National Academies Press: OpenBook

Strategies for Airports to Reduce Local Stormwater Utility Fees (2018)

Chapter: Appendix B - Example Calculations of Stormwater Fees and Credits

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Page 68
Suggested Citation:"Appendix B - Example Calculations of Stormwater Fees and Credits." National Academies of Sciences, Engineering, and Medicine. 2018. Strategies for Airports to Reduce Local Stormwater Utility Fees. Washington, DC: The National Academies Press. doi: 10.17226/25320.
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Page 68
Page 69
Suggested Citation:"Appendix B - Example Calculations of Stormwater Fees and Credits." National Academies of Sciences, Engineering, and Medicine. 2018. Strategies for Airports to Reduce Local Stormwater Utility Fees. Washington, DC: The National Academies Press. doi: 10.17226/25320.
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Page 69
Page 70
Suggested Citation:"Appendix B - Example Calculations of Stormwater Fees and Credits." National Academies of Sciences, Engineering, and Medicine. 2018. Strategies for Airports to Reduce Local Stormwater Utility Fees. Washington, DC: The National Academies Press. doi: 10.17226/25320.
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Page 70
Page 71
Suggested Citation:"Appendix B - Example Calculations of Stormwater Fees and Credits." National Academies of Sciences, Engineering, and Medicine. 2018. Strategies for Airports to Reduce Local Stormwater Utility Fees. Washington, DC: The National Academies Press. doi: 10.17226/25320.
×
Page 71

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68 Below are examples of fee calculations under general types of fee structures. Where useful, the same airport impervious area has been used. Calculations for the first two examples are based on the same base rate (standardized to different impervious area amounts). Credit calculations are provided based on two credit systems. Calculation of Fees in an Equivalent Residential Unit (ERU) Fee Structure A P P E N D I X B Example Calculations of Stormwater Fees and Credits ERU: 2,500 sq. ft. Airport Impervious Area: 21,780,000 sq. ft. (500 acres) Base Rate per ERU per Month: $6.00 Calculation Formula Example Formula Example Amount Number of ERUs: Impervious Area/ERU 21,780,000/2,500 = 8,712 Fees per Month: ERUs x Base Rate 8,712 x $6.00 = $52,272 Fees per Year: Fees per month x 12 $52,272 x 12 = $627,264 Calculation of Fees in an Impervious Area Fee Structure Airport Impervious Area: 21,780,000 sq. ft. (500 acres) Base Rate per 1,000 sq. ft. per Month: $2.40 Calculation Formula Example Formula Example Amount Fees per Month: Impervious Area/1,000 x Base Rate (21,780,000/1,000) x $2.40 = $52,272 Fees per Year: Fees per month x 12 $52,272 x 12 = $627,264

Example Calculations of Stormwater Fees and Credits 69 Calculation of Fees in a Tier Fee Structure Based on Impervious Area Tiers based on percent impervious area, with an area-based rate within each tier % Impervious Area on Property Annual Rate/1,000 sq. ft. Impervious Area Less than 2%: No Fee 2% - 40%: $20.00 41% - 70%: $30.00 71% - 100%: $40.00 Airport Impervious Area: 21,780,000 sq. ft. (500 acres) Airport Total Area: 36,300,000 Airport Percent Impervious Area: 60% (used to determine tier) Base Rate per 1,000 sq. ft. per Year: $30.00 Calculation Formula Example Formula Example Amount Fees per Year: Impervious Area/1,000 x Base Rate (21,780,000/1,000) x $30.00 = $653,400 Calculation of Fees in a Tier Fee Structure with Flat Rates Tiers based on area, with a flat rate within each tier Impervious Surface Area (sq. ft.) Monthly Charge 200 to 600: $10.00 601 to 20,000: $20.00 20,001 to 40,000: $40.00 40,001 to 100,000: $50.00 Greater than 100,000: $100.00 Airport Impervious Area: 21,780,000 sq. ft. (500 acres) Base Rate per Month: $100.00 Calculation Formula Example Formula Example Amount Fees per Month: Base Rate per Month $100 = $100 Fees per Year: Fees per month x 12 $100 x 12 = $1,200

