Water Preserve Areas and Seepage Management along the Marsh/Urban Interface

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PROJECTS Water Preserve Areas Lake Belt In-Ground Reservoir Technology Pilot Project L-31N Seepage Management Pilot and Everglades National Park Seepage Management

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Overview

These projects focus on the control and management of the large volumes of water currently lost from the natural Everglades to the lower east coast. The water preserve areas, an interconnected series of marshlands, reservoirs, and aquifer recharge basins between the Everglades Water Conservation Area and the coast, will reduce seepage, manage the quantity and the quality of the water returned to the Everglades, and provide other benefits, such as urban water supply. Seepage management technologies will be investigated through a number of pilot projects. The L-31N Seepage Management Pilot, Everglades National Park Seepage Management, and Lake Belt In-Ground Reservoir Technology Pilot Project are closely related. The L-31 N pilot will provide the technology needed to support seepage management for Everglades National Park. The in-ground reservoir pilot will address remaining uncertainties related to in-ground storage that are not addressed by the L-31N pilot.

DOI is particularly interested in the success of the water preserve projects as a means of attaining the natural hydrologic targets in the Everglades marshes. The water preserve areas will prove critical in ensuring improvements to the Arthur R. Marshall Loxahatchee National Wildlife Refuge and Everglades National Park, and the habitats of numerous threatened and endangered species. DOI is also concerned about preserving the quality and critical water deliveries to coastal estuaries and offshore areas north and east of Barnes Sound.

Determining the best technology for managing seepage from the water preserve areas involves a number of issues of concern to DOI, including the potential for impeding the recharge of wellfields to the east of any barriers and the potential for disrupting groundwater flows into natural areas to the east and south.

The effects of these projects on water quality are important concerns of DOI. The quality of the water captured in the water preserve areas could be affected by contaminated soils, in areas where former agricultural lands will be flooded, and by unnatural levels of metals and other pollutants leached from geologic formations, where in-ground reservoirs are used.

DOI managers can most effectively participate in CERP projects during three project stages: (1) NEPA scoping in the early stages of project design, to help ensure that hydrologic targets accurately reflect the natural predrainage conditions, (2) review of project alternatives, to ensure that fish and wildlife and parks are adequately considered in compliance with DOI mandates, and (3) monitoring and assessment of project results, to support project modification if needed to ensure that the intended conditions are achieved. The major questions that DOI managers need to answer at each stage to effectively fulfill their responsibilities as partner and steward are summarized below, along with the highest priority science needs for answering those questions. This information is discussed in greater detail for each individual project following this summary.

SUMMARY OF DOI RESPONSIBILITIES AND SCIENCE NEEDS RELATED TO WATER PROJECTS IN WATER PRESERVE AREAS AND SEEPAGE MANAGEMENT ALONG THE MARSH/URBAN INTERFACE

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Water Preserve Areas

Project Purpose and Major DOI Interest
The Water Preserve Area (WPA) Projects consist of nine components³ encompassing 190,000 acres. The shared purposes of these projects are (1) to retain more water in the natural system by reducing seepage losses from the Everglades, (2) to capture, store, and if necessary treat stormwater currently discharged to tide for other uses, such as recharging wellfields, and (3) to provide fish and wildlife benefits where possible while meeting water management goals.

Conceptually, the projects incorporate an interconnected series of marshlands, reservoirs, and aquifer recharge basins east of the Everglades Water Conservation Area. The resulting mosaic of wetlands, buffers, and reservoirs will make possible and complement several CERP water storage projects planned for the future (2010-2020). The WPAs will contribute to natural system water quantity through storage and seepage management. Other benefits include increased aquifer recharge and surface water storage capacity. Together these projects will enhance regional water supplies for urban and agricultural uses and increase the spatial extent of wetlands, providing vital habitat connectivity for species that require large unfragmented tracts of land for survival.

Water preserve areas have the potential to affect nearly all areas within the Everglades Protection Area, which comprises the WCAs, Everglades National Park, and the Arthur R. Marshall Loxahatchee National Wildlife Refuge. DOI has a great interest both in the quantity, timing, and distribution of water deliveries to these areas and in the quality of the water delivered. The primary water quality concerns are the risk of contaminants associated with the rehydration of former agricultural lands. Water soluble contaminants, such as methyl mercury, phosphorus, and nitrogen, are expected to be found in WPA project areas. Initial inundation may lead to water quality issues, as contaminants in the soil are liberated or mobilized.

