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� �� �� e ion Watershed District � g Energy Park Plaza, 1410 Energy Park Dr., Suite 4 St. Paiil, MN 55108 Phone: (651) 644-8888 Fax: (651) 644-8894 www.capitolregionwd.org Apri120,2006 Debra Bloom City of Roseville 2660 Civic Center Drive Roseville, MN 55113-1899 RE: Parker Ave Residential Development, Roseville, MN CRWD Development Review # OS-RV-026 (Review #3) Our office has completed a follow-up review for the above referenced development. Our previous review of this project (January 25,2006) indicated that it likelymet CRWD development review criteria. The previous review letter is enclosed. However, several issues/concerns with the design were identified. Those concerns �e listed below. The applicant's engineer has submitted revised plans that address the CRWD concerns. The revisions to the plans to address CRWD's concerns arc listed below in bold type. 1. The soils boring report indicates that there is a great d�aL of variability in the soils found on site. Soil Boring #1 indicates that the northwest area of the site is suitable for infiltration since the elevation to which excavation will occur for installation of the 4 rows of 60-inch perforated pipes is located within sandy soils. However, no borings were completed in the northeast area of the site where 3 rows of 60-perforated pipe will be installed. Soil Boring #2located to the south of the northwest and northcast infiltration areas indicates a confining layer of clay that would inhibit infiltration. The applicant should consider a soil boring in the northeastern portion of the lot, as it is unknown how the northeast infiltration area will function without soil boring data for this area. The applicant has completed an additional soil boring that indicates soils conducive to infiltration. 2. The infiltration rate used in the modeling is 2 idhr. It should be noted that the maximum infiltration rate recommended in the Minnesota Stormwater Manual is 1.6 in/hr for gravelly soils. The soil borings indicate that the onsite soils with the greatest infiltration capacity are sands which have a Manual recommended infiltration rate of 0.8 idhr. Based on soil borings in the infiltration areas these rates could be revised. The applicant has revised the infltration rates in the HydroCAD model to 0.8 in/hr. 3. The details indicate that aggregate less than 3 inches will be used to provide bedding for the perforated pipes. The specifications should further indicate that aggregate with fines should not be used as fines will clog the system and prevent infiltration. The revised specifications indicate that the aggregate for the infiltration facility will not include fines. "Our mission is to protect, �nanczge, and irnprove the water resources of the Capitol Region Watershecl District. "