Ministry of Environment and Energy Danish EPA
Ad Hoc International Working Group on Contaminated Land
”Natural attenuation in Denmark” by Kim Dahlstrøm, Danish EPA,E-mail:[email protected]
Outline:
Background information
• Groundwater / Drinking water
• Point source
Terminology
Guidelines on Remediation of Contaminated Sites
• Risk Assessment in relation groundwater protection
• Biodegradation or degradation under natural conditions
Experience gained in two cases
Conclusive remarks
Ministry of Environment and Energy Danish EPA
Drinking water based on uncontaminated groundwater
• More than 98 % of all drinking water is based on groundwater
• No advanced treatment (GAC, ozone etc.)
• Only aeration and sand filtration
Ministry of Environment and Energy Danish EPA
Larger waterworks
• 600 million m3 groundwater/yr.
• 3000 waterworks supplying > 10 houses (units)
• Responsible for 90 % of all distributed drinking water
Ministry of Environment and Energy Danish EPA
Smaller waterworks and wells
• 700 waterworks supplying < 10 houses (units)
• 91,000 private wells
• 1250 wells for industrial purposes
Ministry of Environment and Energy Danish EPA
Contaminated sites - point sources
• Point sources e.g. petrol stations, dry cleaning facilities, landfill sites
• 8000 registered and mapped sites 31.12.2000.
• 30,000 - 40,000 sites are suspected to be contaminated and has to be assessed.
• Around 14,000 are anticipated contaminated.
Ministry of Environment and Energy Danish EPA
NA / Intrinsic bioremediation(IB)/ Biodegradation - Terminology
• NA, IB, biodegradation or degradation - not a remediation technique or method
• compare to P&T, air sparging etc.
• No active measures are carried out in order to enhance removal or to decrease further spreading of contaminants
Ministry of Environment and Energy Danish EPA
Monitored NA - Terminology
• Monitoring technique or methodology• Design of network for
observations/monitoring wells, screen interval etc.
• Sampling and choice of parameters for analysis
• Analysis methods
Monitoring is a technique or may involve several techniques
Ministry of Environment and Energy Danish EPA
Where to take account of bio-/ degradation ?
• In the risk assessment• If degradation is sufficient no remedial
actions are needed
• Intent to separate processes• dilution due to dispersion: a mass neutral
process and
• degradation: a mass decreasing process
Ministry of Environment and Energy Danish EPA
Guidelines on Remediation of Contaminated Sites
• Comprises a description on how to handle a contaminated site
• Where to retrieve information on landuse/activities
• Design of survey, samples and analyses
• Risk assessment regarding soil, indoor air and groundwater
• Quality criteria for soil, air and groundwater
• Description of remedial actions and techniques
Ministry of Environment and Energy Danish EPA
Principles in Groundwater Risk Assessment
• Predicting groundwater concentration using simple equations
• Several assumptions• isotropic/homogeneous aquifer
• only dissolved contaminants
• continuous leaching
• pseudo steady state
• Definition of a groundwater risk• If the predicted conc. exceeds groundwater
criterion
Ministry of Environment and Energy Danish EPA
Stepwise risk assessment
• Step 1: Near-source mixing model• mixing in the 0.25 m of the aquifer
• Step 2: Downgradient mixing model• mixing at a distance equal to 1 yr gw. flow,
max. 100 m down gradient• increased mixing zone due to vertical
dispersion of the plume. Std. parameters suggest a mixing zone on 1.8 m
Ministry of Environment and Energy Danish EPA
Step 3: Downgradient mixing model with degradation
• Only applicable if contaminants have reached the aquifer
• Only applicable if groundwater geochemistry indicates condition in favour of degrading the observed contaminants
• Based on 1. order degradation constants from the literature. Time available for degradation is equal to the retardation due to sorption.
• Requires subsequent documentation (monitoring) and determination of the site specific degradation constant.
