Progress Report 1– Saturated Zone Vulnerability Assessment 2004/5
Ross Campbell - CSIR 17 February 2005
AVAP Deliverables & Activities 2004/5Literature review on contaminant buffering in the saturated zone – complete September 2004Case study site selection, data collection & analysis –complete December 2004/due March 2005Generic, one-dimensional reactive transport modelling to assess saturated zone vulnerability – 80% complete/due March 2005/on scheduleFlow and contaminant transport model based on case studies – 25% complete/due March 2005/complete end-May 2005Project management
Generic one-dimensional reactive transport modelling
Developing a method to determine the (relative) saturated zone vulnerability
Two important aquifer typesCoastal primary aquifersWeathered zone aquifers, of dual porosity, developed in the regolith
Three kinds of high-priority contaminant mixture Landfill leachateIndustrial effluent (trace and nutrient elements)Acid mine drainage
Factors determining saturated zone vulnerability(1)
The spatial extent of contamination: aquifer type, flow rate, chemical buffering
FLOW FRACTURE-CONTROLLED……………MIXED…………………..DIFFUSE – (primary porosity-controlled) FAST…………..SLOW FAST…………SLOW
LOW…………………HIGH Chemical attenuation capacity
LOW………………….HIGH Chemical attenuation capacity
LOW………………….HIGH Chem. attenuation capacity
LARGE………………………………………………………………………SMALL
SPATIAL DIMENSIONS OF THE CONTAMINATED ZONE
Factors determining saturated zone vulnerability(2)
The persistence of contamination: flow type, rate, chemical buffering & decomposition, recharge
RECHARGE LOW…………………………………………………………………………..HIGH
LOW…………………………………………………………………………..HIGH
DILUTION RATE HIGH……………………….…………LOW HIGH…………………….……………..LOW Chemical attenuation capacity Chemical attenuation capacity
LONG…………………………………………………………………………SHORT
RESIDENCE TIME OF CONTAMINANT IN AQUIFER
Using PHREEQC to determine saturated zone vulnerability
Simulate the chemical evolution of natural groundwater
Geochemical description of the aquifer environmentRecharge water qualityReactions with aquifer mineralsBeing able to explain the natural groundwater compositions => reasonable geochemical simulation of the aquifer has been achieved
Simulate the reactive transport of contaminant mixtures
Compare reactive transport in the aquifers to derive SZV measures:Spatial retardation of contaminantsThe persistence in time of contaminants in the aquifer
Simulating the chemical development of natural groundwater
Mineralogy
Recharge water quality
Processes & reactionsEvaporative concentrationOxidation of organic matterMineral dissolution and precipitationIon exchange
Groundwater quality in a coastal primary aquifer(1)
MineralogyCalcium (-magnesium) carbonates, quartz, clay, organic matter
Recharge water qualityEssentially dilute seawater
milliequivalents/litre or unitless Seawater Seawater
diluted 500x
Seawater diluted 1000x
Cape Point rainwater (Brunke, pers. comm., 2004)
pH Ca2+
Mg2+
Na+
K+
NH4+
Cl- NO3
- SO4
2-
Total Alkalinity
8.2 20.6 106.3 468.4 10.2 0.002 545.9 0.005 56.5 2.3
- 0.041 0.21 0.94 0.020 3.3 x 10-6
1.1 9.4 x 10-6 0.11 -
- 0.020 0.11 0.47 0.010 1.7 x 10-6 0.54 4.7 x 10-6
0.056 -
5.5-6.5 0.035 0.106 0.854 0.036 0.0 0.853 0.040 0.081 0.116 (est.)
Groundwater quality in a coastal primary aquifer(2)
Processes & reactionsEvaporative concentration
Concentration factor the inverse of recharge proportion, i.e. if recharge is 5% of pptn; concentration factor is 20
Oxidation of organic matterGenerates CO2
Mineral dissolution and precipitationParticularly calcite/aragonite and dolomite/high Mg-calcite
Ion exchangeIn dilute waters, Ca & Mg displace Na while at higher ionic strengths, Na displaces Ca.
