WELSH POWER PLANT ASH LANDFILL. Run-on and Run-off Control System Plan

Transcription

1 WELSH POWER PLANT ASH LANDFILL Run-on and Run-off Control System Plan SEPTEMBER 27, 2016 PREPARED BY: MTG TEXAS FIRM REGISTRATION NUMBER: 354 MTG PROJECT NUMBER:

2 WELSH POWER PLANT - ASH LANDFILL Run-on and Run-off Control System Plan Table of Contents Page 1.0 Introduction Run-on Control Systems Perimeter Grading Conditions Interim and Permanent Perimeter Drainage Systems Summary of Design Requirements & Justifications Run-0ff Control Systems Perimeter Grading Conditions Interim Top Slope Diversion Berms and Swales Permanent Side Slope Terraces, Letdowns Interim and Permanent Perimeter Drainage Systems Interim and Permanent Culvert Systems Permanent Low Water Crossing System Summary of Design Requirements & Justifications Summary of Requirements, Justifications and Conclusions Plan Review and Changes in Welsh Ash Landfill Configuration Professional Engineer Certification 10 Appendix 1: Figures Figure 1 Fly Ash Storage Area Phase I Figure 2 Current Site Development Plan Figure 3 Composite Existing & Proposed Improved Conditions Figure 4 Existing & Proposed Condition - Drainage Area Map Appendix 2: Tables Table 1 Q25 Hydraulic & Hydrological Data Summary Table 2 Q25 Run-on and Run-off Design Justifications Design Justification Calculations Southern Loop Design Justification Calculations Northern Loop Design Calculations Site Development Plan Appendix 3: Plan Review Log Appendix 4: Professional Engineer Certification

3 1.0 Introduction The AEP-SWEPCO Welsh Power Plant has a deed recorded Ash Landfill (also previously known as Fly Ash Storage Area and/or Phase 1 landfill) located in Titus County, Texas. The Welsh Ash Landfill is on record with the Texas Commission on Environmental Quality (TCEQ) as Industrial Solid Waste Registration Number The Welsh Ash Landfill receives bottom ash, economizer ash, and fly ash from Two 528 MW coal fired boilers. The Welsh Power Plant annually produces approximately 150,000 cubic yards of fly ash and 37,000 cubic yards of bottom and economizer ash. Of that amount, approximately 43,500 cubic yards of fly ash and 29,000 cubic yards of bottom ash were deposited in the landfill in Typically, economizer ash is sluiced to the Primary Ash Pond, which must be periodically dredged. The Welsh Ash Landfill is generally operated in two sections. The eastern one-third of the landfill is primarily composed of dredged bottom ash, economizer ash, and possibly fly ash material sluiced to the ash landfill between approximately 1986 and 2000 and currently has limited activity. The contract ash marketer utilizes the western two-thirds of the landfill as a temporary storage and processing area. The ash marketer is contracted to sell all marketable ash material for beneficial reuse in order to extend the life of the landfill. Design Modifications for the Welsh Ash Landfill, complete with run-on and run-off control measures, were submitted to the TCEQ on March 21, 2016, entitled Design Modifications to Fly Ash Storage Area. These design modifications were subsequently authorized by the TCEQ in a letter dated April 25, Federal Regulation Title 40, Part requires the owner or operator of an existing or new landfill or any lateral expansion of a landfill used for Coal Combustion Residuals (CCR) must comply with the following: Design, construct, operate, and maintain: o A run-on control system to prevent flow onto the active portion of the CCR unit during the peak discharge from a 24-hour, 25-year storm. 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 Prepare initial and periodic run-on and run-off control system plans for the CCR unit according to the following timeframes: o For existing CCR landfills, the owner or operator of the CCR unit must prepare the initial run-on and run-off control system plan no later than October 17, Page 1

4 o The owner or operator of the CCR unit must prepare periodic run-on and run-off control system plans every five (5) years. Obtain a certification from a qualified professional engineer stating that the initial and periodic run-on and run-off control system plans meet the requirements of this section. Comply with the recordkeeping requirements specified in (g), the notification requirements specified in (g), and the internet requirements specified in (g). This Run-on and Run-off Control System Plan presents the regulatory-required materials as noted above for the Welsh Ash Landfill. Though design of permanent runon and run-off control measures were prepared for the Welsh Ash Landfill in the previously submitted/approved Design Modification, this Run-on and Run-off Control System Plan addresses a combination of both interim and permanent systems which are hereafter described. Welsh Power Plant personnel will integrate the recordkeeping requirements of (a)(1) and (a)(1) into existing recordkeeping processes and these are, therefore, not addressed in this plan. As the Welsh Ash Landfill is subsequently filled and completed, periodic updates to this Run-on and Run-off Control System Plan will be required. Page 2

