HUNSAKER & ASSOCIATES IRVINE, INC.

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RFP No. 20-154 Santiago Park Main Street Entrance Design Storm Drain System The existing surface runoff patterns were planned to drain toward the creek and then pass thru several stone lined overside drains (it appears these may have been constructed as a WPA project in the 1930's). With today's regulatory focus on water quality, treatment of the runoff before entering the creek may be required. To minimize the amount to be treated, the use of permeable pavements for the access road, parking and bikeway would enable rainfall to permeate into the underlying soil. When compared to the existing surface areas, H&A staff believes we can show the amount of runoff has been reduced and the need for water quality treatment can be done effectively with one of more stone lined swales incorporated into the landscape areas using infiltration and/or biological uptake saving the City both construction and operation costs of alternative water quality treatment systems. Site Plan Deficiencies The site plan in the RFP has several deficiencies that need to be remedied as the design evolves. First the cul-de-sac as shown does not comply with City standards that are based on emergency vehicle maneuvering characteristics. Second the parking located radial to the center will require the minimum width to be available at the "narrow end". The H&A Team has developed an alternative configuration that addresses these deficiencies while remainina generally consistent with the site plan arrangement (see following page). The exceptions are a loss of planting between the roadway and bike trail (we believe the existing pavement may be reused for the bike trail in the H&A layout to save the City money) and some added curves in both the bike trail and decomposed granite walk to accommodate the revised cul-de-sac. HUNSAKER&ASSOCIATES IRVINE, INC.