Hydrogeologic Services for Brackish Ground-Water Supply: Dunedin, Florida
AQUIFER MONITORING AND TESTING PLAN
Hydrogeologic and water use permitting services for the City of Dunedin included many activities. An aquifer monitoring and testing plan was developed by LBG in accordance with the City’s WUP. The plan was submitted to the SWFWMD for review and was implemented upon their approval. This study included investigating the cause and effect relationships for salt-water intrusion at the City’s production wells and future well-field operation and management plans.
An in depth review of published reports and other information was performed by LBG to assist in defining the hydrogeologic conditions of the Dunedin and surrounding area. Reports prepared by the USGS, SWFWMD and other consultants were very beneficial in completing this task. The construction characteristics and historical pumpage and water-quality data were evaluated to determine their effectiveness.
Statistical analysis of hydrologic data including pumpage, chloride concentrations and water levels were performed to determine if trends occurred that explained the causes for salt-water intrusion. The results of this analysis indicated that localized upconing of poor quality water has occurred primarily due to concentrated pumpage.
BRACKISH GROUNDWATER EVALUATION
Another important aspect of the study was the potential for developing a brackish groundwater source. The City of Dunedin constructed a Reverse Osmosis (R.O.) treatment facility several years ago with the intent of utilizing a poorer quality groundwater to minimize effects on the limited fresh-water aquifer in the area. LBG worked with the City, USGS and SWFWMD on a cooperatively funded project to assess the potential for developing brackish groundwater. Several test wells were designed and constructed at the R.O. plant site. LBG prepared an aquifer testing program that was submitted to the SWFWMD and approved for implementation. Results from geophysical logs, water-quality analysis and specific-capacity tests have indicated that their is great potential for developing a brackish groundwater supply.
A groundwater flow model, using MODFLOW, was developed for the Dunedin and surrounding area. The model was used to accomplish several tasks. First, to define the groundwater flow system of the area. Next it was used to assess upconing effects of pumping the current wells versus effects from pumping deeper, brackish water wells. This analysis also indicated that development of brackish water was favorable while minimizing effects of upconing in the fresh-water aquifer. A safe yield of the limited fresh-water aquifer was also determined. The model has also been utilized to modify the Water Use Permit.
WELLFIELD MANAGEMENT PLAN
As a result of all evaluations, LBG prepared a well-field management plan. This plan included the use of existing wells, modification of existing wells, the phasing out of some wells and the construction of new supply wells. The plan also includes well-field layout production rates, monitoring well recommendations and production well maintenance requirements.