5 2.0 Run on Controls Run-on Controls are provided and accomplished for the interim condition of the Welsh Ash Landfill by a combination of perimeter grading conditions and interim/permanent perimeter drainage systems. The design and function of these systems are as follows: 2.1 Perimeter Grading Conditions As shown in Figure 1 Fly Ash Storage Area Phase I (WEPX-88), the Welsh Ash Landfill was constructed with a screen dike on the entire west, north and east sides with drainage culverts located on the north and the southeast areas. A berm of minimal length was constructed on the eastern side of the south boundary with the subsequent extension by an ash berm with truck entrance areas. The net effect of this original construction is a perimeter grading condition that is an average of fifteen feet above the surrounding area. As a result of this perimeter grading condition and the hydraulic and hydrological conditions demonstrated in perimeter drainage systems hereafter, a run-on control system to prevent flow onto the active portion of the CCR unit during the peak discharge from a 24-hour, 25-year storm is in place. 2.2 Interim & Permanent Perimeter Drainage Systems As shown in Figure 2 Current Site Development Plan, the future condition of the Welsh Ash Landfill provides for a perimeter drainage system consisting of varying depth perimeter drainage systems (ditches). These perimeter ditches are designed as both a run-on and run-off control system to prevent flow onto or away from the active portion of the landfill during the peak discharge from a 24-hour, 25-year storm (Design Event). In the interim condition, as shown in Figure 3 Composite Existing & Proposed Improved Conditions and the associated Figure 4 Existing & Proposed Condition - Drainage Area Map, both interim and permanent perimeter drainage systems (ditches) have been provided. Currently the Run-on and Run-off Control System includes permanent components of the perimeter drainage systems along a portion of the east and north east sides of the Welsh Ash Landfill. All other perimeter drainage systems are interim. With one exception, these perimeter ditches are designed to likewise prevent flow onto the active portion of the landfill during the peak discharge from the Design Event. The exception is the existing perimeter ditch along the western side of the Welsh Ash Landfill in Drainage Area 13 (DA-13). This existing perimeter ditch primarily functions to direct run-off from both the western landfill slope and the non-landfill areas west of the ditch to a point at the northwest corner. All runoff collected by this ditch does not come in contact with ash. Page 3

6 2.3 Summary of Design Requirements & Justifications Both Table 1 Q25 Hydraulic & Hydrological Data Summary and Table 2 Q25 Run-on and Run-off Design Justifications, as contained in Appendix 2 (with calculation support) provide a summary of hydraulic and hydrologic of the interim run-on/run-off control system. These analyses demonstrate that, in all instances, both the interim and permanent drainage systems are designed, implemented and shall be maintained to function in addition to the perimeter grading features and, as a result prevent flow onto the active portion of the CCR unit during the peak discharge from a 24-hour, 25-year storm. Page 4

7 3.0 Run 0ff Control Systems Run-off Controls are provided and accomplished for the interim condition of the Welsh Ash Landfill by a combination of perimeter grading conditions and interim/permanent perimeter drainage systems. The design, operation and maintenance of these perimeter drainage systems provide for conveyance of all 24-hour, 25-year storm run-off from within the Welsh Landfill to the Primary Bottom Ash Pond, a management unit designed to accommodate these flows and other process discharges from the Welsh Power Plant. The design and function of these systems are as summarized follows: 3.1 Perimeter Grading Conditions As previously noted, the original construction resulted in a perimeter grading condition that is an average of fifteen feet above the surrounding area. As a result of this perimeter grading condition and the hydraulic and hydrological conditions demonstrated in perimeter drainage systems hereafter, an uncontrolled run-off control system to prevent flow away from the active portion of the CCR unit during the peak discharge from a 24-hour, 25-year storm is in place. 3.2 Interim Top Slope Diversion Berms and Swales Due to proximity to interim perimeter drainage systems, Drainage Areas 01, 03 and 04 (DA-01, DA-03 & DA-04) currently require a top slope diversion. Currently, the interim grading conditions dictate a drainage swale; however, future conditions may suggest a diversion berm or combination berm and swale. As shown in Figure 3 Composite Existing & Proposed Improved Conditions and the associated Figure 4 Existing & Proposed Condition - Drainage Area Map, these swales run along the perimeter top of slope, and are designed with the purpose of preventing run-off from the 24-hour, 25- year storm event down the adjacent, above grade side slopes. 3.3 Permanent Side Slope Terraces and Letdowns Currently the Run-on and Run-off Control System includes permanent components of the Side Slope Terraces and Letdowns along a portion of the east and north east sides of the Welsh Ash Landfill. The full future side slopes of the landfill will extend at a 3H:1V slope to a height of approximately 75-feet above the flowline of the permanent perimeter drainage systems (ditch). Currently the Run-on and Run-off Control System provides for permanent side slopes terraces and letdowns for a portion of this overall slope construction in what is termed a closed condition; e.g., clay stability dikes, clay closure cap, erosion/vegetation soil, side slope terraces, letdowns, and interim top of slope perimeter berm (although it serves no run-on or run-off function) at the north east and south east corners, extended Page 5

