Run-On and Run-Off Control System Plan Neal North Energy Center Monofill

Transcription

1 Run-On and Run-Off Control System Plan Neal North Energy Center Monofill MidAmerican Energy Company, Neal North Energy Center Coal Combustion Residual Rule Compliance October 10, 2016

2 Run-On and Run-Off Control System Plan Neal North Energy Center Monofill Prepared for MidAmerican Energy Company, Neal North Energy Center Coal Combustion Residual Rule Compliance Sergeant Bluff, Iowa October 10, 2016 Prepared by Burns & McDonnell Engineering Company, Inc. Kansas City, Missouri COPYRIGHT 2016 BURNS & McDONNELL ENGINEERING COMPANY, INC.

3 INDEX AND CERTIFICATION MidAmerican Energy Company, Neal North Energy Center Run-On and Run-Off Control System Plan Neal North Energy Center Monofill Chapter Number Chapter Title Report Index Number of Pages 1.0 Introduction Site Hydrology Stormwater Run-On and Run-Off Control System Stormwater Best Management Practices Periodic Assessment and Ammendment Revisions and Updates 1 Appendix A Existing Permit Plans, Attachment 23 (Calculations for Run- On/Run-Off Controls) 25 Appendix B Verification Calculations 7 Certification I hereby certify, as a Professional Engineer in the State of Iowa, that the information in this document was assembled under my direct personal charge. This report is not intended or represented to be suitable for reuse by the MidAmerican Energy Company, Neal North Energy Center or others without specific verification or adaptation by the Engineer. Kira E. Wylam, P.E. Date: 10/10/2016 Kira E. Wylam License Number My license renewal date is December 31, 2016 Pages or sheets covered by this seal: As noted above.

4 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Table of Contents TABLE OF CONTENTS Page No. 1.0 INTRODUCTION Existing Design Document Review Permit Design Calculation - Methodology Plan Requirements SITE HYDROLOGY Site Characteristics Design Storms STORMWATER CONTROL SYSTEMS Run-On Analysis Leachate Collection System Existing Conditions Run-Off Analysis Post-Closure Conditions Run-Off Analysis Intermediate Swales Inner Perimeter Channel Channel Compliance Summary STORMWATER BEST MANAGEMENT PRACTICES PERIODIC ASSESSMENT AND AMMENDMENT REVISIONS AND UPDATES REFERENCES EXISTING PERMIT DOCUMENT PLANS & APPENDIX 4 (DESIGN DRAWINGS FOR POST CLOSURE RUN-OFF CONTROLS) - ACTIVE MONOFILL PORTION CALCULATIONS MidAmerican Energy Company TOC-1 Burns & McDonnell

5 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Table of Contents LIST OF FIGURES Page No. Figure 2-1. Neal North Monofill Extent Figure 2-2. Hydrologic Soil Groups Figure 2-3. Elevations Surrounding Neal North Monofill Figure 2-4. Point Precipitation Location Figure 2-5. NOAA Point Precipitation Frequency Estimates Figure 3-1. Neal North Monofill Drainage Areas Figure 3-2. Neal North - FEMA Floodplain Boundaries Figure 3-3. Neal North Monofill Drainage Areas MidAmerican Energy Company TOC-2 Burns & McDonnell

6 Run-On and Run-Off Control Plan Neal North Energy Center Monofill List of Abbreviations LIST OF ABBREVIATIONS Abbreviation BMP CCR CFR EPA HSG IAC IDNR MEC NOAA RCRA SCS Term/Phrase/Name Best Management Practice Coal Combustion Residual Code of Federal Regulations Environmental Protection Agency Hydrologic Soil Group Iowa Administrative Code Iowa Department of Natural Resources MidAmerican Energy Company National Oceanic and Atmospheric Administration Resource Conservation and Recovery Act Soil Conservation Service TR-55 Technical Release 55 TSS U.S.C. Total Suspended Solids United States Code MidAmerican Energy Company i Burns & McDonnell

