Remedy Analysis for Sierra Army Depot, Building 210 AreaHerlong, California

Desert Remedial Action Technologies WorkshopPhoenix, Arizona

Jackie Saling, PE

Outline

Site Background Historical Investigations Interim Remedial Activity Pilot Tests Conceptual Site Model Enhanced Reductive Dechlorination Soil Vapor Extraction Conceptual Site Model- Revisited Moving Forward

Site Location and Historical Operations

1942 – storage of supplies and inert materials

1950s – explosives, guided missiles, and fuels

Current – storage of war reserves and munitions

Activities at the Site fluctuate

Building 210 Area

Site Location and Surrounding Features

Surrounded by Mountains Honey Lake Valley Arid Climate Annual precipitation less

than 5”

Fort Sage Mountains

Amedee Mountains

Diamond Mountains

Honey Lake

Building 210 Area

Regional Geology

Diamond MountainsDiamond Mountains

Fort Sage MountainsFort Sage Mountains

Amedee MountainsAmedee MountainsHoney LakeHoney Lake

Block faulted mountains Alluvial fans- poorly sorted coarse

grained Fine grained lake deposits

Regional Hydrogeology

Honey Lake

398239843986

3988

3988

3988

Building 210 Area

Regional groundwater flow toward Honey Lake

Closed hydrologic basin

Intermittent streams Surface area of Honey

Lake fluctuates Horizontal K:Vertical K

100:1

Building 210 Area

Vehicle Maintenance Popping furnace Sand blasting, spray painting,

steam cleaning, engine fogging Degreasing solvents, oils, sludge

Potential Source AreasTCE and TCA

degreaser tanks

Possible dumping in ditches behind

buildings

TCE degreaser tanks

Solvent recovery activities

Waste discharged to shallow ditch

Site Investigation Timeline

1994

1983

1992

1995

2002

1997

• Surface Soil (6 samples)• Subsurface Soil (5 borings)• Background Soil

• Subsurface Soil (52 samples)• Soil Gas (294 samples)• Groundwater (20 samples)

• Geophysics• Hydraulic Testing

• Groundwater Investigation• Plume Delineation

• Additional Hydraulic Testing• Groundwater Treatment Analysis

• CP Testing (20 locations)•Soil Gas (20 samples)

Investigation Findings – Soil and Soil Gas

Soil gas isocontours developed from 1992 investigation

Unsaturated zone consists of interbedded silty sand and poorly-graded sands and gravel

Depth to groundwater 95 ft Lower permeability silt zones were encountered from approximately 105

to 155 feet bgs No soil impacts observed TCE in soil gas

10

1

100

TCE in groundwater detected up to 5,000 g/L in shallow groundwater (95-115’ bgs)

Hydraulic conductivity 8 x 10-3 to 3.22 x 10-2 cm/s in shallow groundwater

TCE in groundwater near or below criteria in intermediate groundwater (160-170’bgs)

Investigation Findings - Groundwater

B21EX

B23EX

B24EX

0 1000 2000

50

500

Building 210

5

Pump and Treat System Layout

5024-EX

23-EX

21-EX

500

50

5

5

Building 210

Reinjection Trenches

Interim Remedial Activity- Pump and Treat

Pump and Treat Performance Data

0

5

10

15

20

25

30

1999 2000 2001 2002 2003 2004 2005 2006Year

Ave

rag

e T

CE

Rem

ova

l R

ate

(lb

s/m

o)

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

160,000

180,000

Averag

e Daily F

low

(gp

d)

Monthly TCE Removal Rate Average Daily Flow

Pump and Treat Issues

Fouling decreased efficiency of groundwater recovery

HRC Area, 2000

ZVI PRB Area, 2003

Follow Up HRC Area, 2002

ZVI Injection Area, 2001

ERD Injection Area, 2004

Building 210

SVE Area, 2006

Pilot Test – Hydrogen Release Compound®

Injection of HRC® into injection wells surrounded by monitoring wells in 2000, follow up 2002

Limited TCE degradation was observed, release rate of hydrogen was not high enough to overcome aerobic conditions

Pilot Test – Zero Valent Iron Injection

Conducted in October 2001 Injection of micro-scale into 9

injection points surrounded by monitoring wells

TCE concentrations decreased initially, but have rebounded

Pilot Test - Zero Valent Iron PRB

Implemented in May 2003 Construction of a micro-scale

permeable reactive barrier with 5 injection points

0

500

1,000

1,500

2,000

2,500

Jul-02 Jun-03 Jun-04 Jun-05 Jun-06 Jun-07

TC

E C

on

ce

ntr

ati

on

(u

g/L

)

