City Council Meeting Date: December 12, 2017
To: Mayor and City Council
City Administrator
From: David E. Bennett, Public Works Director/City Engineer
Sean M. Simonson, Engineering Manager
Title
Review of the 2017 Pond Assessment Study
Body
Action Requested:
The Northfield City Council discusses the 2017 Pond Assessment Study.
Summary Report:
In December 2016, the City released its Request for Proposals (RFP) for the Stormwater Pond Assessment. The RFP laid out a detailed scope of work that included a multi-phase approach for understanding the ponds current capacities for water quality improvements and set in motion a plan for cleaning the highest priority basins. The scope included the following phases:
* Phase 1: Perform bathymetric survey and compare results to as-built surveys and grading plans. Evaluate the ponds to determine the estimate life expectancy based on historical and anticipated loadings. Provide GIS mapping of bathymetry and original construction. Provide table of sediment accumulation.
* Phase 2: Identify stormwater ponds with the highest percent sediment accumulation. Sample and test the sediment in the highest priority ponds. Determine the respective disposal category. Provide project cost estimates.
* Phase 3: Determine the Total Suspended Solids (TSS) and Total Phosphorus (TP) treatment effectiveness.
Bolton and Menk, Inc., along with the City of Northfield, performed assessments on 50 ponds within the City of Northfield. The following information was collected during the 2017 Pond Assessment Project:
* Stormwater pond bathymetric assessment
* Field-collected data summary
* Pond cleaning prioritization
* TSS and TP treatment effectiveness
* Estimated pond cleaning costs
After data collection, the ponds surveyed were prioritized based on the "percent full" of accumulated sediment in each pond. The Minnesota Stormwater Manual highly recommends sediment removal activities after 50% of the total forebay capacity has been lo...
Click here for full text