7 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Introduction 1.0 INTRODUCTION On April 17, 2015, the Environmental Protection Agency (EPA) issued the final version of the federal Coal Combustion Residual Rule (CCR Rule) to regulate the disposal of coal combustion residual (CCR) materials generated at coal-fired units. The rule is administered as part of the Resource Conservation and Recovery Act [RCRA, 42 United States Code (U.S.C.) 6901 et seq.], using the Subtitle D approach. MidAmerican Energy Company (MEC) is subject to the CCR Rule and as such must develop a Run-On and Run-Off Control System Plan per 40 Code of Federal Regulations (CFR) This report provides and certifies the Run-On and Run-Off Control System Plan for the Neal North Energy Center Landfill located near Sergeant Bluff, Iowa. Run-on controls for the Neal North Energy Center Landfill were designed by MWH, Inc. as part of past permit applications to the State of Iowa. Post-closure run-off controls for the Neal North Energy Center Landfill were designed by MWH, Inc. as part of past permit applications to the State of Iowa. The Run- On and Post-closure Run-Off Control System Plans provided herein are based on review and assessment of those certified drawings and a current analysis of existing conditions based on recently obtained elevation data of the active portion of the landfill. The most recent control plan was developed in 2007 and approved in The applicable section of the 2007 Permit Application, Appendix 2, prepared by MWH, Inc. is included as Appendix A of this document. 1.1 Existing Design Document Review The CCR Rule requires the run-off volume from a 24-hour, 25-year storm from the active portion of the landfill be collected and controlled by run-off control measures, and that a run-on control system be in place. The EPA defines run-on as any rainwater, leachate, or other liquid that drains over land onto any part of a CCR landfill or lateral expansion of a CCR landfill. The EPA defines run-off as any rainwater, leachate, or other liquid that drains over land from any part of a CCR landfill or lateral expansion of a CCR landfill. The drawings depicted in Appendix 2 of the 2007 Permit Application document support compliance with the CCR Rule run-off control system plan requirements, post-closure Permit Design Calculation - Methodology The design calculations in Appendix A for post-closure peak flow in the intermediate swales and flume pipes were performed using generally accepted engineering practices. Due to the 2015 CCR rule requirements, new investigations and calculations were performed for stormwater run-on and run-off of the current conditions of the Neal North Monofill. These calculations MidAmerican Energy Company 1-1 Burns & McDonnell

8 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Introduction were also performed for current conditions using generally accepted engineering practices. The NRCS TR-55 methodology was used, as implemented in the U.S. Army Corps of Engineers HEC-HMS model (USACE, 2010). 1.2 Plan Requirements The Run-On and Run-Off Control System Plans under the CCR Rule must contain the following per (c): Documentation of how the run-on and run-off control systems have been designed and constructed to meet the following requirements: o A run-on control system to prevent flow onto the active portion of the CCR unit during peak discharge from a 24-hour, 25-year storm; and o A run-off control system from the active portion of the CCR unit to collect and control at least the water volume resulting from a 24-hour, 25-year storm. Run-off from the active portion of the CCR unit must be handled in accordance with the surface water requirements under Supporting engineering calculations for the plan. Certification by a qualified professional engineer. The seal certifies that the initial run-on and run-off control system plan provided herein meets the requirements of 40 Code of Federal Regulations There are two relevant parts of the Iowa Administrative Code (IAC) that the CCR unit must adhere to, which are listed below: Chapter 103 for Sanitary Landfills: Coal Combustion Residue (3) c. Surface run-off must be diverted from all active or closed areas, both during the active life of the facility and during the postclosure period. Chapter 113 for Sanitary Landfills for Municipal Solid Waste (8) a. Owners or operators of all MSWLF units must design, construct, and maintain the following: (1) A run-on control system to prevent flow onto the active portion of the landfill during the peak discharge from a 25-year storm; (2) A run-off control system from the active portion of the landfill to collect and control at least the water volume resulting from a 24-hour, 25-year storm. b. Run-off from the active portion of the MSWLF unit must be handled in accordance with paragraph (1) a. MidAmerican Energy Company 1-2 Burns & McDonnell

