What makes a good risk based closure: lessons from a review of closed cases from Northern Virginia

Alex Wardle

Petroleum Program, Northern Regional Office, Department of Environmental Quality, Commonwealth of Virginia

National Tanks Conference, September 2013

Denver, Colorado

Outline

• DEQ petroleum program risk based closure objectives

• What does a case manager need to know to make risk based closure decisions?

• A release time line and how that helps understand our “release”

• A review of groundwater conditions at closure compared with those from future investigations

DEQ Petroleum Program Objectives

• Prevent harm to human health and the environment from petroleum releases:

– Risk based

• “Real” receptors

• Source/pathway/receptor complete

– Groundwater (Drinking water and vapor intrusion) is primary concern

– Remove free phase as reasonably practicable

DEQ Petroleum Program and Land Use Decisions

• Decisions based on current or planned use

• Limited interaction with local government

– Program notifies health department of new releases

– No Program involvement in the planning process

– No Program involvement in groundwater use decisions

What is a good risk based closure decision?

• Protective of at risk receptors

• Allows property use and reuse

• Is protective of that known use at the time of case closure and in the future

What do we need to know to make a good risk based decision?

• Safe:

– Receptors protected

• Stopped:

– the release has ended and is not a continuing source

• Stable:

– plume defined in space and time and not spreading

Release time line C

on

tam

inan

t co

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ntr

ati

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Time

Release

Steady state

reduction

degradation MCL

Target level

10-6 RML

An example of a single release

A

Co

nta

min

ant c

on

cen

trat

ion

Time

Release

Steady state

reduction

degradation

Target level

MCL

10-6 RML 300

A

Case closure at A or B?

B

What do we have at closure? C

on

tam

inan

t co

nce

ntr

ati

on

Time

Release

Steady state

reduction

degradation

no change

rebound

Target level

MCL

10-6 RML

Closure

Normalize data to compare multiple releases

0

0.5

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1.5

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3.5

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nta

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Time

degradation

no change

rebound

Getting better!

Stable

Something’s not quite right

Closure

NRO regulated case closure history

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d Regulated

releases

Cases closed

Closed facilities – Post 94 Phase II ESAs

• Tanks removed

• Source stopped

• Receptors safe?

• Plume stable?

• 17 cases

Degradation since closure for cases with tanks removed

0.001

0.010

0.100

1.000

10.000

0 2 4 6 8 10 12 14

Be

nze

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d M

TBE

rati

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Time since closure

MTBE ratio

Benzene ratio

Half life = 0.6 yrs (Benzene)

Half life = 2 yrs (MTBE)

Half life = 4 yrs

Free product

Closed facilities – Post 94 Phase II ESAs

• Plume stable

• Receptors safe: no new impact

Stable and falling…

• Closed tank, inactive, sites – 94% cases <1,000 ug/l benzene or MTBE at

closure were <1,000 ug/l with new data

– All degradation ½ lives without free product less than four years

– Sites closed with more than 1,000 ug/l had free product and still had free product with new data 11 years later

Active facilities – Post 1996

• New data from divestment investigations completed from 1996 to 2013

• 55 cases Identified from DEQ database

Ratio of concentrations at closure to concentrations and time since closure

0.001

0.010

0.100

1.000

10.000

100.000

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Be

nze

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d M

TBE

rati

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Time since closure, yrs

MTBE ratio

Benzene ratio

Half life = 0.6yrs (benzene)

Half life = 2 yrs (MTBE)

Half life = 4 yrs

Receptors

• No “new” impacted receptors

• Sites with degradation ratio > 1

– new releases

– or plume not fully characterized

1994 DEQ NRO closures

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d Regulated releases

Cases closed

1994 closures

500 regulated case closures

86 regulated cases with post closure dissolved phase data (new or reopened case, PIIESA)

– 40 cases closed without groundwater data

– 46 cases with groundwater data

• 28 cases had more than one groundwater sampling event before closure

The 86 “new” cases

• 81 cases (94%) as a result of divestment investigation, “detection of petroleum” other than at tank closure or offsite impacts.

– 78 new cases

– 3 cases reopened

Receptors protected?

• Groundwater characterization

– One contaminated residential drinking water well

• No groundwater characterization

– Eight contaminated residential drinking water wells

1994 post closure benzene and MTBE ratios

0.0001

0.001

0.01

0.1

1

10

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10000

0 5 10 15 20

rat

io f

rom

clo

sure

years since closure

benzene ratio from closure

MTBE ratio from closure

benzene half life at 0.66 yrs

MTBE half life at 2 years

Half life of 4 years

2006: MTBE removed

Post closure Benzene and MTBE

0%

10%

20%

30%

40%

50%

60%

70%

80%

benzene>1mg/l MTBE>1mg/l

1994 no SCR

1994 closure SCR

post 1994 active

post 1994 closed

Degradation ratios > 1

0%

10%

20%

30%

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100%

1994 closures post 1994 closures tanks not removed

post 1994 closures tanks removed

% Degradation rates >1

benzene

MTBE

Receptors protected?

Of the 600 cases reviewed as part of this analysis only nine documented instances of a “missed” receptor at the time of the first case closure

Conclusions

• Risk based closure requires comprehensive characterization over time showing:

Receptors identified, protected and safe

Release stopped

Plume stable or reducing (degradation ratio one or less)

Questions

• alexander.wardle@deq.virginia.gov