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AHMP National Conference – 2015

Joe Jenkins, PG, CHMM, CPESC

POWER PLANT STORMWATER

STABILIZATION THROUGH

REVEGETATION, A CASE STUDY

Topics

• Black Hills Corporation Overview

• Post Construction BMPs and Controls

• Risk Assessment

• BMP Repair

• Engineering Design and BMP Selection

• Soil Sampling and Amendments

• Construction Phase

• One Year Later

BMP: Best Management Practice

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• Based in Rapid City, SD, with corporate offices in Denver, CO, and Papillion, NE

• Utility operations serve 765,000 utility customers in CO, IA, NE, SD, WY

• Non-regulated businesses generate wholesale electricity, and produce natural gas, crude oil and coal.

Utilities

Electric Utilities Gas Utilities• Black Hills Power

• Cheyenne Light*

• Colorado Electric

• Colorado Gas

• Kansas Gas

• Nebraska Gas

• Iowa Gas

Non-Regulated Energy

Power Generation Coal Mining

• Black Hills Electric Generation

• Wyodak Resources

Oil and Gas

• Black Hills Exploration and Production

Black Hills Corp. Overview

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Pueblo Airport Generating Station (PAGS)January 2012

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W. N. Clark StationCanon City, CO• 48 MW• 255,425 mT CO2e

• 24 employees

PAGS• 380 MW, 29 MW wind• 317,683 mT CO2e

• 14 employees• Replaced 300 MW of

coal-based purchased power

Impact of PAGS on GHG Emissions Reduction

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37% reduction in GHG Emissions

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Location of PAGs in Respect to Arkansas River

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Facility with Respect to Local Topography

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PAGS

Arkansas River

Approx. 3.6 miles

April 2012

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Area Designations

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Site of new turbine unit, construction beginning 2016

Pueblo County Stormwater Considerations

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No stormwater retention allowed by County

Army Corp Non-Jurisdictional WOTUS

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Natural Vegetation in and Around PAGS

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Shortgrass prairie co-dominant with Greasewood shrubland:• Blue Grama• Alkali saction grass• Galetta grass• Sand dropseed• Rabbitbrush• Cholla

Post-Construction BMPs and Controls

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Engineer’s Design 2010

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Power Block March 2013

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SE Stockpile and Detention Pond Area

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March 2013

West of Powerblock

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Culvert 9, 4 ft. box culvert

Culvert 10, 3 ft. round culvert

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Floodplain Analysis Culvert 10

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10 yr

25 yr100 yr

Culvert 10 – 100 yr Flood Level Determination

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100 yr FP

10 yr FP

July 2013 – 2.05” rainfall

Culvert 10 – 100 yr Flood Level Determination

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100 yr FP

September 2013 – 2.86” rainfall

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Rain Event July 15, 2014

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Pond Slope Design

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Evaporation Ponds

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Laydown Yard March 2013

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Shale Stockpiles

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RISK ANALYSIS

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Risk Analysis – August 2013

• Review of existing stormwater restoration practices and BMPs

• State of Colorado Stormwater Civil Penalty Matrix

• Determine Base Gravity Penalty

• Account for Duration of Violation (multi-day penalties)

• Apply Aggravating or Mitigating Factors

• Add Economic Benefit

• Multiple Violations

• Ability to Pay

• Multi-Day Penalties

• Conducting Covered Activities without a Stormwater Permit

• Failure to Prepare Stormwater Management Plan (SWMP)

• Deficient Stormwater Management Plan (SWMP)

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Violation Matrix Multi-Day Penalties Example

Day 1 ($1037.50) = $ 1,037.50

+ Days 2-10 ($1037.50) X (9 days) X (50%) = $ 4,668.75

+ Days 11-50 ($1037.50) X (40 days) X (40%) = $16,600.00

+ Days 51-100 ($1037.50) X (50 days) X (30%) = $15,562.50

+ Days 101-200 ($1037.50) X (100 days) X (20%) = $20,750.00

+ Days 201-270 ($1037.50) X (70 days) X (10%) = $ 7,262.50

Multi-Day Base Gravity Penalty = $65,881.25

Applicable to each identified violation:

• Failure to Install, Maintain, or Properly Select BMPs

• Failure to Perform Inspections of Stormwater Management System

• Pollution, Contamination, or Degradation of State Waters

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PAGS at Risk Stormwater Management System

• Permit expanded in phases but no evidence of communication with State on expansions

• Initial permit described access road and plant

• Did not include evaporation ponds or shale stockpiles

• No post-construction version of the SWMP• Inadequate SWMP

− Site description changes not addressed

− Site map not updated

− BMPs not updated

− Final stabilization practices not described

• Examples of Recent Violations• 2011, Timnah Ranch, $90,223 penalty

• 2012, Sumo Development, $100,000 penalty

• 2013, Rock Mt. Materials, $65,000

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PAGS at Risk for Stormwater Management

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Maintenance and Replacement of Failed BMPs• The potential to discharge sediment-laden water from numerous outfalls around the plant site. Each outfall is a separate violation.