9 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Site Hydrology 2.0 SITE HYDROLOGY The run-on and run-off control features are to be designed to collect and control the run-off from the 25-year, 24-hour storm event. The methods of determination of the peak flow rates and run-off volumes are based on the Soil Conservation Service (SCS) run-off curve number method (USDA, 1986), to calculate losses, the Rational Method and the TR-55 methodology via HEC-HMS as outlined in the Iowa Stormwater Manual (IDNR, 2009); Manning s equation to calculate channel depths. This section provides an analysis of run-on control, an analysis of existing run-off controls, and a review of the calculations of the run-off controls during the post-closure phase of the Monofill lifespan, which are included in Appendix A. 2.1 Site Characteristics The Monofill encompasses approximately 83 acres in two adjacent parcels and is located approximately 5 miles south of the Sioux City Municipal Airport and approximately 3,500 feet southeast of the Neal North generating station near the east bank of the Missouri River. The active portion of the Monofill is approximately 15 acres. The Monofill is located within Section 30, T87N, R47W in Woodbury County, Iowa. The Monofill site is composed of existing and potential future fill areas. The site is located on the relatively level alluvial plain of the Missouri River. The active fill area, and other landfill cells in their post-closure phase, are the dominant topographic features. Surface drainage ultimately enters the Missouri River either by overland or channelized flow. Run-off is curtailed in many areas because level topography and shallow permeable soils promote significant infiltration to shallow groundwater. Discussion of the surface topographic features and run-off routes from the fill area follows. The extent of the active fill area is shown in Figure 2-1. The site soils belong to hydrologic soil groups (HSG) A, B, C/D, and D (see Figure 2-2). Group A is characterized by having low run-off potential and a high infiltration rate, even when fully wetted. Group B is characterized by having soils with a moderate infiltration rate when thoroughly wetted, consisting chiefly of moderately-deep to deep, moderately-well to well-drained soils, with moderately-fine to moderately-coarse texture. Group C is characterized by having soils with low infiltration rates when thoroughly wetted and consist chiefly of soils with a layer that impedes downward movement of water. Group D is characterized by having soils with a high run-off potential and a very slow infiltration rate when thoroughly wetted, consisting chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a clay pan or clay layer at or near the surface, and shallow soils over nearly impervious material. The C/D group is a mixture of Group C and Group D soils. The hydrologic soil classifications were obtained from the Iowa Geological and Water Survey. MidAmerican Energy Company 2-1 Burns & McDonnell

10 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Site Hydrology A curve number (CN) of 82 was used to determine rainfall losses due to infiltration from the area. The curve number was obtained using guidance from Table 3 in Section 2C-5 of the Iowa Stormwater Manual (IDNR, 2009). The Monofill area is surrounded by drainage channels, beyond them, to the north are capped monofill cells, to the south and east are agricultural row crops and to the west are agricultural row crops and the Missouri River. These surrounding land cover can be seen in Figure 2-1. The elevations in the vicinity of the Monofill are shown in Figure 2-3. This figure shows that the Monofill is at a higher elevation than the surrounding area, with the exception of nearby capped landfills. 2.2 Design Storms The 25-year, 24-hour design storm rainfall depth for the site is 5.14 inches. This value was obtained from the Hydrometeorological Design Studies Center of the National Oceanic and Atmospheric Administration (NOAA) (NOAA, 2016). The point precipitation location is shown in Figure 2-4. The table of rainfall depths for various frequencies and durations is presented in Figure 2-5. MidAmerican Energy Company 2-2 Burns & McDonnell

11 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Site Hydrology Figure 2-1. Neal North Monofill Extent MidAmerican Energy Company 2-3 Burns & McDonnell

12 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Site Hydrology Figure 2-2. Hydrologic Soil Groups MidAmerican Energy Company 2-4 Burns & McDonnell

13 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Site Hydrology Figure 2-3. Elevations Surrounding Neal North Monofill MidAmerican Energy Company 2-5 Burns & McDonnell