8 to a point. As such, the letdowns are only extend to a point approximately 30-feet above the flowline of the permanent perimeter ditch and berms are in place at the top of the slope to prevent runoff that has contacted ash from flow across these closed slopes. In accordance with Figure 2 Current Site Development Plan and associated design, these terraces and letdowns are designed as run-off control systems to accommodate runoff from a 24-hour, 25-year storm (Design Event). 3.4 Interim & Permanent Perimeter Drainage Systems As shown in Figure 2 Current Site Development Plan, the future condition of the Welsh Ash Landfill provides for a perimeter drainage system consisting of varying depth perimeter drainage systems (ditches). These perimeter ditches are designed as both a run-on and run-off control system to prevent flow onto or away from the active portion of the landfill during the peak discharge from a 24-hour, 25-year storm (Design Event). In the interim condition, as shown in Figure 3 Composite Existing & Proposed Improved Conditions and the associated Figure 4 Existing & Proposed Condition - Drainage Area Map, both interim and permanent perimeter drainage systems (ditches) have been provided. Currently the Run-on and Run-off Control System includes permanent components of the perimeter drainage systems along a portion of the east and north east sides of the Welsh Ash Landfill. All other perimeter drainage systems are interim. With one exception, these perimeter ditches are designed to likewise prevent flow onto the active portion of the landfill during the peak discharge from the Design Event. The exception is the existing perimeter ditch along the western side of the Welsh Ash Landfill in Drainage Area 13 (DA-13). This existing perimeter ditch primarily functions to direct run-off from both the western landfill slope and the non-landfill areas west of the ditch to a point at the northwest corner. All runoff collected by this ditch does not come in contact with ash. 3.5 Interim and Permanent Culvert Systems Interim. Two driveways cross the interim southern perimeter drainage systems in support of the contract ash marketing operation located within the western two-thirds of the Welsh Ash Landfill, and requiring interim culvert systems (Note: a third driveway crosses in support of the ash landfill operations in the eastern one-third; however, it is located at a drainage divide and requires no culvert). The driveway culverts in support of contract ash marketing include a single 24-inch diameter culvert at the west driveway and double 24-inch diameter culverts at the east driveway. Each of these driveway culvert crossings were designed for the 25-year, 24 hour storm event. Page 6

9 3.5.2 Permanent. Two HDPE culverts, one 30-inches in diameter and one 36-inches in diameter, are designed to convey in excess of the 25-year, 24-hour storm event from the perimeter ditch at the north east corner of the Welsh Ash Landfill to the Primary Bottom Ash Pond. 3.6 Permanent Low Water Crossing System Both the permanent and interim run-on and run-off designs provide for run-off to be routed through the Bottom Ash Storage Area, shown as Drainage Area 19 (DA-19), via a low water crossing. The Bottom Ash Storage Area functions as a storm water detention area both for interim and permanent configurations. In the interim condition, Drainage Areas 01, 02, 07, 08, 09, and 18 (DA-01, DA-02, DA-07, DA-08, DA-09, and DA-18) are routed to this location via the permanent low water crossing. This low water crossing is comprised of a textured reinforced concrete trapezoidal broadcrest section, 10-feet wide by 2.76 deep with 12H:1V side slopes and a -1.1% slope along the flowline. The crossing is sized and configured for in excess of the 25- year, 24-hour storm event. 3.7 Summary of Design Requirements & Justifications Both Table 1 Q25 Hydraulic & Hydrological Data Summary and Table 2 Q25 Run-on and Run-off Design Justifications (and supporting design calculations), as contained in Appendix 2, provide a summary of hydraulic and hydrologic of the interim run-on/run-off control system. These analyses demonstrate that, in all instances, both the interim and permanent drainage systems are designed, implemented and shall be maintained to function in addition to the perimeter grading features and, as a result, prevent flow onto the active portion of the CCR unit during the peak discharge from a 24-hour, 25-year storm. Page 7

10 4.0 Summary of Requirements, Justifications and Conclusions As previously stated, Federal Regulation Title 40, Part requires the owner or operator of an existing or new landfill or any lateral expansion of a landfill used for Coal Combustion Residuals (CCR) to comply with design, construction, operation, maintenance, certification and recordkeeping requirements that are summarized as follows: Design, construct, operate, and maintain: o A run-on control system to prevent flow onto the active portion of the CCR unit during the peak discharge from a 24-hour, 25-year storm. 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 Prepare initial and periodic run-on and run-off control system plans for the CCR unit according to the following timeframes: o For existing CCR landfills, the owner or operator of the CCR unit must prepare the initial run-on and run-off control system plan no later than October 17, o The owner or operator of the CCR unit must prepare periodic run-on and run-off control system plans every five (5) years. Obtain a certification from a qualified professional engineer stating that the initial and periodic run-on and run-off control system plans meet the requirements of this section. Comply with the recordkeeping requirements specified in (g), the notification requirements specified in (g), and the internet requirements specified in (g). Welsh Power Plant personnel will integrate the recordkeeping requirements of (a)(1) and (a)(1) into existing recordkeeping processes and these are, therefore, not addressed in this plan. Both Table 1 Q25 Hydraulic & Hydrological Data Summary and Table 2 Q25 Run-on and Run-off Design Justifications, as contained in Appendix 2, provide a summary of hydraulic and hydrologic of the interim run-on control system. These analyses demonstrate that, in all instances, both the interim and constructed permanent drainage systems are designed, implemented and shall be maintained to function in addition to the perimeter grading features and, as a result, prevent flow onto the active portion of the CCR unit during the peak discharge from a 24-hour, 25-year storm. Page 8