Ministry of Environment and Energy Danish EPA
Groundwater criteria
Parameter Groundwater criterion, µg/lBenzene 1Toluene 5Ethylbenzene + xylenes 5Total hydrocarbons (mineral oil) 9MTBE 5 (2-5)Chlorinated solvents(PCE+TCE+DCE)
1
Vinyl Chloride (VC) 0,3
Ministry of Environment and Energy Danish EPA
Case 1 ”Drejøgade”
Landuse and contaminants
• Former industrial dry cleaning facility
• Contaminants: mineral spirits (BTEX,THC) and chlorinated solvents (PCE, TCE, DCE and VC)
• Present landuse
• Housing / flats
Note that indoor air is at risk.
Ministry of Environment and Energy Danish EPA
Case 1 ”Drejøgade” cont.
Geology• Limestone covered by fine sand having a
thickness of 18 m
• The unsaturated zone is 8.5 m
• The plume is located in the sand aquifer
Ministry of Environment and Energy Danish EPA
Redox sensitive species
• Organic matter in the groundwater is degraded through reduction of electron acceptors
• Example:
C6H5CH3+ 4,5SO42-+ 3H2O2,25H2S+2,25HS-+ 7HCO3-+ 0,25H+
• Method:• consumption of electron acceptors (O2, NO3
-, SO42-)
• occurrence of intermediates (N2O)
production of reduced species (Fe2+, Mn2+, H2S, CH4)
Ministry of Environment and Energy Danish EPA
Site specific criteria for redox level assessment
Aerobicrespiration
Nitratereduction
Ironreduction
Sulfatereduction
Methano-genesis
Oxygen > 1 mg/l < 1 mg/l < 1 mg/l < 1 mg/l < 1 mg/l
Nitrate <30 mg/l <30 mg/l <30 mg/l
Dinitrogenoxide
yes
Iron < 1 mg/l < 1 mg/l
Manganese <0,5 mg/l <0,5 mg/l
Sulfate
Sulfide 0 0 0 yes
Methane <1 mg/l <1 mg/l <1 mg/l <1 mg/l <1 mg/l
Ministry of Environment and Energy Danish EPA
Effect of biodegradation
BTEX+Chl. ethenes plume:
• 99,5 % PCE degradation
Chlorinated ethenes plume:
• 5 % PCE degradation
• Reductive dechlorination requires strongly reduced conditions, i.e. the presence of a carbon source
Ministry of Environment and Energy Danish EPA
Is there a risk ?Parameter, BTEX+Chl. ethenes Gw-criterion
, µg/lConc. 60m(MB11)downstream, µg/l
Exceedingfactor
Benzene 1 48.4 48Toluene 5 4.4 <1Ethylbenzene + xylenes 5 <0.1 <<1Total hydrocarbons (mineral oil) 9 530 >50Chlorinated solvents(PCE+TCE+DCE)
1 PCE:38TCE:14DCE:157
>200
Vinyl Chloride (VC) 0,3 VC:82 >270
Ministry of Environment and Energy Danish EPA
Is there a risk ?Parameter, Chl. ethenes Gw-criterion
, µg/lConc. 60m(MB14)downstream, µg/l
Exceedingfactor
Benzene 1 3.5 >3Toluene 5 <0.1 <1Ethylbenzene + xylenes 5 <0.1 <1Total hydrocarbons (mineral oil) 9 490 >50Chlorinated solvents(PCE+TCE+DCE)
1 PCE:1400TCE:180DCE:1337
>2900
Vinyl Chloride (VC) 0,3 VC:1200 4000
Ministry of Environment and Energy Danish EPA
Case 2 ”Radsted”
Landuse and contaminants• Former petrol station, closed in 1975
• Contaminants: mineral spirits (BTEX,THC)
• Source removal in 1996
• Residual contamination in unsaturated zone c. 25-50 kg, mainly BTEX compounds
Ministry of Environment and Energy Danish EPA
Groundwater flow direction
H4H3
H2H1
G6
F2
F1G3D1
FC9G2
G5 FC2
PB1
D2 D3
G1
F3
Nykøbingvej
0 5 10 15 20 m
Underground storage tanks
N
Legend :
Building
Well
Piezometric surface contour lines