14 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Site Hydrology Figure 2-4. Point Precipitation Location Figure 2-5. NOAA Point Precipitation Frequency Estimates MidAmerican Energy Company 2-6 Burns & McDonnell

15 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Stormwater Control Systems 3.0 STORMWATER CONTROL SYSTEMS The following sections describe the use of appropriate engineering calculations to investigate the run-on and run-off systems used at the Neal North Monofill to collect and control the 25-year, 24-hour storm event run-on and run-off. 3.1 Run-On Analysis Run-on channels or ditches intercept off-site drainage and prevent it from running on to the working surface of the landfill. For the Neal North Monofill site, the surrounding topography and drainage channels are such that stormwater drains away from the Monofill site. The drainage area that drains to the perimeter channels is shown in Figure 3-2. Given the drainage channels surrounding the Monofill and the size of the watershed, stormwater will not run onto the active Monofill face during the 25-year, 24-hour event. A HEC-HMS model, using TR-55 methodology was generated, for purposes of this report, to determine conveyance capacity of the conveyance ditches. These conveyance ditches have adequate capacity for the 25-year, 24-hour event. These results are presented in Appendix B. Additionally, as shown in Figure 3-2, the FEMA floodplain data shows the Monofill will not be inundated during a 500-year flood event. MidAmerican Energy Company 3-1 Burns & McDonnell

16 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Stormwater Control Systems Figure 3-1. Neal North Monofill Drainage Areas MidAmerican Energy Company 3-2 Burns & McDonnell

17 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Stormwater Control Systems Figure 3-2. Neal North - FEMA Floodplain Boundaries MidAmerican Energy Company 3-3 Burns & McDonnell

18 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Stormwater Control Systems 3.2 Leachate Collection System The active Neal North Monofill cells 1 and 2 have leachate collection systems. The leachate collection system includes leachate collection media and pipe bedding. 3.3 Existing Conditions Run-Off Analysis Locally, surface water runoff from beyond the perimeter road flows around the base of the Monofill and does not flow over the Monofill. For precipitation that lands on the Monofill, some leaching from the CCR surface will occur. Based on calculations in the 2007 Permit Application, leachate flows can be expected to be over 1,000 cubic feet per day. An analysis of the topography of the active portion of the Monofill and the surrounding drainage areas called for delineating two separate areas. The Monofill topography is shown in an exhibit produced by HGM & Associates (October, 2015) included in Appendix B. The drainage area delineations are shown in Figure 3-3. Stormwater run-off from the outer drainage area flows to perimeter conveyance channels, while run-off from the inner drainage area flows to a diagonally located conveyance channel. The perimeter conveyance channels drain to a detention pond. Outflow from the detention pond flows into another conveyance channel, forming a confluence with the interior drainage channel. Then, both flows discharge into an approximately five-acre slough near the eastern bank of the Missouri River. Using the TR-55 methodology, an analysis was performed on the run-off from the drainage areas, the capacity of the perimeter conveyance channels, and the capacity of the detention pond. The results of the analysis are presented in Appendix B. The analysis shows the perimeter conveyance channels have ample capacity to convey the 25-year, 24-hour storm event. Also according to the analysis, during the 25-year, 24-hour storm event, the detention pond performs by detaining and discharging the flow over its spillway as designed. MidAmerican Energy Company 3-4 Burns & McDonnell

19 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Stormwater Control Systems Figure 3-3. Neal North Monofill Drainage Areas MidAmerican Energy Company 3-5 Burns & McDonnell

