SMART GYPSUM STACK MANAGEMENT FROM CONCEPT TO REALITY Phong Vo, Manager - Engineering/Gypsum, Mosaic Fertilizer, LLC. 13830 Circa Crossing Drive Lithia, Florida 33547, USA and Ashraf H. Riad, Ph.D., P.E., Principal Engineer, Ardaman & Associates, Inc. 8008 South Orange Avenue, Orlando, Florida 32809, USA Prepared for American Institute of Chemical Engineers Central Florida Section 4798 S. Florida Avenue, #253 Clearwater Conference June 2013 1
ABSTRACT Phosphogypsum, a by-product from phosphoric acid production, is currently produced at Florida phosphoric production facilities at a rate of about 30 million tons per year. Current practice is to store the gypsum in engineered stacks. A typical gypsum stack covers an area of about 200 to 400 acres and is raised to heights up to 200 to 300 feet. Gypsum stacks are generally managed to safely contain the phosphogypsum (and process water) during the active life of the stack. Rainfall runoff from the top settling compartment(s) and from the active gypsum side slopes are comingled with process water and generally managed within the phosphogypsum stack pond system. After the stack reaches maturity, process water is removed by treatment or consumption, and the entire system is closed in a manner that clean rainfall runoff on the closed surfaces can be discharged off site through the permitted NPDES Outfalls. An overview of gypsum stack management using conventional method from inception to closure is presented. The conventional technique is compared to an alternative concept of smart gypsum stack management that allows for reduction of the watershed area during the active life of the gypsum stack. The authors will discuss technical challenges and regulatory constraints associated with the site and how solutions were developed to transfer the concept to reality over a six year period. The concept was successfully implemented which led to effective gypsum stack management, minimize environmental exposures, and realize significant cost savings. ii
TABLE OF CONTENTS ABSTRACT... iii BACKGROUND...2 CONVENTIONAL CONCEPT OF GYPSUM STACK MANAGEMENT...2 THE CONCEPT...4 NEW CONCEPT OF GYPSUM STACK MANAGEMENT...7 COMPARISON BETWEEN THE NEW AND CONVENTIONAL CONCEPT OF GYPSUM STACK MANAGEMENT...10 CONCLUSIONS...11 iii
LIST OF FIGURES Figure Page 1. 2012 Aerial Photograph of Central Florida Showing Gypsum Stacks... 2 2. Conventional Phosphogypsum Stack Management... 2 3. 2007 Condition of Side Slopes... 5 4. 2007 Aerial photograph of Riverview Active Stack... 5 5. 2007 The Concept... 5 6. The Concept... 5 7. Typical Stack Cross-section with Side Slope Drains... 5 8. Alternative Decant System.... 5 9. Interceptor Ditch... 6 10. 2009 Aerial Photograph Showing Completed Interceptor Ditch... 6 11. Side Slope Grading & Re-Vegetation Plan... 6 12. 2012 Aerial Photograph Showing Completion of the Concept... 6 13. Toe Swale Restoration - Typical Cross Section... 6 14. Photograph of Closed Toe Swale... 7 15. Smart Gypsum Stack Management System... 7 16. Looking South 1/2013 Aerial Photo Shown Completion of Closure CONCEPT. 11 1
SMART GYPSUM STACK MANAGEMENT FROM CONCEPT TO REALITY BACKGROUND Phosphogypsum, a by-product from phosphoric acid production, is currently produced at the phosphoric production facilities in Florida at a rate of about 30 million tons per year. The present practice is to store the gypsum in engineered stacks. Currently, there are over 25 gypsum stacks in central Florida at different stages (i.e., actively receiving phosphogypsum, inactive but not closed, under closure and fully closed). A 2012 aerial photograph of central Florida showing locations of various gypsum stacks is presented as Figure 1. Mosaic Fertilizer, LLC operates four chemical plants with gypsum stack systems in Central Florida and Louisiana. There are 16 gypsum stacks within Mosaic facilities in Florida and Louisiana at various stages of the stack lifecycle. CONVENTIONAL CONCEPT OF GYPSUM STACK MANAGEMENT A typical gypsum stack covers an area of about 200 to 400 acres and is raised to heights that can vary from about 200 feet to up to 300 feet. Gypsum stacks are generally managed to safely contain the phosphogypsum and associated process water during the active life of the stack. Different stages in the life cycle of a gypsum stack are illustrated on Figure 2 and are described below: 1. Inception. During this stage, the gypsum disposal area is prepared to receive gypsum slurry from the chemical plant. The base of the disposal area is graded and perimeter