Five federally listed species are present in the project area: West Indian manatee, wood stork, Everglade snail kite, eastern indigo snake, and Cape Sable seaside sparrow.

DOI will recommend improvements in the design and operation of the aboveground reservoirs to provide ancillary benefits to fish and wildlife wherever possible.

What Is Known
Water quality in South Florida has been the target of extensive field and laboratory investigation over the past two decades, but only recently has there been considerable scientific and technical investigation of large water storage areas (WPAs and STAs) and their use in improving water quality. The SFWMD's 2002 Consolidated Everglades Report summarizes the current scientific knowledge about the water quality effects of nutrients and mercury in the Everglades.

What Is Needed
Baseline surveys for long-term monitoring comparison. Surveys will measure baseline conditions (water quality, flora, and fauna) as a reference for future evaluations of post-restoration response to hydrologic change. Long-term monitoring of plant and animal communities and biomonitoring within the WPAs should be initiated to generate data sets to be used for adaptive management of hydrologic restoration targets. Baseline, mid-project, and post-project monitoring will determine the effects of WPAs on migratory and federally listed species. Post-project vegetation studies will be conducted on target plant communities to monitor the success of hydrologic restoration of wetlands and to provide information for effective adaptive management.

Environmental risk assessments of water-quality contaminants. This is another project with potential for ecological effects associated with increases in toxic contaminant loads in stored waters. Studies will be conducted to assist the USACE in designing techniques to minimize water quality degradation during the conversion of agricultural land to water storage areas. Other studies will focus on improving water quality within the conveyance and seepage canals during operation.

Research and possible model refinement to establish operating protocols. Many studies have documented the importance to fish and wildlife of maintaining plant diversity, providing horizontal and vertical vegetative structure, tree islands, snags, underwater substrate, and deep water zones within artificial water bodies such as aboveground reservoirs. The hydrologic requirements of some species are well documented; however, an integrated approach will be needed to address the needs of multiple species.

DOI needs to identify operating protocols to achieve desired hydrologic targets appropriate for each of the WPAs. These operating protocols will have a specific target or range and will be used to indicate how well, or poorly, each WPA alternative meets project objectives for restoration.

These operating protocols will help determine how to best manage the fringes of the marsh to achieve water storage, reduced seepage, maintain aquifer recharge, and other project objectives. The hydrologic targets need to address appropriate timing, cleanliness, and distribution to replicate natural function in the marsh. The operational protocols should provide water managers more flexible management techniques based on actual rainfall (real-time conditions) rather than projection of annual averages, in order to avoid engineering the wetlands into an unnatural state. Monitoring and assessment will continue to provide information that will help evaluate the response of the system to the new operating parameters.

Research to support design and operational rules to enhance fish and wildlife resources. FWS needs to identify ways in which the WPA projects can be managed and operated to provide favorable habitat for fish and wildlife while maintaining the water management functions. An important design consideration will be to ensure that there are adequate dry season refugia, such as alligator holes, to accommodate species during dry seasons.

Seepage measurements. Research regarding the design, implementation, and management of water storage areas of this magnitude does not currently exist. The seepage management pilot projects need to be completed and analyzed to provide the information needed to fully implement this program.⁴

Lakebelt In-Ground Reservoir Technology Pilot Project

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Due to the porous nature of these pits, water storage without a seepage barrier around them would cause the water to enter the surficial groundwater aquifer system, raising the water table and causing flooding. Drawing water from these areas without a seepage barrier would impact wellfields, drain adjacent wetlands, and increase seepage from the water conservation areas to the west.

The Lake Belt In-Ground Reservoir Technology Pilot Project was initiated to address uncertainties with using seepage barriers in four CERP components: Central Lake Belt Storage Area; North Lake Belt Storage Area; L-31N Levee Seepage Management; and L-8 / C-51 Reservoir. The uncertainties include appropriate construction technologies, storage efficiencies, impacts on local hydrology, and water quality effects. Water quality assessments will include a determination as to whether the in-ground reservoirs and seepage barriers will allow for storage of untreated waters without concern for groundwater contamination. Upon completion of the pilot, the USACE will be able to better design the in-ground water storage projects listed above.