20 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Stormwater Control Systems 3.4 Post-Closure Conditions Run-Off Analysis As previously described, surface water flows around the base of the Monofill. There are no calculations provided in the 2007 Permit Application, but it does contain design drawings depicting the post-closure plan. Terraces and interior drainage channels will be constructed as part of the final cover to control erosion and promote controlled run-on and run-off for the Monofill, as indicated in the design plan set (Appendix A). The terraces and drainage channels will be constructed as development of the Monofill approaches final elevations. All erosion control structures in the permit application documents were designed according to a 25-year, 24-hour storm event, and approved by IDNR Intermediate Swales Swales on the Monofill cap will intercept stormwater run-off at intermediate points along the slope face of the landfill cap. Intermediate swales will be placed with a maximum overland flow distance of 200 feet on a varying 10- to 25-percent slope. Each intermediate swale will discharge to the downslope, riprap lined channel located on opposite corners of the covers. The use of the terrace channel will reduce the distance run-off travels over the slope face, resulting in decreased velocity and reduced sediment load. The planned swale locations are shown in the figures included in Appendix A Downslope Rip Rap Lined Channel Intermediate swales will discharge to the downslope channel located at the northwest and southeast corners of the landfill cover. The downslope channel will discharge into another channel which discharges into the natural channel to the east of the cover. The downslope channel locations are shown in the figures in Appendix A Inner Perimeter Channel Inner perimeter channels will collect the flows from the terraced slopes of the post-closure Monofill and discharge to the perimeter conveyance channels. The inner perimeter channels are depicted in Appendix A. 3.5 Channel Compliance Summary The post-closure stormwater management practices, as designed, are discussed in Appendix 2 of the 2009 Permit Application, which has been included as Appendix A. The post-closure channels were sized to convey run-off from the 25-year, 24-hour storm event. Additional analysis, for existing conditions in the active portion of the Monofill are included in Appendix B, as well as calculations for the proposed cover system. The results of these analyses show that the stormwater management designs meet and exceed the CCR Rule requirement to convey run-off from the 25-year storm event. In addition, due to the MidAmerican Energy Company 3-6 Burns & McDonnell

21 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Stormwater Control Systems elevation of the existing Monofill, and further increased elevation of the proposed final Monofill cap, the design meets the 25-year, 24-hour run-on criteria. MidAmerican Energy Company 3-7 Burns & McDonnell

22 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Stormwater Best Management Practices 4.0 STORMWATER BEST MANAGEMENT PRACTICES Stormwater best management practices (BMPs) shall be employed at the site to comply with CFR , which in summary stipulates that a facility shall not cause a discharge of pollutants, dredged material, or fill material to waters of the United States; or cause non-point source pollution of waters of the United States. In addition to the collecting stormwater on the active portion of the Monofill discussed in Section 3.0, drainageways will be maintained or created, as necessary, to control run-on/run-off and to serve as sedimentation basins for potentially eroded material prior to leaving the Monofill site. The drainage channels will be cleaned out, as necessary, to maintain flow conditions. Any recovered erosion materials (CCR) will be placed at the working face of the Monofill, or will be used to repair minor erosion on the Monofill. Vegetation enhances evapotranspiration and reduces erosion, thus playing an important part in surface water control. Channels not requiring riprap shall be prepared for seeding as they are constructed. Final cover shall be prepared for seeding after it is applied. Post-closure, the use of terraces and downdrain channels for stormwater conveyance provides a means to control run-off velocities and reduce sediment transport. MidAmerican Energy Company 4-1 Burns & McDonnell

23 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Periodic Assessment and Ammendment 5.0 PERIODIC ASSESSMENT AND AMMENDMENT MEC must place the initial run-on and run-off control system plan in the CCR Operating Record by October 17, MEC may amend the plan at any time, and is required to do so whenever there is a change in conditions which would substantially affect the written plan in effect. MEC must prepare periodic run-on and run-off control system plans every five years. Preparing the periodic plans may be achieved by reviewing the current plan in effect and amending the plan as required. In all cases, the date for completing the previous plan is the basis for establishing the deadline to complete the subsequent periodic plan. Each periodic plan shall be certified by a qualified professional engineer in the State of Iowa. All amendments and revisions must be placed on the CCR public website within a reasonable amount of time following placement in the facility s CCR Operating Record. A record of revisions made to this document is included in Section 6.0. MidAmerican Energy Company 5-1 Burns & McDonnell

24 Run-On and Run-Off Control Plan Neal North Energy Center Monofill Revisions and Updates 6.0 REVISIONS AND UPDATES Revision Number Date Revisions Made By Whom 0 10/10/2016 Initial Issue Burns & McDonnell MidAmerican Energy Company 6-1 Burns & McDonnell

