Stormwater Treatment 1500 & 1600 Alvarado Street

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3.1.2 Distribution Pipe Some installations may include a distribution pipe to distribute inflows across the surface of the facility. Distribution pipes are typically 4- to 8-inch-cliameter (100- to 200-rniIli meter -diameter) perforated or slotted pipes installed on top of or within the soil media. Maintenance activities should preserve the ability of the pipe to distribute the water effectively by removing clogs and repairing or replacing cracked or broken pipes as needed. 3.1.3 Irrigation Systems If the Silva Cells have been designed to include irrigation, follow the n-ianufacturer instructions for operating and maintaining your chosen irrigation system. Also see the section above (3.1.2) if the irrigation systern is passive and includes distribution pipes. 3.1.4 Silva Cell Modular Units Silva Cell modular units are made from fiberglass -reinforced, chemically -coupled, impact -modified polypropylene with galvanized steel tubes. DeepRoot provides a 20-year vvarranty for the Silva Cell product, which is included for reference in Appendix A. Each module provides a 92% void volume, which is backfilled with a specified type and depth of soil media (Section 3.1.5) to support tree growth and promote stormwater management. When used in a typical pedestrian application, the Silva Cell system has an estimated design life of approximately 100 years (DeepRoot 2014). The units themselves are not expected to require maintenance within that design life duration when properly designed and installed. 3.1.5 Soil Media The soil media filled within the Silva Cell units (Section 3.1.4) performs critical functions of supporting tree growth and managing stormwater runoff. Organic matter in the soil media is important for both of these functions; because it helps trees build soil structure, provides a nutrient reservoir, and increases soil water Holding capacity. In order to preserve a healthy balance of soil organic matter and soil biology, excess soil compaction must be prevented and proper drainage through the system irrust be maintained. Silva Cells protect soils under pavement from excessive compaction by providing a post and beam structure that supports the pavement, allowing the soil media baekfill to be lightly compacted. The lightly compacted soil media creates a healthy rooting environment for trees, which deliver increasing amounts of organic content to the soil system as the roots grow and decay. Stormwater inputs also deliver nutrients, such as nitrogen and phosphorus, helping to maintain soil organic matter over time. Routine maintenance of the soil media is generally not needed provided the installation process of the cell and soil has been carried out correctly and the inlet (Section 3.1.1) and distribution (Section 3.1.2) systems are properly designed, installed, and maintained. 3.1.6 Underdrain Pipe and Flow Control Devices Silva Cells may include underdrains when infiltration of treated stormwater runoff into native soil is not feasible or not desirable. Underdrains n,ay be located at the bottom of the facility, or may be elevated to promote nitrogen: removal and peak flow detention, depending on the design intent. Typically, Underdrain systems consist of 6- or 8-inch- diameter (100- to 200-millimeter-diameter) perforated or slotted pipe. The pipe may be installed in an aggregate filter blanket layer or may be wrapped with a geotextile liner for separation. Proper design and specification of the aggregate filter blanket or geotextile liner is critical to minimizing or preventing fines from the soil media or the native site soils from clogging the pipe. Some Underdrains may be designed with flow control devices (e.g., oriIN or upturned elbows; to enhance nitrogen removal, detain peak flows, increase infiltration, or sorne combination ':hereof. These flow control devices should be maintained to prevent clogging and allow treated flows to discharge to the downstream conveyance system or receiving water as intended by design. Silva Cell Operation and Maintenance Manual