earthen containment dikes are constructed along with toe inspection roads and freshwater runoff collection ditches. The base of the disposal area is typically lined with a protective High Density Polyethylene (HDPE) liner system (except gypsum stacks constructed prior to the Florida Department of Environmental Protection (FDEP) Phosphogypsum Management Rules). A stack underdrain system is designed and installed above the liner in order to support the stack growth and maintain stability of the future side slopes of the stack. In addition to the underdrain system above the liner, some gypsum stack system requires underdrain system below the liner (due to hydrogeological conditions at the site) to control the water table below the liner and to prevent liner uplift until the gypsum stack is adequately 2
loaded with gypsum and process water. Gypsum discharge pipes and decant system are also placed within the disposal facility. 2. Startup. During this stage, gypsum slurry is discharged into the disposal facility. Prior to gypsum slurry discharge, the gypsum disposal area is often charged with adequate amount of process water to help managing gypsum depositions and gypsum beaches within the disposal area. The slurry discharge point and the decant system locations are optimized to efficiently develop rim ditches and starter dikes around the perimeter of the stack. An engineering and operation decision to have more than one settling compartment is typically made during this stage. 3. Active Stack. After developing rim ditches, seepage and runoff collection ditches at the toe of the stack, the gypsum stack is raised using the upstream method of construction along with rim ditching techniques. Depending on the condition of the facility and overall water balance, the stack is managed to maximize gypsum disposal while at the same time, optimize the process water storage within the stack compartments. Operational constraints (i.e., side slopes, minimum freeboard, crest road and inside gypsum roads, crest drainage, etc.) are typically mandated by the safety of the stack with regard to overtopping and slope stability and also regulatory constraints. One or more setback of the side slopes may be implemented based on the stack design to improve the stability and/or to reduce the side slope length in order to minimize erosion. 4. Mature Stack. The stack is considered at the mature stage when it reaches the design maximum height, and contains the maximum design gypsum storage volume. At this stage, the settling compartment on top of the stack is typically at the minimum ponded area required for clarification of decant water for the specific gypsum production. Ponded process water on top of the stack is managed within the system until closure starts. For most facilities, the life of the stack is typically designed to provide approximately 20 to 30 years of gypsum storage. During the life of the stack, minimal grading, if any, is performed on the side slopes or any intermediate benches. Side slopes are typically 2.5H: 1V for gypsum stacks in Florida and 6H: 1V for gypsum stacks in Louisiana. The top grade of the stack is typically bowl shaped with beaches around the perimeter. Gypsum grades on top of the stack are typically at 3% to 4% towards the middle of the stack. 5. Closure Stage I. After the stack retires and is ready for closure, the first closure stage is to remove the ponded water from the top of the stack. When the free water is removed from the top settling compartment, the phreatic surface on the side slopes starts to drop, allowing for closure of the side slopes. The drained free water must be consumed by treatment and discharged (or consumed in the plant if the plant is still active). During the 3
initial phase of settlement, a relatively large amount of seepage/consolidation process water will have to be consumed within a short period of time (about 6 to 12 months). 6. Closure Stage II. After draining the free water from the top of the settling compartment, the stack top gradient is prepared for closure. Construction activities include, excavating dewatering ditches spaced to efficiently dewater the gypsum surface in preparation for grading. The top of the stack is typically bowl-shaped with low points near the center of the pond. The top gradient is typically graded toward internal low points to follow the existing contours, thus minimizing earthwork. Stormwater is conveyed from the internal low points for controlled release. The top gradient is typically closed with an HDPE liner and 2-foot thick vegetated protective soil cover graded to promote drainage and minimize ponding of water on top of the final cover. 