This design memorandum presents the design and discussion of planning for stage 3 which consists of a diversion channel that protects Chaska from flooding of East Creek. Works includes trapezoidal riprap channel, articulated concrete channel, drop structures, outlets with gatewells, roadway bridges, landscaping, recreation trail and the remaining stage 4 levee at the East Creek intersection.

This report will enable the Minnesota Pollution Control Agency (MPCA) to provide recommendations to the Corps of Engineers regarding a search of the available regulatory, historical, and geological sources of information. The findings, conclusions, and engineering considerations contained within this report will form the foundation for optimizing future field investigation strategies for determining the existence of environmental hazards. This report summarizes the environmental investigation findings based on historical, geological, and regulatory agency records for Stages 3 and 4 of the Chaska Flood Control Project. The investigation was conducted to minimize the possibility that unexpected hazardous, toxic, or otherwise regulated materials and/or contaminants will be encountered during construction phases of the Chaska Flood Control Project. This study will enable the project designers to anticipate requirements for special handling of materials and groundwater during construction and to make alignment changes to minimize the need for special handling. The proposed flood control project is located in east central Minnesota, on the southern and eastern edges of the City of Chaska, in Carver County. Chaska is located approximately thirty miles southwest of St. Paul. Stage 3 of the flood control project consists primarily of a diversion channel which will protect Chaska from flooding in East Creek during a 5,500 cfs flow event. The diversion originates near Highway 17 and Engler Boulevard with a 3400 foot twin levee riprapped lined channel which merges into a 1,300 foot grass lined channel. Stage 4 of the flood control project consists of 2,800 feet of new levee and an elaborate system of relief wells and interceptor pipes on the landward side of the levee, as well as the use of wick drains and a staged construction of the levee to consolidate and strengthen the foundation soils under the new levee prism.