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ARROYO LAGO RESIDENTIAL PROJECT ADDENDUM FCS 51 Https://adecinnovations.sharepoint.com/sites/PublicationsSite/Shared Documents/Publications/Client (PN-JN)/2148/21480036/Addendum/21480036 Arroyo Lago Residential Project Addendum.docx Domestic Water Water service for the proposed project would be provided by the City via connection to an existing 12- inch diameter water line along Busch Road and an off-site existing 16-inch diameter water line on Mohr Avenue. To access the existing water line in Mohr Avenue, as shown in Exhibit 9c, the proposed project would construct a new 12-inch diameter water line extending from the northwest corner of the project site, following the existing utility road, to Mohr Avenue. Stormwater Drainage Two options are being studied for handling the proposed project’s stormwater drainage: one involving conveyance to the City’s existing storm drain system (City Stormwater Option) and the second option involving the stormwater discharging into Zone 7’s facilities (Zone 7 Stormwater Option). The Zone 7 Stormwater Option would be subject to Zone 7 approval. Both options are described further below.19 City Stormwater Option Stormwater generated by the proposed project would be collected via 6-inch storm gutters along the proposed internal streets and conveyed through an on-site network of 18-inch underground storm drain pipes to the City’s existing storm drain system. Under normal operating conditions, stormwater would be conveyed via an approximately 45-inch diameter pipe to a proposed primary bioretention area located approximately 0.45 mile east of the project site, adjacent to El Charro Road (Exhibits 9b and 9d). The applicant would be responsible for the maintenance and ongoing operations of this facility in compliance with City standards as conditioned through the Conditions of Approval or the PADA . The primary bioretention area would include a treatment area of approximately 40,000 square feet. The bioretention area would contain two layers: an approximately 18-inch layer of bioretention soil mix and an approximately 12-inch layer of Class II permeable rock. After being treated, the stormwater would be pumped out of the bioretention basin into a storm drain force main that would be located in El Charro Road and would flow south to Busch Road where it would flow west and connect to an existing City storm drainpipe in Busch Road (Exhibit 9a). In larger storm events, stormwater would be temporarily stored in a detention basin just northeast of the bioretention area. The detention basin has been sized to accommodate back-to-back 100-year storm events in accordance with all applicable standards and requirements, allowing stormwater discharge to be metered to ensure that the capacity of the City’s storm drain system is not exceeded. In addition to the normal stormwater system, the proposed project is also designed with overland release, which includes a path for surface floodwater to flow through the development in a manner that protects structures should the underground storm drain system be blocked or overwhelmed. 19 The proposed project would implement one of the two stormwater options, and thus, both stormwater options are being considered in this Addendum for purposes of a conservative analysis.