11 5.0 Plan Review and Changes in Welsh Ash Landfill Configuration Landfill Owner and/or Operator will review and evaluate this Plan every five (5) years from initial plan preparation and when there are changes in the facility design, construction, operation, or maintenance that materially affect the facility s potential for run-on and run-off control. Amendments to the Plan made to address changes of this nature are referred to as technical or major amendments, and must be certified by a P.E.. Non-technical amendments can be performed by the facility owner and/or operator. Non-technical amendments include the following: Technical and administrative amendments to the Plan will be documented on the Plan Review Log. Owner/Operator will make the necessary revisions to the Plan as soon as possible, but no later than six months after the change occurs. The Plan must be implemented as soon as possible following a technical amendment, but no later than six months from the date of the amendment. The Designated Person is responsible for initiating and coordinating revisions to the SPCC Plan. Scheduled reviews and Plan amendments will be recorded in the Plan Review Log provided in Appendix 2. The log will be completed even if no amendment is made to the Plan as a result of the review. Page 9

12 6.0 Professional Engineer Certification The original plan and all reviews and amended plans must obtain certification from a qualified professional engineer stating that the initial and periodic run-on and run-off control system plans meet the requirements 40 CFR 257. This certification in no way relieves the owner or operator of the facility of his/her duty to fully implement this Plan. The Profession Engineer Certification page is provided in Appendix 4. Page 10

13 Appendix 1: Figures Figure 1 Fly Ash Storage Area Phase I Figure 2 Current Site Development Plan Figure 3 Composite Existing & Proposed Improved Conditions Figure 4 Existing & Proposed Condition - Drainage Area Map

14 Figure 1 Fly Ash Storage Area Phase I (WEPX 88)

15 Figure 2 Current Site Development Plan

16 Figure 3 Composite Existing & Proposed Improved Conditions

17 Figure 4 Existing & Proposed Condition Drainage Area Map

18 Appendix 2: Tables Table 1 Q25 Hydraulic & Hydrological Data Summary Table 2 Q25 Run-on and Run-off Design Justifications* * With Backup Hydrological & Hydraulic Study

19 Table 1 Q25 Hydraulic & Hydrological Data Summary

20 Table 2 Q25 Run on and Run off Design Justifications

21 DESIGN JUSTIFICATION CALCULATIONS SOUTHERN LOOP

22 DESIGN JUSTIFICATION - SECTION S-01 PROJECT: WELSH ASH LANDFILL RUN-ON & RUN-OFF CONTROL PLAN HYDROLOGIC REPORT DEVELOPED UNIVERSAL RATIONAL HYDROGRAPH Q(PEAK) = C*I*A 25 YEAR STORM FREQUENCY BASIN IDENTIFIER SECTION S-01 DISCHARGES INTO WELSH ASH LANDFILL BASIN AREA = 4.58 ACRES RUNOFF COEFF. = 0.50 RAINFALL INT. = 8.94 IN/HR TIME OF CONC. = MINUTES TIME RUNOFF (MIN) (CFS) PEAK FLOW = CFS TIME TO PEAK = MIN TOTAL VOLUME = CU FT

23 DESIGN JUSTIFICATION - SECTION S-01 (CONT) S-01 DITCH: 0.86% V-DITCH, 3:1 SIDES, 0.75-FEET MINIMUM DEPTH MANNING N VALUE: 0.03 (GRASSED CONSERVATIVE) SOLVE FOR NORMAL DEPTH = 0.59-FEET, MEETS Q25 REQUIREMENT* * Bentley FlowMaster V8i Triangular Channel Analysis

24 DESIGN JUSTIFICATION - SECTION S-02 PROJECT: WELSH ASH LANDFILL RUN-ON & RUN-OFF CONTROL PLAN HYDROLOGIC REPORT DEVELOPED UNIVERSAL RATIONAL HYDROGRAPH Q(PEAK) = C*I*A 25 YEAR STORM FREQUENCY BASIN IDENTIFIER SECTION S-02 DISCHARGES INTO WELSH ASH LANDFILL BASIN AREA = 5.00 ACRES RUNOFF COEFF. = 0.50 RAINFALL INT. = 8.94 IN/HR TIME OF CONC. = MINUTES TIME RUNOFF (MIN) (CFS) PEAK FLOW = CFS TIME TO PEAK = MIN TOTAL VOLUME = CU FT

25 DESIGN JUSTIFICATION - SECTION S-02 (CONT) S-02 DITCH: 0.3 % V-DITCH, 3:1 SIDES, 5-FEET MIN. DEPTH MANNING N VALUE: 0.03 (GRASSED CONSERVATIVE) SOLVE FOR NORMAL DEPTH = 0.74-FEET, MEETS Q-25 REQUIREMENT* * Bentley FlowMaster V8i Triangular Channel Analysis S-02 CULVERT: 70 X 24" DIA HDPE CULVERT, 5 MAX HW SOLVE FOR DISCHARGE CAPACITY = CFS, MEETS Q-25 REQUIREMENT* * Bentley CulvertMaster Culvert Analysis

26 DESIGN JUSTIFICATION - SECTION S-03 PROJECT: WELSH ASH LANDFILL RUN-ON & RUN-OFF CONTROL PLAN HYDROLOGIC REPORT DEVELOPED UNIVERSAL RATIONAL HYDROGRAPH Q(PEAK) = C*I*A 25 YEAR STORM FREQUENCY BASIN IDENTIFIER SECTION S-03 DISCHARGES INTO WELSH ASH LANDFILL BASIN AREA = 5.55 ACRES RUNOFF COEFF. = 0.50 RAINFALL INT. = 8.44 IN/HR TIME OF CONC. = MINUTES TIME RUNOFF (MIN) (CFS) PEAK FLOW = CFS TIME TO PEAK = MIN TOTAL VOLUME = CU FT

