Groundwater Quality Source Evaluation for the Rainbow Springs Group
Southwest Florida Water Management District (SWFWMD) • Marion County, FL
Solution Overview
Client:
Southwest Florida Water Management District (SWFWMD)
Business Challenge:
- Minimized stresses which have diminished water quantity and quality observed at the springs, including increased nitrate concentrations in spring discharge
Solution:
- Used an enhanced solution of water quality problems by streamlining a spatially focused, cost‑effective means for spring protection and source identification
Results:
- Pilot program demonstrated the surgical approach and economically identified “hot spot” areas in need of further evaluation in a karst environment
- Program results were provided to the Florida Department of Environmental Protection (FDEP) for consideration as part of their Basin Management Action Plan (BMAP)
Challenge
There are more than 150 springs within the SWFWMD, all of which have become threatened to varying degrees by anthropogenic activities and other factors. The SWFWMD has established a “Springs Team” comprised of in-house experts charged with evaluating and applying a variety of techniques—such as regulation, monitoring, research and development, restoration, and education—to minimize stresses which have diminished water quantity and quality observed at the springs. Of these stresses, increased nitrate concentrations in spring discharge over the last 50 years is paramount.
Traditional approaches to springs protection and restoration have focused on areas proximal to the spring or spring group. While many projects have evaluated the quantity and quality of water discharging from specific springs or spring groups, these efforts have been focused on delineation of the spring sheds and identification of spring protection areas based on proximity to the spring or pre-existing knowledge from dye traces or other site-specific evidence.
Solution
Rather than large scale, “catch-all” approaches of the past, such as delineation of a spring protection zone near the spring, staff with Water Science Associates, an Apex Company—working closely with Dr. Sam Upchurch (University of South Florida emeritus)—evaluated a “surgical” approach to hydrogeologic evaluation and establishment of site‑specific, nutrient-reduction target areas. This approach hopes to provide a solution to water quality problems by streamlining a spatially focused, cost-effective means for spring protection and source identification. SWFWMD data, such as existing monitoring well and spring water-quality data, was utilized to identify the most probable primary source areas of nutrients and related recharge water from within the Rainbow Springs Group spring shed.
The pilot program evaluation method increases in complexity with each step of the evaluation; however, the end result links aqueous geochemical statistics to potential karst features and land uses evaluated during the three 10-year time frames. Like any hydrogeological investigation, the foundation is a sound conceptual site model. This included a regional and site-specific review from a stratigraphic, geomorphic, and karst science perspective. Once potentially relatable karst features were identified, statistical analyses of the SWFWMD water quality data were completed to cluster the water quality data into process-related factors. Site-specific loadings of water quality data to process-related factors can be mapped to identify potential sites of interest within a spring shed. The statistical approach included geochemical fingerprinting by pattern recognition and analysis; principal component analyses; and factor analyses. These geostatistical/geochemical analyses along with the karst hydrogeological evaluation allowed for the identification of potential “hot spots”.
Aqueous geochemical analyses aid in sorting out chemical variables related to hydrogeologic processes beyond strict lithologic controls. In this study, the technique improved the conceptual model for recharge to the Upper Floridan aquifer and included: (1) confirming that recharge rates and pathways are related to topographic regions; (2) identifying possible fracture traces that influence recharge and groundwater movement; and (3) delineating areas in the vicinity of the Rainbow Springs Group where groundwater is impacted by artificial recharge from urban and agriculture sources.
Results
Water Science Associates used principal component analyses and factor analyses as means of identifying sources and processes of groundwater quality in a spring shed. The analysis was constrained in such a way as to force inclusion of analytes related to rock-water interactions into a single factor. The remaining two factors reflected analytes related to phosphate mining, fertilization and, possibly, soil amendment application.
Depending on the amount of available information, this pilot program demonstrated the applicability of the surgical approach and economically identified “hot spot” areas in need of further evaluation in a karst environment. The pilot program and results were provided to the FDEP for consideration as part of their BMAP.