25 Run-On and Run-Off Control Plan Neal North Energy Center Monofill References 7.0 REFERENCES MWH, on behalf of MidAmerican Energy Company. August, Permit Application for the Coal Combustion Residue Monofill Neal North Generating Facility. Sioux City, Iowa. Permit #97-SPD-12-95P. Geographic Information Systems (GIS Section), Iowa Geological and Water Survey, Iowa Department of Natural Resources. Accessed 3/7/2016. HGM Associates, Inc. October 15, Neal North Monofill Topographic Data Exhibit Iowa Department of Natural Resources Iowa Stormwater Management Manual, Version 3. Manual Iowa Department of Natural Resources. December 21, MidAmerican-Neal North CCR Landfill Permit #97-SPD-12-95P. Iowa Department of Natural Resources. December 29, MidAmerican-Neal North Coal Combustion Residue (CCR) Monofill. Permit #97-SPD-12-95P.National Agriculture Imagery Program, Aerial Photography Field Office (APFO), Farm Service Agency (FSA), United States Department of Agriculture (USDA). Accessed 3/7/2016. National Oceanic & Atmospheric Administration Hydrometeorological Design Studies Center. Accessed 3/7/2016. United States Army Corps of Engineers (USACE). August Hydrologic Modeling System HEC- HMS Version 3.5. U.S. Army Corps of Engineers, Hydrologic Engineering Center: Davis, California. United States Department of Agriculture, Natural Resources Conservation Service. Urban Hydrology for Small Watersheds, Technical Release 55. June (210-VI-TR-55, Second Ed., June 1986) United States Environmental Protection Agency (EPA) Federal Register, Vol. 80. No. 74. April 17, CFR Parts 257 and 261. Page MidAmerican Energy Company 7-1 Burns & McDonnell

26 - EXISTING PERMIT DOCUMENT PLANS & APPENDIX 4 (DESIGN DRAWINGS FOR POST CLOSURE RUN-OFF CONTROLS)

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28 APPENDIX 2 DEVELOPMENT DRAWINGS AND SITE MAPS

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52 - ACTIVE MONOFILL PORTION CALCULATIONS

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54 TIME OF CONCENTRATION (Tc) AND TRAVEL TIME (Tn) WORKSHEET Project Neal North Monofill Computed GAH Date 3/22/2016 Location Rural Iowa Checked Date Sub-bas Main Drainage Area Sheet 1 Of 2 check one: check one: x Tc (Time of Concentration) x Existing Conditions Tt (Travel Time) Future Conditions SHEET FLOW (OVERLAND FLOW) Flow Segment Flow Segment (applicable to Tc only) No. 1 No. 2 1 Surface Description Grass 2 Manning's Roughness Coefficient, n Flow Length (L), ft, (total < 300 ft) Year, 24-Hour Precipitation (P2), in Land Slope (S), ft / ft Compute Tt for Sheet Flow, hr = 0.81 Tt = x (nl) 0.8 P2 0.5 x S 0.4 SHALLOW CONCENTRATED FLOW (SWALE FLOW) 7 Surface Description 8 Flow Length (L), ft 9 Watercourse Slope (S) ft / ft 10 Average Velocity (V), fps 11 Compute Tt for Shallow Flow, hr + = CHANNEL FLOW Tt = L 3600 x V 12 Cross Sectional Flow Area (A), sq. ft Wetted Perimeter (Pw), ft Hydraulic Radius, (R = A / Pw) Channel Slope (S), ft / ft Manning's Roughness Coefficient (n) Compute Velocity, fps 3.04 V = 1.49 x R 2/3 x S 1/2 n 18 Flow Length (L), ft 2, Compute Tt for Channel Flow, hr = 0.23 Tt = L 3600 x V COMPUTE Tc OR Tt 20 Compute Tc or Tt for for Sub-basin (Total Items 6, 11, & 19), hrs = 1.03 TOTAL RUNOFF, RATIONAL METHOD ProjecNeal North Monofill Computed GAH Date 3/22/2016 Locat Rural Iowa Checked Date Sub-bMain Drainage Area Sheet 1 Of 2 C * i (in/hr) ** A (ac) Q=CiA cfs