7. Closure Stage III. Following complete closure of the top of the stack (or during the closure period after draining ponded water), closure of side slopes of the stack begins. The side slopes of the stack are graded to provide smooth, uniform slopes minimizing earthwork and erosion. The side slope final cover typically consists of placing soil cover and grassing or amending the upper 12-inches of gypsum with dolomitic limestone, and grassing. Side slope drains are typically incorporated into the side slope closure to depress the water table within the stack slope and prevent seepage from exiting onto the surface of the slope. Stormwater runoff from the closed side slopes of the stack is collected within one or more side slope drainage swale(s) and within a toe drainage swale. The side slope and toe drainage swales are also lined with HDPE liner and covered with a 2-foot thick vegetated protective soil cover. 8. Closed Stack. After completion of closure of the top gradient of the stack, side slopes and toe drainage swales, the stack is considered closed stack. Stormwater runoff from the closed stack slopes are routed from the toe drainage swale for discharge through NPDES permitted outfall. Water quality is monitored for compliance with the permit requirements. Monitoring and maintenance activities for the closed stack top gradient and side slopes will be performed for the duration of the long term closure care period. THE CONCEPT Mosaic s Riverview Gypsum Stack System contains 736 acres of active footprint. The active gypsum stack was constructed and operated under a set of permits (Development 4
Orders and Florida Department of Environmental Protection) where Permit Conditions required grassing of the side slopes every 10 foot rise for meeting aesthetic look which is beyond the Florida Phosphogypsum Management Rules, Chapters 62-672 and 62-673, F.A.C. In order to comply with the Permit Conditions, numerous repeated trials and large financial commitments to grass the side slope have been committed by the Company over the years but were not sustained successfully. As the gypsum stack increased in heights, pond acreage on top of the gypsum stack was reduced and additional side slope acreages were included in the stack system which creates additional challenges to protect the vegetated side slopes on the lower slopes from the acidic contaminated rainfall runoff from the upper slopes. Figure 3 shows an aerial photograph of the stack dated January 2007. Figures 3 and 4 illustrate the condition of the side slopes of the stack in 2007. The side slopes had sporadic vegetation and the toe swale appeared to contain process water. In order to overcome these challenges a concept was generated in 2007, supported by regulatory agencies (Florida Department of Environmental Protection FDEP & Environmental Protection Commission of Hillsborough County - EPCHC), and successfully implemented over a six year period. An illustration of the concept is shown on Figure 5. The concept required gradual approaches and critical steps (see Figure 6) such as defining the overall growth plan of the gypsum stack, redesign the decant system, identify and isolate the Inactive slopes from the active slopes with the Interceptor Ditch, inspect and repair the slope drain system, re-vegetate the side slopes, restore the contaminated toe swale, and isolate the underdrain systems within the swale. On May 2012, installation of The Concept was completed and allowed the Riverview facility to meet its permit obligations, rainfall runoff on the closed lower portion of the slope met the NPDES discharge criteria and was discharged off site, improved water balance for the facility, and eliminated over 130 acres of rainshed from the gypsum stack system nearly 30 years earlier than the end of life of the stack. Main features of operational and environmental issues of the Concept are discussed below: 1. Side Slope Drains. Side slope drains were installed along the perimeter of the stack in phases during the 2004/2006 period. The purpose of the side slopes drains is to depress the water table within the stack slope and prevent seepage from exiting on the surface of the slope see Figure 7. 2. Decant Process Water. The Riverview facility always used a siphon line for decanting process water from the top compartment of the stack to the cooling pond system. The siphon line was located at the southeast corner of the stack. Maintenance issues associated with crystal growth (see photo on Figure 8) during the cold periods necessitated that the pipe be periodically cut in small sections and 5
