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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
nce
ntr
ati
on
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
1
1.5
2
2.5
3
3.5
Co
nta
min
ant r
atio
s
Time
degradation
no change
rebound
Getting better!
Stable
Something’s not quite right
Closure
NRO regulated case closure history
0
100
200
300
400
500
600
700
800 1
98
7
19
88
19
89
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
19
98
19
99
20
00
20
01
20
02
20
03
20
04
20
05
20
06
20
07
20
08
20
09
20
10
20
11
20
12
Re
leas
es
rep
ort
ed
an
d c
ase
s cl
ose
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
ne
an
d M
TBE
rati
os
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
0 5 10 15 20
Be
nze
ne
an
d M
TBE
rati
os
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
0
100
200
300
400
500
600
700
800 1
98
7
19
88
19
89
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
19
98
19
99
20
00
20
01
20
02
20
03
20
04
20
05
20
06
20
07
20
08
20
09
20
10
20
11
20
12
Re
leas
es
rep
ort
ed
an
d c
ase
s cl
ose
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
100
1000
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%
40%
50%
60%
70%
80%
90%
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
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