mapping groundwater vulnerability to contamination in texas l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Mapping Groundwater Vulnerability to Contamination in Texas PowerPoint Presentation
Download Presentation
Mapping Groundwater Vulnerability to Contamination in Texas

Loading in 2 Seconds...

play fullscreen
1 / 28

Mapping Groundwater Vulnerability to Contamination in Texas - PowerPoint PPT Presentation


  • 519 Views
  • Uploaded on

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?

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Mapping Groundwater Vulnerability to Contamination in Texas' - salena


Download Now An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
mapping groundwater vulnerability to contamination in texas

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
Presentation Outline
  • Problem Development – Why do we need to model groundwater vulnerability?
  • Objectives
  • Specific Goals
  • DRASTIC
    • What is it?
    • Summary of each DRASTIC Parameters
    • Downfalls of DRASTIC
  • What’s left for me to do
  • Conclusions
overall objective
Overall Objective

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

how do we do this
How Do We Do This??
  • Protect Water Supply from Contamination
  • Remediate Contaminated Soils and Aquifers if spills do occur
  • Limited Financial Resources… If we cannot remediate every contaminated site immediately, which sites should we address first?
specific goals
Specific Goals
  • Use GIS and DRASTIC to determine what PSWs are most vulnerable to contamination

Specifically…

    • Use GIS, ACCESS and EXCEL files to get DRASTIC input parameters
    • In EXCEL calculate DRASTIC INDEXES for groundwater PWS
    • Show the DRASTIC INDEXES graphically in GIS
what is drastic
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)

drastic parameters
DRASTIC PARAMETERS
  • D- Depth to Water
  • R- Recharge
  • A- Aquifer Media
  • S- Soils
  • T- Topography
  • I- Impact of Vadose Zone
  • C- Hydraulic Conductivity
drastic index
DRASTIC INDEX
  • Higher the Value, greater vulnerability

Drastic Index =

DrDw+RrRw+ArAw+SrSw+TrTw+IrIw+CrCw

Where w = weight

r = rank

stacking of drastic layers to produce a vulnerability map
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.

d epth to water
Depth to Water
  • Depth 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
slide18

0-100 ft

100-300 ft

300-600 ft

Greater than 600 ft

net r echarge
Net Recharge
  • Using data from Climate Rasters available from USGS Datasets
  • Apply a mass balance on the water

Net Recharge = Precipitation – Evaporation – Runoff

  • Higher Recharge  Greater vulnerability
s oil media

Range

Rating

Thin or Absent

10

Gravel

10

Sand

9

Peat

8

Shrinking and/or Aggregated Clay

7

Sandy Loam

4

Loam

5

Silty Loam

4

Clay Loam

3

Muck

2

Nonshrinking and Nonaggregated Clay

1

Soil Media

* Source: Aller et al., EPA, 1987.

t opography
Topography
  • Low Slope  higher DRASTIC rating
    • Contaminant released is less likely to become run-off and therefore more likely to infiltrate to the aquifer
  • Slope data is available from DEM
hydraulic c onductivity
Hydraulic Conductivity
  • Relates the factures, bedding planes and intergranular voids which become pathways for fluid movement
  • High Hydraulic Conductivity  high movement once contaminant has entered aquifer  high DRASTIC rating
  • Requires transmissivity (m2/day) and

aquifer thickness (m)

a quifer media
Aquifer Media
  • Ratings are based on the permeability of each layer of media
    • High Permeability  high DRASTIC rating
  • Some 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.
i mpact of vadose zone
Impact of Vadose Zone
  • Zone below the typical soil horizon and above the water table
  • Unsaturated or discontinuously saturated
  • High Permeability of vadose zone  high DRASTIC rating
    • Not clear where I can find this data. May have to make assumptions based on well log data.
major assumptions of drastic
Major Assumptions of DRASTIC
  • Contaminant is introduced at ground surface
  • Contaminant is flushed into the groundwater by precipitation
  • Contaminant has the mobility of water
next steps
Next Steps
  • Finish collecting data for DRASTIC layers
  • Export DRASTIC parameter ratings to EXCEL to calculate DRASTIC Indexes
  • Prepare GIS map of DRASTIC Indexes
  • Overlay DRASTIC map with PWS to get a better understanding for what water supplies are vulnerable
  • Get everything done by Dec. 7!!
conclusions
CONCLUSIONS
  • 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 contaminant
  • GIS can help make the results of a complicated model more clear through visual representation