10/24/2012 Env Bd Packet - Laserfiche WebLink

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RCWD Permit Number 12 -078 the project specifications incorporate soil amendments in accordance with District Soil Amendment Guidelines. • Verify pipe size on CB7P in HydroCAD model matches plan. (Assuming the Pond node refers to CB -104, the model shows a 12 -inch pipe while the pipe shown on the plans is 15- inches.) • Provide an explanation why the surface area for elevation 910.00 on IP2 is larger than the subsequent elevations or fix as necessary. • Under existing conditions, the storage in the low area of Drainage Area 3 should be taken into account. • The drainage maps and hydraulic analysis must analyze the specific key points where run -off leaves the site. • Resubmit the proposed conditions map with legible drainage areas. 3. Per Rule C.6, stormwater runoff rates for the proposed project at the site boundary, in aggregate, must not exceed existing runoff rates for the critical two -year and 100 -year (both rainfall and snowmelt) frequency events. Any increase in a critical event rate at a specific point of discharge from the site must be limited and cause no adverse downgradient impact. Applicant must address hydrologic comments above show compliance with Rule C.6. 4. Applicant must address pre- treatment to prevent hydrocarbons from infiltrating in the pre- treatment area. 5. Per Rule C.10(m), complete the District worksheet explaining better site design techniques that were evaluated during project design, the results of the evaluation of each and, for any techniques deemed infeasible, the reasoning for the determination. 6. Per Rule C.4(c), the proposed project must not adversely affect water level off the site during or after construction. Specifically, the applicant must show that the overflow of infiltration Basin 1 will not adversely impact the infiltration basin currently under construction in the CSAH 14 right- off -way. Further, the applicant needs to analyze the effect of the project on the water levels in the ditch on the north side of CSAH 14 and ensure that there will be no adverse impacts to the road or adjoining properties. 7. Per Rule C.1 -0(d), the applicant must submit soil borings at the location of the infiltration features to establish the feasibility of infiltration, including showing 3 -foot of separation from the seasonal groundwater. Additionally, soil borings showing a field classification of SM must undergo additional sieve and hydrometer analysis per District Design Infiltration Rate Guidance Worksheet, or conduct an in situ test, such as a double- ringed infiltrometer to measure the actual rate. Ultimately the basins must draw down within 48 -hour following the storm event. Rule D — Erosion and Sediment Control 8. Submit the following information per Rule D.4: (c) Name, address and phone number of party responsible for maintenance of all erosion and sediment control measures. (g) Provide documentation that an NPDES Permit has been applied for and submitted to the Minnesota Pollution Control Agency (MPCA). Houston Engineering Inc Page 2 of 5 10/9/2012 • • •