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Hydraulic Containment, Natural Attenuation and Phytoremediation asa Combined Remediation Strategy for an Industrial Waste Site in
South Africa
D. Duthe1, S. Lorentz2, I. Cameron-Clarke1 and A.J. Oliver3
1 Steffen, Robertson and Kirsten Consulting, Johannesburg, South Africa.
2 School of Bioresources Engineering and Environmental Hydrology,University of KwaZulu-Natal, Pietermaritzburg, South Africa.
3 Project Manager
Third International Phytotechnologies Conference, EPA, ORD, TIFSDAtlanta, GA, 20-22 April 2005
Outline
• Introduction
• Remediation strategy
• ET cover performance
• Conclusion
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
020406080
100120140160180
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecR
ain,
Pot
entia
l eva
p (m
m)
Rain Potential evap.
MAP 1025 mm
MAPE 1528 mm
Alt. 90 m
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
Ash waste dams
Dam 3/4
Dam 2
Dam 1
Dam 6
Buried drums area
Dam 5
Aerial view of the dams and buried drums area
Dam footprint: 30haCommission: 1958Decommission: 1994+
Contaminants of concern:
TetrachloroetheneTrichloroethene1,2 Cis DichloroetheneVinyl chlorideTDS
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
Remediation Strategy
• Management intervention:
- Alternative water supply to the KwaMakutha village andreversal of off-site contamination by groundwaterdrawdown,
- Dewatering of the slimes dams by drawdown of phreaticsurface below the dams,
- Surface water control by installation of drainage works,
- Seepage water control by subsurface drains around thedams and in Kwamakutha.
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
Remediation Strategy
• Management intervention:
- Alternative water supply to the KwaMakutha village and reversal of off-site contamination by groundwater drawdown,
- Dewatering of the slimes dams by draw down of phreatic surface below the dams,
- Surface water control by installation of drainage works and
- Seepage water control by subsurface drains around the dams and in Kwamakutha.
• Proposed remediation:
- Hydraulic containment by groundwater gradient control and surface runoff control,
- Monitored Natural Attenuation and possibly enhanced attenuation by recirculation in the groundwater and
- Evapotranspiration cover. Planting of some 1600 indigenous species tolimit fluxes through the slimes and promote natural attenuation.
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
Source attenuation in the slimes profile
Contaminant concentrations inthe groundwater in and bellow the slimes dam
Tensiometer nest 100 - 2000 mm
Deep tensiometer nest
Automatic rain gauge
Bowen ratio evapotranspiration
Heat pulse velocity
Automatic weather stationA-pan evaporation
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
Pessuretransducers
Rain gauge and logger
Ceramic cupTensiometers
Monitoring of subsurface liquid fluxand water content:
Material hydraulic/physical properties: - Porosity/density - Water retention characteristic - Hydraulic conductivity characteristic
Data logger
Slimes dam surface
Bowen ratio ET
Sap flow: heatpulse velocity
DeepTensiometers
Met stationand logger
Root zone
Automaticgroundwater level recorder
Groundwater
Schematic of instrumentation for measurement of components of the slimes dam water balance
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
Vegetation on slimes dam 2
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
Shallow rooting system of the Natal Fig Grass growth on slimes dam 2
Slimes Dams Water Balance Modelling
• Since the groundwater recharge component flux cannot be measured directly, as is the case in lysimeter experiments, the observations and material properties are combined to calculate this flux.
• We also wish to evaluate the potential of the full slimes profile (15m) in absorbing peak rainfall events, retarding fluxes to the groundwater and releasing water back up to the root zone during dry periods.
