8.2. SR 11-03-2014 - Laserfiche WebLink

Home Browse Search

Rivers Edge Commons Park Alley Improvements 10/28/14 O Page 2 SCOPE OF SERVICES On October 23rd, 2014,Bolton&Menk staff met with City staff on site to review the current paver issues, discuss site constraints, and brainstorm ideas for water quality retro fits. Porous pavers will be installed with an integrated filtration/infiltration subgrade system. The slope of the alley from Main Street to the River will be a challenge, especially if filtration/infiltration is utilized along the entire slope. Bolton& Menk has prepared the following scope of services and associated fees to analyze the watershed, determine the expected improvements in water quality,recommend alternatives, and prepare design plans. TASK 1 - DEVELOP DRAINAGE AREAS AND ANALYZE WATER QUALITY Task 1.1—Delineate Watersheds Bolton&Menk will utilize Light Detection and Ranging(LiDAR)topographic information to delineate watersheds contributing stormwater runoff to the River Edge Commons Park alley. We will utilize City storm sewer information to determine the total flow entering the local drainage network. Also, local knowledge and site visits will be utilized to determine the location and contribution of roof drains. Task 1.2—Develop Watershed Characteristics and Hydraulic Model Once watershed areas are determined, Bolton&Menk will develop a preliminary hydraulic model to determine the total surface runoff to the alley based on watershed characteristics (e.g. Curve Number and time of concentration). Soil properties will be analyzed utilizing the National Resources Conservation Services (NRCS) soils information and any available soil boring data in the area to determine the hydraulic soil group and preliminary infiltration rates. These properties will ultimately be used to determine the potential volume reduction capacity of the proposed system. Task 1.3—Calculate Theoretical Pollutant Loadings Watershed calculations will be used to determine theoretical pollutant loadings based on design recommendations from the Minnesota Pollution Control Agency(MPCA),the Minimal Impact Design Standards (MIDS), and the Minnesota Stormwater Manual. This includes theoretical pollutant loading assuming an Event Mean Concentration(EMC)for total phosphorus (TP)and total suspended solids (TSS) for specific combinations of hydraulic soil group, land cover, and percent imperviousness. While these values are theoretical,the results will provide us an idea of the extent of pollutant loading in the area as well as an apples-to-apples comparison of the anticipated removal efficiency of the proposed water quality system. Bolton& Menk will analyze the proposed pollutant loading and provide recommendations to the efficacy of a water quality system. If the anticipated pollutant loading is relatively negligible relative to the City's overall water quality goals,it may be worth utilizing funds in areas where water quality treatment will have a larger impact. If so,it may be more prudent to augment the pervious paver system to focus on volume control only. We will not proceed to Task 2 until the preliminary water quality results are presented to the City.