cleaned along the side slopes of the stack. An alternative decant system consisting of ditches, stilling basin, receiving basin and shorter decant pipe was designed and constructed in 2007/2008. The alternative decant system allows for decanting water from the top of the stack without affecting the side slopes (i.e., eliminating flow from siphon pipes on side slopes and/or eliminating pipe cleaning on the lower slopes), thus allowing for the closure of lower side slopes. Figure 8 shows layouts of the alternative decant system. 3. Interceptor Ditch. This is the key component of the concept. An interceptor ditch was constructed at about El 140 feet (NGVD) to collect and convey contaminated runoff and seepage from the upper active slopes to the cooling pond system. The interceptor ditch acts as a separator between the active and the inactive slopes. Figure 9 shows a photograph of the completed interceptor ditch. The alignment of the ditch is shown on Figure 10 with a 2009 aerial photograph. The interceptor ditch also provides a redundancy for environmental protection by intercepting and conveying any incidental spills from the top of the stack to the cooling ponds. 4. Grading and Grassing Side Slopes. The side slopes below Elevation 140 feet (NGVD) along the east, west and north side of the stack are approximately 100 acres. The side slopes on the south side are part of an expansion project and were not included in the closure project. The 100-acre side slope area was divided into 7 separate areas to control grading and grassing activities. Limits of the various areas are shown on a 2010 aerial photograph of the facility presented as Figure 11. 5. Restore Toe Swale for Conveying Clean Rainfall Runoff. The toe swale was originally designed and built with the intention to convey clean rainfall runoff from the closed side slopes. Due to the inability to close the side slopes and contain incidental spills the swale used to collect runoff from the side slopes of the stack and convey it to the cooling pond. Re-establishing a storm water swale was one of the critical steps of the Concept. Swale restoration involved capping all manholes and cleanouts of the stack underdrain system, removal of fine gypsum, installing a gravel underdrain system to collect seepage from the stack; grading the swale to provide positive drainage from the southeast corner to the southwest corner; lining the swale with HDPE liner covered with a 2-foot thick vegetated protective soil cover. Figure 12 shows an April 24, 2012 aerial photograph of the stack at the end of the swale restoration construction period. A cross section showing the closure design of the swale is shown on Figure 13. The Swale was divided into six sections using check dams and valves as redundant measures for environmental protections to contain any incidental spills from the upper slopes, failure in the drains or any other mishap in the runoff quality. The check dam closest to the outfall structure was provided with an 6
automatic ph meter and automatic shut-off valve. Any impacted water flow would be timely collected and pumped into the cooling pond. Photographs of the swale before closure and after closure are presented in Figure 14. 6. Outfall Structure. The outfall structure from the toe Swale to the NPDES outfall was provided with an automatic monitoring system, automatic shut-off valves, redundant manual valve, and quick connect port to pump any impacted water to the cooling pond system. This should prevent excursions of water from the system. NEW CONCEPT OF GYPSUM STACK MANAGEMENT With a proven concept, different stages in the life cycle of a gypsum stack can be modified as following (see Figure 15): 1. Inception. All activities during this stage are exactly the same as for the Inception stage of the conventional management system. The designer of the stack system must give additional thoughts to specific details that may affect early closure of slopes while raising the stack (i.e., location of the stack drain outlets, toe ditch elevations, side slopes setback, etc.). 2. Startup. This stage is also similar to the Startup stage mentioned above with extra care given to specific details that may affect the early closure of the slopes of the stack (i.e., invert elevations of the seepage and runoff collection ditches; number of compartments, method of decanting water and location of the decant structures, etc.). 