Susceptibility Assessment for Public Water Supply sources Gil Strassberg

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

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.

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 10000. 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

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

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

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.

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.