27 DESIGN JUSTIFICATION - SECTION S-03 (CONT) S-03 DITCH: 0.3% V-DITCH, 3:1 SIDES, 2.28-FEET MIN. DEPTH MANNING N VALUE: 0.03 (GRASSED CONSERVATIVE) SOLVE FOR NORMAL DEPTH = 0.75-FEET, MEETS Q-25 REQUIREMENT* * Bentley FlowMaster V8i Triangular Channel Analysis S-03 CULVERT: 2-60 LONG X 24" DIA HDPE CULVERT, 2.28 MAX HW SOLVE FOR DISCHARGE CAPACITY = CFS, MEETS Q-25 REQUIREMENT* * Bentley CulvertMaster Culvert Analysis

28 DESIGN JUSTIFICATION - SECTION S-04 PROJECT: WELSH ASH LANDFILL RUN-ON & RUN-OFF CONTROL PLAN HYDROLOGIC REPORT DEVELOPED UNIVERSAL RATIONAL HYDROGRAPH Q(PEAK) = C*I*A 25 YEAR STORM FREQUENCY BASIN IDENTIFIER SECTION S-04 DISCHARGES INTO WELSH ASH LANDFILL BASIN AREA = ACRES RUNOFF COEFF. = 0.50 RAINFALL INT. = 7.47 IN/HR TIME OF CONC. = MINUTES TIME RUNOFF (MIN) (CFS) PEAK FLOW = CFS TIME TO PEAK = MIN TOTAL VOLUME = CU FT

29 DESIGN JUSTIFICATION - SECTION S-04 (CONT) S-04 DITCH: 0.3% V-DITCH, 3:1 SIDES, 2.55-FEET MIN. DEPTH MANNING N VALUE: 0.03 (GRASSED CONSERVATIVE) SOLVE FOR NORMAL DEPTH = 1.12-FEET, MEETS Q-25 REQUIREMENT* * Bentley FlowMaster V8i Triangular Channel Analysis S-04 LOW WATER CROSSING: 1.1%,11.8L/12.6R:1, 10' CHANNEL, 2.76-FEET MIN. DEPTH MANNING N VALUE: 0.02 (ROUGHENED CONCRETE) SOLVE FOR NORMAL DEPTH = 0.22-FEET, MEETS Q-25 REQUIREMENT* * Bentley FlowMaster V8i Trapezoidal Channel Analysis

30 DESIGN JUSTIFICATION - SECTION S-05 PROJECT: WELSH ASH LANDFILL RUN-ON & RUN-OFF CONTROL PLAN HYDROLOGIC REPORT DEVELOPED UNIVERSAL RATIONAL HYDROGRAPH Q(PEAK) = C*I*A 25 YEAR STORM FREQUENCY BASIN IDENTIFIER SECTION S-05 DISCHARGES INTO WELSH ASH LANDFILL BASIN AREA = ACRES RUNOFF COEFF. = 0.50 RAINFALL INT. = 7.47 IN/HR TIME OF CONC. = MINUTES TIME RUNOFF (MIN) (CFS) PEAK FLOW = CFS TIME TO PEAK = MIN TOTAL VOLUME = CU FT

31 DESIGN JUSTIFICATION - SECTION S-05 S-05 CHANNEL: 5' CHANNEL, 1.48%, 3:1 SIDES, 1.2-FEET MIN. DEPTH MANNING N VALUE: 0.03 (GRASS - CONSERVATIVE) SOLVE FOR NORMAL DEPTH = 0.39-FEET, MEETS Q-25 REQUIREMENT* * Bentley FlowMaster V8i Trapezoidal Channel Analysis

32 DESIGN JUSTIFICATION - SECTION S-06 S-06 DETENTION: ATTENUATION OF Q-25 FLOWS SEE ANALYSIS BELOW HYDROLOGIC REPORT - SUMMARY OF PEAK FLOW RATES BASIN: BOTTOM ASH POND ID: WELSH ASH LANDFILL AREA = AVERAGE BASIN SLOPE = 0.77 HYDRAULIC LENGTH = TIME OF CONCENTRATION = BASIN C-FACTOR = 0.55 Q(PEAK) = C*I*A 25 YEAR STORM FREQUENCY BASIN IDENTIFIER BOTTOM ASH POND DISCHARGES INTO WELSH ASH LANDFILL BASIN AREA = ACRES RUNOFF COEFF. = 0.55 RAINFALL INT. = 0.93 IN/HR TIME OF CONC. = MINUTES TIME RUNOFF (MIN) (CFS) PEAK FLOW = CFS TIME TO PEAK = MIN TOTAL VOLUME = CU FT

33 DESIGN JUSTIFICATION - SECTION S-06 (CONT) HYDROLOGIC REPORT STAGE/DISCHARGE SUMMARY POND: BOTTOM ASH POND - AVERAGE AVAILABLE STORAGE =USER DEFINED OUTLET DISCHARGE 1) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q 23.91

34 DESIGN JUSTIFICATION - SECTION S-06 (CONT) HYDROLOGIC REPORT - STAGE, STORAGE, AND DISCHARGE POND: BOTTOM ASH POND - AVERAGE AVAILABLE STORAGE ELEV STORAGE OUTFLOW 2S/T+O (CU.FT.) (CFS) (CFS)