The proposed design of the full-scale in-ground reservoirs will enclose approximately 15 square miles of existing rock mines and areas permitted for future excavation with seepage barriers. The Lake Belt Pilot Project will involve installing a seepage barrier around an existing smaller rock-mined area with geology similar to the geology at the proposed locations for the full-scale in-ground reservoirs.

The in-ground reservoir projects are of particular interest to DOI because they will provide important flows into Everglades and Biscayne Bay National Parks that are needed to achieve restoration. The overall purpose of the North and Central Lake Belt Storage Projects will be to store excess water and provide environmental water supply deliveries to Northeast Shark River Slough, WCA-3B, and Biscayne Bay. In addition to concerns about how the water will be delivered into the wetlands,⁵ DOI is concerned with the quality of water discharged from the in-ground reservoirs. The depth of these lakes and their method of construction ensure connection with deep groundwater strata typically containing high concentrations of dissolved solids, whose potential effects on the ecosystem are unknown. One of the signature features of un-impacted Everglades waters is relatively low concentrations of dissolved solids, especially as compared to ground water. Increases in dissolved solids due to the connection of deep groundwater strata to surface water could be problematic.

DOI is also interested in the potential to design these projects to be as compatible as possible with wildlife use without interfering with their primary purposes and to ensure that the barriers used to confine the reservoirs will not adversely effect groundwater flow into the natural areas further south Deep water lakes exhibit characteristics that would be very different from those typically experienced by Everglades plants and animals. DOI managers need to understand the management issues raised by these differences so that they can recommend design improvements to the USACE that will benefit fish and wildlife and mitigate any potential impacts on vegetation.

What Is Known
Dissolved solids concentrations in the Everglades have increased over decades as the result of agricultural and urban development. The ecological impacts of these increases are currently being investigated.

What Is Needed
Information about the effectiveness of seepage barriers in Lake Belt reservoirs. Construction of seepage barriers around the rock pits may alleviate the concerns associated with storing and removing water from these in-ground reservoirs; however, seepage barrier technology of this magnitude has not been used in South Florida, which creates uncertainties regarding constructability, storage effectiveness, groundwater impacts, and water quality effects.

Research to determine the ecological function of deep lakes. From an ecological standpoint, there are no similar deep water habitats in the Everglades, so the ecological value and function of large acreages of such habitats are unknown.

Research into biochemical processes that occur in deep lakes and how they will affect outflow. Research into the biogeochemical processes that will occur in these very deep lakes, and how those processes will affect the water quality of the outflow, will be needed to determine the extent of necessary treatment, so that the outflow will be of adequate quality to discharge into natural areas.

Groundwater assessments of water quality inside and outside seepage barriers of deep lakes. Assessments of water quality at various locations will aid in determining the locations to be monitored over time to assess effects on water quality .

L-31N Seepage Management Pilot and Everglades National Park Seepage Management

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The CERP plan contains several components to control seepage out of natural areas. The most complex seepage management projects are the L-31N Seepage Management Pilot Project and the Everglades National Park Seepage Management Project, which together are intended to investigate then apply the most appropriate and effective technology to control and manage the large volumes of water currently lost from Northeast Shark Slough to the urbanized lower east coast. The two projects are considered together because the science needs are similar.

The purpose of the pilot project is to investigate seepage management technologies and to determine the appropriate amount of wet season groundwater flow to return to Everglades National Park while minimizing the impacts to downstream water users such as Miami-Dade County and Biscayne National Park. This pilot is expected to provide the technology needed to reduce levee seepage flow across L-31N adjacent to Everglades National Park and to reduce groundwater flows during the wet season by capturing groundwater flows with a series of groundwater wells adjacent to L-31N then backpumping those flows to Everglades National Park.

The purposes of the Everglades National Park Seepage Management Project are to improve water deliveries to Northeast Shark River Slough and to restore wetland hydropatterns in Everglades National Park by reducing levee and groundwater seepage and increasing sheetflow. This project will reduce levee seepage flow across L-31N adjacent to Everglades National Park. Groundwater flows during the wet season will be captured and pumped back to the park. Water from upstream natural areas will be diverted into a buffer area adjacent to the park, where sheetflow will be reestablished. Further, this project includes relocation of the Modified Water Deliveries Project structure S-356 to provide more effective water deliveries to Everglades National Park. The increased flows into Northeast Shark Slough resulting from the Modified Water Deliveries Project will increase the potential for seepage from the slough, and pump station S356 is intended to return this additional seepage flow back to the slough.

