Hydrological Analysis – Preliminary Report: Report #2e80d4f9

Hydrological Analysis Report

Generated: 2025-09-17T14:55:06.271849 File: 1381684648_184231742_property_line.shp.kmz

Executive Summary

Location: Unknown, Macoupin County, Illinois Flood Zone: C - Low Risk (minimal flood hazard) Site Area: 83.3 acres (0.13 sq mi)

Site Location

Plot

Site Information

Geographic Data

  • Center Coordinates: 39.490062, -89.783421
  • Bounding Box:
    • North: 39.493726
    • South: 39.486397
    • East: -89.781004
    • West: -89.785838
  • Dimensions: 0.26 mi × 0.51 mi

Flood Zone Analysis

Primary Flood Zone: C

Risk Level: Low Risk (minimal flood hazard) DFIRM Panel: 17117C

Flood Zone Implications

  • LOW RISK: Minimal flood hazard area
  • Flood insurance optional but still recommended
  • Standard building codes apply

Precipitation Data

[✓] Using ACTUAL NOAA Atlas 14 precipitation data

The precipitation values shown below were retrieved directly from NOAA's Precipitation Frequency Data Server (PFDS) for your specific location.

Location: 39.49006169977109°, -89.78342055407427° Region: Eastern US Data Source: NOAA Atlas 14 - Actual Data Rainfall Distribution: NRCS Type II

Design Storm Summary

  • Water Quality Volume (WQv) - 1-year, 24-hour storm
    • Depth: 2.47 inches
    • Use: BMP sizing for water quality treatment
  • Channel Protection Volume (CPv) - 2-year, 24-hour storm
    • Depth: 2.98 inches
    • Use: Extended detention for channel erosion prevention
  • Overbank Flood Protection - 10-year, 24-hour storm
    • Depth: 4.31 inches
    • Use: Detention sizing for flood mitigation
  • Extreme Flood Protection - 100-year, 24-hour storm
    • Depth: 6.36 inches
    • Use: Emergency spillway and freeboard design

Precipitation Frequency Estimates

Return Period 5-min 15-min 60-min 24-hr
1-yr 0.397 in 0.756 in 1.22 in 2.47 in
2-yr 0.473 in 0.903 in 1.48 in 2.98 in
10-yr 0.634 in 1.2 in 2.13 in 4.31 in
25-yr 0.723 in 1.37 in 2.5 in 5.1 in
100-yr 0.865 in 1.62 in 3.12 in 6.36 in

For complete precipitation data including all durations, visit the NOAA Atlas 14 Homepage

Rainfall Intensity (for Rational Method)

  • 10 yr, 5 min: 7.61 inches/hr
  • 25 yr, 5 min: 8.68 inches/hr
  • 100 yr, 5 min: 10.38 inches/hr

Precipitation Visualizations

Intensity-Duration-Frequency (IDF) Curves

Plot

Precipitation Summary

Plot

100-Year Design Storm Hyetograph

Plot

Regulatory Analysis

Jurisdictional Overview

  • Federal: FEMA, USACE (if wetlands present)
  • State: Illinois
  • County: Macoupin
  • City: Unincorporated area

Permit Requirements

Research conducted: 2025-09-17T14:55:10.181812

Based on the jurisdiction analysis for Macoupin County, Illinois, here are the EXACT requirements for your 83.3-acre site in Zone C:

1. STATE-LEVEL PERMIT REQUIREMENTS

Illinois Environmental Protection Agency (IEPA)

Required State Permits for 83.3-acre Site:

  • NPDES ILR10 General Stormwater Permit - REQUIRED (site exceeds 1-acre threshold)
    • Application: Notice of Intent (NOI) Form
    • Fee: $400 (as of 2024)
    • Timeline: 30-day review period
    • Download: Search "IEPA NPDES ILR10 NOI" on Illinois EPA website

State Thresholds Triggering Requirements:

  • Construction stormwater permit: ≥1 acre disturbance (YOUR SITE REQUIRES)
  • No separate state stormwater management permit exists
  • No state erosion control permit (covered under NPDES)
  • No state wetland permits (relies on federal Section 404)

Professional Certifications:

  • Professional Engineer (PE) required for NPDES permit drawings
  • No state-specific stormwater certifications required
  • No Registered Landscape Designer (RLD) program in Illinois

CONTACT INFORMATION (APPROXIMATE - Please verify):

  • IEPA Bureau of Water: 217-782-3362
  • Regional Office (Region 4 - includes Macoupin): Search "IEPA Region 4 Office"
  • NPDES Permits: Search "IEPA NPDES stormwater permits"