• Stormwater sediment retention basin SE corner of facility

• Multiple locations along both arroyos on each side of the shale pile

• All silt fence at the site

• Partially riprapped channels

• Slopes along the substation

• Unstabilized drainage along access road

• Unstabilized drainage (no controls) along the dirt road west of shale pile

• Unstabilized slopes (no controls) around evaporation ponds

• Unstabilized surfaces (no controls) around evaporation ponds

• Unstabilized surfaces (no controls) around sediment retention basin

• No perimeter control around stockpile northwest of plant

• No perimeter control around stockpile southeast of plant

• No perimeter control around small stockpile by arroyo south of access road

• No or incomplete perimeter control around shale piles

• Sediment tracking on roadways at dirt road access west of shale pile

• Sediment on road east of arroyo where it flows with run off being tracked along roadway above arroyo (potential discharge to state waters)

• Erosion (rills) on shale pile

• Erosion (rills) on evaporation pond slopes

• Erosion (rills) on access road slopes

• Erosion (rills) on south side of substation

• Erosion (rills) on sediment retention basin

• Erosion (rills) on slopes of drainage channels

• Improperly designed sediment retention basin with direct discharge potential off site

• Failed controls in “laydown yard”

• Failed controls on horizontal surfaces in power block area

• Lack of weed control

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INITIAL REPAIR OF FAILED BMPS

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Initial Repair of Failed BMPs

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Initial Repair of Failed BMPs

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Initial Repair of Failed BMPs

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Total Cost of repairs $160,000

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Initial Repair of Failed BMPs

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5/13/13 South Powerblock Drainage

Power Block 4, 2014

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BMP Maintenance 2014

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Engineering Design and BMP Selection

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• Control Technology and BMP Selection

• Available Technologies• Revegetation‒ Soil sampling

‒ Amend and revegetate

‒ Addition of topsoil

• Rock, riprap, grouted rip rap

• Manufactured drainage

• Retaining walls

• Budgetary Considerations• Previously budgeted expense

• Will raise customer rates

• Rock versus Vegetation• SWOT analysis

• Cost comparison

Engineering Evaluations

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Soil Sampling

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South Shale Stockpile (1, 2), Laydown Yard (3)

North Shale Stockpile (1), SE Shale Stockpile (2)

TDS: Total Dissolved Salts; SAR: Sodium Absorption Ratio; CEC Cation Exchange Capacity

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SWOT Analysis• Rock

• Strengths / Opportunities− No watering, not affected by drought

− Potentially low maintenance

− Immediate results

• Weaknesses / Threats− High Cost

− Windblown dust may cover riprap over time

− Potentially high cost to maintain

• Vegetation• Strengths / Opportunities

− Lower cost

• Weaknesses / Threats− Watering required to support growth

− Semi/arid conditions accentuated by drought

− Heavy downpour could impact structures and wash away seeds

− Greater maintenance anticipated due to time to establish seeds

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Rock versus Vegetation

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$1,155,223 for vegetation versus $3,178,261 for primarily rock and riprap cover

Final Engineering Design June 2014

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Amendments and Seed Mixture

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Construction Phase

BMP Construction

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Began 7/15/2014

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Permanent BMP Installation and Revegetation

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Permanent BMP Installation and Revegetation

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Complete 9/1/2014

June 2015

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Lessons Learned

• Prior to Project Start

• Establish effective communication with all parties before construction begins

• Communicate compliance risk early and effectively

• Critically evaluate engineering design to determine if effectively addresses site conditions

• Establish effective communication with federal, state and local agencies as needed

• During the Project

• Provide ongoing comprehensive oversite to assure compliance is addressed along with construction activities

• Carefully manage records

• Reevaluate compliance as site condition change

• Do it right the first time!

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Contact Information

Joe Jenkins, PG, CHMM, CPESCSr. Environmental Professional

Black Hills Corporation

1515 Wynkoop St, Denver CO 80202

303-566-3446

Joe.jenkins@blackhillscorp.com

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