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 – Amanda.R.Michels.civ@mail.mil

• US Army Corps of Engineers – Celso Sabiniano –Celso.F.Sabiniano@usace.army.mil

Questions