35 DESIGN JUSTIFICATION - SECTION S-06 (CONT) HYDROGRAPH RESERVOIR ROUTING POND: Bottom Ash Pond T I1 I2 2S1/T O1 2S2/T+O2 O2 2S2/T YEAR STORM FREQUENCY TIME TO PEAK = HOURS MAXIMUM OUTFLOW = CFS MAXIMUM STORAGE = CU FT MAXIMUM ELEVATION = FT INFLOW VOLUME = CU FT OUTFLOW VOLUME = CU FT

36 HYDROLOGIC REPORT FOR BOTTOM ASH POND SUMMARY OF PEAK 25-YEAR FLOW RATE FREQ PRE-DEVELOPED POST-DEVELOP POND ROUTED FLOW FLOW ELEVATION STORAGE OUTFLOW (yr) (c.f.s.) (c.f.s.) (ft.) (cu.ft.) (c.f.s) * NOTE: 25 YEAR STORM FREQUENCY IS ATTENUATED BY 49% AND THE THE TIME TO PEAK IS DELAYED BY 12 HOURS, ESSENTIALLY MAKING RUNOFF FROM THIS AREA NON-IMPACTING TO THE SYSTEM STORM WATER MANAGEMENT SYSTEM AT RETURN TO SAME. THEREFORE THESE FLOWS ARE NOT INCLUDED IN THE BALANCE OF ANALYSIS.

37 DESIGN JUSTIFICATION - SECTION S-07 PROJECT: WELSH ASH LANDFILL RUN-ON & RUN-OFF CONTROL PLAN HYDROLOGIC REPORT DEVELOPED UNIVERSAL RATIONAL HYDROGRAPH Q(PEAK) = C*I*A 25 YEAR STORM FREQUENCY BASIN IDENTIFIER SECTION S-07 DISCHARGES INTO WELSH ASH LANDFILL BASIN AREA = 0.54 ACRES RUNOFF COEFF. = 0.50 RAINFALL INT. = 8.94 IN/HR TIME OF CONC. = MINUTES TIME RUNOFF (MIN) (CFS) PEAK FLOW = TIME TO PEAK = 2.41 CFS MIN TOTAL VOLUME = CU FT

38 DESIGN JUSTIFICATION - SECTION S-07 (CONT) S-07 DITCH: 0.3% V-DITCH, 2.5:1 SIDES, 1.78-FEET MIN. DEPTH MANNING N VALUE: 0.03 (GRASS - CONSERVATIVE) SOLVE FOR NORMAL DEPTH = 0.35-FEET, MEETS Q-25 REQUIREMENT* * Bentley FlowMaster V8i Triangular Channel Analysis

39 DESIGN JUSTIFICATION - SECTION S-08 PROJECT: WELSH ASH LANDFILL RUN-ON & RUN-OFF CONTROL PLAN HYDROLOGIC REPORT DEVELOPED UNIVERSAL RATIONAL HYDROGRAPH Q(PEAK) = C*I*A 25 YEAR STORM FREQUENCY BASIN IDENTIFIER SECTION S-08 DISCHARGES INTO WELSH ASH LANDFILL BASIN AREA = 5.03 ACRES RUNOFF COEFF. = 0.75 RAINFALL INT. = 8.94 IN/HR TIME OF CONC. = MINUTES TIME RUNOFF (MIN) (CFS) PEAK FLOW = CFS TIME TO PEAK = MIN TOTAL VOLUME = CU FT

40 DESIGN JUSTIFICATION - SECTION S-08 (CONT) S-08 CHANNEL: 0.61% - 5' CHANNEL, 3:1 SIDES, 0.51-FEET MIN. DEPTH MANNING N VALUE: 0.03 (GRASS - CONSERVATIVE) SOLVE FOR NORMAL DEPTH = FEET, MEETS Q-25 REQUIREMENT* * Bentley FlowMaster V8i Trapezoidal Channel Analysis

41 DESIGN JUSTIFICATION - SECTION S-09 PROJECT: WELSH ASH LANDFILL RUN-ON & RUN-OFF CONTROL PLAN HYDROLOGIC REPORT DEVELOPED UNIVERSAL RATIONAL HYDROGRAPH Q(PEAK) = C*I*A 25 YEAR STORM FREQUENCY BASIN IDENTIFIER SECTION S-09 DISCHARGES INTO WELSH ASH LANDFILL BASIN AREA = 6.26 ACRES RUNOFF COEFF. = 0.69 RAINFALL INT. = 8.44 IN/HR TIME OF CONC. = MINUTES TIME RUNOFF (MIN) (CFS) PEAK FLOW = CFS TIME TO PEAK = MIN TOTAL VOLUME = CU FT

42 DESIGN JUSTIFICATION - SECTION S-09 (CONT) S-09 DITCH:.3% V-DITCH, 3:1 SIDES, 5.84-FEET MIN. DEPTH MANNING N VALUE: 0.03 (GRASS - CONSERVATIVE) SOLVE FOR NORMAL DEPTH = 0.89-FEET, MEETS Q-25 REQUIREMENT* * Bentley FlowMaster V8i Triangular Channel Analysis

