STORMWATER MANAGEMENT

ORDINANCE IMPLEMENTATION

Presented by:

Butler County Planning Commission

AGENDA

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Introduction and Review

The Model Ordinance

Brief Discussion of SWM Report Technical Criteria

Easements

Miscellaneous Requirements

Test

IMPORTANCE OF STORMWATER MANAGEMENT

Pre-developed

ConditionDeveloped

Condition

IMPORTANCE OF STORMWATER MANAGEMENT

FloodingCosts Associated with Storm Events

County

10-year Event 100-year Event

Buildings Damaged

Tons of Debris

Economic Loss

Buildings Damaged

Tons of Debris

Economic Loss

Crawford 374 25,153 $237.78 495 36,898 $306.15

Erie 110 8,007 $57.52 169 12,502 $72.31

Venango 154 13,211 $60.73 360 28,542 $112.75

Warren 262 19,916 $92.98 470 34,487 $148.92

total 900 66,287 $449.01 1,494 112,429 $640.13

TRADITIONAL SWM STANDARDS

• Collection & Conveyance

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• Rate Control

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Traditional design standards addressed:

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The problem with traditional standards:

• Application of Theory

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• Technical Shortcomings

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Post-Development with SWM

Post-Development with no SWM

Existing

TRADITIONAL SWM STANDARDS

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The problem with traditional standards:

• Content (cont.)

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Total hydrograph at confluence A-B

Watershed B

Watershed A

tpA Tp tpB

“Controlled” Total hydrograph

“Controlled” Watershed A

Watershed APre-Development

TRADITIONAL SWM STANDARDS: UNDER ACT 167

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3 Technical Components:

• Volume Control

• Rate Control

• Water Quality Treatment BIO-RETENTION [RAIN GARDENS] CAN PROVIDE ALL

THREE COMPONENTS

BIO-RETENTION [RAIN GARDENS] CAN PROVIDE ALL

THREE COMPONENTS

CURRENT SWM STANDARDS: UNDER ACT 167

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Focus is on volume control

Why?

• The majority of rainfall occurs

during small storms

• Provides benefits during all

storms (Tech Components)

• Increases groundwater

recharge

• Assumed to meet WQ

standardsDistribution of precipitation by storm magnitude ( Or ig in a l D a te fr o m Pe n n S t a te C l i m a t o l og ic a l O f f ic e, 1 9 2 6- 2 0 0 3 )

2-year, 24-hour design storm = 2.50 inches2-year, 24-hour design storm = 2.50 inches

CURRENT SWM STANDARDS: UNDER ACT 167

Focus on volume control:

How do we remove volume?

• LID / Green Infrastructure

• Non-Structural BMPs

• Structural BMPs

What are the physical processes

employed ?

• Infiltration

• Evapotranspiration

• Capture and Reuse

CURRENT SWM STANDARDS : UNDER ACT 167

LID / GREEN INFRASTRUCTURE

What is Low Impact Development (LID)?

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S o u r c e: L I D T e c hn i c a l G u i d an c e M an u a l f o r P u g e t S o un d ( 2 0 0 5 )

Core Design Principals of LID:

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Uses Best Management

Practices (BMPs). What are

they?

• Non-Structural

• Structural

���� Prevention

���� Mitigation

Reduce Impervious Area Disconnect Downspouts

Vegetated SwaleRain Garden

Non-Structural BMPs

Structural BMPs

LID / GREEN INFRASTRUCTURE

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INTEGRATING SWM W/DESIGN - Residential

BUTLER COUNTY ACT 167 PLAN and Model Ordinance

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Sizing Criteria Description of Stormwater Sizing Criteria

Volume Control –Using Design Storm

(CG1)

Regulation of the 2-year storm event:

• No Increase in the post development total runoff

• Applicable for any size of regulated activity

• No increase in total runoff volume for the 2-yr/24-yr event

• Consider existing non-forest pervious area as meadow

• 20% of existing impervious area considered as meadow

Volume Control -

Using SimplifiedMethod

(CG2)

Regulation of stormwater runoff from new impervious:

• capture of first 2” of runoff

• 1” of captured runoff shall be permanently removed

• ½” of captured runoff shall be infiltrated

Peak Rate Controls No Increase in the post development total runoff rate

Water Quality

Calculations

BMP Control of 90% of Disturbed Area

Specific BMP’s for Pollution Prevention

Pollutant Load Estimates

Pollutant Load Reduction for BMP’s

Nitrate (N), Total Suspended Solids (TSS), and Total Phosphate(TP) Requirements

MODEL ORDINANCE – Control Standards

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MODEL ORDINANCE – Release Rates

MODEL ORDINANCE – Exemptions

New Impervious Area1, 2

(square footage)Applicant Must Provide

0 – 2,500 No Submission is required

2,500 – 5,000 Documentation of Impervious surfaces3

> 5,000Rate Controls, Volume Controls & SWM Site

Plan

NOTES:

1 New Impervious Area since the date of Adoption of this Ordinance.

2 Gravel in existing condition shall be considered pervious and gravel inproposed condition shall be considered impervious.

3 The Small Project Stormwater Management Application included inAppendix E shall be used to document new impervious surfaces.

MODEL ORDINANCE – Exemptions

1. Comply with Sections 301.G,

MODEL ORDINANCE – Exemptions

2. Comply with Sections 302.A,

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MODEL ORDINANCE – Exemptions

2. Comply with Sections 302.B,

MODEL ORDINANCE – Exemptions

2. Comply with Sections 302.C,

MODEL ORDINANCE – Exemptions

MODEL ORDINANCE– Small Project Application

• Simple Process using Application.

• 5,000 SF threshold for Volume Control.

• Can be integrated into the building permit process.

MODEL ORDINANCE– Small Project Example

+75’

MODEL ORDINANCE– Small Project Example

0.65 acre lot

New garage

Paved Driveway

MODEL ORDINANCE– Bigger Project Example

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MODEL ORDINANCE – Waivers

Must meet the provisions of Section

303.G and 303.H.

Cannot issue waivers if conditions

prevent -

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The Technical/Construction

Standards are at discretion of the

municipality

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MODEL ORDINANCE – Waivers

Section 303.G (Municipality may

impose reasonable conditions to

substantially meet objectives of the

requirements that are to be

modified.)

Example:

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MODEL ORDINANCE – Waivers

Section 303.H (Lists items that will

guide Municipalities in granting

waivers.)

Example:

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MODEL ORDINANCE – Technical Criteria

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MODEL ORDINANCE – Easements

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Maintenance

Inspections of Facilities

Enforcement Options

Fees

MODEL ORDINANCE – Miscellaneous

Questions