2. LOCAL PERMIT REQUIREMENTS

Macoupin County Requirements for 83.3-acre Site in Zone C:

Required Local Permits:

  • Floodplain Development Permit - NOT REQUIRED for Zone C
    • Zone C is outside the 100-year floodplain
    • Chapter 40 of County Code only regulates Zones A, AE, AH, AO
  • Subdivision Approval - MAY BE REQUIRED if creating new lots
    • Chapter 55 of County Code
    • Contact Planning Department to confirm
  • Building Permits - Required for structures
  • Zoning Compliance - Verify zoning district requirements

Local Submittal Requirements:

  • Number of copies: Typically 3 paper sets (VERIFY with county)
  • Format: 24"x36" plan sheets typical
  • Scale: 1"=100' or larger for site plans

CONTACT INFORMATION (APPROXIMATE - Please verify):

  • Macoupin County Planning & Economic Development
  • Phone: Search "Macoupin County Planning Department"
  • Address: 215 S. East Street, Carlinville, IL 62626

3. PERMIT SEQUENCING AND COORDINATION

Required Sequence:

  1. FIRST: IEPA NPDES ILR10 permit (file NOI)
  2. SECOND: County permits (if subdivision or building)
  3. No combined applications available
  4. State and local reviews are independent

Timeline:

  • IEPA NPDES: 30 days from complete NOI
  • County permits: Varies (contact county for current timelines)

4. TECHNICAL CALCULATIONS

State Requirements (IEPA):

  • Methodology: No specific state-mandated methodology
  • Software: No specific software required by state
  • Storm Events: Follow local requirements

Local Requirements (Macoupin County):

  • Methodology for 83.3 acres: SCS/NRCS methods required (>40 acres)
  • Software: No specific software mandated
  • Design Storms:
    • 10-year, 24-hour for conveyance design
    • 100-year, 24-hour for overflow routes

Precipitation Data:

CRITICAL VERIFICATION NEEDED: Contact Macoupin County to confirm if NOAA Atlas 14 values are accepted:

  • 100-year, 24-hour: 6.36 inches
  • 10-year, 24-hour: 4.31 inches
  • Storm distribution: Type II (typical for Illinois)

5. DESIGN STANDARDS

State BMP Standards:

  • Illinois Urban Manual (IUM) - GUIDANCE ONLY, not mandatory
  • No state-mandated detention requirements
  • No state water quality volume requirements

Local Standards for Zone C:

CRITICAL FREEBOARD VERIFICATION:

  • State freeboard requirement: NONE beyond FEMA
  • Macoupin County freeboard requirement: 1 foot above BFE
  • For Zone C specifically: NOT APPLICABLE (Zone C has no BFE)
  • Is local requirement GREATER than FEMA minimum? NO (follows FEMA)
  • Source: Chapter 40, Macoupin County Code

Detention Requirements:

  • No formal county detention ordinance
  • Agricultural drainage tiles must be maintained if impacted

6. SUBMITTAL DETAILS

State Submittal (IEPA):

  • Electronic submittal via IEPA website
  • PE certification required on plans
  • SWPPP required with NOI

Local Submittal:

  • Paper copies (verify number with county)
  • PE stamp typically required for engineering plans
  • No specific plan sheet order mandated

7. STATE AGENCY CONTACTS

APPROXIMATE INFORMATION - Please verify current contacts:

  • IEPA Main Office: 217-782-3362
  • Search "IEPA Bureau of Water NPDES permits"
  • Search "IEPA Region 4 office" for regional contact

8. LOCAL CONTACTS AND RESOURCES

APPROXIMATE INFORMATION - Please verify:

  • Search "Macoupin County Planning Department"
  • Search "Macoupin County floodplain administrator"
  • County website: macoupincountyil.gov

CRITICAL ACTIONS FOR YOUR 83.3-ACRE ZONE C SITE:

  1. File IEPA NPDES ILR10 NOI (definite requirement)
  2. Verify with county if subdivision approval needed
  3. Confirm NOAA Atlas 14 precipitation data acceptance
  4. Use SCS/NRCS methodology for calculations (>40 acres)
  5. No floodplain permit needed for Zone C

Additional Jurisdictional Information

Based on my research of hydrological permitting requirements for Macoupin County, Illinois:

1. STATE-LEVEL REGULATORY AGENCIES

  • Primary Agency: Illinois Environmental Protection Agency (IEPA)
  • Stormwater Division: IEPA Bureau of Water, specifically the Watershed Management Section
  • State Permits Required:
    • NPDES ILR10 (General Stormwater Permit for Construction)
    • NPDES ILR40 (Industrial Stormwater Permit)
    • Section 401 Water Quality Certification
    • Joint Permit Application with USACE for wetlands
  • Erosion Control: No standalone state E&SC program - handled through NPDES
  • Wetland Program: Illinois has no independent state wetland program; relies on federal Section 404
  • Water Quality: Illinois follows EPA-approved water quality standards under 35 Ill. Adm. Code Part 302

2. STATE REGULATORY REQUIREMENTS

  • Construction Permits: NPDES ILR10 required for ≥1 acre disturbance
  • Threshold: 1 acre (following federal minimum)
  • BMP Standards: Illinois Urban Manual (IUM) provides design guidance but is not mandatory statewide
  • Freeboard: No state-mandated freeboard beyond FEMA requirements
  • Post-Construction: No statewide post-construction standards (delegated to locals)
  • Certifications: No state-specific RLD or similar program; PE required for certain submissions

3. COUNTY/LOCAL REGULATORY STRUCTURE

  • Macoupin County:
    • Planning and Economic Development Department handles floodplain permits
    • No separate stormwater management district exists
    • Floodplain Ordinance (Chapter 40 of County Code)
  • Municipalities: Cities like Carlinville may have additional requirements
  • Key Ordinances:
    • Macoupin County Floodplain Ordinance
    • Subdivision Regulations (Chapter 55)
    • Zoning Ordinance (Chapter 90)

4. UNIQUE LOCAL REQUIREMENTS

  • Freeboard: County requires 1 foot above BFE (FEMA minimum)
  • Calculation Methods: Rational Method for <40 acres; SCS/NRCS methods for larger areas
  • Software: No specific software mandated
  • Design Standards: County relies on IDOT Drainage Manual for public projects

5. STATE-LOCAL INTERACTION

  • Permit Sequence: IEPA NPDES permit typically obtained before local permits
  • No Joint Applications: State and local permits are separate processes
  • Local Standards: Counties can exceed state minimums but Macoupin County generally follows state standards
  • Coordination: Limited formal coordination between state and county

6. TECHNICAL STANDARDS

State Requirements:

  • 10-year, 24-hour storm for conveyance
  • 100-year for floodplain analysis
  • No specific state detention requirements

Local Requirements:

  • 10-year design storm for drainage systems
  • 100-year for overflow routes
  • No formal detention ordinance in Macoupin County
  • Agricultural drainage tiles must be maintained/replaced if impacted

7. KEY DOCUMENTS TO REFERENCE

  • IEPA NPDES General Permit ILR10
  • Illinois Urban Manual (IUM) - guidance document
  • IDOT Drainage Manual
  • Macoupin County Code Chapter 40 (Floodplain)
  • Macoupin County Code Chapter 55 (Subdivision)
  • IEPA Notice of Intent (NOI) forms
  • County floodplain development permit application

SURPRISES FOR OUT-OF-STATE ENGINEERS

  1. No State Stormwater Management Act: Unlike neighboring states (Wisconsin, Indiana), Illinois has no comprehensive state stormwater law
  2. Weak Post-Construction Requirements: No statewide post-construction stormwater standards
  3. Limited County Authority: Macoupin County has minimal stormwater regulations beyond floodplain management
  4. Agricultural Exemptions: Extensive agricultural drainage exemptions due to Illinois Drainage Code
  5. No State Wetland Program: Complete reliance on federal Section 404 permitting
  6. Minimal Professional Certifications: No state-specific erosion control or stormwater inspector certifications required
  7. Drainage Districts: Historic drainage districts may have authority over certain areas, creating additional jurisdictional complexity

The regulatory framework in Macoupin County is notably less stringent than many other states, with minimal county-level stormwater management requirements beyond basic floodplain regulations.

Recommended Next Steps

  1. Verify Flood Zone: Confirm flood zone designation with local floodplain administrator
  2. Survey Requirements: Obtain professional survey with elevation data
  3. Preliminary Consultation: Meet with local planning/permitting department
  4. Engineering Analysis: Engage qualified engineer for required studies
  5. Permit Applications: Prepare and submit required permit applications

Data Sources

  • Location Data: OpenStreetMap Nominatim
  • Flood Zone Data: National Flood Data API v3
  • Precipitation Data: NOAA Atlas 14 Precipitation Frequency Data Server
  • Analysis Date: 2025-09-17 14:56:26

This report is for preliminary analysis only. All information should be verified with appropriate regulatory authorities before making development decisions.