Groundwater Remediation Project
Hinkley Gas Compressor Station
Presentation to the
Lahontan Regional Water Quality Control Board
June 8, 2011

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• Feasibility study for comprehensive final groundwater cleanup plan
• Progress of current remedial actions and containment activities
• PG&E’s bottled drinking water program and other community initiatives

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• Protect human health and the environment
• Contain and clean up the plume
• Apply green and sustainable practices
• Enhance and restore beneficial use of groundwater
• Create opportunities for beneficial reuse of land
• Contribute to economic vitality of the community

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Alternatives assembled from array of proven effective technologies
• Submitted to Water Board August 2010
• Over 60 remedial technologies evaluated:
• In-situ reactive zones (multiple configurations)
• Agricultural land treatment units
• Pump and treat (multiple technologies)
• Infiltration galleries
• Direct push amendment delivery
• Freshwater injection
• Review of on-site pilot studies is included
• Alternatives assembled for detailed analysis

Range of options considered and estimated years to completion
Alternative
4B
4A
Aggressive in-situ treatment and beneficial agricultural use with targeted pumping
Aggressive in-situ treatment and beneficial agricultural use
6 Combined alternative
5
4
3
Plume-wide pump and treat
Core in-situ treatment and beneficial agricultural use
Plume-wide in-situ treatment
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5
1
Containment
No action
50 ppb
MCL
6
6
28
50
6
8
120
750 – 1000
80% Mass
Removal
3.1 ppb
Background
10 40
10
18
37
13
10
95
>780
75
90
140
150
110
260
>1000

Containment
Extraction
Agriculture
Area
Fresh Water
Injection
Multiple remedial components target specific areas of plume
Agricultural Treatment
Fresh Water Injection
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Locations approximate and not to scale
In-situ
Treatment
Hinkley
Compressor
Station
In-situ Treatment

In-Situ Treatment and Beneficial Agricultural Use
Core plume remediated in 6 years; only traces left after 20 years
Initial Chromium
Concentrations
After 10 Years of Remediation
After 20 Years of Remediation
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Computer generated estimates of 10-year and 20-year results

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Technically sound remediation plus multiple local / regional benefits
• Achieves plume containment
• Provides rapid remediation of plume core
• Offers beneficial land and aquifer use for farming
• Promotes a “green” / sustainable remedial approach
• Improves legacy nitrate issues

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Primary public questions:
• Did the Feasibility Study consider enough technologies?
 Yes. 60 technologies were evaluated, including use of a treatment plant and resins as in municipal facilities
 DTSC stated in their review:
“DTSC agrees that Table 6-1 and 6-2 of the FS provided a reasonable list of processes and technologies available for the remediation of groundwater contaminated with hexavalent chromium. We believe that the ‘best available technology’ for remediation of the site would likely be a combination of the processes and treatment parameters presented in the two FS addenda.”

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Primary public questions:
• Do agricultural units allow plume escape during winter months?
 No. Pumping rates vary by season but net direction of groundwater flow is toward extraction wells all year
Groundwater typically flows about 300 feet toward extraction wells during spring, summer and fall pumping
Groundwater may flow 100 feet away from extraction wells during winter pumping
The net annual movement of groundwater is about 200 feet toward extraction wells
• Is chromium conversion in soil permanent?
 Chromium-6 converts to chromium-3, binds to the existing soil, and then becomes the same as natural chromium-3

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Additional DTSC suggestions include:
• Update computer model runs to current plume
• Allow flexibility for future plume understanding
• Provide additional level of cost details
• Provide particle track analysis in addition to current fate and transport model
• Review issues surrounding seasonality of pumping, and develop contingency plans should capture be inadequate
• Document permanence of chromium conversion in soil
We will work with the Water Board to address reviewer suggestions

Diffuse Plume
North of Hwy 58, chromium concentrations are below 50 ppb
Plume Core
South of Hwy 58, chromium concentrations are above 50 ppb
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Locations approximate and not to scale
Hinkley
Compressor
Station
“DTSC also recommends consideration of focus areas for remediation goals and strategy”
• Diffuse plume strategy:
Immediately contain, and treat via extraction
• Plume core strategy:
Immediately cut off continuing source to diffuse plume, and treat in place for maximum speed

