Project Work Plan

Greater Everglades Science Program: Place-Based Studies

Project Work Plan FY 2003

A. GENERAL INFORMATION:

Project Title: Simulated effects of ASR injection in the Floridan aquifer system near Lake Okeechobee Florida - a first approximation
Project start date: July 2002 Project end date: September 2003
Principal Investigator: Nick Sepulveda
Email address: nsepul@usgs.gov
Phone: (407) 865-7575 Fax: (407) 865-6733
Mail address: 224 W. Central Parkway , Suite 1006, Altamonte Springs, FL 32714

Project Summary: CERP's Aquifer Storage and Recovery (ASR) Project proposes to inject and then withdraw up to 1.0 billion gallons per day (bgd) of surface water into and out of the Upper Floridan aquifer during wet and dry weather conditions at selected sites near Lake Okeechobee. Concern exists, however, that the injection and withdrawal of such large volumes of water may affect water levels in the Floridan aquifer system for considerable distances away from the proposed well sites in South Florida. As a result, project team scientists agree that a regional GW-flow model will eventually be needed to evaluate the magnitudes and extents of head changes resulting from ASR operations. At this time, however, uncertainty exists in just how far the northern boundary for such a model would need to be extended to avoid the undesirable effects caused by assignment of other than natural aquifer boundaries (i.e., constant head or flux boundaries). Also, because water-use data collection represents such a large investment of manpower in the construction of any regional model, it is desired not to extend the boundary any further north than necessary.

Project Objectives and Strategy: The primary objective of this study is to assess the potential effects of injecting and then withdrawing 1.0 bgd of water into the Upper Floridan aquifer near Lake Okeechobee on changes in Floridan aquifer system heads near the well sites and north of the lake.

The project objectives will be met by simulating the effects of injecting, and then withdrawing, water near Lake Okeechobee on the Floridan aquifer flow system using the USGS 'Mega' model (Sepulveda, 2002). The Mega model extends from the Suwannee River south to the middle of Lake Okeechobee, and from coast to coast. The model has a constant surficial aquifer fixed head array and is vertically discretized to simulate ground-water flow in both the Upper and Lower Floridan aquifers. The model input files, which are presently formatted for inclusion in the original version of the MODFLOW model, will need to be converted to the newer USGS MODFLOW-2000 format (Harbaugh and others, 2000). The locations of injection/withdrawal sites and accompanying rates will be provided by project development team members. Because of the close proximity of the model's southern boundary to the proposed injection sites, the model cannot be used to evaluate the possible effects of injections and withdrawals to areas south of the lake.

Transient simulations will be conducted to simulate the temporal nature of head changes at and away from the well sites with monthly changes in municipal 1993-94 pumpage rates (period used to calibrate the model and for which water-use data are readily available for model input). Steady-state simulations will also be conducted to analyze the maximum possible effects of ASR injection and withdrawal. Because the Mega model's southern boundary is comprised of specified heads and is relatively close to proposed injection sites, simulated head changes near this boundary may be subject to considerable error. It is possible that these errors may also affect simulated heads north of the well sites, which are of greater interest in this study. Accordingly, it will be necessary to conduct two simulations to bracket a possible range of affected heads. In the first scenario, where specified 1993-94 heads will be assigned along the model's southern boundary, simulated heads will be unrealistically low during the injection period but unrealistically high during the withdrawal phase. In the second scenario, where constant 1993-94 lateral fluxes will be specified along the southern boundary, simulated heads will be too high during the injection period but too low during the withdrawal phase. Thus, the two simulations considered together should establish upper and lower bounds for simulated heads in the Upper and Lower Floridan aquifers.

Potential Impacts and Major Products: . Although the results of the proposed study will not provide the basis for evaluating the feasibility of ASR, results should prove useful for later conceptualization and construction of the ASR regional model.

Collaborators: ASR PDT members, including those from USACE and SFWMD
Clients: na

B. WORK PLAN

Title of Task 1: Identify well locations and injection/withdrawal cycling periods and rates.
Task Leaders: Nick Sepulveda
Phone: (407) 865-7575
Fax: (407) 865-6733
Task Status (proposed or active): proposed
Task priority: this task is required before others can be addressed.
Task Personnel: Nick Sepulveda

Task Summary and Objectives: locate probable ASR injection/withdrawal sites around Lake Okeechobee. Well locations are needed for assignment to appropriate model cells.

Work to be undertaken during the proposal year and a description of the methods and procedures: The locations of injection/withdrawal sites and accompanying rates will be provided by project development team members, including those from USACE, SFWMD, and USGS.

Planned Outreach: na

Title of Task 2: Simulate changes in the potentiometric surfaces of the Upper and Lower Floridan aquifers under both steady-state and transient conditions for bracketed (boundary) scenarios.
Task Leaders: Nick Sepulveda
Phone: (407) 865-7575
Fax: (407) 865-7575
Task Status (proposed or active): proposed
Task priority: task is required to meet project objectives
Task Personnel: Nick Sepulveda

Task Summary and Objectives: Simulation results will be used to help locate the northern boundary of the ASR Regional model, as well as the possible head build-ups (and drawdowns) that may be expected at and away from the project well sites.

Work to be undertaken during the proposal year and a description of the methods and procedures: Transient simulations will be conducted to simulate the temporal nature of head changes at and away from the well sites with monthly changes in municipal 1993-94 pumpage rates (period used to calibrate the model and for which water-use data are readily available for model input). Steady-state simulations will also be conducted to analyze the maximum possible effects of ASR injection and withdrawal. Because the Mega model's southern boundary is comprised of specified heads and is relatively close to proposed injection sites, simulated head changes near this boundary may be subject to considerable error. It is possible that these errors may also affect simulated heads north of the well sites, which are of greater interest in this study. Accordingly, it will be necessary to conduct two simulations to bracket a possible range of affected heads. In the first scenario, where specified 1993-94 heads will be assigned along the model's southern boundary, simulated heads will be unrealistically low during the injection period but unrealistically high during the withdrawal phase. In the second scenario, where constant 1993-94 lateral fluxes will be specified along the southern boundary, simulated heads will be too high during the injection period but too low during the withdrawal phase. Thus, the two simulations considered together should establish upper and lower bounds for simulated heads in the Upper and Lower Floridan aquifers.

Planned Outreach: na

Title of Task 3: Prepare figures and tables depicting modeling results.
Task Leaders: Nick Sepulveda
Phone: (407) 865-7575
Fax: (407) 865-6733
Task Status (proposed or active): proposed
Task priority: this task is required to meet project objectives.
Task Personnel: Nick Sepulveda

Task Summary and Objectives: figures and tables will be generated to summarize modeling results. No formal USGS report will be produced.

Work to be undertaken during the proposal year and a description of the methods and procedures:

Planned Outreach: na