Aquifer Vulnerability Assessment Project Review in Columbia County

June 11, 2009 Columbia County, Florida AQUIFER VULNERABILITY ASSESSMENT: PROJECT REVIEW COLUMBIA COUNTY Advanced GeoSpatial Inc. Alan Baker, P.G. James Cichon

Presentation Overview • Conceptual Definition • Model Results • Implementing Model Results • Generalization with examples

Model Limitations • Vulnerability is relative; all aquifers are vulnerable • Based on features of the natural system that have association with location aquifer vulnerability • Does not account for human activity • Does not take account for contamination types • Does not estimate ground-water flow paths • Does not model fate/transport of chemical constituents • Large surface water features omitted

Study Area over which to search for a particular occurrence • Usually a county or some political boundary • Can be aquifer or springshed specific Conceptual Definition

Development of evidential layers used as predictors: • Soil Properties • Confinement or Overburden Thickness • Sinkhole Features or closed topographic depressions Conceptual Definition

Training Sites • Dataset of occurrences in our case ground water wells • Maximize knowledge by locating as many as possible • Evaluate water quality records to locate upper quartile • Ultimately use a subset of total wells Conceptual Definition

Conceptual Model • Evidential layers are spatially associated with the distribution of known occurrences and then generalized into binary patters • Individual evidence layers are combined together as a map depicting the best areas to search for contamination

Conceptual Model • Use known locations and assess their distribution spatially with respect to each factor causing occurrence • Where are the relationships or breaks between the data and the training points?

Input • Soil Permeability • Overburden Thickness • Hydraulic Head Difference • Karst Features

Soil permeability • Determine spatial association between theme and training points • Analysis reveals that highest contrast occurs at a soil permeability rate of 7.66 in/hr

Overburden thickness • Determine spatial association between theme and training points • Analysis reveals that highest contrast occurs at a overburden thickness of 117 feet

Karst Features • Determine spatial association between theme and training points • Analysis reveals that highest contrast occurs at a distance of 210 m from a karst feature

Aquifer Vulnerability Maps • We now have a map showing where to focus our efforts in similar locations • Results are based on data collected about existing occurrences • Model reveals a map showing favorable areas with greater probablity of finding occurrence Relative Vulnerability Vulnerable More Vulnerable Most Vulnerable

Local versus regional assessment • Larger scale study area: Wekiva Aquifer Vulnerability Assessment • Results are normalized across smaller study area, not entire statewide extent of aquifer system • Can include refined input data such as LIDAR • Provides more usable final product for planners, developers, regulators, and local government Local versus Regional

Regional Local

Aquifer Vulnerability Assessment Benefits • Assists local government, planners and developers in guiding growth into areas delineated as lower vulnerability • Enables more focused protection of sensitive areas, e.g., springsheds and ground-water recharge areas • Public tax dollars used more wisely as a result • Has be used to help guide wastewater management requirements – septic zones vs. centralized sewer • Leon County & Alachua County Purpose, End Users, and Benefits

Implementing model results • Results are not static; model is based on best available data and is snapshot in time • New and refined data reveals more accurate or complex statistical patterns allowing higher confidence in results • Lidar: Karst and Overburden • Accuracy is function input data • Approach is highly adaptable and useful tool for implementing ongoing protection of ground-water resources Implementing Model Results

Generalization of CAVA Model Results • Alachua and Leon Counties contracted with AGI for development of derivative protection-zone maps based on each of the County Aquifer Vulnerability Models • Deliver an aquifer protection zone map based on individula results that is directly applicable to land use and environmental regulatory decisions

Methodology • Generalization of the vulnerability map into specific aquifer protection zones • Raster Smoothing techniques employed • Help guide implementation • Avoid use of results on parcel to parcel scale • Account for highly resolved but isolated areas of vulnerability • Use of ArcGIS Spatial Analyst extension

Determination of Appropriate Analysis Window • Recent projects recommended that model results be applied on a local scale of greater than or equal to approximately 1.0 mi2 for statewide studies (Florida Aquifer Vulnerability Assessment) • Or approximately 0.75 mi2 for localized studies (Alachua, Wekiva, Leon and Marion County Aquifer Vulnerability Assessments). • Based on similarities to larger scale projects, AGI determined that model results be used at a recommended scale of 0.75 mi2, or an approximate 4,500-ft grid cell size.

ACAVA Model Results

Draft test results Focal Mean Filters on a window with a radius of 12 cells Cell size is 345 m. Calculates a statistic on a raster over a specified neighborhood. Focal Mean Finds the mean of the values for each cell location on an input raster within a specified neighborhood and sends it to the corresponding cell location on the output raster.

http://www.1000friendsofflorida.org/water/WakPowerPoits/Wayne%20Tedder%20TLCPD%20Wakulla%20Springs%20Workshop.ppt.pdfhttp://www.1000friendsofflorida.org/water/WakPowerPoits/Wayne%20Tedder%20TLCPD%20Wakulla%20Springs%20Workshop.ppt.pdf

Note on CCAVA • Protection zone map will be a derivative product of the original model CCAVA results • Not intended as a replacement of the CCAVA results • As a result, the protection zone map will represent a standalone map product based on CCAVA results and additional supplemental datasets

Any Questions? 1949 Raymond Diehl Rd, Ste. D Tallahassee, FL 32308 abaker@adgeo.net 850/580-4GIS

Aquifer Vulnerability Assessment Project Review in Columbia County