Groundwater Quality Modeling in Hillsborough County, Florida

The Environmental Protection Commission (EPC) is involved in the Tampa Bay, Florida, watershed management project. A large part of the project involves assessing the county’s groundwater vulnerability to contamination at major population centers and those centers’ relationship with impaired waterways. Maps and analyses compiled by the GIS team enhance the ongoing research and enable EPC to properly protect and enhance the water quality within the Tampa Bay region for all citizens.

Population analysis was completed using the Census 2000 block data for Hillsborough County, Florida. The population data was calculated by the census block and converted to raster files representing population per square mile. Values of less than 2,500 people per square mile are not displayed.

The U.S. Environmental Protection Agency, working with the National Water Well Association and a large number of other experts, has identified the following seven key factors that determine aquifer vulnerability: (1) depth to groundwater, (2) recharge rate to groundwater, (3) aquifer media, (4) soil type, (5) topography, (6) impact of the vadose zone, and (7) conductivity of the aquifer. Each of these factors is assigned a combination of weights and ratings, and a numerical index called the DRASTIC index is computed. The DRASTIC index is used to evaluate the relative vulnerability of different aquifers or different segments of a given aquifer. On this map, the sites with high DRASTIC values are more vulnerable to contamination and consequently need to be managed more closely.