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Presentation to the on Former Orion Park Housing Area (OPHA) Supplemental Site Investigation (SSI) for Groundwater Project Update February 9, 2012
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Former Orion Park Housing Area(OPHA)
Supplemental Site Investigation(SSI)
for Groundwater
Restoration Advisory Board ProjectUpdate
February 9, 2012
Supplemental Site Investigation
(SSI) Topics• Background
o Historical site use
o Trichloroethene (TCE) plume in groundwater
• SSI Investigationo Purpose
o Investigation Methods
o Results
• Questions
OPHA Site Location
SF BAY
OPHA
OPHA Historical Aerial
Stevens Creek
Meandering Stream –Typical Geology
ClaySilt and ClaySiltFine SandSandGravelSurface Water
Historical Site Use
Groundwater Flow
TCE Plume in GroundwaterUpper A1 Aquifer
(≈ 0 to 25 feet bgs)
Lower A2 Aquifer
(≈ 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 OrionPark Housing Area. September.
Previous Investigations
Investigation Title Year Investigator Report Conclusions
Federal FacilitiesAgreement
1989 EPA, Navy NA
Soil and GroundwaterInvestigation
1999 NASA Detected TCE on-site at downgradientboundary
Groundwater Investigation 2000 Navy Detected TCE on-site at upgradient anddowngradient 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 Investigationand Monitoring WellInstallation
2007 Navy No on-site sources identified
Septic Tank and Drain FieldInvestigation
2009 Army Septic tank and drain field not a source
Supplemental Site Investigation
(SSI)
• Voluntary investigation by Army
• Work Plan approved by EPA and Water Board
• SSI Purposeo Investigate locations of concern (LOCs) previously identified with input from
EPA and Water Board
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)
Investigation Methods
Soil lithologyCPT (cone
penetrometertechnology)
VOCsMIP (membraneinterface probe)
VOCs
TCEDPT (direct push
technology)
= electroncapturedetector(ECD)
Groundwater
-
• 5 LOCso 14 CPT/MIPs
• Upgradient TCE plumepreferential pathwayso 6 CPT/MIPs
CPT/MIP Investigation
in Upper A1 Aquifer
• 4 LOCso 13 CPT/MIPs
• Upgradient TCE plumepreferential pathwayso 5 CPT/MIPs
CPT/MIP Investigation
in Lower A2 Aquifer
Screening Criteria to IdentifyPotential On-Site Source
• If YES → Investigate further
• If NO → Not a Source
Criterion
Primary Characteristics:
InvestigateFurther
ECDmax in capillary fringe?If 1 of 2 = Yes
ECDmax ≥ 7e+6 µV?
Secondary Characteristics:
ECDmax ≥ 4e+6 µV
If 2 of 3 = YesECD decreasing with depth?
ECD higher in fine-grain?
Example - ECD Profile Evaluation
ElectricalConductivity
A1 Aquifer
A2 Aquifer
Aquitard
Electron CaptureDetector (ECD)
(microvolts [µV]) x 106
Cone Resistanceand SoilLithology
Example: HighestECD in silty clay toclay (secondary)
CPT/MIP Investigation Results
LOCMIP ECD Profile
Results
Confirmed LOCConnected with
Upgradient Plume?
FurtherInvestigationWarranted?
1, 2a, 4, 5a,5b, 5c
< Screening criteria Confirmed No
3 < Screening criteria Not Confirmed Yes
2b/6b (A1Aquifer)
Upgradient ECDs> Screening criteria
Not Confirmed Yes
6b (A2Aquifer)
< Screening criteria Not Confirmed Yes
• 8 groundwater grabsampleso LOC 3 – 3 samples (from 2
locations)
o LOCs 2b/6b – 5 samples
DPT Investigation
in Upper A1 Aquifer
• 3 groundwater grabsampleso LOC 6b – 3 samples
DPT Investigation
in Lower A2 Aquifer
3-D Model - Lithology
Lithology (2002 - 2011 CPT)
Outputs
Inputs
A1/A2 Aquitard
3-D Model – TCE Plume andGroundwater Contours
OutputsInputs
ECD responses (2011 MIP)Groundwater water levels
3-D TCE Plume Model(TCE ≈ ECD Lower Level - 5e+5µV)
North
South
O
NorthTCE Above A1/A2 AquitardA1/A2 AquitardTCE Below A1/A2 Aquitard
Previous Boring
SSI Boring
3-D TCE Plume Model(TCE ≈ ECD Mid Level - 7.5e+5µV)
North
South
TCE Above A1/A2 AquitardA1/A2 AquitardTCE Below A1/A2 Aquitard
Previous Boring
SSI Boring
O
3-D TCE Plume Model(TCE ≈ ECD Higher Level - 1e+6µV)
North
South
North
TCE Above A1/A2 AquitardA1/A2 AquitardTCE Below A1/A2 Aquitard
Previous Boring
SSI Boring
O
TCE Plumes
• A1 Aquifer Plume (≈ 0 to 25 feet bgs)
• A2 Aquifer Plume (≈ 27 to 65 feet bgs)
DPT and 3-D Model
Investigation Results
LOC Method Results
1, 2a, 4, 5a, 5b,5c
Screened outduring CPT/MIP
InvestigationNo on-site source
3DPT Confirmed localized area of low ECD
responses were caused by residual TCE infine-grained soils3-D Model
2b/6b (A1Aquifer)
DPT Confirmed connection with upgradient A1plume3-D Model
6b (A2 Aquifer)DPT Confirmed connection with upgradient A2
plume3-D Model
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 Stepso SSI Report will be available for review upon finalization
OPHA Project Team Contacts
• US Army Environmental Command – AmandaMichels – [email protected]
• US Army Corps of Engineers – Celso Sabiniano –[email protected]
Questions