• These calculations are best performed using the soil water physics inherent in the HYDRUS2D software. Once calibrated against the observations over three years, HYDRUS2D is used to predict long-term performance of a full canopy cover
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
0.01
0.1
1
10
100
Hyd
raul
ic c
ondu
ctiv
ity (m
m/h
)
1E1 1E2 1E3 1E4Matric pressure head (mm)
Fig 0mm (1) Fig 0mm (2) Fig 250mm (1) Fig 250mm (2)
0
2000
4000
6000
8000
10000
Mat
ric p
ress
ure
head
(mm
)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Volumetric water content
AECI Fig 0mm
Water retention characteristic
Hydraulic conductivity characteristic
HYDRUS2D inputs: hydraulic characteristics of the slimes materials
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
HYDRUS2D inputs: rainfall characteristics (short & long term)
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
0
200
400
600
800
1000
1200
1400
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Cum
ulat
ive
Rai
n (m
m)
Median (1977)Max (1997)Min (1992)2002
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
Feb-02 Mar-02 Apr-02 May-02 Jun-02 Jul-02 Aug-02 Sep-02
Sap
Flow
(mm
/day
)Small treeLarge tree
HYDRUS2D inputs: Transpiration
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
Feb-02 Mar-02 Apr-02 May-02 Jun-02 Jul-02 Aug-02 Sep-02 Oct-02 Nov-02 Dec-02 Jan-03
Sap
Flow
(mm
)
Large treeSmall tree
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
Sap flow rates for Bugweed trees (2002)
Sap flow rates for Pigeonwood trees (2002)
HYDRUS2D inputs: potential evaporation and transpiration
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
160.0
180.0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
ETa,
ETo
(mm
)
Linacre 1977 Bowen ratio (2002/3) Sap flow (2002)
Observation nodes for long-term simulation
1
2
3
4
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
11000
12000
13000
14000
15000
Depth (mm)
0
Soil Water Pressure (mm)
-4000
-6000
-2000
Initial Conditions
0
1000
2000
Detail of top 2m.
2
1
4
3
Depth (mm)Observation nodes
HYDRUS-2D Finite Element Mesh Boundary conditions
Constant head ground water
Atmospheric boundary condition
Root zone
HYDRUS2D finite element configuration
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
0
2000
4000
6000
8000
10000
01-Sep-02 15-Sep-02 29-Sep-02 13-Oct-02
Cap
illar
y pr
essu
re h
ead
(mm
)
0
20
40
60
80
Cum
ulat
ive
rain
(mm
)
300mm
1000mm
sim 300mm
sim 1000mm
rain
Typical comparison of measured and simulated soil water tension from which fluxes are derived
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
0
200
400
600
800
1000
1200
Feb-02 Apr-02 Jun-02 Aug-02 Oct-02
Cum
ulat
ive
wat
er v
olum
e (m
m)
Rain (measured) Actual ET (measured)
Drainage (estimated from measurements) Store (estimated from measurements)
Components of the root zone water balance for the monitored period
Duthe et al: Hydraulic Containment, Natural Attenuation and Phytoremediation..
-150
-100
-50
0
50
100
150
200
250
Wat
er B
alan
ce C
ompo
nent
s (m
m)
Apr May June Jul/Aug Sep Oct Nov Dec Jan Feb
Precip Soil Evap Transpiration Drainage
-150
-100
-50
0
50
100
150
200
250W
ater
Bal
ance
Com
pone
nt (m
m)
Apr May Jun Jul/Aug Sep Oct Nov Dec Jan Feb/Mar
Precip Soil Evap Transpiration Drainage
Simulated root zone water balance for monitored period for Fig Tree site.
Simulated water balance for monitored period for Bare site (2000mm depth)
Long term slimes dam water balance simulation
• Long term ground water recharge fluxes are simulated by
- Correlating meteorological parameters for short term records between stations at the site and Durban International Airport,
- Simulating full vegetation cover performance using HYDRUS2D with adjusted long term inputs of rainfall and potential evaporation (28yr record),
- Extracting the discharge time series for groundwater recharge from the base of the slimes dam.
-60
-40
-20
0
20
40
60
Cum
mul
ativ
e dr
aina
ge (m
m)
1973 1977 1981 1985 1989 1993 1997 2001
Cumulative simulated long term recharge to groundwater: Vegetated scenario
Results of simulated fluxes to groundwater
Scope of current investigations
• Groundwater hydraulic control and Natural Attenuation assessment
- Groundwater tracer study.
- Assess natural attenuation capacity
- quantify recirculation water and mass balance
• Phytoremediation assessment
- Improving ET estimates using scintillometry
- Characterizing spatial distribution of hydraulic performance
- Evaluating capacity of slimes profile for natural attenuation
• Surface hydraulic control
- Evaluation and design of cap for buried drums area
- Design of surface runoff and seepage controls
Conclusions
• Natural attenuation has been observed in the slimes profile and groundwater
• A combined train of technologies, comprising
- hydraulic control (surface and subsurface)- phytoremediation and - managed natural and enhanced attenuation
has been defined for long term management of the site
• Phytoremediation is a valuable component in the system of remediation:
- limiting groundwater recharge to less than 0.3% of rainfall and- providing an environment for natural attenuation of VOC’s