55 Main_Channel Project Description Friction Method Solve For Manning Formula Normal Depth Input Data Roughness Coefficient Channel Slope ft/ft Left Side Slope 3.00 ft/ft (H:V) Right Side Slope 3.00 ft/ft (H:V) Bottom Width 5.00 ft Discharge ft³/s Results Normal Depth 1.14 ft Flow Area 9.55 ft² Wetted Perimeter ft Hydraulic Radius 0.78 ft Top Width ft Critical Depth 0.58 ft Critical Slope ft/ft Velocity 1.60 ft/s Velocity Head 0.04 ft Specific Energy 1.18 ft Froude Number 0.31 Flow Type Subcritical GVF Input Data Downstream Depth 0.00 ft Length 0.00 ft Number Of Steps 0 GVF Output Data Upstream Depth 0.00 ft Profile Description Profile Headloss 0.00 ft Downstream Velocity Infinity ft/s Upstream Velocity Infinity ft/s Normal Depth 1.14 ft Critical Depth 0.58 ft Channel Slope ft/ft 4/22/ :48:57 AM Bentley Systems, Inc. Haestad Methods Solution Bentley Center FlowMaster V8i (SELECTseries 1) [ ] 27 Siemons Company Drive Suite 200 W Watertown, CT USA Page 1 of 2

56 Main_Channel GVF Output Data Critical Slope ft/ft 4/22/ :48:57 AM Bentley Systems, Inc. Haestad Methods Solution Bentley Center FlowMaster V8i (SELECTseries 1) [ ] 27 Siemons Company Drive Suite 200 W Watertown, CT USA Page 2 of 2

57 TIME OF CONCENTRATION (Tc) AND TRAVEL TIME (Tn) WORKSHEET Project Neal North Monofill Computed GAH Date 3/17/2016 Location Rural Iowa Checked Date Sub-bas Interior Diagonal Area Sheet 2 Of 2 check one: check one: x Tc (Time of Concentration) x Existing Conditions Tt (Travel Time) Future Conditions SHEET FLOW (OVERLAND FLOW) Flow Segment Flow Segment (applicable to Tc only) No. 1 No. 2 1 Surface Description CCR 2 Manning's Roughness Coefficient, n Flow Length (L), ft, (total < 300 ft) Year, 24-Hour Precipitation (P2), in Land Slope (S), ft / ft Compute Tt for Sheet Flow, hr = 0.36 Tt = x (nl) 0.8 P2 0.5 x S 0.4 SHALLOW CONCENTRATED FLOW (SWALE FLOW) 7 Surface Description 8 Flow Length (L), ft 9 Watercourse Slope (S) ft / ft 10 Average Velocity (V), fps 11 Compute Tt for Shallow Flow, hr + = CHANNEL FLOW Tt = L 3600 x V 12 Cross Sectional Flow Area (A), sq. ft. 13 Wetted Perimeter (Pw), ft 14 Hydraulic Radius, (R = A / Pw) 15 Channel Slope (S), ft / ft 16 Manning's Roughness Coefficient (n) 17 Compute Velocity, fps V = 1.49 x R 2/3 x S 1/2 18 Flow Length (L), ft n 19 Compute Tt for Channel Flow, hr + = Tt = L 3600 x V COMPUTE Tc OR Tt 20 Compute Tc or Tt for for Sub-basin (Total Items 6, 11, & 19), hrs = 0.36 TOTAL RUNOFF, RATIONAL METHOD Project Neal North Monofill Computed GAH Date 3/17/2016 LocationRural Iowa Checked Date Sub-bas Interior Diagonal Area Sheet 2 Of 2 C * i (in/hr) ** A (ac) Q=CiA cfs

58 HEC-HMS Results Main Drainage Channel and Detention Pond Area Area (sq mi) Initial Abstraction (in) Curve Number Impervious (%) Main Drainage Area

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