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SWROA Training May 2013 Potential Retention / Detention Techniques for Surface Mine Sites.

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Presentation on theme: "SWROA Training May 2013 Potential Retention / Detention Techniques for Surface Mine Sites."— Presentation transcript:

1 SWROA Training May 2013 Potential Retention / Detention Techniques for Surface Mine Sites

2 Disclaimer The following presentation was prepared by, and represents the views and opinions of: R. B. (Barry) Doss, PE, PS, MBA President, Doss Engineering, Inc.

3 38CSR2 5.6.a Storm Water Runoff 5.6.a. Each application for a permit shall contain a storm water runoff analysis. Provided, however, an exemption may be considered on a case by case basis for mining operations with permitted acreage less than 50 acres. Furthermore, haulroads, loadouts, and ventilation facilities are excluded from this requirement. The storm water runoff analysis shall include the following:

4 38CSR2 5.6.a Storm Water Runoff 5.6.a.1 An analysis showing the changes in storm runoff caused by the proposed operation(s) using standard engineering and hydrologic practices and assumptions.

5 38CSR2 5.6.a Storm Water Runoff 5.6.a.2. The analysis will evaluate pre- mining, worst case during mining, and post-mining (Phase III standards) conditions. The storm used for the analysis will be the largest required design storm for any sediment control or other water retention structure proposed in the application.

6 38CSR2 5.6.a Storm Water Runoff 5.6.a.2. (cont) The analysis must take into account all allowable operational clearing and grubbing activities. The applicant will establish evaluation points on a case-by case basis depending on site specific conditions including, but not limited to, type of operation and proximity of man-made structures.

7 38CSR2 5.6.a Storm Water Runoff 5.6.a.3. The worst case during mining and post-mining evaluations must show no net increase in peak runoff compared to the pre-mining evaluation.

8 38CSR2 5.6.a Storm Water Runoff 5.6.b. Each application for a permit shall contain a runoff-monitoring plan which shall include, but is not limited to, the installation and maintenance of rain gauges. The plan shall be specific to local conditions. All operations must record daily precipitation and report monitoring results on a monthly basis and any one (1) year, twenty-four (24) storm event or greater must be reported to the Secretary within forty-eight (48) and shall include the results of a permit wide drainage system inspection.

9 38CSR2 5.6.a Storm Water Runoff 5.6.c. Each application for a permit shall contain a sediment retention plan to minimize downstream sediment deposition within the watershed resulting from precipitation events. Sediment retention plans may include, but are not limited to decant ponds, secondary control structures, increased frequency for cleaning out sediment control structures, or other methods approved by the Secretary.

10 Land Disturbance and Man-Made Systems (Includes Surface Mines & Their Drainage Requirements) Can Increase Runoff Volume and Peak Discharge by Removal of Forest Cover and Vegetation Change in Infiltration Rates and Runoff Characteristics Compacted, Impervious, or Semi-Impervious Surfaces Removal of Natural Drainways Replacement w/ Engineered Channels and Drainways Disturbance in Multiple Sub-Watersheds Extended Project Life or Duration (time) Permanent Land Use Change(s)

11 Land Disturbance and Man-Made Systems Historically, Design Concepts Have Favored The Rapid Removal of Storm Water Runoff From, or Around, Disturbed Areas Get and Keep The Water Off The Project Area Usually This Was Accomplished by: Channelization Diversions Drainage Control Designed to Discharge Quickly and Minimize Impounded Volume

12 Land Disturbance and Man-Made Systems Engineered Systems, Without Detention / Retention Controls in Place, Can Result in: Increased Peak Flow, And/or Reduced Time to Peak of Runoff Hydrograph

13 Fundamental Principles of Storm Water Management (All Project Types) Reduce During- & Post-Development Peak Flow Rates to be Equal or Less Than The Pre- Development Runoff Peak Flow Rate First, Utilize All Available and Practicable Measures to Control and/or Reduce Runoff Volume and Runoff Characteristics Then, Control Remaining Quantity of Excess Storm Water Runoff by Temporary Storage Retention, Wet Storage Detention, Dry Storage

14 Fundamental Principles of Storm Water Management

15 Storm Water Runoff Management Why No Net Increase? Reducing Peak Flow & Storing Storm Water Runoff Will Reduce Frequency and Extent of: Downstream Flooding Potential Property Damage Soil Erosion and Scouring Sedimentation and Release of Pollutants Its Also A Requirement For All Surface Mine Permit Applications, and Its Prudent and In The Public Interest

16 Storm Water Runoff Management Why No Net Increase? What Can We Learn From Plaintiffs Attorneys and The Media? Floods Will Continue to Occur and They Will Be Somebodys Fault It Never Rained Like That Around Here Before They Put That Coal Mine In

17 Storm Water Runoff Management Why No Net Increase? There are Tremendous Costs in Defending Litigation, Even If Unfounded There are Tremendous Costs (Public and Private) Involved in Cleaning Up Property Damage Regardless of the Cause Risk of Loss of Life is Unacceptable and Must be Minimized

18 Examples of Flooding and Damage

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24 Storm Water Runoff Management Professional Engineers Role We As Engineers: Must Conduct Thorough and Diligent Reviews Propose Prudent and Adequate Designs, and Only Certify Those Project Plans Which Meet the Requirements of the Regulations Engineers, In The Fulfillment of Their Professional Duties, Shall Hold Paramount the Safety, Health, and Welfare of the Public

25 Measures to Control and Reduce Runoff Volume and Characteristics Reduce Overall Disturbed Acreage Limit Incremental Disturbance by W/S Design Project Features to Realistically Lower Runoff Curve Numbers (CN) Reduce Compaction of Backfill & Regrade Practice Reforestation - FRA Approach Introduce Attenuating Features in Landscape Revegetate Timely Reestablish Native Species and Buffers Reduce Grades and Slopes When Possible Both Channels and Regrade Area

