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

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

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

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

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

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

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

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

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),

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

The DRASTIC Model-- Introduction Developed by EPA & National Water Well Assoc , Aller et al. (1987) Original publication: http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=20007KU4.txt Most widely accepted, and applicable over a wide range of area Simplified qualitative Produces a relative-risk scale

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

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 2.8-8.5 8.5-14.8 14.8-21.9 21.9-29.7 29.7-38.2 38.2-48.8 48.8-96.2 96.2+ 10 9 8 7 6 5 4 3 1

The DRASTIC Model– Working Principle EX: Topography Rate

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

Aquifer Media Ar X 3 =

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

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

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

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