6 µV?
Investigate
Secondary Characteristics: Further
ECDmax ≥ 4e+6 µV
ECD decreasing with depth? If 2 of 3 = Yes
ECD higher in fine-grain?
• If YES → Investigate further
• If NO → Not a Source

15. Example - ECD Profile Evaluation
Cone Resistance Electron Capture
and Soil Detector (ECD)
Lithology (microvolts [µV]) x 106
Electrical
Conductivity
Example: Highest
ECD in silty clay to
clay (secondary)
A1 Aquifer
Aquitard
A2 Aquifer

16. CPT/MIP Investigation Results
Confirmed LOC Further
MIP ECD Profile
LOC Connected with Investigation
Results
Upgradient Plume? Warranted?
1, 2a, 4, 5a,
< Screening criteria Confirmed No
5b, 5c
3 < Screening criteria Not Confirmed Yes
2b/6b (A1 Upgradient ECDs
Not Confirmed Yes
Aquifer) > Screening criteria
6b (A2
< Screening criteria Not Confirmed Yes
Aquifer)

17. DPT Investigation
in Upper A1 Aquifer
• 8 groundwater grab
samples
o LOC 3 – 3 samples (from 2
locations)
o LOCs 2b/6b – 5 samples

18. DPT Investigation
in Lower A2 Aquifer
• 3 groundwater grab
samples
o LOC 6b – 3 samples

19. 3-D Model - Lithology
Inputs
Lithology (2002 - 2011 CPT)
Outputs
A1/A2 Aquitard

20. 3-D Model – TCE Plume and
Groundwater Contours
ECD responses (2011 MIP)
Groundwater water levels
Inputs
Outputs

21. 3-D TCE Plume Model
(TCE ≈ ECD Lower Level - 5e+5µV)
O
South
North
North
TCE Above A1/A2 Aquitard
A1/A2 Aquitard
TCE Below A1/A2 Aquitard
Previous Boring
SSI Boring

22. 3-D TCE Plume Model
(TCE ≈ ECD Mid Level - 7.5e+5µV)
South
O
North
TCE Above A1/A2 Aquitard
A1/A2 Aquitard
TCE Below A1/A2 Aquitard
Previous Boring
SSI Boring

23. 3-D TCE Plume Model
(TCE ≈ ECD Higher Level - 1e+6µV)
South
O
North
North
TCE Above A1/A2 Aquitard
A1/A2 Aquitard
TCE Below A1/A2 Aquitard
Previous Boring
SSI Boring

24. TCE Plumes
• A1 Aquifer Plume (≈ 0 to 25
feet bgs)
• A2 Aquifer Plume (≈ 27 to 65
feet bgs)

25. DPT and 3-D Model
Investigation Results
LOC Method Results
Screened out
1, 2a, 4, 5a, 5b,
during CPT/MIP No on-site source
5c
Investigation
DPT Confirmed localized area of low ECD
3 responses were caused by residual TCE in
3-D Model fine-grained soils
2b/6b (A1 DPT Confirmed connection with upgradient A1
Aquifer) 3-D Model plume
DPT Confirmed connection with upgradient A2
6b (A2 Aquifer)
3-D Model plume

26. Conclusions and Next Steps
• Conclusions
o No on-site sources
o Historical migrating TCE plume extends from southern boundary
o TCE held up in fine-grained soils
• Next Steps
o SSI Report will be available for review upon finalization

27. OPHA Project Team Contacts
• US Army Environmental Command – Amanda
Michels – Amanda.R.Michels.civ@mail.mil
• US Army Corps of Engineers – Celso Sabiniano –
Celso.F.Sabiniano@usace.army.mil

28. Questions