Grand Traverse Town CenterStorm Water Management

Acme Township MeetingHorizon Environmental

December 2, 2014

Construction Soil Erosion and Sedimentation Control (“SESC”)◦ Temporary Measures/Best Management Practices Intended to Limit

Soil Erosion and Sedimentation Silt Fence, Hay Bales, Matting Overlay of Seeded Areas

◦ Governed by County (SESC) and State (NPDES) Permits

◦ Applicable During Construction Until Vegetation Established

Post-Development Storm Water Management◦ Permanent Measures Intended to Reduce Contaminants in Storm Water

Runoff from Development to Acme Creek Storm Water Detention Ponds, Planted Swales, Check Dams

◦ Governed by SUP and Development Agreement

◦ Applicable Post-Construction to Developed Property

Original Scope of SESC Measures per SESC Permits◦ Silt Fencing at Perimeter to Intercept Sediment in Runoff◦ Use of Permanent Detention Ponds for Water Clarification◦ Seeding and Matting of Disturbed Areas

Site Conditions Necessitating Additional SESC Measures◦ Site Geology (e.g., Low Permeability Clay Substrate) Results in “Flashy”

Surface Runoff◦ Clay Particles are Very Fine (<1 um) and Not Readily Removed via

Traditional SESC Measures ◦ Small Masses of Clay Produce Large Volumes of Turbid Water (“Colorant”) ◦ SUP Mandates Disruption of Majority of Site for Utility/Roadway Installation

and Grading during Phase I Construction

Traditional SESC Measures◦ Silt Fence/Hay Bales at Discharge Locations◦ Additional Riprap Check Dams/Velocity Reducers◦ Improved Ground Surface Matting and Dormant Seeding in Swales◦ Placement of Polyacrylamide (PAM) Blocks ◦ Grading/Construction of Berms to Sequester Storm Water in

Disturbed Areas

Enhanced SESC Measures◦ Pumping of Storm Water from Discharge Locations Back to Ponds◦ Trucking of Storm Water/Off-Site Disposal (6.0 million gallons)◦ On-Site Treatment of Storm Water (4.9 million gallons)◦ Construction of Berm/Swale to Reduce Surface Runoff◦ Continuous Staffing of SESC Measures During Rainfall Events

Interim Monitoring of Acme Creek During Construction Augmentation of Wetland Plantings in Storm Water Basins

and Swales◦ Vegetation Augmentation Plan (January 2015)◦ Implementation of Vegetation Augmentation Plan in Spring of 2015

Design Validation for Permanent Basins/Swales◦ Verify Constructed Features Achieve Performance Objectives◦ Document Consistency with SUP Requirements

Evaluation of Runoff to Adjacent Theatre Property SESC Improvements ◦ Limit Areal Extent of Future Land Disturbances◦ Promote Use of Localized SESC Measures in Future Development Areas