25F - AGMT - DELHI DIVERSION PROJECT

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Conceptual Design Iteration(s) Design Iteration 1— URS Preliminary Design Report(PDR). Submitted as part of OCTA Environmental Cleanup Tier 2 Grant Application. Process included grate inlet catch basin located along the bottom of the Santa Ana Delhi channel followed by a storm water treatment device, CDS Unit, with the capacity to capture sediment, trash, and debris prior to discharging the flows into an underground storage tank, and then eventually be pumped into the Orange County Sanitation District for further treatment and final discharge, Features • CDS units sized for Dry- weather Flow only ' System installation may not require extensive construction ' System maintenance requirements are low Design iteration2— URS PDR Addendum No. 1 This iteration included a revised • Increased treatment process that included in- channel radial gates to divert majority of dry- weather flow capacities and up to 100 cfs of first flush wet - weather flow to an off -line treatment facility ® Incorporated direct irrigation consisting of bar screens, sediment trap and fine screening chamber, and followed reuse options. by a discharge storage chamber prior to pumping to the Newport Beach Golf Club for • Minimized off -site pumping irrigation purposes or discharging to near -by Costa Mesa Sanitary District (CMSD) requirements. sewer facilities and then conveying flows to the Orange County Sanitation District for ' Minimized off -site final treatment and discharge. infrastructure improvements. Design Iteration 3 —URS PDR Addendum No 2. Refined the channel diversion • Radial gates capable of options to include radial gates, and inflatable rubber dams. Improved the intake and diverting dry- weather and treatment process to meet 100 cfs operational capacities and refined life cycle costs wet- weather flows for the development of an operational agreement between the project Stakeholders ' Discharge captured flows to and the County of Orange. On -site irrigation options eliminated due to potential risk OCSD trunk sewer line or seen by the OC John Wayne Airport. Process includes an in- channel diversion used for irrigation structure, intake structure, pretreatment and trash removal unit, a bypass structure to return up to 100 cfs of the first flush storm flow to Delhi Channel, pretreated water storage tanks and a dry- weather pump station discharging treated flows to an OCSD sanitary sewer main via an 8 -inch force main or used at the adjacent Newport Beach golf course for irrigation. The final design for the proposed project will be based on a refinement of Design Iteration No. 3 that will include the development of an in- channel trash screening structure. The proposed design refinement will have the ability to screen trash and debris from channel storm flows up to approximately 1200 cfs or equivalent to the stormwater quality flow event. 'The intent of the refinement will be to qualify the proposed improvements as a regional BMP and, therefore, satisfy the proposed amendments to the MS4 permit addressing trash removals. URS will prepare up to two additional design refinements to serve as the basis for the final design as follows: In- channel Screening — Perforated Radial Gates URS has researched and developed an alternative design to the radial gates diversion structure that incorporates in- channel screening by perforating the front face of the gate and, therefore, screening out debris and trash from the channel. In general, the perforated gates will be approximately 8 feet tall and 25 feet wide, similar to the radial gates that were presented in the 2�d and Yd design iterations. Operationally, the surface of the radial gates will be customized with perforated plates with 3/16" diameter punched orifices for the entire surface area of the gate. During dry - weather conditions, the low flow will be screened through the 3/16" orifices and diverted to storage /pump station facility for discharge to the sanitary sewer system. Theoretically, the perforated radial gates will be capable of screening the storm flows up to 1,200 cfs and have a total capacity of 3,683 cfs channel capacity in the closed position combining both the proposed screen flow and the flows over the screens in a bypass configuration. The combination of orifices in the gates and flow over the gates, below the overall channel lieeboard, will have a total capacity to pass a 2 -year storm event. During the non -storm season, dry- weather flows will be collected downstream of the radial screens through two depressed grated inlets and a pipeline to a 25P 33