1. Groundwater Vulnerability To Contamination
Multi-Layer analysis of Geological Information
Anteneh Z Abiy---MS Geoscinces
Advisor- Professor Assefa Melesse

2. Objective To be able to map vulnerable aquifer zones
Rank the degree of vulnerability
A Problem Defined is a Problem Half Solved

3. Groundwater Vulnerability assessment
Groundwater vulnerability assessment is a systematic approach to identify sites where groundwater is susceptible to pollution,
It plays a vital role to well fields delineation and groundwater management,
Groundwater Vulnerability is a function of:
the nature of the geologic materials
the physical environment,
Nature of pollutants
Pollutant source

4. Intrinsic Vulnerability
The vulnerability of groundwater to contamination attributed to the nature of the geologic materials and the physical environment,
The concept was primarily introduced by US National Research Council in 1993

5. Intrinsic Vulnerability Assessment--Types
Physical process based methods: using the physical process of contaminant loading and transport

6. Intrinsic Vulnerability Assessment--Types
Physical process based methods: using the physical process of contaminant loading and transport
Statistical method: using the contaminant concentrations distribution or probabilities of contamination

7. Intrinsic Vulnerability Assessment--Types
Physical process based methods: using the physical process of contaminant loading and transport
Statistical method: using the contaminant concentrations distribution or probabilities of contamination
Overlay-Index method: using the nature of geologic material and physical environment, only

8. Intrinsic Vulnerability Assessment--Types
Physical process based methods: using the physical process of contaminant loading and transport
Statistical method: define the contaminant concentrations distribution or probabilities of contamination
Overlay-Index method: nature of geologic material and physical environment to control the spatial distribution of vulnerability of the groundwater in an area
The first two require high level annalist and encore money,
The third approach doesn’t show actual contaminant loads, however it is an important tool in planning

9. Overlay-Index methods of groundwater vulnerability assessment
GOD (Foster 1987),
DRASTIC (Aller et al., 1987),
SEEPAGE (Moore and John, 1990),
AVI (Van Stempvoort et al., 1993),
SINTACS (Civita 1994),
ISIS (Civita and De Regibus 1995),
EPIK (Doerfliger and Zwahlen 1997)
The German method (von Hoyer and Söfner 1998)
IRISH (Daly and Drew 1999),
Gogu et al., (2003; 2000),

10. DRi= DwDr + RwRr+AwAr+SwSr+TwTr+IwIr+CwCr
The DRASTIC Model-- Parameters
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
DRi= DwDr + RwRr+AwAr+SwSr+TwTr+IwIr+CwCr

11. The DRASTIC Model-- Introduction
Developed by EPA & National Water Well Assoc , Aller et al. (1987)
Original publication:
Most widely accepted, and applicable over a wide range of area
Simplified qualitative
Produces a relative-risk scale

12. The DRASTIC Model– Working Principle
DRASTIC Weight
the relative influence of the seven parameters to favor/ against to enhance vulnerability.
Value in a scale of 1 to 5

13. The DRASTIC Model– Working Principle
DRASTIC RATE
the rate of importance of the verities in a parameter,
Value of 1 to 10
High value to more susceptible categories
Example
Factors
Range
Rate
Topography/ slope (%)
0-2.8
96.2+ 10 9 8 7 6 5 4 3 1

14. The DRASTIC Model– Working Principle
EX: Topography Rate

15. S – Soil Media The DRASTIC Model– Working Principle
Layer Index= Weight X Rate
S – Soil Media

16. Aquifer Media Ar
X 3 =

17. The DRASTIC Model– Working Principle
DRASTIC INDEX = Sum Layer Weight X Layer Rate 5 X 4 3 2 1

18. The DRASTIC Model– Working Principle
DRASTIC INDEX =
DRi= DwDr + RwRr+AwAr+SwSr+TwTr+IwIr+CwCr
Where:
DRi= DRASTIC index
w= weight of respective DRASTIC factor
r=rate of respective DRASTIC factor

19. DRASTIC INDEX DRi= DwDr + RwRr+AwAr+SwSr+TwTr+IwIr+CwCr

20. Key Points
Fractures in the Tana Sub-Basin Karst and High K in Florida