Mapping Groundwater Vulnerability to Contamination in Texas .


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Mapping Groundwater Vulnerability to Contamination in Texas. Shannon Nicole Stokes GIS for Water Resources CE 394K.3 Term Project Presentation University of Texas at Austin November 19, 2001. Presentation Outline. Problem Development – Why do we need to model groundwater vulnerability?
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Slide 1

Mapping Groundwater Vulnerability to Contamination in Texas Shannon Nicole Stokes GIS for Water Resources CE 394K.3 Term Project Presentation University of Texas at Austin November 19, 2001

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Presentation Outline Problem Development – Why do we have to demonstrate groundwater helplessness? Targets Specific Goals DRASTIC What is it? Outline of each DRASTIC Parameters Downfalls of DRASTIC What\'s left for me to do Conclusions

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Overall Objective To Adequately Protect Human Health, We Need to Ensure that Potential Contaminants Do not Enter the Public Water Supply

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How Do We Do This?? Shield Water Supply from Contamination Remediate Contaminated Soils and Aquifers if spills do happen Limited Financial Resources… If we can\'t remediate each tainted site promptly, which destinations would it be advisable for us to address first?

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Specific Goals Use GIS and DRASTIC to figure out what PSWs are most powerless against sullying Specifically… Use GIS, ACCESS and EXCEL documents to get DRASTIC info parameters In EXCEL ascertain DRASTIC INDEXES for groundwater PWS Show the DRASTIC INDEXES graphically in GIS

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What is DRASTIC ?? A technique created by the EPA to give a precise assessment of the potential for groundwater defilement that is predictable on a national premise (Aller, L et. al. NWWA/EPA Series. 1987)

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DRASTIC PARAMETERS D-Depth to Water R-Recharge An Aquifer Media S-Soils T-Topography I-Impact of Vadose Zone C-Hydraulic Conductivity

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DRASTIC INDEX Higher the Value, more prominent weakness Drastic Index = D r D w +R R w +A r A w +S r S w +T r T w +I r I w +C r C w Where w = weight r = rank

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Stacking 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.

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D epth to Water Depth to Water influences the Time accessible for a contaminant to experience synthetic and organic responses (Dispersion, Oxidation, Natural Attenuation, Sorption, and so forth.) Greater Depth  Lower Vulnerability Rating

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0-100 ft 100-300 ft 300-600 ft Greater than 600 ft

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Net R echarge Using information from Climate Rasters accessible from USGS Datasets Apply a mass adjust on the water Net Recharge = Precipitation – Evaporation – Runoff Higher Recharge  Greater helplessness

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Range Rating Thin or Absent 10 Gravel 10 Sand 9 Peat 8 Shrinking as well as Aggregated Clay 7 Sandy Loam 4 Loam 5 Silty Loam 4 Clay Loam 3 Muck 2 Nonshrinking and Nonaggregated Clay 1 S oil Media * Source: Aller et al., EPA, 1987.

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Soil Media – Raster Map from USGS

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T opography Low Slope  higher DRASTIC rating Contaminant discharged is more averse to wind up keep running off and in this manner more inclined to invade to the aquifer Slope information is accessible from DEM

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Hydraulic C onductivity Relates the factures, bedding planes and intergranular voids which get to be pathways for smooth motion High Hydraulic Conductivity  high development once contaminant has entered aquifer  high DRASTIC rating Requires transmissivity (m 2/day) and aquifer thickness (m)

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A quifer Media Ratings depend on the porousness of every layer of media High Permeability  high DRASTIC rating Some of this information is accessible in the well logs for the general population water supplies. I have not decided the amount more data I require yet.

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I mpact of Vadose Zone underneath the ordinary soil skyline or more the water table Unsaturated or intermittently soaked High Permeability of vadose zone  high DRASTIC rating Not clear where I can discover this information. May need to make suppositions in view of well log information.

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Major Assumptions of DRASTIC Contaminant is presented at ground surface Contaminant is flushed into the groundwater by precipitation Contaminant has the versatility of water

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Next Steps Finish gathering information for DRASTIC layers Export DRASTIC parameter appraisals to EXCEL to ascertain DRASTIC Indexes Prepare GIS guide of DRASTIC Indexes Overlay DRASTIC guide with PWS to show signs of improvement comprehension for what water supplies are powerless Get everything done by Dec. 7!!

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CONCLUSIONS DRASTIC can be utilized to show groundwater powerlessness Results of applying DRASTIC model must be utilized painstakingly. This applies a system yet does not represent every one of the particulars of the chemicals discharged. A point by point investigation of a specific spill must consolidate the synthetic properties of the contaminant GIS can make the aftereffects of a muddled model all the more clear through visual representation

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