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Welcome to NCDEQ's Stormwater Nitrogen and Phosphorus (SNAP) Tool
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How to Use SNAP v4.2.0
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How are you using SNAP?
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Helpful Links and Resources:
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New Development - Regulatory Compliance:No New Development / Non-Regulatory:Precipitation Station Map
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Falls Lake Stormwater RulesCCAP ProjectSNAP Users' Manual
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Jordan Lake Stormwater Rules
Grant Programs:
319(h)Land & Water FundNCSU BAE Stormwater Resources
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Neuse Stormwater Rule205jWater Resources Development
Bioretention HyPerTool
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Tar-Pamlico Stormwater RuleStormwater Retrofit
PermPave HyPerMod
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Other State or Local Stormwater Nutrient RequirementsSCM-Based Nutrient Bank
Rainwater Harvester
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Who is your stormwater regulator? (check map)Landcover ConversionDEMLR Stormwater Manual
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Research Project
SCM Design Specs & Guidelines
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Etc.NPS Planning webpage
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Review Project With Regulator:
All Nutrient Management Strategies
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Identify Existing Built-Upon Area(s) on Site
Nutrient Reduction Practices and Crediting
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Review project info against regulation applicability:Gather Info & Enter Data:2023 NC SCM Credit Document
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• Landuse type, part of Commmon Plan of Development?Pre-Project Land Covers (sqft)
Background documentation on SCMs
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• Is Net Change in Built-Upon Area (BUA) > Zero?Post-Project Land Covers (sqft)
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• Nitrogen and Phosphorus Export Rate Targets?Find Your Precipitation Station
SNAP broken / not working???
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• Onsite Stormwater Treatment Requirements/Targets?Go To --> Land Cover Characteristics SheetMany Excel functions like cut & paste or drag & drop can damage internal spreadsheet setup and functioning
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• Disturbance thresholds?Stormwater Control Measure (SCM) Type
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• Project Density & thresholds?Hydrologic Soil Group at SiteIf you encounter strange spreadsheet behavior we recommend you download SNAP a second time
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• Other project information related to applicability?Area draining to SCM, including SCM footprint
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Is nutrient calculation required?Go To --> SCM Characteristics Sheet
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Is onsite stormwater treatment required? How much?
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Does project receive runoff from offsite or Existing BUA?
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• See Users Manual for Help with more complex scenariosFind Your Nutrient Reduction:
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Go To --> Nutrient Export Summary Sheet
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Look up results - Project Area Post-Project after Treatment:
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Gather Info & Enter Data:• Total Nitrogen Change (lb/yr)
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Project Information Needed for Recordkeeping• Total Phosphorus Change (lb/yr)
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• Go To --> Project Info SheetDONE!
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Pre-Project Land Covers (sqft)
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Post-Project Land Covers (sqft)
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Find Your Precipitation Station
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• Go To --> Land Cover Characteristics SheetCheck Post-Project Condition Against Targets:
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Stormwater Control Measure (SCM) Type(s)Review Results with Regulator:
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Hydrologic Soil Group at SiteIs onsite treatment/nutrient reduction met?
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Area draining to SCM(s), including SCM footprint(s)Is Runoff Volume Match an option?
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• Go To --> SCM Characteristics SheetIs there Offsite run-on or Existing BUA?
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Multiple SCM arrangements possible:--> Check Users Manual for complex site nutrient accounting
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• Max 6 catchments, series or parallelIs there a nutrient export balance after treatment?
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• 3 SCMs in series per catchment• Go To --> Nutrient Export Summary Sheet
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• See Users Manual for HelpLook up:
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A: TN and TP export targets scaled to to Project Area (lb/yr)
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B: Project Area Post-Project after Treatment: TN and TP Load (lb/yr)
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Meeting RequirementsIf B > A = remaining nutrient treatment balance
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DONE!
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Email Workbook to Regulator
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Not Fully Meeting Requirements
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Use Runoff Volume MatchNot meeting onsite treatmentMeeting onsite treatment but still have a balance
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See Regulator for instructionsUse a Regional SCM, consult with RegulatorRemaining balance can be met with Nutrient Offsets:
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Mark "yes" Project uses LID/Runoff Volume MatchGo To --> Project Info SheetConsult with Regulator and Nutrient Offset Program
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Go To --> Project Info SheetOR: Adjust Post-Project Landcovers• Go To --> Nutrient Offset Sheet
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Adjust Landcover details as neededGo To --> Land Cover Characteristics SheetDONE! - Email Workbook to Regulator
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Go To --> Land Cover Characteristics SheetOR: Scope out best SCMs for objectivesOR: Adjust Landcovers/SCMs until meeting targets onsite
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Adjust SCM details as needed(see Users Manual for help)Go To --> Land Cover Characteristics Sheet
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Go To --> SCM Characteristics SheetGo To --> SCM Characteristics SheetGo To --> SCM Characteristics Sheet
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DONE! - Email Workbook to RegulatorGo back to Check Post-Project Against TargetsGo back to Check Post-Project Against Targets
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