3. Active Stack. Initial raising of the stack slopes using rim ditch techniques and upstream method of construction is similar to the conventional management system. However, the designer and the operator of the stack must decide on an initial side slope set back elevation, location of the interceptor ditch and the size of the interceptor ditch. The size/location of the Interceptor ditch is the key element of the concept and must be determined based on the optimization of the storage life of the gypsum stack footprint, proper prediction of the stack consolidation, stability of the dike system, contributing watershed of the active slopes, and operational issues of the gypsum stack system. 7
4. Simultaneous Active / Closure Stage I. During this stage, the stack will continue to be raised using the rim ditch techniques and the upstream method of construction (Active Slopes), while simultaneously preparing the lower slopes for closure (Inactive Slopes). The first Interceptor Ditch will be excavated on the scheduled setback. The interceptor ditch is designed to handle runoff from the design storm (typically 12-inch storm event) along with process water decant, when needed. a. Active Stage I. The active slopes of the stack will continue to be raised above the scheduled setback. The gypsum stack operator may excavate the interceptor ditch as part of operation activities. A slight modification in the operation to allow for use of a wider rim ditch could be implemented, if needed to reduce seepage into the side slopes of the stack. The Interceptor ditch must be operated, as designed, at the recommended operating water levels for the corresponding height of the stack. The depth of the interceptor ditch must be monitored for loss of capacity due to silting or settlement and corrective actions must be implemented. All other operation constraints which are similar to the conventional raising of the stack must be adhered to for safe operation of the stack. b. Closure Stage I. When the stack reaches the design height above the initial setback and the interceptor ditch, closure of the Inactive Slopes of the stack below the interceptor ditch begins. The design engineer should select the proper height above the interceptor ditch prior to start of closure activities. Selection of the proper design height above the interceptor ditch is based on many factors such as properties of the sedimented gypsum, piezometric water levels in the gypsum, settlement and consolidation behavior, permeability and seepage conditions, etc. The closure design features of the side slopes are similar to those described above. The design/ construction of the side slopes drains must consider performance of the drain at higher heights and age of gypsum, as well as additional seepage volumes from the future upper drains. At some instances, depending on the specific condition of the stack, the closure construction of the toe swale may need to be delayed until the grass is established on the side slopes and runoff quality improves. Automatic ph monitoring and diversion gates may have to be installed within the conveyance structures to control the direction of runoff flow. 5. Simultaneous Active / Closure Stage II. This stage can be a single or multiple stages depending on the maximum height of the stack, number of interceptor ditches, and design of the liner system and stack closure progress. Similarly to the previous stage, an additional setback and another interceptor ditch are installed to 8
separate the active from the inactive slopes. Closure of the inactive slopes is performed in accordance with a procedure similar to the previous stage. Additional concerns are listed below: a. Active Stage II. Changes to the side slope geometry and/or rim ditching techniques may have to be considered and implemented based on performance monitoring of the lower slopes (both active and closed). b. Closure Stage II. The closure of the inactive slopes will be performed in a similar way to the closure of the slopes described above. Stormwater runoff quality must be considered during the conveyance analyses to decide when and how to combine the runoff from the recent closed slopes to runoff from the established closed areas. Automatic ph monitoring and automatic diversion gates may have to be installed within the conveyance structures. 