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HomeMy WebLinkAboutResponse to CrossRoad 6-5-2013 LettersMr. Gregory J. Ilko, P.E. December 12, 2013 Page 1 December 12, 2013 Mr. Gregory J. Ilko, P.E. CrossRoad Engineers, P.C. 3417 South Sherman Drive Beech Grove, IN 46107 Re: Health and Wellness Suites of Carmel – TAC Review Project No. 201300569 Dear Mr. Ilko: American Structurepoint, Inc., has revised the design, construction plans and drainage report for the Health and Wellness Suites of Carmel project per the review comments listed in the June 5, 2013 letter (Technical Advisory Committee Engineering Review for Development Drainage Designs). Each comment listed from the review letter contains a response addressing each issue. Below are the original comments with the response in italics. 1. Per Section 102.02 v.b, please provide normal water elevation for the pond adjacent to the southeast corner of the project site. Normal water elevation for the adjacent pond has been added to the Existing Topography sheet on C.100, Demolition Plan on C.102 as well as the Grading Plan on C.400 2. Per Section 102.02 v.g, please provide the land uses of the adjacent properties. Owners and land uses are shown on the Existing Topography sheet on C.100-C.101, Demolition Plan on C.102 and the Site Plan on C.200. 3. Per Section 102.02 vii, please revise the plan/profile sheets to include the elevations, location of all proposed storm sewers, including subsurface drains, top of casting elevations, structure numbers, pipe invert elevations, casting type, structure type, and all existing and proposed utility crossings also shall be indicated. Plan and profile sheets are subject to further review and comment after aforementioned information is provided. Revised Storm Sewer Plan and Profile sheets can be found on pages C.404-C.410. Structure and casting types are identified on the Storm Sewer Structure Data Table, Sheet C.411. Mr. Gregory J. Ilko, P.E. December 12, 2013 Page 2 4. Per Section 102.02 xi, a grading plan shall include the following: g. Please provide the 100 year overflow paths ponding areas shown as hatched areas with all associated easements. 100 year overflow paths have been added and can be found on the Emergency Overflow Routing Plan on sheet C.412-C413. h. Indication as to the system being public or private. The storm system as well as the proposed roadway is private. General note #11 on Sheet C.400 has been added to state the system is to remain private. j. Location, size and dimensions of detentions facilities including pond elevations, pond bottom elevations, top of bank elevations, spillway location and elevations, and transverse slopes of dry detention areas. Pond size, dimensions and elevations can be found on the Grading Plan on sheet C.400. Note that the pond cross-section is located on C.401. Emergency spillway detail shown on Sheet C.602. k. Emergency flood routing path(s) and their invert elevations from detention facilities to the receiving system. 100 year overflow paths have been added and can be found on the Emergency Overflow Routing Plan on sheet C.412-C-413. Sheet C.413 shows the elevations from the detention facility to the receiving system (Fertig Regulated Drain). l. One or more typical cross sections of all existing/proposed channels (swale at the outlet of the detention pond) and other open drainage facilities (detention pond) carried to a point above the 100-year high water and showing the existing land and proposed changes together with the high water elevation expected from the 100- year storm. Please provide typical cross sections of the detention facility. Grading sheets are subject to further review and comment after aforementioned information is provided. Pond size, dimensions and elevations can be found on the Grading Plan Mr. Gregory J. Ilko, P.E. December 12, 2013 Page 3 on sheet C.400. Note that the pond cross-section is located on C.401. Typical swale detail is added to Sheet C.602. 5. Per Section 102.02 xiv, please revise the Structure Data Table in the plan set to include, at minimum, the following: upstream structure number, downstream structure number, upstream pipe elevation, downstream pipe elevation, pipe length, pipe material, type of structure, and detail reference to the type of structure and any notes related to the structure. Please review and revise accordingly. Revised Storm Sewer Structure Data Table and Pipe Data Tables can be found on sheet C.411. 6. Per Section 102.03 i.a.i, the pre-development watershed map shall include the drainage area designation corresponding to the designation in the drainage calculations, the area in acres for each drainage area and any off-site drainage areas that need to be accommodated by the system, including the fully developed right-of-way per the City of Carmel Thoroughfare Plan. It appears the fully developed Right-of-Way per the City of Carmel Thoroughfare Plan was not included in the existing drainage basin. Please review and revise accordingly. Fully developed Right-of-Way has been included. See revised Drainage Report. 7. Per Section 102.03 i.b.ii, the proposed watershed map shall show that all off-site acreage draining through the site is accommodated, including the fully developed right-of-way per the City of Carmel Thoroughfare Plan. It does not appear the fully developed Right-of-Way was included in the proposed watershed map. Please review and revise accordingly. Fully developed Right-of-Way has been included. See revised Drainage Report. 