The Village at Grand Traverse Phase 1

Stormwater Management Recommendations

December 22, 2011

Prepared for: Gourdie-Frasier, Inc. 123 West Front Street

Traverse City, Michigan 49684 (231) 946-6874

Prepared by: King & MacGregor Environmental, Inc.

40595 Koppernick Road Canton, Michigan 48187

(734) 354-0594

King & MacGregor Environmental, Inc. December 22, 2011 VGT Phase 1 – Stormwater Recommendations 2

INTRODUCTION King & MacGregor Environmental, Inc. was retained by Gourdie-Frasier, Inc. to provide recommendations on how wetland vegetation might be used to increase the ability of stormwater management basins to detain and treat stormwater as part of Phase 1 of The Village at Grand Traverse (VGT) development. Stormwater management is proposed to occur in two locations, with both locations consisting of a series of three tiered basin. One recognized approach to using wetland vegetation in stormwater management can be described as the best management practice (BMP) “constructed wetland use in nonpoint source control” as defined by the Michigan Department of Environmental Quality’s Guidebook of Best Management Practices for Michigan Watersheds. A subset of this BMP is a pond/wetland system. Using the MDEQ’s Guidebook as a framework, we offer the following recommendations for the development of a pond/wetland system at VGT Phase 1. PROJECT GOALS Typical goals in pond/wetland systems are to develop a stand of vigorous wetland vegetation that slows stormwater flow through ponding and meandering flow pathways, provides opportunity for suspended solids to settle out of the stormwater, and uses vegetation growth to take up nutrients and soluble pollutants in the water. CONCEPTUAL DESIGN RECOMMENDATIONS As shown in Figures 1-3, we recommend creating microtopograpraphic features that create a heterogeneous surface along the bottom of the first and second basins. The goal of creating these varying water depths is to establish differences in environmental conditions that can support a greater diversity of vegetation. The different elements are described as follows:

Plunge Pool. This pool dissipates energy and allows for initial settling of suspended

sediments. Under normal conditions (i.e. not during a storm event), this pool would have a minimum water depth of 3 feet.

Low Marsh Zone. Water depths of 3-9 inches under normal conditions.

High Marsh Zone. Water depths of 0-3 inches under normal conditions.

Pond. Water depths greater than 2 feet under normal conditions. The proposed design establishes a sinuous stormwater pathway in the first and second basins within the Low Marsh Zone. This pathway is a way to create a longer treatment train for runoff generated by first-flush and other lower-volume events (first-flush runoff is typically understood to contain a higher concentration of pollutants and therefore in need of maximum treatment). If runoff volumes are sufficient to fill both the first and second basins, the excess water will flow into the final “pond” basin. This pond will provide necessary storage volume in the system while also providing final treatment of any remaining suspended sediments. To aid in the establishment of plants in the first and second tier basins, we recommend spreading six inches of topsoil over the basins and then broadcasting a native wetland seed mix. A suggested planting mix is provided in Figure 4. Our goal is to provide a diverse assemblage of plants that are native to Michigan and recognized in the trade as capable of withstanding the hydrologic conditions anticipated in these basins. Although the proposed wetland plants can withstand inundation, excessive water depths for extended periods of time will reduce their vigor. It is also our understanding that the native soils are very impermeable, thereby making infiltration of stormwater not feasible. Therefore, we recommend placing some engineering constraints on the maximum depths and duration of flooding in the vegetated cells.

King & MacGregor Environmental, Inc. December 22, 2011 VGT Phase 1 – Stormwater Recommendations 3

We have represented those constraints as slow-release control structures and emergency spillways in the conceptual plans and have developed the planting schemes with a targeted maximum increase in water depth of 12 inches during storm events and a return to “normal” water levels within 72 hours. The proposed basin design also has the potential for the development of public access and educational programs. The berms that divide the individual basins in each series can be maintained as trails, which afford the public the opportunity to walk “into” the system and experience its component parts. Coupled with informational signage, it is possible to use this system as a demonstration that educates the public on how stormwater runoff can affect our natural environment and how BMPs such as this wetland/pond system seek to mitigate those impacts. The conceptual plans identifies possible trail alignments and educational sign locations. MANAGEMENT AND MAINTENANCE RECOMENDATIONS Once constructed, the stormwater basins should be inspected annually and maintained as needed to ensure proper function. Typical inspections should include tasks such as:

Inspections for failures such as eroding banks or undermining of riprap;

An estimation of sediment accumulation in plunge pools and ponds;

An examination of plant establishment and vigor;

An examination of invasive plant species establishment such as purple loosestrife (Lythrum salicaria), giant reed (Phragmites australis) and reed canary grass (Phalaris arundinacea); and

Inspection of the operation of any mechanical structures such as water control structures.

Typical maintenance should occur as warranted by the inspection results and may include such tasks as:

Removal of trash, debris, and excessive sediment deposits;

Mowing of access corridors;

Harvesting of wetland vegetation to promote plant growth and uptake of soluble nutrients and pollutants;

Controlling invasive species using best management practices; and

Reseeding areas of sparse vegetation. WATER QUALITY MONITORING RECOMMENDATIONS The Michigan Department of Environmental Quality has established water quality rules mandating that toxic substances shall not be present in the surface waters of the state at levels that are or may become injurious to the public health, safety, or welfare, plant and animal life, or the designated uses of the waters. Scientific studies suggest that pond/wetland systems such as the one proposed here are effective at reducing the contribution of pollutants from a developed site that may degrade natural systems such as wetlands and streams. Furthermore, stormwater detention systems in general function to reduce spikes in peak flow volume in receiving waters. However, the actual impact of any specific development on adjacent natural systems can only be determined through site specific monitoring. The receiving water for this site is Acme Creek. How stormwater from this development may affect the water quality of Acme Creek could be monitored by establishing a water testing program. Parameters that can be used to judge possible impacts include the composition of the aquatic macroinvertebrate population, dissolved oxygen concentration, water temperature,

King & MacGregor Environmental, Inc. December 22, 2011 VGT Phase 1 – Stormwater Recommendations 4

specific conductivity, pH, volatile organic compounds, total organic carbon, total dissolved solids, total suspended solids and E. coli, of which have testing methods established by the US Environmental Protection Agency and the Michigan Department of Environmental Quality. Possible changes to the flow regime in Acme Creek can be evaluated by installing and monitoring stream gauges that measure both velocity and water level. To facilitate such a program, we recommend establishing two fixed testing locations with one at the upstream point where the Acme Creek enters the property and one at the downstream point where Acme Creek leaves the property. A recommended monitoring and reporting schedule is as follows:

Monitoring & Reporting Frequency

Study Parameter Baseline Year 1 Years 2-4 Years 5+ Macroinvertebrates Prior

Dissolved Oxygen To Monthly Quarterly Spring/Fall

Water Temperature construction

Specific Conductivity

pH

Volatile Organic Compounds

Total Organic Carbon

Total Dissolved Solids

Total Suspended Solids

Water Velocity & Level

Maintenance Inspection Annually Annually Annually

A comparison of the upstream and downstream values over time can be used by interested parties to develop lessons learned from how this BMP was implemented at VGT Phase 1 and how its use might be improved for other projects in the future. REFERENCES Center for Watershed Protection, National Pollutant Removal Performance Database, version 3. 2007

Michigan Department of Environmental Quality, Guidebook of Best Management Practices for Michigan Watersheds. 1998 Michigan Department of Environmental Quality, Water Bureau, Water Quality Standards.

Administrative Rules filed 200

United States Environmental Protection Agency, Field Operations Manual: Wadeable Streams Assessment. 2004

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