Black Hills Corp. Overview 8/14/2015 POWER PLANT STORMWATER STABILIZATION THROUGH REVEGETATION, A CASE STUDY. Topics

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POWER PLANT STORMWATER STABILIZATION THROUGH REVEGETATION, A CASE STUDY AHMP National Conference 2015 Joe Jenkins, PG, CHMM, CPESC Topics Black Hills Corporation Overview Post Construction BMPs and

1 POWER PLANT STORMWATER STABILIZATION THROUGH REVEGETATION, A CASE STUDY AHMP National Conference 2015 Joe Jenkins, PG, CHMM, CPESC 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 3 Black Hills Corp. Overview 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 Black Hills Power Cheyenne Light* Colorado Electric Gas Utilities Colorado Gas Kansas Gas Nebraska Gas Iowa Gas Non-Regulated Energy Power Generation Black Hills Electric Generation Coal Mining Wyodak Resources Oil and Gas Black Hills Exploration and Production 4 1

2 Pueblo Airport Generating Station (PAGS) January W. N. Clark Station Canon City, CO 48 MW 255,425 mt CO 2e 24 employees PAGS 380 MW, 29 MW wind 317,683 mt CO 2e 14 employees Replaced 300 MW of coal-based purchased power 6 Impact of PAGS on GHG Emissions Reduction 37% reduction in GHG Emissions 7 2

3 Location of PAGs in Respect to Arkansas River 8 Facility with Respect to Local Topography PAGS Approx. 3.6 miles Arkansas River 9 April

4 Area Designations Site of new turbine unit, construction beginning 2016 Go to master slide > 11 Pueblo County Stormwater Considerations No stormwater retention allowed by County 12 Army Corp Non-Jurisdictional WOTUS 13 4

5 Natural Vegetation in and Around PAGS Shortgrass prairie co-dominant with Greasewood shrubland: Blue Grama Alkali saction grass Galetta grass Sand dropseed Rabbitbrush Cholla 14 Post-Construction BMPs and Controls 15 Engineer s Design

6 Power Block March SE Stockpile and Detention Pond Area March West of Powerblock Culvert 10, 3 ft. round culvert Culvert 9, 4 ft. box culvert 19 6

7 Floodplain Analysis Culvert yr 25 yr 100 yr 20 Culvert yr Flood Level Determination 100 yr FP 10 yr FP July rainfall 21 Culvert yr Flood Level Determination 100 yr FP September rainfall 22 7

8 Rain Event July 15, Pond Slope Design 24 Evaporation Ponds 25 8

9 Laydown Yard March Shale Stockpiles 27 RISK ANALYSIS 28 9

10 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) 29 Violation Matrix Multi-Day Penalties Example Day 1 ($ ) = $ 1, Days 2-10 ($ ) X (9 days) X (50%) = $ 4, Days ($ ) X (40 days) X (40%) = $16, Days ($ ) X (50 days) X (30%) = $15, Days ($ ) X (100 days) X (20%) = $20, Days ($ ) X (70 days) X (10%) = $ 7, Multi-Day Base Gravity Penalty = $65, 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 30 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,

PAGS at Risk for Stormwater Management 32 Maintenance and Replacement of Failed BMPs The potential to discharge sediment-laden water from numerous outfalls around the plant site.

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

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

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

11 PAGS at Risk for Stormwater Management 32 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 33 INITIAL REPAIR OF FAILED BMPS 34 11

12 Initial Repair of Failed BMPs 35 Initial Repair of Failed BMPs 36 Initial Repair of Failed BMPs Total Cost of repairs $160,

13 Initial Repair of Failed BMPs 5/13/13 South Powerblock Drainage 38 Power Block 4, BMP Maintenance

Engineering Design and BMP Selection 41 Engineering Evaluations Control Technology and BMP

topsoil Rock, riprap, grouted rip rap Manufactured drainage Retaining walls Budgetary

analysis Cost comparison 42 Soil Sampling South Shale Stockpile (1, 2), Laydown Yard (3) North

14 Engineering Design and BMP Selection 41 Engineering Evaluations 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 42 Soil Sampling 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 43 14

SWOT Analysis Rock Strengths / Opportunities No watering, not affected by drought Potentially low maintenance

cost to maintain Vegetation Strengths / Opportunities Lower cost Weaknesses / Threats Watering required to

away seeds Greater maintenance anticipated due to time to establish seeds 44 Rock versus Vegetation

15 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 44 Rock versus Vegetation $1,155,223 for vegetation versus $3,178,261 for primarily rock and riprap cover 45 Final Engineering Design June

16 Amendments and Seed Mixture 47 Construction Phase 48 BMP Construction Began 7/15/

17 Permanent BMP Installation and Revegetation 50 Permanent BMP Installation and Revegetation Complete 9/1/ June 2015 Go to master slide > 52 17

18 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! 53 Contact Information Joe Jenkins, PG, CHMM, CPESC Sr. Environmental Professional Black Hills Corporation 1515 Wynkoop St, Denver CO

Re: Erosion Control Report and Drawings Requirements Accompanying Document

Re: Erosion Control Report and Drawings Requirements Accompanying Document This document was created to help engineers and other design staff to better understand, meet and exceed the erosion control requirements