26 Storage of Storm Water Runoff There Are No Magic Bullets The Designer Must Provide Either: Increased Retention Additional Wet Storage From Existing or Modified Structure Delayed Flow Discharge, Outlset Control or, Detention Structures Dry Ponds or Embankments Located On or Below the Project Area All Sites Different, Detailed Modeling Required

27 General Concept of Retention Wet Storage, Similar to Our Sediment Pond

28 General Concept of Retention Staged Discharge and Storm Water Release

29 Typical Surface Mine Sediment Ditch Standard Acre Foot Design

30 Typical Surface Mine Sediment Ditch Decant Proposed at 60% Cleanout Elev

31 Typical Sediment Ditch Barrier Overflow Between Cells at 100% C/E

32 Sediment Ditch Barrier Outlet Control Via Notched Overflow

33 Typical Surface Mine Sediment Pond Standard Acre Foot Design

34 Typically-Sized Sediment Pond Decant Proposed at 60%

35 Pond Embankment Typical Open Channel Spillway

36 Open Channel Embankment Spillway Outlet Control to Increase Retention

37 Over-Sized Sediment Pond Decant Proposed at 40% Cleanout

38 Over-Sized Sediment Pond (150%) Decant Proposed at 40% Cleanout Example: 40 acres of disturbance X ac-ft/ft Requires 5 ac-ft pond that must be cleaned at 60% or 3 ac-ft of accumulated sediment Increase total pond volume by 150% For a 7.5 ac-ft pond, 3 ac-ft equals 40% 2.5 ac-ft storm water storage gained below n/p DEP can approve such designs if included in the SWROA & Section P, and justified with demonstration water quality can be met

39 Over-Sized Sediment Ditch Decant Proposed at 40% Cleanout

40 Example of Downstream Retention Embankment

41 Structure Design Considerations On-Bench Sediment Ditches are Most Common Form of Sediment Control On WV Mine Sites Increasing Ditch Volume or Size Is Not Necessarily Difficult, But Must Be Planned & Coordinated into Mine Plan Increasing Ditch Sizes Can Affect Backfill Storage Volume, May Need to Be Addressed in AOC Model Outlet & Dewatering Controls in Perimeter Sediment Ditches Can Be Difficult to Maintain The True Dip of Seam Outcrop Can Foil the Best Laid Plans

42 Structure Design Considerations Increasing In-Stream Pond Sizes Can Be Effective Form of Retention Topography Is Often Limiting Factor Construction & Maintenance Costs Can Vary Widely, Location Specific Outlet Control by Narrowing Spillways Generally Increases Discharge Velocities Increased Embankment Heights Understand MSHA & Dam Control Regs

43 Structure Design Considerations Detention Structures Work Best In On-Bench Areas, or Flatter Areas Below Project Stream Impacts From Retention / Detention Structures May Require 404 Authorization Can Be NWP 21 Eligible Detention Dams Can Create Wetland Features Wetlands in Mountainous Topography Generally Less Effective Then Ponds at Retention Can Yield Water Quality Benefits

44 Discussion Example SWROA Pond

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47 Discussion Example SWROA Detention Basin

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51 Discussion Example Detention Embankment

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53 Discussion Example SWROA Pond

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55 Discussion Example On-Bench Wildlife Pond

56 Discussion Example On-Bench Wildlife / Agriculture Pond

57 Potential Issues w/ Off-Site Retention / Detention Facilities Potential Problem Areas to Consider During Design Storm Water Quantity Control Facilities Release Timing Safety Maintenance

58 Potential Issues w/ Off-Site Retention / Detention Facilities Release Timing Can Be Critical Structures Are Intended to Reduce Peak Discharge and Increase Flow Duration While This May Be Desired Result for Individual Tributary, Shifting of Peak Flow Time and Duration Can In Some Instances Cause Adverse Effects Downstream May Need to Model Receiving Stream or Main Tributary – Particularly If Discharging into lower Portions of Larger Watersheds

59 Potential Issues w/ Off-Site Retention / Detention Facilities Safety Structures Should Be As Simple As Possible Lessen Chances for Murphys Law and Tampering at Off Site Facilities Evaluate Potential for Unintentional Clogging, Debris Buildup, Blockage Off Site Impounding Structures Can be Attractive Nuisance Consider Signage, Restricted Access, Fencing

60 Potential Issues w/ Off-Site Retention / Detention Facilities Maintenance Attenuating Structures Can Be More Problematic Than Simple Sediment Control Potential for Clogging, Debris Buildup, & Malfunction Can Be Higher Inspection and Monitoring Should Be Accelerated In Early Stages of Use Inlet and Outlet Devices, Particularly Standpipe or Riser Structures, Deteriorate Over Time - May Need Periodic Replacement

61 Comments on SWROA Submissions Include Well-Written Narrative Clearly Explain Assumptions & Sources SedCad Printouts Alone Wont Do It Identify Any Practices & Controls That Were Added During the SWROA Process Be Sure SWROA Plan Matches All Other Applicable SMCRA Permit Sections Take Care in Selecting Worst Case, Can Require More Than One Case Per W/S Propose In-Pit Storage w/ Great Caution

62 Discussion Example - Do You Know What Your W orst Case Will Be?

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65 Discussion Example Post-Mining Case

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67 Discussion Example (or How Many Valley Fills Are In This Picture?

68 Discussion Example In-Pit Storage?

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81 What Can We Learn From Other Activities & Industries?

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89 What Can We Learn From Others? Retention, Retention, Detention …

90 Questions / Comments ?


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