aquifer vulnerability assessments and protocols

October 2005October 2005

Aquifer Vulnerability Assessments and ProtocolsAquifer Vulnerability Assessments and Protocols-- Intermediate Zone Intermediate Zone --

Shafick Adams and Nebo Shafick Adams and Nebo JovanovicJovanovic

Department of Earth Sciences

University of the Western Cape

OUTLINE

-- ObjectivesObjectives

-- Research ApproachResearch Approach

-- Preliminary ResultsPreliminary Results

-- ProblemsProblems

-- Future OutlookFuture Outlook

OBJECTIVES•• Improve on the rating of “I” in DRASTICImprove on the rating of “I” in DRASTIC

•• Prediction of properties without extensive Prediction of properties without extensive drilling and sampling programsdrilling and sampling programs

•• Establish the effects of fractures/Establish the effects of fractures/macroporesmacropores on on contaminant transportcontaminant transport

•• Application of simulation models to specific case Application of simulation models to specific case studies (Cape Flats [studies (Cape Flats [iThembaiThemba labs] and labs] and SecundaSecunda[SASOL])[SASOL])

•• Develop guidelinesDevelop guidelines

APPROACH

1.1. Improve on the rating of “I” in DRASTICImprove on the rating of “I” in DRASTIC

2.2. Prediction of soil and contaminant properties without Prediction of soil and contaminant properties without extensive drilling and sampling programsextensive drilling and sampling programs

3.3. Establish the effects of fractures/Establish the effects of fractures/macroporesmacropores on on contaminant transportcontaminant transport

4.4. Application of simulation models to specific case studiesApplication of simulation models to specific case studies

1. Improve on the rating of “I” in DRASTICImprove on the rating of “I” in DRASTIC2. Prediction of soil and contaminant properties without extensi2. Prediction of soil and contaminant properties without extensive drilling and sampling ve drilling and sampling programsprograms

•• Identified most important factors affecting vulnerabilityIdentified most important factors affecting vulnerability-- Hydraulic properties of the unsaturated zoneHydraulic properties of the unsaturated zone-- Thickness of the unsaturated zoneThickness of the unsaturated zone-- Topography/SlopeTopography/Slope-- Flow mechanismFlow mechanism-- Drainage/rechargeDrainage/recharge-- Travel timeTravel time-- Sorption capacitySorption capacity-- Contaminant halfContaminant half--lifeslifes

•• Prediction of properties without Prediction of properties without extensive drilling and sampling extensive drilling and sampling programsprograms

-- Existing databasesExisting databases-- Prediction tools (RETC, Rosetta, etc.)Prediction tools (RETC, Rosetta, etc.)


Excel spreadsheet program

CAPE FLATS AQUIFER

Factors Description Comments Impact

Physical Characteristics

Hydraulic properties

1. Sand, minor silt, clay lenses, heterogeneous,

2. K = 15-50 m/day, T = 30-980 m2/day

1. Sieving analysis (UWC)2. Available information Medium

Thickness of the unsaturated zone 1-5m (average 4.6m) Some areas water table at surface High

Flow mechanism Matrix, Fingering 95% matrix flow assumed Medium

Recharge/drainage1.10-13% of MAP (Bredenkamp et al.,

1995). 2. CMB = 10% MAP 3. 60-80 mm/yr

1. Tritium profiling and CMB (Atlantis) 2. CMB (UWC CAT Site) High

Sorption capacity

1. High silica, Ca sands. 2. The fraction of organic carbon of

the sands (0.3-0.4%) is relatively low and sorption will thus be low (Sililo, 1997)

Peat layers can increase Sorption capacity High

Chemical characteristics

Travel time Thickness = 3m; effective porosity 25-40%, K = 15-50 m/day

Foster and Hirata equation:Gross surcharge: <1 dayNatural infiltration: > 3 yearsQuick estimate < 5 days

High

Half-lifes Contaminant specific High travel time, low sorption, thin unsaturated zone

Medium to high vulnerability ratingMedium to high vulnerability rating

APPROACH


2.2. Prediction of properties without extensive drilling and Prediction of properties without extensive drilling and sampling programssampling programs



3. Establish the effects of fractures/3. Establish the effects of fractures/macroporesmacropores on contaminant transporton contaminant transport

Sampling and moisture extraction equipment

3. Numerical models3. Numerical models-- Identify matrix and preferential flow characteristicsIdentify matrix and preferential flow characteristics-- Data intensiveData intensive-- Calibration and sensitivity analysesCalibration and sensitivity analyses

2. Geology/geomorphology2. Geology/geomorphology-- Infer from borehole logs and Infer from borehole logs and lithologieslithologies-- Not quantitativeNot quantitative-- Remote sensing/GISRemote sensing/GIS