Groundwater quality in a coastal primary aquifer(3)
milliequivalents/litre or unitless
Rainwater (seawater
diluted 1000x)
Step 1: Concentrate
(20x) & equilibrate with calcite & dolomite
Step 2: Add
organic matter & lower
pO2
Step 3a:
Reduce pO2 to zero &
add more OM
Step 3b: With
cation exchange in steps 2 & 3, CEC
= 2 eq/litre
Cape Flats
aquifer – near
Coastal Park
landfill
pH Ca2+
Mg2+
Na+
K+
Cl-
NO3-
SO42-
Total Alkalinity
5.5 0.02 0.11 0.47
0.010 0.54
4.7 x 10-6
0.056 10-3
8.2 2.0 1.7 9.4 0.2
11.1 10-4 1.1 1.0
7.1 4.6 4.0 9.4 0.2 11.1 0.3 1.1
5.7
7.1 4.7 4.0 9.4 0.2 11.1 0.08 1.1 5.9
7.2 3.4 2.9 12.0 0.2 11.1 0.08 1.1 6.2
7-8 5-7 3-5
8-25 0.25-0.75
10-30 0-0.03 0.2-0.4 6-10
Groundwater quality in a weathered zone aquifer(1)
MineralogyDiverse – primary silicate minerals most soluble, and important source ofmetal ions
Recharge water qualityVariable, but of very low concentrations – simulated by very dilute (0.05 millimolar calcium chloride, in equilibrium with atmospheric CO2
Groundwater quality in a weathered zone aquifer(2)
Processes & reactionsEvaporative concentration
Concentration factor the inverse of recharge proportion, i.e. if recharge is 2% of pptn; concentration factor is 50
Oxidation of organic matterGenerates CO2
Mineral dissolution and precipitationParticularly dissolution of calcium-magnesium pyroxenes & Na-plagioclase feldspar
Ion exchangeEstimated CEC of 200 meq/litre, from secondary clay minerals
Groundwater quality in a weathered zone aquifer(3)
milliequivalents/litre or unitless
Recharge Step 1: Concentrate
(50 x)
Step 2: Equilibrate with Ca-
Mg pyroxene and Na-
feldspar at 3.5% CO2
Step 3: Allow some
calcite to precipitate
& equilibrate with cation exchangers
Karoo Supergroup
aquifer, Secunda
pH Ca2+
Mg2+
Na+
Cl- Alkalinity
5.7 0.1 0 0
0.1 10-10
5.7 5.0 0 0
5.0 10-8
7.4 12.0 7.0
0.002 5.0
14.0
6.9 3.3 1.8
0.005 5.0 5.2
7.2-8.5 2.8-7.0
2-4 2.5-7.0 0.5-9.9
4.2-10.1
Reactive transport of landfill leachate(1)
Variable millimolar pH Ca Mg Na K Cl NO3
- NH4
+ SO4
2-
Total Alkalinity
7-8 5 5 45 25 92 1 55 1 50
Reactive transport of landfill leachate(2)
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
0 500 1000 1500 2000 2500 3000
Time (seconds)
Cl (molar)
Coastal AquiferCoastal Aquifer-Pulse
Reactive transport of landfill leachate(3) –saturated zone vulnerability – spatial dimension
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0 2 4 6 8 10 12
Distance (cells)
NH4+ (molar) at t = 360 s
Coastal Aquifer-zero CEC
5% of initial concentration
Weathered Zone Aquifer
Reactive transport of landfill leachate(3) –saturated zone vulnerability – time dimension
0.000
0.005
0.010
0.015
0 1000 2000 3000 4000 5000 6000 7000 8000
Time (s)
NH4+ (molar) in final cell
Coastal Aquifer-zero CEC
5% of initial concentration
Weathered Zone Aquifer
Progress Report 2 – Case study areas
Ross Campbell - CSIR 17 February 2005
Case study areas
Cape Flats Focus on Coastal Park (saturated zone)
SecundaPossibility of Sasol co-funding to enhance data set
Secunda
What Sasol is getting from the AVAP project:
Independent review & assessment of data collected by SasolA groundwater vulnerability assessmentA groundwater flow and contaminant transport model for one site (Goedehoop)
SecundaPossible expansion with Sasol funding:
Additional soil, unsaturated zone and groundwater sampling and new boreholesGroundwater vulnerability assessments for Indaba and Dam 10Groundwater flow and contaminant transport models for Indaba & Dam 10An expanded summary and assessment reportEstimated cost: R900 000
SecundaRough cost estimate for the additional work 1.1 Field time, digger loader hire, sampling and analysis of 200 samples
R130 0001.2 Intact core sampling and analysis R175 000 1.3 Drilling 6 boreholes at total est. cost of R200 000, field time, sampling and analysis of 3 x 20 = 60 samples.
R 260 0001.4 & 2 Data interpretation and reporting, including vulnerability assessments for each site and models (8 weeks) R 100 000 3. Incorporating new data into Geodehoop model and 2 models for Indaba & Dam 10 (20 weeks) R 250 000 TOTAL R 915 000
Planning for 2005/6
Ross Campbell - CSIR 17 February 2005
Flow and contaminant transport model based on case studies – 25% complete/due March 2005/complete end-May 2005Project managementPreliminary model for degradable organic contaminants at selected site – due March 2006Development of a decision support framework – due March 2005/est. complete end May 2005Development of a decision support system – due 31 December 2005
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