Reg 2018-09-17 Item 3G - Contract Amendment #2 - Riverton Creek Flap Gate Removal with Otak Inc for $37,064

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(47t Aw r' % I ;,! ;< ''it Allan Ekberg, Mayor 0 a Public Works Department-Henry Hash,Director INFORMATIONAL MEMORANDUM TO: Transportation and Infrastructure Committee FROM: Henry Hash, Public Works Director , ,4 - BY: Mike Perfetti, Habitat Project Manager DATE: September 7, 2018 SUBJECT: Surface Water Fund - Riverton Creek Flapgate Removal Project Project Number 99830103 Contract 17-070, Amendment No. 2 ISSUE Approve Amendment No. 2 to Contract No. 17-070 with OTAK, Inc. BACKGROUND In May 2017,the City entered into a consultant agreement with OTAK, Inc.for design and permitting services for the Riverton Creek Flapgate Removal Project. This project will increase salmonid accessibility to rearing habitat in Riverton Creek by removing two culverts and flap gates at the mouth of the creek and replacing a section of at-grade trail with a bridge over the restored open channel. DISCUSSION Under the original scope of work, Otak performed a review of the previous design work(Berger ABAM, 2009),and found that on- site geotechnical evaluation,cultural resources, and hydraulic modeling and scour analysis had not been provided,though stability concerns had been documented. OTAK's Amendment No. 1 added geotechnical services and some additional scope to revise the channel section to address long- term stability concerns. As a result, the team is recommending that a second row of tie-back anchors be installed in the existing sheet pile wall (supporting Tukwila International Blvd.), and a new,taller soldier pile wall be installed on the east side of the channel to minimize disturbance and excavation of the existing soils and parking lot.After a constructability review,the team also recommends revising the construction sequencing shown in the 2009 design in order to reduce the risk for mobilization of sediment into the Duwamish River during channel excavation. Sediment mobilization will likely be a concern to the environmental reviewing agencies. The proposed Amendment No. 2 will incorporate current findings and recommendations into final design and bid documents that will include the realigned creek channel, improved sheet pile wall design, improved construction sequencing, and services to support the City in addressing permit agency comments. FISCAL IMPACT Amendment No. 2 is for$37,064.00, bringing the total contract amount to$182,420. To fund Amendment No. 2,the project will utilize remaining 2018 CIP surface water design funds and the 2019 design budget,then be partially or wholly reimbursed through the 2017 SRFB design and construction grant of$846,965.00 (The match requirement is$149,465.). Agreement 2018/2019 Budget Original OTAK Contract+Amendment No. 1 $ 145,356.00 $ 145,356.00 OTAK Amendment No. 2 37,064.00 40,730.00 $182.420.00 $186,086.00 RECOMMENDATION Council is being asked to approve design Amendment No.2 for$37,064.00 with OTAK, Inc.for the Riverton Creek Flapgate Removal Project and consider this item on the Consent Agenda at the September 17, 2018 Regular Meeting. Attachments:Page 93,Proposed 2019—2024 CIP OTAK Supplemental Agreement#2 61 W:1PW Eng1PROJECTSIA-DR Projects\Riverton Flap Gate Removal(99830103 98-DR03)1Consultant Selection\Phase 21contract\Amendment#21Info Memo Otak PE Amend 42 20180810g1.docx