29312 LAKE CHAPLAIN RD SEPA 017 - 002 - CULVERT REPLACEMENT UNDER LAKE CHAPLAIN Land Use Decision Documents 2025-04-17

page. (Lead agencies may modify this form to include additional specific information on project description.)Jhelpl Woods Lake Creek,a tributary to the Sultan River,flows under the Lake Chaplain Road embankment through an undersized culvert(62-foot-long,6-foot-wide by 4-foot rise pipe arch culvert)roughly 22 feet below the roadway elevation.High flow events result in overtopping the roadway embankment and erosion on the downstream side which is threatening the stability of the roadway.Lake Chaplain Road is the primary access to the water filtration plant,which supplies water to the City of Everett and several surrounding areas.This culvert replacement project is proposed to restore the stability of the road,protect an existing waterline crossing of the creek through channel restoration and provide fish passage per current regulations. The purpose of the new culvert structure is to accommodate larger flow events,improve fish passage across a larger range of flows and allow for more natural stream processes to occur.The proposed pipe crossing will be a single radius open bottom arch culvert on footings, approximately 80 feet long with a 22.9 foot width.Also as part of the proposed culvert,approximately 150 feet of stream channel will be reconstructed and disturbed stream banks will be restored to pre-project conditions.The proposed culvert will allow for increased flows and water levels during heavy rainfall periods. Although existing roadside features will be adjusted to accommodate these improvements,the level of service will not change and there will only be minor increases in impervious surfaces as a result of the culvert replacement project. Project construction activities,which are listed in the approximate anticipated construction sequence,include: • Traffic Control.Traffic Control Devices will be installed prior to beginning construction activities. Signage,barriers and flagging stations,if applicable,will be placed within the road right-of-way and outside of critical areas. • Work Area Exclusion,Fish Removal and Dewatering.Removal of the culvert,roadway embankment and associated fill will require a temporary stream diversion.The channel is typically dry during the anticipated in- water work period. However,dewatering the channel will be proposed prior to the excavation required for the channel reconstruction. It is anticipated that the temporary stream diversion will require a system of coffer dams, pumps and hoses to convey the stream around the work area.The work area will be isolated and fish will be excluded and removed prior to dewatering.Fish exclusion and dewatering will follow approved protocol in accordance with the WDFW HPA permit. Once the removal of the culvert and fill are complete and the channel has been constructed,flow will be redirected back into the stream channel and exclusion systems will be removed. • Temporary Erosion and Sedimentation Control(TESC)BMP Installation.General TESC BMPs will be installed in accordance with an approved TESC and Construction Storrnwater Pollution Prevention Plan. • Vegetation Clearing.The project will require the removal of some existing vegetation along the stream channel within the work area. the clearing activities will be confined to the minimum area required to remove the culvert,install the new culvert,construct the new roadbed,and perform stream channel improvements.Dominant vegetation,within the disturbance areas consists of invasive species such as reed canarygrass and Iimalayan blackberry and various non-native grasses.Native plant species that will be removed include vine maple, thimblebeny,salmonberry,red alder and bigleaf maple.Approximately 4,820 square feet of herbaceous vegetation, 2,090 square feet of Himalayan blackberry, 1,345 square feet of native shrub vegetation and a total of eight red alder trees(approximately 7 to 9-inch diameter at breast height) and three big leaf maple frees(approximately 7 to 12-inch diameter at breast height)will be removed.A total of 3,200 square feet of existing riprap armoring will be replaced in approximately the same location. Some native shrubs are currently growing within the existing riprap area. • Culvert Removal and Replacement. It is anticipated that the proposed culvert will be constructed in one phase.The existing culvert will be removed,the roadway prism will be demolished,the new channel will be constructed and the new culvert and roadway will then be constructed.The culvert will be embedded within the proposed channel material,including cobbles and boulders as designed.During construction the roadway will be temporarily closed. The filtration plant and property to the north of the project will be accessed via a northern route, following Woods Creek Road then north onto South Lake Roesiger Road and then via an existing local roadway that connects to the filtration plant and Lake Chaplain Road. SEPA Environmental checklist(WAC 197-11-960) July 2016 Page 3 of 18