G. Water Resources

Groundwater Pollution Potential (DRASTIC Mapping)

Groundwater pollution potential, or DRASTIC, was developed in 1987 as a method to define the vulnerability of areas within a county to contaminated surface water.  Seven physical characteristics effecting groundwater pollution were identified. 

D – Depth from ground surface to water table

R – Recharge is the total amount of water that reaches the earth’s surface and infiltrates

       the aquifer.

A – Aquifer Media or the rock material capable of yielding sufficient quantities of water

       for use.

S – Soil Media or the upper six of unsaturated soil or rock

T – Topography or slope of the landscape

 I  – Impact of the vadose zone or the area below the soil horizon and above the aquifer   

       that is unsaturated or not always saturated.

C – Conductivity (Hydraulic) which is a measure of the ability of the aquifer to transmit

       water.

Each of these factors do not equally influence groundwater pollution.  To account for this, each factor is weighted to give more value to factors with more importance in determining groundwater pollution.  The two most influential factors are the depth to water and the impact of the vadose zone.

The DRASTIC maps for each county in the watershed illustrate that most areas have low to moderate groundwater pollution potential.  Areas most vulnerable in the watershed are in the floodplain areas along both Big and Little Darby Creeks.  These areas are composed of permeable layers of sand and gravel which are excellent sources of groundwater but highly susceptible to groundwater pollution.  The recharge rates in the watershed are largely between four and seven inches a year with values up to ten inches per year along Big and Little Darby Creeks.  DRASTIC maps are in the process of being converted into GIS files and will be available at a later date for mapping purposes. 

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For problems or questions regarding this website please contact the Darby Watershed Coordinator.
Last updated: June 09, 2008.