Lake Hancock Water and Nutrient Budget and Water Quality Improvement Project
CLIENT: Southwest Florida Water Management District
CONTACT: Janie Hagberg, P.E. - SWIM Section (813-985-7481, x2216)
PROJECT DATES: 1998-1999
PROJECT DIRECTOR: Dr. Harvey H. Harper, P.E.
FIELD OPERATIONS SUPERVISOR: Chip Harper
LABORATORY DIRECTOR: Vanessa Permaul
PROJECT BUDGET AND SCHEDULE
PROJECT BUDGET: $141,000
FINAL COST: $141,000
PROPOSED SCHEDULE: 16 months
ACTUAL COMPLETION TIME: 16 months
During 1998-1999, Environmental Research & Design, Inc. developed a water and nutrient budget for Lake Hancock and evaluated alternatives to reduce pollutant loadings discharging from Lake Hancock into the Upper Peace River. To develop the water budget, ERD performed flow monitoring at each of the three major surface water inflows to Lake Hancock, performed groundwater seepage monitoring in Lake Hancock, and supervised continuous hydrologic and hydraulic modeling performed by Ardaman & Assoc. To develop the nutrient budget for Lake Hancock, ERD collected and analyzed surface water inflow samples, groundwater seepage samples, and performed surface water quality monitoring. ERD developed an overall nutrient budget for Lake Hancock and its watershed for total phosphorus, total nitrogen, BOD, and total suspended solids. A modified Vollenweider Model was developed for Lake Hancock on a monthly basis for a period of 36 months. Monthly evaluations were performed to examine fluctuations in water quality characteristics on a seasonal basis throughout the year. ERD determined that approximately 38% of the estimated annual phosphorus input to Lake Hancock was from stormwater runoff and baseflow discharges, while the remaining 62% was from groundwater seepage, bulk precipitation, and internal recycling from nutrient-rich sediments. Due to the high internal recycling total phosphorus load, it was apparent that the treatment of surface water inflows to Lake Hancock would result in only minimal improvements in water quality.
Since discharges from Lake Hancock adversely affect water quality in the Peace River, one of the primary objectives of this project was to evaluate water quality treatment alternatives to improve the quality of water which discharged from Lake Hancock into the Upper Peace River. The pollutants of primary concern are total phosphorus, total nitrogen, and total suspended solids. Based on the chemical analysis of water discharging from Lake Hancock, a large majority of the total nitrogen and total phosphorus loads are present in the form of algal biomass. Therefore, it was recognized that a significant portion of the total nitrogen and total phosphorus loads can be removed if the algal biomass is removed. Three water quality treatment alternatives were selected for evaluation, including media filtration, wetlands treatment, and settling pond treatment aided by chemical coagulation. The media filtration alternative included constructing gravity sand filters in concrete tanks similar to a drinking water plant. Algae would be physically removed as it passed downward through the sand media. An automated backwash system would be installed to periodically remove filtered algae from the sand filters. The wetland treatment alternative involved construction of multiple wetland cells using marsh vegetation to physically filter algae from lake water. The chemical coagulation/ settling pond treatment alternative involved adding a coagulant to lake water and pumping the treated water into settling pond cells for floc settling and drying. Conceptual designs were prepared for all three treatment alternatives. Estimated pollutant load reductions, conceptual opinions of probable construction cost, estimated annual O&M costs, and present worth costs were developed based on the conceptual designs.
RELEVANT WORK PRODUCTS
- Field monitoring of stormwater runoff, dry weather baseflow, groundwater seepage, and sediment nutrient recycling
- Development of a hydrologic budget for Lake Hancock and its watershed
- Development of a nutrient budget for Lake Hancock and its watershed
- Evaluation of treatment alternatives to reduce discharge of pollutant loads and to improve lake water quality
- Preparation of conceptual design drawings, opinions of cost, and present worth cost
- Preparation of Draft and Final Reports