Ministry of Environment and Energy Danish EPA
Geology, cross section
14 m
FluctuatingWater level
Surface water level in wetland area
Piezometric surface level in aquifer
Legend :
Clayey Till
Sand
Limestone
Direction of flow
Source area
N Nykøbingvej
Radsted maskinstation
Ministry of Environment and Energy Danish EPA
Mapped plume -BTEX and O2
H4H3
H2H1
G6
F2
F1
G3D1
FC9
G2
G5
FC2
PB1
D2 D3
G1
F3
>1
>10
>100
>1000
N
BTEX (µg/l) Oxygen (mg/l)
H4H3
H2H1
.G6
F2
F1
G3D1
FC9
G2
G5
FC2
PB1
D2 D3
G1
F3
<5
>5
<1
<0,5
N
>5
Ministry of Environment and Energy Danish EPA
Mapped Plume - NO3- and Fe(II)
Nitrate (mg/l)
H4H3
H2H1
G6
F2
F1
G3D1
FC9
G2
G5
FC2
PB1
D2 D3
G1
F3
<5
<2
<10
>10
N
Iron (mg/l)
H4H3
H2H1
.G6
F2
F1
G3D1
FC9
G2
G5
FC2
PB1
D2 D3
G1
F3
<0,5
>10
>0,5
N
Ministry of Environment and Energy Danish EPA
Groundw. level and BTEX conc.
D ate
0
1000
2000
3000
4000
BT
EX
co
ncen
trat
ion
(µ
g/l)
1.5
2
2.5
3
Gro
und
wat
er le
vel (
met
ers
abo
ve s
ea
leve
l)
G round w ater leve l ( ) and BTEX concentra tion ( ) in w ell no. FC 2
Ministry of Environment and Energy Danish EPA
Is there a risk ?
Interpretation of data is difficult
• Heterogeneous geology
• Variation in groundw. level and flow direction
• Variation in redox parameters
• Influence of two mixed water types
• Natural geochemical reaction e.g. nitrate reduction due to pyrite oxidation,
FeS2 + 14/5NO3- + 4/10H2O
Fe2+ + 2SO42- + 4/5OH- + 14/10N2
Ministry of Environment and Energy Danish EPA
Is there a risk ?
• H1Ø and H2Ø indicate a risk
• Are location wells and screen interval correct
• THC conc. 70-80 µg/l at 45m down stream
• High detection limit
Ministry of Environment and Energy Danish EPA
Conclusive remarks
• Abstraction wells are located in all parts of DK
• Drinking water is based on pure groundwater that only needs simple treatment before distribution to consumers
• In the coming years around 30,000 sites have to be assessed in order to decide if they pose a threat to the groundwater
Ministry of Environment and Energy Danish EPA
Conclusive remarks
• Bio-/degradation is not seen as remedial technique but is taken into account in the risk assessment
• Conducting monitoring is one technique or involve several techniques
• Interpretation of redox zones can be difficult due to variations in hydrogeology and natural processes changing gw. geochemistry
• High rates of degradation were not sufficient to avoid a groundwater risk
Ministry of Environment and Energy Danish EPA
Acknowledgements and references
Thanks to:• Charlotte Riis & Anders G. Christensen, NIRAS
E-mail: [email protected] (Drejøgade)
• Christian Mossing, Hedeselskabet
E-mail:[email protected] (Radsted)
Selected references:• Naturlig nedbrydning af olie og chlorerede opløsningsmidler i
grundvandet på Drejøgade 3-5, Miljøprojekt nr. 544 2000. Web site: www.mst.dk
• C.E. Riis et al. 2000. Redox Characterization for Natural Attenuation of Chlorinated Ethenes and BTEX. 2. Int. Conf. on Remediation of Chlorinated and Recalcitrant Compounds.
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