43 DESIGN JUSTIFICATION - SECTION S-10 PROJECT: WELSH ASH LANDFILL RUN-ON & RUN-OFF CONTROL PLAN HYDROLOGIC REPORT DEVELOPED UNIVERSAL RATIONAL HYDROGRAPH Q(PEAK) = C*I*A 25 YEAR STORM FREQUENCY BASIN IDENTIFIER SECTION S-10 DISCHARGES INTO WELSH ASH LANDFILL BASIN AREA = 8.05 ACRES RUNOFF COEFF. = 0.63 RAINFALL INT. = 7.47 IN/HR TIME OF CONC. = MINUTES TIME RUNOFF (MIN) (CFS) PEAK FLOW = CFS TIME TO PEAK = MIN TOTAL VOLUME = CU FT

44 DESIGN JUSTIFICATION - SECTION S-10 (CONT) S-10 DITCH:.3% V-DITCH, 3:1 SIDES, 6.22-FEET MIN. DEPTH MANNING N VALUE: 0.03 (GRASS - CONSERVATIVE) SOLVE FOR NORMAL DEPTH = 0.90-FEET, MEETS Q-25 REQUIREMENT* * Bentley FlowMaster V8i Triangular Channel Analysis

45 DESIGN JUSTIFICATION CALCULATIONS NORTHERN LOOP

46 DESIGN JUSTIFICATION - SECTION N-01 PROJECT: WELSH ASH LANDFILL RUN-ON & RUN-OFF CONTROL PLAN HYDROLOGIC REPORT DEVELOPED UNIVERSAL RATIONAL HYDROGRAPH Q(PEAK) = C*I*A 25 YEAR STORM FREQUENCY BASIN IDENTIFIER N-01 DISCHARGES INTO WELSH ASH LANDFILL BASIN AREA = 1.52 ACRES RUNOFF COEFF. = 0.50 RAINFALL INT. = 8.94 IN/HR TIME OF CONC. = MINUTES TIME RUNOFF (MIN) (CFS) PEAK FLOW = 6.79 CFS TIME TO PEAK = MIN TOTAL VOLUME = CU FT

47 DESIGN JUSTIFICATION - SECTION N-01 (CONT) N-01 DITCH: 0.5% (MIN) V-DITCH, 11.83R/3L:1, 7.22-FEET MIN. DEPTH MANNING N VALUE: 0.03 (GRASS - CONSERVATIVE) SOLVE FOR NORMAL DEPTH = 0.30-FEET, MEETS Q-25 REQUIREMENT* * Bentley FlowMaster V8i Triangular Channel Analysis

48 DESIGN JUSTIFICATION - SECTION N-02 PROJECT: WELSH ASH LANDFILL RUN-ON & RUN-OFF CONTROL PLAN HYDROLOGIC REPORT DEVELOPED UNIVERSAL RATIONAL HYDROGRAPH Q(PEAK) = C*I*A 25 YEAR STORM FREQUENCY BASIN IDENTIFIER N-02 DISCHARGES INTO WELSH ASH LANDFILL BASIN AREA = 2.99 ACRES RUNOFF COEFF. = 0.50 RAINFALL INT. = 8.94 IN/HR TIME OF CONC. = MINUTES TIME RUNOFF (MIN) (CFS) PEAK FLOW = CFS TIME TO PEAK = MIN TOTAL VOLUME = CU FT

49 DESIGN JUSTIFICATION - SECTION N-02 (CONT) N-02 DITCH: 1.08% (AVG) V-DITCH, 3:1 SIDES, 1-FEET MIN. DEPTH MANNING N VALUE: 0.03 (GRASS - CONSERVATIVE) SOLVE FOR NORMAL DEPTH = 0.48-FEET, MEETS Q-25 REQUIREMENT* * Bentley FlowMaster V8i Triangular Channel Analysis

50 DESIGN JUSTIFICATION - SECTION N-03 PROJECT: WELSH ASH LANDFILL RUN-ON & RUN-OFF CONTROL PLAN HYDROLOGIC REPORT DEVELOPED UNIVERSAL RATIONAL HYDROGRAPH Q(PEAK) = C*I*A 25 YEAR STORM FREQUENCY BASIN IDENTIFIER N-03 DISCHARGES INTO WELSH ASH LANDFILL BASIN AREA = ACRES RUNOFF COEFF. = 0.50 RAINFALL INT. = 8.13 IN/HR TIME OF CONC. = MINUTES TIME RUNOFF (MIN) (CFS) PEAK FLOW = CFS TIME TO PEAK = MIN TOTAL VOLUME = CU FT

51 DESIGN JUSTIFICATION - SECTION N-03 (CONT) N-03 DITCH: 0.27% (MIN) 25' CHANNEL, 3:1 SIDES, 3-FEET MIN. DEPTH MANNING N VALUE: 0.03 (GRASS - CONSERVATIVE) SOLVE FOR NORMAL DEPTH = 0.27-FEET, MEETS Q-25 REQUIREMENT* * Bentley FlowMaster V8i Triangular Channel Analysis

52 DESIGN JUSTIFICATION - SECTION N-04 PROJECT: WELSH ASH LANDFILL RUN-ON & RUN-OFF CONTROL PLAN HYDROLOGIC REPORT DEVELOPED UNIVERSAL RATIONAL HYDROGRAPH Q(PEAK) = C*I*A 25 YEAR STORM FREQUENCY BASIN IDENTIFIER N-04 DISCHARGES INTO WELSH ASH LANDFILL BASIN AREA = ACRES RUNOFF COEFF. = 0.58 RAINFALL INT. = 7.47 IN/HR TIME OF CONC. = MINUTES TIME RUNOFF (MIN) (CFS) PEAK FLOW = CFS TIME TO PEAK = MIN TOTAL VOLUME = CU FT