70 Strategies for Airports to Reduce Local Stormwater Utility Fees Calculation of Fees in a Residential Equivalency Factor (REF) Fee Structure Tiers based on area, with a flat rate within each tier Land Use REF Low Density Residential: 1.0 Medium Density Residential: 1.7 High Density Residential: 2.0 Commercial/Office: 2.8 Industrial: 2.7 Parks/Open Space/Undeveloped: 0.3 Public/Institutional: 1.4 Airport Total Area (acres): 833 Airport REF (assume industrial REF): 2.7 Base Rate per Acre per REF per Month: $6.00 Calculation Formula Example Formula Example Amount Fees per Month: REF x Base Rate x Net Acreage 2.7 x $6.00 x 833 = $13,494.60 Fees per Year: Fees per month x 12 $13,494.60 x 12 = $161,935.20 Credit Calculations #1 Stormwater utility credit program offers a 50 percent reduction in fees for impervious area treated by approved stormwater BMPs. Credit calculations are explained in A Guide to the Stormwater Quality Credits Program. Impervious Areas Acres Square feet Stormwater BMPs Runways 72.73 3,168,000 Filter strips Taxiways 68.87 3,000,000 Filter strips Terminal 45.91 2,000,000 Bioretention cells Hangars 45.91 2,000,000 Aprons 10.33 450,000 Parking 18.37 800,000 Bioretention cells Access roads 22.96 1,000,000 Bioswales Other 13.77 600,000 Total Impervious Area 298.85 13,018,000 Total Impervious Area Draining to BMPs 228.84 9,968,000 Calculation Formula Example Formula Example Amount Percentage of Impervious Area Treated: Total Impervious Area Draining to BMPs/Total Impervious Area 228.84/298.85 = 76.57% Percent Reduction in Fees: Divide the percentage area treated by 2 for a 50 percent credit. 76.57%/2 = 38%

Example Calculations of Stormwater Fees and Credits 71 Credit Calculations #2 Credits are awarded separately for quantity and quality, with a separate application for each stormwater BMP. Details and applications are provided in the Northeast Ohio Regional Sewer District Stormwater Fee Credit Policy Manual. Examples are given below for credits that would be awarded for two BMPs. BMP 1: Vegetated Swales Impervious area drained: 217,800 sq. ft. (5 acres) Credit Type Credit Criterion Met to Get Credit Quantity—Volume 25% Existing impervious area greater than 50 percent: 25 percent credit for managing runoff from a 2-year 24-hour storm. Quantity—Peak Flow 25% Runoff is managed by a BMP that controls peak flow according to established design standards. Applicant used the Critical Storm Method to receive 25 percent credit. Quality 25% Impervious area falls under industrial NPDES permit. (Credit would be 15 percent for this BMP type without the NPDES permit.) Total Fee Reduction 75% Application Preparation 10% One-time reduction for preparing the credit application. Total Fee Reduction in the Year when Application Is Submitted 85% BMP 2: Infiltration Trench Impervious area drained: 130,680 sq. ft. (3 acres) Credit Type Credit Criterion Met to Get Credit Quantity—Volume 50% Existing impervious area greater than 50 percent: 50 percent exceptional credit for managing runoff from the 100-year 24-hour storm. Quantity—Peak Flow 25% Runoff is managed by a BMP that controls peak flow according to established design standards. Applicant used the Critical Storm Method to receive 25 percent credit. (Other methods are awarded less credit.) Quality 20% Credit according to a tiered list of BMPs that qualify for stormwater quality credits. Total Fee Reduction 95% Application Preparation 10% One-time reduction for preparing the credit application. Total Fee Reduction in the Year when Application Is Submitted 100% Credits cannot exceed 100 percent.

Next: Appendix C - Tools to Prepare for a Stormwater Fee »
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TRB's Airport Cooperative Research Program (ACRP) Research Report 193: Strategies for Airports to Reduce Local Stormwater Utility Fees offers airports guidance in managing the stormwater-related utility fees that many local governments charge to help finance their capital and operating expenses. U.S. airports are experiencing a trend of local governments charging and increasing fees to operate and maintain stormwater infrastructure. These trends are having a growing impact on airport budgets. This report identifies, evaluates, and implements strategies for managing stormwater fees based on each agency's unique situation.

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