2014/12/24 Council Agenda Packet

I. 9 • Parametrix • ENGINEERING.PLANNING.ENVIRONMENTAL SCIENCES mairmirimmoimm SCOPE OF WORK August 22, 2014 City of Everett Evergreen Way Water Quality Retrofit Addendum #1 The City of Everett(City) is seeking ways to provide water quality treatment retrofit Best Management Practices (BMPs)to treat stormwater runoff from Evergreen Way, most of which is currently untreated. Currently,the City is advancing the design of retrofitting a portion of Evergreen Way in the vicinity of Madison Street by modifying an existing biofiltration swale to a bioretention facility. The existing biofiltration swale is located on Albertson's property at 6727 Evergreen Way. The existing facility treats runoff only from the Albertson's property; however, the City currently provides maintenance of the facility through an existing easement from Albertson's. The facility was constructed in approximately 1991. The facility is lower than the adjacent parking lots and is bounded by existing concrete retaining walls. Record drawings, dated March 10,1992,for the existing walls were reviewed for constructability of the proposed bioretention facility. While reviewing the record drawings, potential design concerns were observed. These concerns were summarized in a technical memorandum, Existing Biofiltration Swale Retaining Walls at Evergreen Way and Madison St. (Parametrix,June 2014). The City and Parametrix have been considering alternative approaches for the project,which could defer wall rehabilitation, include wall rehabilitation or replacement in the current project, or retrofitting the existing bioretention swale. Retrofitting the existing swale would include installing an enclosed stormwater treatment Best Management Practice(BMP), backfilling the surrounding void,and constructing sidewalk and paved parking spaces over the construction area. Retrofitting the existing swale would require constructing the bioretention facility for treatment of Evergreen Way stormwater runoff in a different location. Additionally,the City is currently updating its Surface Water Comprehensive Plan. Hydrologic and hydraulic models were developed to support the February 2014 draft Pigeon Creek No. 1 Basin Plan (2014 Basin Plan). The 2014 Basin Plan identified Capital Improvement Project PC1-1 to replace a portion of the existing storm drain in Madison Street and Evergreen Way to alleviate flooding that has been reported in Madison Street on the west side of Evergreen Way. As design of the storm drain replacement has proceeded,several modifications were identified that needed to be made to the models. These model modifications impact the original assumptions regarding proposed storm drain diameter, depth, length of replacement and addition of inlets. This scope of work has been prepared to reflect the changes that have occurred as design has proceeded.This scope of work and associated budget have been prepared as an amendment to the current contract. PHASE 01 IVIADISON STREET AT EVERGREEN WAY INTERSECTION WATER QUALITY ANALYSIS AND RETROFIT DESIGN Task 2 Survey for Base Map Objective: Conduct field survey for expanded project limits. Activities: The following activities are associated with this task: City of Everett 556-1844-007(01/09) Evergreen Way Water Quality Retrofit 1 August 2014 Scope Amendment 1 116