What makes a good risk based closure: lessons from a ......Stable and falling… •Closed tank,...
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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
Transcript of What makes a good risk based closure: lessons from a ......Stable and falling… •Closed tank,...
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
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04
20
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20
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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)