1.1. Chloride solute profiling in the unsaturated zoneChloride solute profiling in the unsaturated zone-- Identify dominant (matrix and/or preferential) flow patternsIdentify dominant (matrix and/or preferential) flow patterns-- Relatively inexpensiveRelatively inexpensive-- Visual inspection of coresVisual inspection of cores

3. Establish the effects of fractures/3. Establish the effects of fractures/macroporesmacropores on contaminant transporton contaminant transport

Categorize into type of preferential flow

Mole tunnelsMole tunnels

APPROACH


2.2. Prediction of properties without extensive drilling and Prediction of properties without extensive drilling and sampling programssampling programs



4. Application of simulation models to specific case studiesApplication of simulation models to specific case studies

1.1. VLEACHVLEACH2.2. MACRO 5.0MACRO 5.0 -- can handle can handle macroporemacropore flow in soilsflow in soils3.3. HYDRUS 2DHYDRUS 2D4.4. SWMS 2DSWMS 2D5.5. SWATSWAT6.6. SWAP SWAP -- preferential flow in cracking/swelling clayspreferential flow in cracking/swelling clays7.7. UGPFUGPF -- GIS based model (BTEX)GIS based model (BTEX)


1. Data that is currently being collected through field and laboratory work:• Porosity, pore size distribution• Water retention• Matric potential• Bulk density• Gravimetric and volumetric water content


VLEACHVLEACH

title...................................CFAsurface area [sq.ft]....................3.3vertical thickness of a cell [ft].......1net recharge rate [ft/year].............0.3dry bulk density [g/cm3]................1.36effective porosity [dim.less]...........0.40volumetric water content [percent]......0.12organic carbon content [dim.less].......0.008contaminant conc. in recharge [mg/l]....{1 for continuous discharge ; 0 for accidental spillage

CONTAMINANT INFORMATION:org.C distrib. coeff., Koc [ml/g].......{48.64 for 1,1,1-trichloroethane; 3380 for lindane}Henry's constant [dimensionless]........ {0.703 for 1,1,1-trichloroethane; 0.00021 for lindane}water solubility [mg/l]................. {1290 for 1,1,1-trichloroethane; 8 for lindane}free air diffusion coef.[sq.m/d]........0


VLEACHVLEACH

1.00E-16

1.00E-14

1.00E-12

1.00E-10

1.00E-08

1.00E-06

1.00E-04

1.00E-02

1.00E+00

0 2 4 6 8 10

Time (a)

Con

tam

inat

ion

rate

(g/a

)

1,1,1-Trichloroethane Lindane

Simulated groundwater contamination rate of 2 contaminants applied through recharge (continuous recharge).

1.00E-07

1.00E-05

1.00E-03

1.00E-01

1.00E+01

0 2 4 6 8 10

Time (a)

Con

tam

inat

ion

rate

(g/a

)1,1,1-Trichloroethane Lindane

Simulated groundwater contamination rate of 2 contaminants applied to the surface at the beginning of the simulation (accidental spillage).

Daughter products!Daughter products!


1D non-steady state model of water flow and solute transport in structured or macroporous field soils.


MACRO 5.0MACRO 5.01. Data requirements:

• Climatic data• Basic soil properties (% sand, silt, clay)• Unsaturated hydraulic conductivity• Solute concentrations

• Can simulate non-reactive tracers, tritium and pesticides• Simulates a full water balance• Model structure enables quantitative evaluation of the impact of

macropore flow on solute transport in structured soils.


MACRO 5.0MACRO 5.01. Data requirements:

• Climatic data• Basic soil properties (% sand, silt, clay)• Unsaturated hydraulic conductivity• Solute concentration

• Can simulate non-reactive tracers, tritium and pesticides• Simulates a full water balance• Model structure enables quantitative evaluation of the impact of

macropore flow on solute transport in structured soils.

Preliminary model indicates that >95% of flow occurs in Preliminary model indicates that >95% of flow occurs in microporesmicropores

PROBLEMS•• SUITABLE DATA !!!!!!!SUITABLE DATA !!!!!!!

•• Direct measurements are cumbersome and require a Direct measurements are cumbersome and require a substantial investment in both time and moneysubstantial investment in both time and money

•• 11--D, 2D, 2--D or 3D or 3--D (increasing data requirements)D (increasing data requirements)

•• Upscaling/downscalingUpscaling/downscaling

FUTURE OUTLOOK

•• Run several models for the two study sites (contrast and Run several models for the two study sites (contrast and compare)compare)

•• Refine approachRefine approach

•• Uncertainty analysisUncertainty analysis

•• Develop a spatial databaseDevelop a spatial database

THANK YOUENKOSIDANKIE

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