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SWROA TrainingMay 2013
Potential Retention / Detention Techniques for Surface Mine Sites
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.
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:
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.
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.
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.
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.
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.
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.
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)
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
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
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
Fundamental Principles of Storm Water Management
Storm Water Runoff ManagementWhy 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
It’s Also A Requirement For All Surface Mine Permit Applications, and
It’s Prudent and In The Public Interest
Storm Water Runoff ManagementWhy No Net Increase?
What Can We Learn From Plaintiff’s Attorneys and The Media? Floods Will Continue to Occur and They Will
Be Somebody’s Fault It Never Rained Like That Around Here Before
They Put That Coal Mine In
Storm Water Runoff ManagementWhy 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
Examples of Flooding and Damage
Examples of Flooding and Damage
Examples of Flooding and Damage
Examples of Flooding and Damage
Examples of Flooding and Damage
Examples of Flooding and Damage
Storm Water Runoff ManagementProfessional Engineer’s 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
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
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
General Concept of Retention
Wet Storage, Similar to Our Sediment Pond
General Concept of Retention
Staged Discharge and Storm Water Release
Typical Surface Mine Sediment DitchStandard 0.125 Acre Foot Design
Typical Surface Mine Sediment DitchDecant Proposed at 60% Cleanout Elev
Typical Sediment Ditch BarrierOverflow Between Cells at 100% C/E
Sediment Ditch BarrierOutlet Control Via Notched Overflow
Typical Surface Mine Sediment PondStandard 0.125 Acre Foot Design
Typically-Sized Sediment PondDecant Proposed at 60%
Pond EmbankmentTypical Open Channel Spillway
Open Channel Embankment SpillwayOutlet Control to Increase Retention
Over-Sized Sediment PondDecant Proposed at 40% Cleanout
Over-Sized Sediment Pond (150%)Decant Proposed at 40% Cleanout Example:
40 acres of disturbance X 0.125 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
Over-Sized Sediment DitchDecant Proposed at 40% Cleanout
Example of Downstream Retention Embankment
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
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
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
Discussion ExampleSWROA Pond
Discussion ExampleSWROA Pond
Discussion ExampleSWROA Pond
Discussion ExampleSWROA Detention Basin
Discussion ExampleSWROA Detention Basin
Discussion ExampleSWROA Detention Basin
Discussion ExampleSWROA Detention Basin
Discussion ExampleDetention Embankment
Discussion ExampleDetention Embankment
Discussion ExampleSWROA Pond
Discussion ExampleSWROA Pond
Discussion ExampleOn-Bench Wildlife Pond
Discussion ExampleOn-Bench Wildlife / Agriculture Pond
Potential Issues w/ Off-SiteRetention / Detention Facilities
Potential Problem Areas to Consider During Design Storm Water Quantity Control Facilities Release Timing Safety Maintenance
Potential Issues w/ Off-SiteRetention / 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
Potential Issues w/ Off-SiteRetention / Detention Facilities
Safety Structures Should Be As Simple As Possible
Lessen Chances for Murphy’s 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
Potential Issues w/ Off-SiteRetention / 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
Comments on SWROA Submissions
Include Well-Written Narrative Clearly Explain Assumptions & Sources
SedCad Printouts Alone Won’t 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
Discussion Example - Do You Know What Your Worst Case Will Be?
Discussion Example - Do You Know What Your Worst Case Will Be?
Discussion Example - Do You Know What Your Worst Case Will Be?
Discussion ExamplePost-Mining Case
Discussion ExamplePost-Mining Case
Discussion Example (or How Many Valley Fills Are In This Picture?
Discussion ExampleIn-Pit Storage?
Discussion ExampleIn-Pit Storage?
Discussion ExampleIn-Pit Storage?
Discussion Example
Discussion Example
Discussion Example
Discussion Example
Discussion Example
Discussion Example
Discussion Example
Discussion Example
Discussion Example
Discussion Example
What Can We Learn From Other Activities & Industries?
What Can We Learn From Other Activities & Industries?
What Can We Learn From Other Activities & Industries?
What Can We Learn From Other Activities & Industries?
What Can We Learn From Other Activities & Industries?
What Can We Learn From Other Activities & Industries?
What Can We Learn From Other Activities & Industries?
What Can We Learn From Other Activities & Industries?
What Can We Learn From Others?Retention, Retention, Detention …
Questions / Comments ?