B21-73-PZ

Conceptual Site Model

Virtually no groundwater movement No connection observed between possible source areas

and groundwater impacts identified No recharge to transport contaminants vertically from

potential source to groundwater Heavy TCE vapor travel through vadose zone and spread

out on top of the groundwater table creating a broad thin groundwater plume

Vapor migration transports TCE, no transport in groundwater

Significant mass in vadose zone

Site Conditions

Current Groundwater Plume Figure

Building 210

Pilot Test – Enhanced Reductive Dechlorination

Monthly injections began July 2004, 30% molasses

Decreased frequency of injections and molasses concentration over time

ERD injections are ongoing

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

Jul-04 Dec-04 Jun-05 Dec-05 Jun-06 Dec-06 Jun-07

TO

C (

mg

/L)

Decreased to 10%

molasses

Decreased to 1% molasses, increased injection volume to 1500 gal/well

Monitoring Well 77-PZ

Enhanced Reductive Dechlorination – Operational Data

Enhanced Reductive Dechlorination – Operational Data

0

1

2

3

4

5

6

7

8

Jul-04 Dec-04 Jul-05 Dec-05 Jun-06 Dec-06 Jun-07

pH (

SU

)

Began injection of NaOH

Monitoring Well 77-PZ

0

5,000

10,000

15,000

20,000

25,000

30,000

Jul-04 Dec-04 Jun-05 Dec-05 Jun-06 Dec-06 Jun-07

Meth

an

e C

on

cen

trati

on

(u

g/L

)

0

2

4

6

8

10

12

14

16

Jul-04 Dec-04 Jun-05 Dec-05 Jun-06 Dec-06 Jun-07

Co

nce

ntr

atio

n (

um

ol/

L)

TCE c-DCE VC Ethene

Enhanced Reductive Dechlorination – Operational DataMonitoring Well

77-PZ

Best results with low concentration, high volume injections Long time before reductive conditions were established Effective in decreasing TCE concentrations in groundwater

after reductive conditions are established Small injection well ROIs due to the flat gradient, full scale

application would require many injection wells and possible groundwater recirculation system

Will not address significant mass in the soil vapor

Enhanced Reductive Dechlorination – Results

Pilot Test – Soil Vapor Extraction One extraction well Six monitoring points Two passive vents 85 cfm, 50 in H2O at the

blower Pilot test ongoing

Passive Vent

Monitoring Well

Extraction Well

Soil Vapor Extraction System - OperationVacuum extracted

airAtmospheric

ventAtmospheric

vent

Soil Vapor Extraction – Vacuum Distribution

0

10

20

30

40

50

60

0 10 20 30 40 50 60

Distance from Extraction Well (ft)

Vac

uu

m (

inch

es o

f w

ater

)

60 6156

120 100 80140 60 40 20 0 20 40 60 80

SVE Well

East-West Cross Section

Soil Vapor Extraction – Operational Data

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

Aug-06 Oct-06 Dec-06 Feb-07 Apr-07 Jun-07 Aug-07 Oct-07

TC

E R

emo

val

Rat

e (l

bs/

mo

)

Soil Vapor Extraction Groundwater Impact

1,500

0 10 20 30 40 50

SVE Well

500

1,00

0

Monitoring Well

Monitoring Well

Monitoring Well

May 2007

Soil Vapor Extraction Groundwater Impact

1,500

0 10 20 30 40 50

SVE Well

500

1,00

01,000

1,00

0

July 2007

Soil Vapor Extraction Summary

Successful in removing mass from vadose zone and groundwater, 2.1 to 9 pounds TCE removed per month from one extraction well

No operational issues, runs 24-7 Vacuum propagation is further to the north and west due to

subsurface heterogeneity Ability to reduce TCE concentrations below surface of the

water table will be diffusion limited May not be able to reduce groundwater concentrations to

regulatory standards

Conceptual Site Model - Revisited ORIGINAL: Virtually no groundwater movement REVISED: Groundwater moving in the SE direction,

observed groundwater velocity 0.5 ft/day

ORIGINAL: Vapor migration transports TCE, no transport in groundwater

REVISED: Updated groundwater model and better understanding of hydrogeology indicates that vapor AND groundwater are transporting TCE. Updated groundwater model shows plume is stable.

Conceptual Site Model - Revisited

ORIGINAL: Heavy vapors travel through vadose zone and spread out on top of the water table creating a broad, thin plume

REVISED: Plume is not as thin as initially thought due to diffusion of TCE in the groundwater over time

Conceptual Site Model - Revisited

No connection observed between possible source areas and groundwater impacts identified

No recharge to transport contaminants vertically from potential source to groundwater

Significant mass in vadose zone

Conceptual Site Model - Revisited

Moving Forward

Groundwater flow direction? Pumping operation on property to the SE? Recharge onsite? Building 210 operations? Geological feature?

Full scale soil vapor extraction implementation

Moving Forward

Proposed full scale SVE system layout

Extraction WellExtraction Well/Passive Vent

Conclusion

Numerous technologies tested at the site SVE and ERD are both viable technologies to use at the

site SVE- proven technology

Best mass removal Low cost Consider and evaluate options to overcome diffusion limitations

associated with soil vapor extraction