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• Feasibility study for comprehensive final groundwater cleanup plan
• PG&E’s bottled drinking water program and other community initiatives

Thompson Rd
Desert View
Dairy Land
Treatment
Unit
Fresh
Water
Injection
DVD, SCRIA Extraction Wells
MW-62A Action Plan Wells
Agricultural Unit & LTU Wells
Central
Area IRZ
South Central
Reinjection
Area
Source
Area IRZ
Locations approximate and not to scale
Hinkley
Compressor
Station
2011
Plume Containment, Treatment, and Monitoring
• Control leading edge of plume with freshwater injection
• Contain plume with groundwater extraction and agricultural land treatment
• Treat plume core and source areas with in-situ remediation
Groundwater and Land Use
Management
• Accomplished through property acquisition and restoration
• Land use/pumping agreements

Desert View
Dairy Land
Treatment
Unit
Gorman
Property
Pumping
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Locations approximate and not to scale
Central
Area IRZ
South Central
Reinjection
Area
Source
Area IRZ
Hinkley
Compressor
Station
2009
New Activities:
• Trend identified at MW-62A
• Additional talks with Gorman of need to control pumping
• Additional extraction wells installed to increase control
Ongoing Activities:
• Containment pumping and agricultural treatment at DVD
• Source reduction through large-scale in-situ treatment

Desert View
Dairy Land
Treatment
Unit
Former
Gorman
Property
Fresh
Water
Injection
16 Locations approximate and not to scale
Central
Area IRZ
South Central
Reinjection
Area
Source
Area IRZ
Hinkley
Compressor
Station
2010
New Activities:
• PG&E purchases Gorman property to control pumping
• Approval and implementation of MW-62A Response Plan
• New monitoring wells confirm thin layer near Summerset
Ongoing Activities:
• Containment pumping and agricultural treatment at DVD
• Source reduction through large-scale in-situ treatment

Thompson Rd
Desert View
Dairy Land
Treatment
Unit
Fresh
Water
Injection
DVD, SCRIA Extraction Wells
MW-62A Action Plan Wells
Agricultural Unit & LTU Wells
Central
Area IRZ
South Central
Reinjection
Area
Source
Area IRZ
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Locations approximate and not to scale
Hinkley
Compressor
Station
2011
New Measures:
• Ag Unit G North
• Ag Unit G South
• Ag Unit C
• Ranch Ag Unit
• Western Ag Unit (in process)
• Additional Ag Unit (in process)
• Additional DVD extraction wells
• Additional in-situ treatment work
• Additional monitoring wells

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Increase in pumping
1350
345
450
Nov.
2009
650
950
MW-62A Response Measures:
• Purchase Gorman property
• New extraction wells
• Increase in pumping rates
Additional Measures:
• More extraction wells
• Additional piping on standby
• Additional injection wells
• Increase agricultural treatment

Encouraging results indicate source reduction within core of the plume
Rapid decrease of chromium concentrations
2007 2011
2008 2009 2010
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Data shown are from upper aquifer

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• Feasibility study for comprehensive final groundwater cleanup plan
• Progress of current remedial actions and containment activities

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Trindall Rd
• Bottled water provided to all residences up to approximately
½-mile surrounding the plume
• Separate Water Board mandated program applies to domestic wells found to be above background levels
• Water currently supplied to about 80 residents plus Hinkley
School and Senior Center
• PG&E program boundaries are periodically reviewed

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• Long-standing PG&E program expanded in 2010 to include properties up to
½-mile beyond bottled water program area

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Program Area
• Program intended for homes or properties:
• On or next to the plume
• Located where agricultural pumping and/or other activities could potentially affect the plume
• Located in an area that could be needed for future remediation activities
• Properties appraised as if the chromium plume is not present, and comparable home values are from communities outside
Hinkley

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• Mission is to advise, share concerns with, and provide direct input to PG&E on its environmental and community programs in Hinkley
• Membership will reflect the composition, diversity, and interests of the Hinkley community
• All meetings open to the public and announced in local newspaper and other media

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