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WS – Item 2 WORK SESSION STAFF REPORT Work Session Item 2 Date: January 6, 2014 To: City Council From: Michael Grochala Re: NE 35E Area Drainage Study Background The City Council authorized preparation of the NE 35E Area Drainage Study in Nov ember of 201 2 . The purpose of the study was to evaluate options to address drainage for a 700 acre area lying NE of the 35E interchange. The majority of this area drains to County Ditch 55, under 35E and ultimately to Clearwater Creek. Land within this area is poorly drained with clay soils that ha ve minimal infiltration capacity. Additionally, the tile line (Ditch 55) that conveys water from this area was constructed in the early 1900’s for agricultural purposes. The size of the tile ranges from 10 to 15 inches and does not have the capacity to c arry new ru noff from developing properties . Given the constraints of the syst em and need to balance agricultural, development and public infrastructure needs , a comprehensive management plan is needed for this area. Addressing both water quality and volume requirements within this area will have an impact on the developability of property within the c orridor. Since this is an area of high importance from an economic development perspective , it appears to be in the best interest of the city and land owners to develop a plan that identifies the best options for stormwater treatment and storage, preservation of natural areas and establishment of a preferred conveyance system and routing for stormwater. The draft concept plan submitted to the Rice Creek Watershed D istrict (RCWD ) proposes the construction of a new storm sewer line running south to Clearwater Creek. The plan would require approval from the RCWD to increase the allowable rate of stormwater discharge d into the creek from this drainage area . The outlet is proposed to include a gate that will limit this discharge to non -peak periods. This is intended to mitigate any potential impacts downstream of the outlet. S ubmittal of the conceptual plan in September has led to additional d iscussion s with the RCWD as well as data production not originally anticipated with the original contract scope . While RCWD has been cooperative and is taking an active role in modeling efforts we are anticipating additional analysis will be needed from W SB. The original contra ct for the study was $16,500. Additional work performed by WSB is being billed on an hourly basis. Staff is requesting authorization to increase the contract amount to $25,000 to address continued work on the project . This work will be funded from the Surface Water Management Fund. This fund is established from fees collected from developing properties to cover city planning, administration, and trunk infrastructure costs related to surface water management. Once an acceptable rate of discharge is arrived at between the City and RCWD it is likely that a more expansive stormwater management plan will need to be submitted to RCWD for approval. This process will be covered under a separate agreement with WSB once the final drainage parameters are determined.