Presentation on theme: "Mapping Groundwater Vulnerability to Contamination in Texas"— Presentation transcript:
1Mapping Groundwater Vulnerability to Contamination in Texas Shannon Nicole StokesGIS for Water ResourcesCE 394K.3Term Project PresentationUniversity of Texas at AustinNovember 19, 2001
2Presentation OutlineProblem Development – Why do we need to model groundwater vulnerability?ObjectivesSpecific GoalsDRASTICWhat is it?Summary of each DRASTIC ParametersDownfalls of DRASTICWhat’s left for me to doConclusions
9Potential Sources of Contamination are very close to PWS
10Overall ObjectiveTo Adequately Protect Human Health, We Need to Ensure that Potential Contaminants Do not Enter the Public Water Supply
11How Do We Do This?? Protect Water Supply from Contamination Remediate Contaminated Soils and Aquifers if spills do occurLimited Financial Resources… If we cannot remediate every contaminated site immediately, which sites should we address first?
12Specific GoalsUse GIS and DRASTIC to determine what PSWs are most vulnerable to contaminationSpecifically…Use GIS, ACCESS and EXCEL files to get DRASTIC input parametersIn EXCEL calculate DRASTIC INDEXES for groundwater PWSShow the DRASTIC INDEXES graphically in GIS
13(Aller, L et. al. NWWA/EPA Series. 1987) What is DRASTIC ??A method developed by the EPA to provide a systematic evaluation of the potential for groundwater contamination that is consistent on a national basis(Aller, L et. al. NWWA/EPA Series. 1987)
14DRASTIC PARAMETERS D- Depth to Water R- Recharge A- Aquifer Media S- SoilsT- TopographyI- Impact of Vadose ZoneC- Hydraulic Conductivity
15DRASTIC INDEX Higher the Value, greater vulnerability Drastic Index = DrDw+RrRw+ArAw+SrSw+TrTw+IrIw+CrCwWhere w = weightr = rank
16Stacking of Drastic Layers to Produce a Vulnerability Map Stenson, M.P. & Stachotta, C.P., Queensland’s Groundwater Vulnerability Mapping Project. Queensland’s Department of Natural Resources.
17Depth to WaterDepth to Water affects the Time available for a contaminant to undergo chemical and biological reactions(Dispersion, Oxidation, Natural Attenuation, Sorption, etc.)Greater Depth Lower Vulnerability Rating
180-100 ft 100-300 ft 300-600 ft Greater than 600 ft Explain – Depth of wells not depth of aquifers. Using this as a surrogate measure for the depth of aquifer at a particular location. Not the best estimate. If anyone knows where one can find the actual depth of aquifer info, I’d love to know it.0-100 ftftftGreater than 600 ft
19Net RechargeUsing data from Climate Rasters available from USGS DatasetsApply a mass balance on the waterNet Recharge = Precipitation – Evaporation – RunoffHigher Recharge Greater vulnerabilityHigher recharge – more dilution, but also recharge is a major transportation mechanism for pollutants to reach the aquifer
20Soil Media Range Rating Thin or Absent 10 Gravel Sand 9 Peat 8 Shrinking and/or Aggregated Clay7Sandy Loam4Loam5Silty LoamClay Loam3Muck2Nonshrinking and Nonaggregated Clay1* Source: Aller et al., EPA, 1987.
21Soil Media – Raster Map from USGS Raster Data of Soils. Need to classify into Drastic Index values
22Topography Low Slope higher DRASTIC rating Contaminant released is less likely to become run-off and therefore more likely to infiltrate to the aquiferSlope data is available from DEM
23Hydraulic Conductivity Relates the factures, bedding planes and intergranular voids which become pathways for fluid movementHigh Hydraulic Conductivity high movement once contaminant has entered aquifer high DRASTIC ratingRequires transmissivity (m2/day) andaquifer thickness (m)
24Aquifer MediaRatings are based on the permeability of each layer of mediaHigh Permeability high DRASTIC ratingSome of this data is available in the well logs for the public water supplies. I have not determined how much more information I need yet.
25Impact of Vadose ZoneZone below the typical soil horizon and above the water tableUnsaturated or discontinuously saturatedHigh Permeability of vadose zone high DRASTIC ratingNot clear where I can find this data. May have to make assumptions based on well log data.
26Major Assumptions of DRASTIC Contaminant is introduced at ground surfaceContaminant is flushed into the groundwater by precipitationContaminant has the mobility of water
27Next Steps Finish collecting data for DRASTIC layers Export DRASTIC parameter ratings to EXCEL to calculate DRASTIC IndexesPrepare GIS map of DRASTIC IndexesOverlay DRASTIC map with PWS to get a better understanding for what water supplies are vulnerableGet everything done by Dec. 7!!
28CONCLUSIONS DRASTIC can be used to model groundwater vulnerability Results of applying DRASTIC model must be used carefully. This applies a framework but does not account for all the particulars of the chemicals released.A detailed study of a particular spill must incorporate the chemical properties of the contaminantGIS can help make the results of a complicated model more clear through visual representation