New discharges to the park will be designed to meet applicable water quality criteria. Scheduled to begin at the conclusion of the pilot study, the project is slated for completion in 2013.

Improved water deliveries are expected to improve the ecological conditions in Northeast Shark River Slough and in the downstream estuaries. Reduced hydroperiods in the slough resulting from seepage losses have caused negative ecological impacts such as invasions of non-wetland species, and have the potential to disrupt nesting of alligators and wading birds, including wood storks. Evidence suggests that flow volumes and/or velocities are also important to maintaining the ridge and slough landscape.

What Is Known
Northeast Shark Slough has been the focus of numerous hydrologic investigations in recent years, and a reasonable hydrologic database is available. Extensive water level monitoring is currently being conducted by the NPS and the USGS. Outside of Everglades National Park, flow in L-31N, a direct indicator of seepage, is measured, and the SFWMD keeps detailed records of water levels and estimated flows at all of the C&SF structures. A relatively long database related to fish communities in Northeast Shark Slough is available and has been used in conjunction with hydrologic data to develop linkages between the hydrology and the response of aquatic communities. Wading birds and American alligators are among the keystone species that are routinely monitored in this area. Water quality is also monitored at several structures in the footprint of this project, and the monitoring data could be used as baseline water quality information.

A number of studies conducted by the USGS and others document the geology and hydrologic characteristics of the surficial aquifer. Additional studies provide more focused information about the subsurface characteristics of the West Dade Wellfield, located just 2 miles east of L-31N, and the rock-mining area located adjacent to L-31N.

Several hydrologic models are available for use in this area. The USGS has calibrated and verified MODBRANCH, which combines a widely used groundwater model (MODFLOW) with a one-dimensional model for canals and structures (BRANCH). This model has seen wide use in South Florida and is a viable candidate for use in evaluating alternatives for seepage management. The SFWMD has nearly completed development of the RSM, which also could have applications in these projects.

What Is Needed
Monitoring and assessment of pilot project information. Monitoring and analysis of the pilot project information will address most of the management questions. Hydrologic monitoring and assessment will evaluate the physical response of the system and any impacts to downstream water supply. Ecological monitoring and assessment of vegetation changes and impacts on American alligators and wading birds will address the ecological response to the physical changes in the system. In addition, water quality monitoring and biomonitoring will assess potential impacts to the system from introduction of water from other sources.

Determination of the source of flow. An additional flow gauge in the canal at the L29 intersection will support a determination of the source of flow measured by the other gauges.

Research and possible model refinement to establish operating protocols. Research will be conducted to determine the appropriate hydrologic response to rainfall and to translate that information into appropriate performance targets for input into the design and operating rules to manage water levels and flow volumes.

Research to define how back pumping and groundwater hydraulic gradients affect the flow of water and groundwater recharge in the surficial aquifer. Further research to assess the origin and the amount of water delivered to the coastal estuaries, Biscayne Bay, Card Sound and Barnes Sound via freshwater and groundwater flows.

Additional research and modeling are needed to determine how extensive seepage control actions will affect groundwater flows and recharge within the surficial aquifer and ultimate delivery of groundwater between the Everglades and Biscayne Bay. Modeling is needed to quantify the amount of water east of the Coastal Ridge that is entering the coastal estuaries. Better definition of the hydrologic framework and geohydrology of the Biscayne aquifer and overlying confining soils and sediments are needed. Baseline high-resolution groundwater level monitoring is needed between WPAs, Everglades National Park, and groundwater connection to Biscayne Bay. Further, research is needed to understand how changing water levels will affect groundwater flow within the surficial aquifer and how changing water levels, increase in flood duration in the natural system, and seepage management will affect the recharge of this aquifer, and, ultimately, groundwater flows to Biscayne Bay.

³ The WPA components are Acme Basin B Stormwater Treatment Area (STA) and Impoundment; Strazzula Wetlands; Agricultural Reserve Reservoir; Hillsboro Impoundment; Broward County WPA; WCA 3A/3B Flows to Central Lake Belt; WPA Conveyance; Bird Drive Recharge; and Eastern C-4 Structure and WCA-2B Flows to Everglades National Park.

⁴ See "L31N Seepage Management Pilot Project," page 54.

⁵ Water deliveries are addressed under the DECOMP and CSOP Projects, pages 67 and 71.