53 DESIGN JUSTIFICATION - SECTION N-04 (CONT) N-04 DITCH: 0.3% V-DITCH, 3:1 SIDES, 1.96 FEET MIN. DEPTH MANNING N VALUE: 0.03 (GRASS - CONSERVATIVE) SOLVE FOR NORMAL DEPTH = 1.08-FEET, MEETS Q-25 REQUIREMENT* * Bentley FlowMaster V8i Triangular Channel Analysis

54 DESIGN JUSTIFICATION - SECTION N-05 N-05 CULVERTS/DETENTION: ATTENUATION OF Q-25 FLOWS SEE ANALYSIS BELOW PROJECT: WELSH ASH LANDFILL RUN-ON & RUN-OFF CONTROL PLAN HYDROLOGIC REPORT UNIVERSAL RATIONAL HYDROGRAPH Q(PEAK) = C*I*A AREA = AVERAGE BASIN SLOPE = 1.60 HYDRAULIC LENGTH = TIME OF CONCENTRATION = BASIN CURVE NUMBER = YEAR STORM FREQUENCY BASIN IDENTIFIER N-05 COMBINED NORTH & SOUTH POND: PERIMETER DITCH/CHANNEL SYSTEM DISCHARGES INTO WELSH PRIMARY ASH POND TIME RUNOFF (MIN) (CFS) PEAK FLOW = CFS TIME TO PEAK = MIN TOTAL VOLUME = CU FT

55 DESIGN JUSTIFICATION - SECTION N-05 (CONT) HYDROLOGIC REPORT STAGE/DISCHARGE POND: PERIMETER DITCH/CHANNEL SYSTEM =USER DEFINED 1) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q ) Q

56 DESIGN JUSTIFICATION - SECTION N-05 (CONT) HYDROLOGIC REPORT - STAGE, STORAGE, AND DISCHARGE POND: PERIMETER DITCH/CHANNEL SYSTEM ELEV STORAGE OUTFLOW 2S/T+O (CU.FT.) (CFS) (CFS)

57 DESIGN JUSTIFICATION - SECTION N-05 (CONT) HYDROGRAPH RESERVOIR ROUTING POND: PERIMETER DITCH/CHANNEL SYSTEM T I1 I2 2S1/T O1 2S2/T+O2 O2 2S2/T YEAR STORM FREQUENCY TIME TO PEAK = 0.38 HOURS MAXIMUM OUTFLOW = CFS MAXIMUM STORAGE = CU FT MAXIMUM ELEVATION = FT INFLOW VOLUME = CU FT OUTFLOW VOLUME = CU FT

58 HYDROLOGIC REPORT FOR COMBINED NORTH & SOUTH SUMMARY OF PEAK FLOW RATES FREQ PRE-DEVELOPED POST-DEVELOP POND ROUTED FLOW FLOW ELEVATION STORAGE OUTFLOW (yr) (c.f.s.) (c.f.s.) (ft.) (cu.ft.) (c.f.s) * NOTE: 25 YEAR STORM FREQUENCY IS ATTENUATED BY 29% AND THE THE CULVERTS CARRY THE CAPACITY WITH THIS ATTENTUATION. OUTLET CULVERTS: 429' OF 30" & 36" HDPE CULVERTS, MAX HEIGHT 5.3-FT OPERATE AS DETENTION - MAX WATER Q25: FT PEAK FLOW RATE FOR Q25: CFS OPERATE AS DETENTION - MAX Q100: FT PEAK FLOW RATE FOR Q100: CFS MAXIMUM DISCHARGE CAPACITY: CFS MAXIMUM ELEVATION: FT TIME TO PEAK: 0.38 HOURS* * NOTE: TIME TO PEAK FOR THE 100 YEAR STORM AT N-06 IS 0.38 HOURS. THE TIME TO PEAK FOR THE 100 YEAR STORM OF THE BOTTOM ASH POND IS 12 HOURS AND THUS IS NOT INCLUDED IN THIS ANALYSIS.

59 DESIGN CALCULATIONS PREPARED FOR TCEQ NOR UPDATE WELSH ASH LANDFILL SITE DEVELOPMENT PLAN

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67 Appendix 3: Plan Review Log

68 Plan Review and Changes in Facility Configuration Scheduled reviews and Plan amendments shall be recorded in the Plan Review Log below. This log must be completed even if no amendment is made to the Plan as a result of the review.

69 Appendix 4: Professional Engineer Certification

70 Professional Engineer Certification Page The undersigned licensed Professional Engineer (P.E.) attests that this Run-on and Run-off Control Plan has been prepared, reviewed, and/or revised in accordance with good engineering practice, including consideration of applicable industry standards and the requirements of 40 CFR 257. This certification in no way relieves the owner or operator of the facility of his/her duty to fully implement this Plan. Engineer: Registration Number: State: Date: Robert H. Murray, P.E. _59111 Texas September 27, 2016 P.E. certification is required for the original Plan and Plan reviews and amendments.