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DRAFT (As of 2/1//2013) CHAPTER 2 POLICIES The policies outlined in this section were used to develop the 2012 Storm Drain Master Plan (2012 SDMP), and they provide guidance for the planning and design of all site‐specific drainage projects within the City. 2.1 Stormwater Disposal Methodology The South San Joaquin Irrigation District (SSJID) owns a complex network of irrigation Laterals and Drains that run throughout the City’s limits. These facilities deliver irrigation water to various farming operations, and they convey excess irrigation water and field runoff to downstream receiving waters, specifically the San Joaquin River. The City relies on SSJID’s facilities to convey its stormwater runoff to the San Joaquin River, and will continue to do so through buildout of the City’s General Plan. 2.2 City / SSJID Master Drainage Agreement The City and SSJID have a long‐standing agreement that authorizes the City to discharge its stormwater runoff into SSJID facilities for ultimate disposal to the San Joaquin River. In 1975 the City first entered into a storm drainage agreement with SSJID, and in 2006 the City renewed its drainage agreement with SSJID. See Appendix A1 for a copy of the City / SSJID Master Drainage Agreement. Of the many requirements in the 2006 Agreement, the two most significant new requirements are: 1. All stormwater discharges into SSJID facilities must be monitored and controlled such that the capacity of SSJID’s facilities is not exceeded. 2. Stormwater quality must be controlled such that it complies with all applicable laws. The City meets the first requirement by requiring all new development to attenuate its runoff in a storage facility before pumping it into SSJID’s facilities. In addition, the City uses real‐time water level monitoring stations at critical low points in the conveyance system complete with SCADA (Supervisory Control and Data Acquisition) facilities. Regarding the water quality requirement, the City is classified as a Phase II city by the State Water Resources Control Board. As such, the City, and consequently new development, is required to comply with the State Board’s stormwater NPDES permit for Phase II cities. 5
2.3 Direct Discharge Area DRAFT (As of 2/1//2013) The Direct Discharge Area (DDA) is an area located primarily in the older areas of the City where most of the storm runoff is not attenuated, but instead flows directly to SSJID facilities without any storage or control. The DDA is largely built out with just small‐parcel, in‐fill areas remaining. See Figure 2‐1 for a depiction of the DDA. Per the City / SSJID Master Drainage Agreement, SSJID now prohibits the direct discharge of stormwater runoff to its facilities. The existing, non‐attenuated storm runoff flows are exempt from this requirement, but new development in the DDA is required to install attenuation facilities with positive control for any new storm runoff. There are, however, exceptions to this requirement as specified in Chapter 3. 2.4 Attenuate Peak Stormwater Runoff Flows Per the City / SSJID Master Drainage Agreement, SSJID prohibits the direct discharge of stormwater runoff to its facilities. Accordingly, the City requires all new development to attenuate its runoff in a storage facility before pumping it into SSJID’s facilities. For surface attenuation facilities, the three allowable basin types are described below. (1) Permanent Detention Basin: Residential Applications Permanent detention basins in Residential areas are to be sized to hold a 10‐year, 48‐hour duration storm runoff volume resulting from 3.56 inches of rainfall occurring over the entire contributing area. All basins shall have positive shut‐off control. Regional detention basins designed to serve several developments are preferred over smaller, individual basins. Water quality treatment is to be included in detention storage basins to meet stormwater NPDES permit requirements. Detention basins are to be designed as multi‐purpose facilities when practical. The volume of detention basins shall be determined with no allowance for percolation or outlet facilities. The full design criteria for permanent detention basins are summarized in Chapter 3. (2) Interim Percolation Basin: Residential and Non‐Residential Applications Percolation basins may be used as an interim measure for retention and disposal of stormwater runoff in those areas that will not receive storm drainage service from a major storm drain system by the time development occurs. When discharge capability to a major storm drain system becomes available, the basins are to be exchanged for or converted to detention basins with pumped discharge facilities. Interim percolation basins are to be sized to store two (2), 10‐ year, 48‐hour duration storm runoff volumes over the entire contributing area. The full design criteria for interim percolation basins are summarized in Chapter 3. 6
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43 STADIUM CENTER 2470 DANIELS ST.
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