Stormwater Treatment 1500 & 1600 Alvarado Street

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2.2 Permit Requirements Silva Cells may be designed and installed as LID BMPs that fully or partially satisfy applicable soil and/or stormwater requirements for new or redevelopment projects. Check the local permit requirements to determine whether such requirements apply to your project. While Silva Cells can be designed as LID BMPs, they can also be used to promote large, healthy trees in dense urban environments, without the intent of formally managing stormwater runoff. In such cases, stormwater permit requirements would not apply. 2.3 How to Use this Manual Operations and maintenance guidelines are provided in Section 3.0, organized in three subsections, as follows: • Subsection 3.1 Key Maintenance Considerations - Provides details regarding maintenance activities that should be considered to maintain function of the facility. • Subsection 3.2 Key Operations to Preserve Facility Function - Discusses the functions of the BMP that need to be preserved to maintain the intended performance. • Subsection 3.3 Maintenance Guidelines - Provides information that can be used to develop a site specific maintenance plan. Successful use of this manual requires understanding of the design intent, site and as -built conditions, and knowledge of applicable permit requirements (Section 2.2). 2.4 Definitions Definitions 'for important terms used throughout this manuaf are as follows: • Best management practices (BMPs) - Activities, practices, procedures, structural features, or products that are designed to reduce the risk of causing adverse impacts to downstream water bodies. • Drawdown Time - The time it takes water from a given runoff event to completely drain through an infiltration I3MP, typically measured from the end of the event to the time the water level in the system r'etl.tr?'t5 to lbaseflow conditions. • Infiltration — Percolation of stormwater runoff into soil media or native site soils. • Low Impact Development (LID) - A development approach that manages stormwater by working with nature and the existing site conditions in a manner that will reduce or prevent adverse impacts to the site or downstream environment. • Macropores — Large, free -draining soil pores, oftentimes found between aggregates or near tree roots. 3.0 f�iaint.:inincj `�ilr<s _� :>ils This section identifies key component design functions and maintenance considerations, provides guidance on inspection and maintenance activities and recommended frequencies, lists needed equipment and materials, and discusses skills and staff needed to perform the recommended maintenance. 3.1 Key Component Design Function and Maintenance Considerations Key components of the Silva Cell system include the inlet structures, distribution pipes, the modular Silva Cell units ant:] frarnes, fill soils, under -drain pipe, flow control structures, trees/vegetation, and surface treatments. Intended general design functions and maintenance considerations for each of these key components are discussed below. 3.1.1 Inlet system Silva Cell inlet systems can be designed to allow stormwater runoff to flow into the facility in a nurnber of ways. Water can sheet flow from adjacent hardened surfaces, infiltrate via overlying or adjacent permeable surfaces, flow through curb cuts, or be piped from a catch basin, roof drains, or yard drains. I {owever the inlet systems) are configured, they must be properly sized and maintained to allow stormwater runoff from the intended contributing drainage area to enter the facility. Key maintenance considerations include providing pre-treatment through temporary erosion and sedimentation control measures in the tributary drainage basin during construction and long-term pre-treatment through stabilization of open soil areas in the tributary basin with plants or mulch and maintenance of inlet capacity by removing sediment, trash, and debris from inlets and the contributing drainage area. Silva Cell Operation and Maintenance Manual