DRASTIC GROUNDWATER
VULNERABILITY MAP OF
TENNESSEE
GEOG 596A
James Bond – Capstone Proposal
Overview of Presentation




Introduction
Methodology
Anticipated Results & Problems
References
INTRODUCTION
Introduction

My Project
 DRASTIC

Groundwater Vulnerability Map of Tennessee
DRASTIC
 What
is it?
 Identifies
areas where groundwater is susceptible to
pollution
 What
are the applications?
 Guides
land development & resource protection
 Flexible


Used at a variety of scales
Can be modified to include or exclude parameters
Example DRASTIC Map
METHODOLOGY
DRASTIC Overview

DRASTIC – methodology guided by EPA
 Developed
by EPA & National Water Well Assoc.
 600+ page guidance document
 Link to Guidance:
 http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=20007KU4.t
xt

Purpose – Over large areas, used to identify
regions where groundwater is more or less
susceptible to impact from pollution.
DRASTIC Overview Cont.

Overview of DRASTIC
 Simplified
GW vulnerability model
 Qualitative
 Produces a relative-risk scale
 Applicable over large areas
 Used as a screening tool
 Results guide land development & resource protection
 For small, specific sites, more detailed assessment
needed
DRASTIC Method Assumptions

DRASTIC Makes Four Assumptions:
1.
2.
3.
4.

Contamination is introduced at the ground surface
Contamination is flushed into the groundwater by
precipitation
Contamination has the mobility of water
Area being evaluated is 100-acres or larger
If these assumptions are not met, then DRASTIC is
not the appropriate methodology
DRASTIC Factors
Seven hydrogeologic factors used. They form the
acronym DRASTIC
D – Depth to Water
R – Net Recharge
A – Aquifer Media
S – Soil Media
T – Topography
I – Impact of Vadose Zone Media
C – Hydraulic Conductivity of Aquifer
Weights & Ratings


Significance of each factor in contaminant transport
varies
Relative weight is assigned to each factor
 Scale
of 1 to 5
 1 is least important factor
 5 is most important factor

Feature
Depth to Water
Net Recharge
Aquifer Media
Soil Media
Topography
Impact of Vadose Zone Media
Hydraulic Conductivity of Aquifer
Weight
5
4
3
2
1
5
3
Each factor also has a rating applied according to
a category or range of values.
DRASTIC – The Equation


Once ratings and weights have been applied, they
are multiplied and added
DRASTIC equation:
DrDw + RrRw + ArAw + SrSw + TrTw + IrIw + CrCw = Pollution Potential
r = rating
w = weight

Results are symbolized on a map overlaying study
area
Methodology - Example



Example of how ratings and weights are applied
Will use D Factor (Depth to Water) as example
D receives a weight of 5
 It

is very significant in potential impact to GW
Based on actual depth to groundwater, D also
receives a rating.
DEPTH TO WATER (ft bgs)
Range
Rating
0-5
10
5-15
9
15-30
7
30-50
5
50-75
3
75-100
2
>100
1
Methodology – Example Cont.



If depth to water was 10 ft then D rating would be
9
DrDw = 9 x 5 = 45
If depth to water was 100 ft, then D rating would
be 2
DrDw = 2 x 5 = 10
This process is repeated for each of the factors
Capstone Process
Review of
DRASTIC
methodology
Identify
data
needed
Gather data
Identify
Data Gaps
Fill Data
Gaps or
revise
methodology
Perform
analysis
Create Map
Present
Results
Data Analysis Process
Organize data
Re-project into common coordinate system and datum
Clip to boundary of TN if necessary
Convert vector data to raster data
Generalize data where appropriate
Apply ratings to values and categories in each factor layer
Apply weights to each input layer
Sum factors
Relative Risk Index is created and overlain on study area
Self-Imposed Project Parameters




Due to time constraints, need to impose parameters
on the analysis
Use unmodified version of method
Use existing datasets as much as possible
To fill datagaps will use the easier of two
approaches:
 Derive
missing data from other existing data
 Use generalized values in EPA guidance
ANTICIPATED RESULTS & PROBLEMS
Anticipated Results



State of TN groundwater vulnerability map
Detailed report of methodology and data used
Map will be technically correct
 Considered
FINAL within context of capstone project
 Considered DRAFT by public and professionals who
may use it
Anticipated Problems

Low Resolution Data
 Anticipate

using only small scale data
Missing data
 Not
all inputs may be available
 May have to infer data or use generalized inputs

Room for improvement
 Analysis
can be easily re-run with better data
 Better data = better results
 Additional refinement outside the scope of this capstone
project
Summary
Summary






Project to produce groundwater vulnerability map
of Tennessee
Has not been done for Tennessee
Use EPA DRASTIC vulnerability methodology
Use small scale, publicly available data
Result will be a first cut at groundwater vulnerability
mapping
Model will have room for refinement
 Outside
the scope of this project
Q&A
Questions?
Thank you
REFERENCES
References
U.S. EPA DRASTIC Guidance Document

United States Environmental Protection Agency (EPA), 1987, DRASTIC: A Standardized System for Evaluating
Ground Water Pollution Using Hydrogeologic Settings, EPA/600/2-87-035, Robert S. Kerr Environmental
Research Laboratory, Ada, OK 74820
Examples of the Application of DRASTIC

Arthur, Jonathan D., et al., 2005, Florida Aquifer Vulnerability Assessment (FAVA): Contamination Potential of
Florida’s Principal Aquifer Systems, Division of Resource Assessment and Management, Florida Geological
Survey

Chowdhury, Shafiul, et al, 2003, Comprehensive approach of groundwater resource evaluation: a case study
in the Chippewa Creek watershed in Ohio, The Ohio Journal of Science, December 2003

Crider, S.S., 1989, A Cursory Application of DRASTIC to the Savannah River Site, WSRC-RP-89-744, DE92
009778, Division of Engineering Fundamentals, Virginia Polytechnic Institute and State University,
Blacksburgh, VA 24061-0218

Evans, Barry, et al, 1990, A GIS-Based Approach to Evaluating Regional Groundwater Pollution Potential with
DRASTIC, Journal of Soil and Water Conservation, March-April, pp. 242-245

Rupert, Michael G., 1999, Improvements to the DRASTIC Ground-Water Vulnerability Mapping Method,
USGS Fact Sheet FS-066-99, Department of the Interior, US Geological Survey, Denver, CO 80225