6. Mature Stack. When the stack reaches maturity under the Smart Gypsum Management Process, almost 70% of the stack side slopes should be completely closed as well as the intermediate ditches and toe swale. Moreover, hydraulic connection between the closed stack and the NPDES outfall should also completed and operational. 7. Final Closure Stage. The remaining closure activities after reaching a mature stack should be limited to less than 30% of the side slopes of the entire stack. The remaining closure activities can be performed simultaneously (i.e., closing the top of the stack prior to closing the remaining side slopes or vice versa). The final closure period is expected to be much shorter in duration than the closure period for stacks managed using the conventional method. Rainfall runoff and seepage volumes during the final closure period would also be a much smaller for stacks managed using the Smart Process. a. Final Closure A. Draining process water from top of the stack is performed similarly to the previously described activity with the exception that additional care must be exercised while transferring process water crossing closed slopes or ditches (e.g., use double lined pipes when crossing the closed areas.). b. Final Closure B. Closing the top of the stack is also similar process as described above with exceptions related to crossing the closed areas and excessive use of access ramps for construction equipment. 9
c. Final Closure C. Closure activities of the remaining active side slopes are similar to the previously described methodology, except that drains may have to be modified or eliminated based on the seepage pattern of the stack at the final closure time. The uppermost slope swale may be eliminated based on the engineering design and the remaining height of the stack at that time. 8. Closed Stack. Stormwater runoff from the closed stack slopes are routed from the toe drainage swale to the NPDES permitted outfall for offsite discharge. Water quality is monitored for compliance with the permit requirements. Monitoring and maintenance activities for the closed stack top gradient and side slopes will be performed for the duration of the long term closure care period. COMPARISIONS BETWEEN THE NEW & CONVENTIONAL CONCEPT ON GYPSUM STACK MANAGEMENT The following items summarizes major difference between the two Concepts 1. Safety. For a stack managed using the new concept, the side slopes drains are installed during the early stages of closure, thus improves the slope stability safety factor over a stack without side slopes drains (as in conventional management process). 2. Environmental Protections: the new concept will reduce environmental exposure by reducing the footprint of the gypsum stack system especially during the hurricane season. 3. Closure Construction Cost. For a stack managed using the new concept, closure cost is distributed over the life of the stack rather than during the initial few years after closure starts for the case of a stack managed using the conventional process. However some additional costs could be incurred with the new concept due to ongoing operational issues of the gypsum stack system and sizing of the drain system. 4. Operability of the Gypsum Stack System: Without a complete evaluation, the new concept can create interferences with the operability of the gypsum stack system such as return water conveying issues, gypsum stacking, and access roads. 10
5. Cost of Water Treatment, Water Balance and Pond Inventory Management. With the new concept, it is anticipated that the pond inventory will be significantly reduced due to early reduction of land surface footprint which will translate into lower costs in pond water management, lower water treatment costs, and improving the overall water balance of the facility. Early elimination of one hundred and thirty acres (130) of land surface from the gypsum stack system footprint on this Project allows the facility to avoid pond inventory gain from 60 to120 million gallons per year for the next 30 years (assuming 52 inches per year of normal rainfall). 6. Closure Period. The new concept should reduce the closure period after the stack reaches maturity because much of the stack has already been closed. 7. Aesthetics. A gypsum stack operated using the new concept has a better aesthetics for the surrounding communities than a stack operated using the conventional method, thus resulting in more favorable acceptance by public. 