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