Dilution Attenuation Factors in Susceptibility Assessments: A
GIS Based Method
by Gil Strassberg, M.S.E.
ABSTRACT
The 1996 Amendments to the Safe Drinking Water Act require each
state to prepare a source water assessment for all public water
supplies, emphasizing the importance of protecting water sources.
States are required to determine the drinking water source and the
origin of contaminants for each public water supply. These assessments
determine the susceptibility of individual water sources to contamination
from various sources of contamination.
The Texas Source Water Assessment Program is a joint effort of the
U.S. Geological Survey (USGS) and the Texas Commission on Environmental
Quality (TCEQ). Its objective is to construct a methodology for
evaluating the relative susceptibility of Texas' Public Water Supplies
(PWS) to contamination. The program is a combination of different
source and transport components, that when linked together, yield
the final susceptibility assessment.
The work presented focuses on the development of a dilution attenuation
factor component that is integrated into the ground water susceptibility
assessment using GIS. This component is based on a Tier 2 screening
model presented in the Texas Risk Reduction Program (TRRP). The
Tier 2 model is a steady state model that calculates concentration
ratios between contaminated soils and groundwater. The model describes
the major natural processes taking place in the environment during
contaminants migration in groundwater systems. These processes include
dilution, sorption, dispersion and degradation Model inputs include
soil, aquifer and chemical properties. The output gives a dilution
attenuation factor, which is the ratio between the concentration
of pollutants in the soil, at the source of contamination, and in
the groundwater at the water supply well.
The numerical relationship, between sources of contamination and
contaminant concentrations at water supply wells can be used to
better estimate the susceptibility of water supplies to contamination.
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reserved. Copyright 2002 Center for Research in Water Resources.
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