8. Closure Design and Construction for slopes while the stack is being raised should incorporate additional safety measures with regards to depressing water levels beneath the slopes, grassing methods, process water and freshwater conveyance among other closure design items. 9. Monitoring and Maintenance. With the new concept closure monitoring programs and maintenance activities must be implemented earlier than the conventional concept. 10. Permitting and Regulatory Obligations. The new concept allows the Riverview Facility to meet its permit obligations. CONCLUSIONS A new concept of gypsum stack management that allows for early reduction of the watershed areas during the active life of the gypsum stack was introduced. A proven case history that successfully implemented the new concept at the Mosaic Riverview Facility (see Figure 16) was reviewed. The new concept of gypsum stack management can be very effective in terms of gypsum stack closure costs, safety improvements, and environmental protection when the following elements are carefully considered: proper planning and design, maintain strict discipline on benching, proper growth projections and monitoring of consolidation progress, proper approaches on construction sequences, and continuous monitoring and maintenance of the closed areas. 11
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5/10/2013 ( 11 Miles West) 2012 Aerial Photograph of Central Florida Showing Gypsum Stacks Figure 1 4 Mature Stack: Stack reached maximum capacity 5 Closure Stage I: Draining Processed Water from Top of Stack Closure Stage II: Lining/Closure of Top of Stack 6 3 ACTIVE STACK: Raising Stack using Rim Ditch/Upstream Method CONVENTIAL PHOSPHOGYPSUM STACK MANAGEMENT Closure Stage III: ClosingSide Slopes & Perimeter Dikes 7 2 STARTUP: Developing Rim Ditches, Gypsum Dikes & Compartments INCEPTION: Installing Liner, Drain & Perimeter Containment Dikes 1 Closed Stack: Runoff to NPDES outfalls Conventional Phosphogypsum Stack Management Figure 2 8 1
5/10/2013 Gypsum Stack Settling Pond side slope without grass Contaminated runoff Siphon line to Decant Process Water to Cooling Ponds Grassed side slope Cooling Ponds Swale Figure 3 2007 Condition of Side Slopes SOURCE: GOOGLE, INC. UNDER LICENSE BY ARDAMAN & ASSOCIATES, INC. USING GOOGLE EARTH PROFESSIONAL Toe Swale Rim Ditch Active Gypsum Stack Vegetated Side Slopes 2008 Aerial photograph of Riverview Active Stack Figure 4 2
5/10/2013 Gypsum Stack Modified Siphon line & Decant Open Ditch Contaminated runoff Interceptor Ditch Active side slope Clean runoff Closed Side Slope Swale Clean Storm water Runoff to Permitted Outfall Figure 5 2007 The Concept SOURCE: GOOGLE, INC. UNDER LICENSE BY ARDAMAN & ASSOCIATES, INC. USING GOOGLE EARTH PROFESSIONAL Swale to Restore Install Interceptor Ditch Existing Rim Ditch Active Gypsum Stack New Decant System Side Slopes to be Re-Vegetated The Concept SOURCE: GOOGLE, INC. UNDER LICENSE BY ARDAMAN & ASSOCIATES, INC. USING GOOGLE EARTH PROFESSIONAL Figure 6 3
5/10/2013 Typical Stack Cross-section with Side Slope Drains Figure 7 Alternative Decant System Figure 8 4
5/10/2013 Interceptor Ditch Figure 9 Interceptor Ditch SOURCE: GOOGLE, INC. UNDER LICENSE BY ARDAMAN & ASSOCIATES, INC. USING GOOGLE EARTH PROFESSIONAL Interceptor Ditch 2009 Aerial Photograph Showing Completed Interceptor Ditch Figure 10 5
5/10/2013 SOURCE: GOOGLE, INC. UNDER LICENSE BY ARDAMAN & ASSOCIATES, INC. USING GOOGLE EARTH PROFESSIONAL II I III IV V VI VII Figure 11 Side Slope Grading & Re-Vegetation Plan Permitted Outfall SOURCE: GOOGLE, INC. UNDER LICENSE BY ARDAMAN & ASSOCIATES, INC. USING GOOGLE EARTH PROFESSIONAL Clean Storm Water Runoff: Seepage & Contaminated Storm Water Runoff: 2012 Aerial Photograph Showing Completion of the Concept Figure 12 6
5/10/2013 Toe Swale Restoration - Typical Cross Section Figure 13 Photograph of Closed Toe Swale Figure 14 7
5/10/2013 Active Stack Stage I 4 Simultaneous Active / Closure Stage I Active Stack Stage II Closure Stage I 5 Simultaneous Active / Closure Stage II Closure Stage II Mature Stack: Stack reached maximum capacity 6 3 ACTIVE STACK: Raising Stack using Rim Ditch/Upstream Method SMART PHOSPHOGYPSUM STACK MANAGEMENT Final Closure A Drain Top Final Closure B Close Top Final Closure C Close side slope Final Closure Stage 7 2 STARTUP: Developing Rim Ditches, Compartments & Perimeter Ditches INCEPTION: Installing Liner, Drain & Perimeter Containment Dikes 1 Closed Stack: Runoff to NPDES outfalls Smart Gypsum Stack Management System Figure 15 8 Looking South 1/2013 Aerial Photo Shown Completion of Closure CONCEPT Figure 16 8