Stormwater Treatment 1500 & 1600 Alvarado Street

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.0 c".�c1,ncv,,iec rYle1?ts There are many dedicated, brilliant people working on the challenge of creating healthier, more sustainable, and more efficient cities. We believe the most successful of these places will be those grounded in the principle that nature and engineering can coexist successfully. Soil, urban trees, and sustainable stormwater management are at the core of this effort. We wish to express our tremendous appreciation and gratitude to the many researchers and practitioners whose work we have relied on to inform the guidelines contained in this manual. Thank you to the following people for their specific: r..ontribut:ions. Authors: DeepRoot Green Infrastructure, LLC John Erickson, HDR Engineering Robin Kirschbaum, HDR Engineering Technical Review Committee: Tim O'Hare, Tim O'Hare and Associates Jonathan Page, North Carolina State University (Engineering Intern to Dr. Bill Hunt) Dr. Jessica Sanders, Casey Trees Nathalie Shanstrom, Kestrel Design Group James Urban, Urban Trees Soils %.i introductio;; Silva Cells are a modular suspended pavement system that provides soil volume to support large tree growth and provides stormwater management through interception, storage, evapotranspiration, and pollutant uptake. When -filled with soil media of suitable depth and quality, Silva Cells also promote filtration of stormwater runoff through the soil media and infiltration of treated runoff into native site soils, making them a versatile Low Impact Development (LID) Best Management Practice (BMP). In March 2013, the Washington State Department of Ecology approved Silva Cells as functionally equivalent to bioretention (Ecology 2013a). This approval allows designers in Washington State to design Silva Cells to fully or partially satisfy minimum stormwater requirements for LID, water quality treatment, and flow control it accordance with the National Pollutant Discharge Elimination System (NPDES) Municipal Separated Storm Sewer System (MS4) permit (NPDES stormwater permit). Similar approvals are in place in Montgomery County, Maryland; St. Louis, Missouri; Calgary, Alberta; and North Vancouver, British Columbia. Additional approvals are currently pending in other areas across the United States and Canada as of the date of this manual. When Silva Cells are installed as part of a permanent storr-nwater management system to meet stormwater permit requirements, they should be maintained as required by the local jurisdiction for maintenance of stormwater and LID BMPs. The remainder of this section discusses the purpose of this document, applicable permit requirements, how this manual is intended to be used, and ir-nportant definitions. Section 3 presents key maintenance considerations, maintenance guidelines, equipment and materials lists, and skills and staffing needs to accomplish the recommended maintenance. Section 4 discusses the repair of Silva Cell facilities. Section 5 discusses programmatic and administrative guidance, while Section 6 provides a list of additional resources relating to LID BMP design, inspection, operation, and maintenance and Section 7 provides a list of additional resources with relevant information on stormwater and LID BMP maintenance. 2.1 Purpose This document provides guidance to assist owners and operators of Silva Cell facilities with planning and implementation of maintenance to promote long-term system performance in accordance with the design intent. These recommendations should be considered as general guidelines, not requirements, and they should be reviewed and adapted as appropriate to develop site - specific maintenance plans based on the specific design configuration of a given site. Silva Cell Operation and Maintenance Manual