Post on 14-Jan-2016
description
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:kda@mst.dk
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
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
Mapped plumes
Ministry of Environment and Energy Danish EPA
Two plume types
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
Horizontal and vertical redox zonation
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
Monitoring from 1997 to 2001
• See Slidepak
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: niras@niras.dk (Drejøgade)
• Christian Mossing, Hedeselskabet
E-mail:hedeselskabet@hedeselskabet.dk (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.