Item 17 - Amend Design Services Agreement for Santiago Park Main Street Entrance

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RFP No. 20-154 k Santiago Park Main Street Entrance Design H&A Resnonsibilities VIEW DECKS There are 2 to be constructed on concrete retaining walls extending to below the creek bottom. To accommodate the new retaining walls a portion of the existing walls will be removed since there is no documentation available to determine if the new structure can be safely supported by the existing walls. The deck will be constructed of wood and cantilever 2 feet from the face of the new retaining wall above the creek. The design of the view decks will require that the present H&A Team be augmented by adding back a structural engineering firm Cho Design Associates who will develop the design and provide support during construction. A foundation report will be prepared for each location including a boring, field and laboratory testing and analysis to establish the foundation design parameters. Related construction includes demolition of a portion of the existing wall, grading of the disturbed section of the creek bank and landscaping to stabilize the slope and prevent erosion CREEK FLOODPLAIN EFFORTS FEMA has adopted a Flood Insurance Rate Mate for this location support by a Flood Insurance Study. This defines the 100-year floodplain limits as being within the channel banks, but the base flood elevation is close to the top of the channel. Additional field topo will be done to establish the existing creek cross sections extending from 100 feet upstream of the pedestrian bridge to 100 feet downstream of the Main Street bridge for purposes of hydraulic modeling. Hydraulic modeling of the existing creek conditions will be done using HEC-RAS software and calibrated to fit the supporting calculations doe to establish the FEMA floodplain. Next the view decks and retaining walls will be added to the model to determine the impact on the base flood elevation, extent of the floodplain and related characteristics. The results will be the basis for submittal to the U.S. Corps of Engineers for a CLOMR (Conditional Letter of Map Revision). The wood portion for the view decks will be built about the revised base flood elevation and grading of pedestrian pathways for access done in accordance with ADA requirements. CREEK RELATED PERMITTING Due to the construction within the creek and related floodplain, the project will require approval of the Corps under Section 404 (discharge of fill into waters), Regional Water Quality Control Board under Section 401 and a Section 1601 Streambed Alteration agreement from the California Fish and Wildlife agency in addition to completion of the CLOMR procedure. OTHER ACTIVITIES ADDED TO SCOPE Due to the lengthy reviews done to date and the anticipated permitting efforts, H&A has added 6 progress reports since the completion date has been extended 6 months from the schedule established at the June 2021 kick-off meeting. Additional design components include the "pseudo -pedestrian bridge" over the rock lined ditch (modify City detail to fit project specific location), relocation of entry gate for increased space from Main Street to gate, expanded site plans to include creek bank to show disturbed areas and added construction. HUNSAKER&ASSOCIATES IRVINE, INC.