2015/06/03 Council Agenda Packet

_. i EXHIBIT A Scope of Work Lake Chaplain Road Embankment and Culvert Evaluation 1. Project Understanding and Scope of Work: Geotechnical engineering, biology, hydrology, permitting and conceptual design services are requested to evaluate the Lake Chaplain Road embankment where a tributary to the Sultan River flows through a 4 foot by 6 foot structural plate pipe roughly 20 to 25 feet below the pavement surface. We understand that water flows over the roadway threatening the stability of the roadway embankment during significant storm events. A storm event in January 2015 resulted in a circular erosion feature that developed on the north side of the culvert outfall. The failure was described to be about 6-feet to 8-feet in diameter located on the embankment slope, near the same elevation as the culvert outlet. Seepage was reported to be flowing from the bottom of the failure through the embankment slope. The cause of the failure is unknown, however it may be related to seepage through the embankment or exfiltration of water through separation joints or corrosion in the culvert. City crews provided an emergency response to stabilize the slope which included pumping the creek over the roadway during the high-flow period, and placing rock on the downstream slope face. Larger rock(about 1 to 3 feet in dimension)were placed within the failure and in the lower portion of the embankment slope, and 6-to 8-inch spells were placed in the upper portion of the slope. GeoEngineers services are requested to assist City staff in evaluation of: • The long-term stability of the roadway embankment. • Alternatives for culvert replacement that meet hydraulic criteria and current fish passage standards. • The permit requirements and projected permit pathway for completion of the culvert replacement, road improvements,and slope stabilization. Specifically, GeoEngineers proposes to complete the following tasks in response to the City's request: Geotechnical Tasks: 1. Review existing information including site plans, geologic maps, topographic maps, and City data as available and appropriate. 2. Complete a geologic reconnaissance of the existing culvert vicinity and adjacent roadway features. Our evaluation will include evaluation of soil exposures along.the embankment, existing and potential seepage/piping conditions, and near-surface soil conditions by excavating with shallow hand tools. We will also identify locations for two boring explorations to evaluate the current density/consistency of the roadway prism and for use in future design tasks. 3. Explore subsurface soil and groundwater conditions by drilling two borings with a hollow- stem auger drill rig. We expect that the borings will extend.to depths of about 30 feet, or about 5 to 10 feet below the culvert. We will complete continuous sampling during drilling to look for potential loose zones or voids that may have developed from piping. One boring will be located on the north side of the culvert to evaluate the soil conditions Lake Chaplain Roadway Embankment and Culvert Evaluation GeoEngineers File No.0661-100-04 121 Scope of Work-Page 1