1. Susceptibility Assessment for Public Water Supply sources
Gil Strassberg

2. What is a Susceptibility Assessment?
The traditional risk assessment – Point effects an Area
What is a susceptibility assessment?
We want to know how the area supporting the water intake affects the water quality at the intake.
We are trying to determine a quality relationship between the area and the water source.
Need to consider
Point sources and non point sources – petroleum storage tanks, Toxic release sites, land fills etc.
Non Point source – land use (pesticides in agriculture), urbane areas, some types of soil have influence on water quality.
The good news is we can use similar physical properties that have been researched in the risk assessment analysis in the past
Susceptibility Assessment – Area effects a Point
Point Source
Non Point Source
We can use the similar physical properties
for both assessments

3. Schematic Overview Schematic overview of the assessment procedure.
An example using the datasets for lake aquilla.
We start with a point that represents the intake (surface water intake or a well for ground water)
All the different layers that represent the watershed. – Topographic, Annual and seasonal averages for Climate, Soils, land coverage.
Demonstration of the different layers available.
Potential sources coverage
Length Zones, calculation of zones that represents the flow distance upstream from the intake, will enable us to do zonal statistics and simplify the assessment, will talk more and show how we calculate.
Based on the information we Want to implement Business Rules to evaluate the susceptibility, we will use chemical grouping and properties of these groups and also compare to water quality monitoring data.
Outcome will be the final assessment.

4. Calculating Length Zones –Time Zones
Flow Direction Grid
Flow Length Grid
Using flow length function
in arc info workstation
Explain how we calculate the zones – the same thing in ground water we use time of travel.
Using function “Flow length” we calculate the length of flow from a point to the outlet.
Each cell in the grid has a value that represents the flow distance to the intake.
Give unique values to the cells so that each value represents a zone e.g: zone number 1 from 0 to
Transform the grid into a coverage – enables us to intersect different layers.
Length Zones Coverage
Calculate new grid with unique values
From grid
to coverage

5. Intersecting sources and length zones
Using select by location function
Zone
number
Petroleum Storage tanks
Toxic release inventory 1 2 3 11 4 5 6
Intersecting the length/ time zones with the source locations will give us an inventory of the sources and there location from water source.
The number of Sources in the Area
Relative location of the sources

6. Physical Model Qin Co Qout Ce
Want to apply some physical model to determine the effect of the sources on the water supply source.
Applying an attenuation factor is a simple approach to calculate the relative effects of sources on the intake.
However calculating the attenuation Factor is not simple due to multiple Process that effect attenuation.
Two faze attenuation: 1. Attenuation due to Filtration from surface to the saturated zone. 2. Attenuation during transport in the saturated zone
Physical Attenuation:
Sorption
Decay
Volatilization
Advection
Dispersion

7. Summary
What do we know?
Area that effects the intake and its properties.
Number of sources in the area.
Relative location of point and non point sources.
Attenuation Factor in groundwater
Future Work?
Refine attenuation factors for ground and
surface water.
Apply the methodology on case studies.
Compare to available water quality data.

8. Acknowledgments Dr. Maidment and Dr. Katz USGS: Randy Ulery
Richard Kiesling
Toby Welborn
TNRCC – SWAP team
Research Team at Pickle
Dr. Maidment and dr. Katz for there guidance and help.
USGS – for guiding me through the data and help process it.
TNRCC- for there contribution.