8. Per Section 102.03 i.b.iv, please include the runoff curve numbers and time of concentration on the existing drainage basin map. Runoff Curve Number and Time of Concentration have been included. See revised Drainage Report, sheet EX (Existing Drainage Conditions Map) Mr. Gregory J. Ilko, P.E. December 12, 2013 Page 4 9. Per Section 104.02, the buildings lowest entry elevation that is adjacent to and facing the road shall be a minimum of 15 inches above the road. Also, finished floor elevations or the lowest building entry elevations shall be no less than 6 inches above the finished grade around the building. Also, minimum flood protection grade of all structures fronting a pond shall be no less than 2 feet above any adjacent 100-year local or regional flood elevations, whichever is greater. Please provide elevations for the finished floor and the minimum lowest adjacent grade, as well as the 100-year elevation in all storage basins including underground storage facilities in the pervious pavement. Lowest building entry elevation is 854.50. The elevation of Pennsylvania Street is approximately 856.60 to 860.80. Due to site constraints, we request a variance for the requirement that the FFE is 15” above the road elevations. The finished grade around the building is 854.00, which is 6 inches below the finished floor elevation. The minimum lowest elevation of the building is greater than 2 feet above the 100-year elevation of the pond. The minimum flood protection grade and minimum lowest adjacent grades are shown on Sheet C.400. 10. Per Section 302.04, the initially determined hydrologic group for disturbed areas should be changed to the next less infiltrating capacity category (i.e., A to B, B to C, and C to D). It does not appear that the on-site soils have been adjusted accordingly. Please review and revise accordingly. The revised drainage design has used the next less infiltrating capacity categories for the soil types. This can be found in the revised Drainage Report. 11. Per Section 302.06.1, the detention facility shall be designed in such a manner that a minimum of 90% of the maximum volume of water stored and subsequently released at the design release rate shall not result in storage duration in excess of 48 hours from the start of the storm. Please review and revise accordingly. Using the 6 inch orifice size, over 90% original detention capacity is released within the 48 hours from start of the storm. Refer to the revised Drainage Report. 12. Per Section 302.06.4, all stormwater detention facilities shall be separated from any road right of way by no less than fifty (50) feet. Please review and revise accordingly. Mr. Gregory J. Ilko, P.E. December 12, 2013 Page 5 The Stormwater detention facility is less than the 50 feet, but the proposed road is private. There will not be any right-of-way dedicated for this private drive. 13. The proposed wet detention basin shall be designed in accordance with allowable release rates per Section 302.03 of the Manual and the restricted release rates of the Hamilton County surveyor. Detention calculations are required to be provided that indicates the orifice size required to limit the release to acceptable rates, the resulting critical pond and spillway elevations, and that sufficient volume provided to accommodate the release rates being limited to the acceptable rates ( they have been provided within the submitted drainage report). The critical pond elevations resulting from this method of modeling shall be used in the MFPG/MLAG determinations. Since the resulting orifice size is less than the minimum 6-inch orifice requirement of Section 302.06.07, the lower orifice shall be upsized to a 6- inch diameter orifice. The upper orifice should then be sized appropriately to restrict the 100-year storm to the required restricted release rate. Stormwater modeling information shall be provided for both scenarios in the drainage report. Please note that the invert elevations of the orifices shall be designed so that the outlet structure can be revised to meet the restricted release rates, if required in the future. Please review and revise accordingly To meet the allowable stormwater release rates, a 4.5” upper orifice and a 4” lower orifice must be used. Given the information listed in the comment above, a 6” lower orifice was used. All associated data is provided in the revised Drainage Report. 14. Per Section 302.06.12, detention basins shall be sized to detain the runoff from the fully developed right-of-way per the City of Carmel 20-year Thoroughfare Plan across all frontages, regardless of existing watershed boundaries or drainage breaks/divides. The acreage of the full right-of-way width may be included in the overall acreage of the development in determining the allowable release rates. Please review and revise accordingly. Fully developed Right-of-Way has been included. See revised Drainage Report. 15. Per Section 303.07, the ponding and overflow path throughout the development resulting in the 100-year storm event, in the instance the drainage system is completely plugged should be clearly shown in a hatched area. Also, all buildings shall have a minimum flood protection grade no less than 2 feet above any adjacent 100-year local or regional flood elevation. 100 year overflow paths have been added and can be found on the Emergency Overflow Routing Plan on sheets C.412-C.413. Mr. Gregory J. Ilko, P.E. December 12, 2013 Page 6 16. Per Section 305.05, the inlet grate design shall be adequate to pass the design 10-year flow with 50% of the sag inlet clogged. It does not appear this was taken into account, please review and revise accordingly. Revised drainage design accounted for the 50% of the sag inlet clogged. See the revised Casting Capacity sheet in the Drainage Report. 17. Per Section 306.02.D, a minimum of 15 feet beyond the actual footprint (top of the bank or the 100-year pond elevation if no top of bank is present) of stormwater detention facilities shall be designated as drainage easement. A minimum 20-foot width easement shall also be required as access easement from a public right-of-way to the facility. Drainage easement has been included and can be seen on the Site Plan, C.200 and in the revised Drainage Report on the Proposed Storm Sewer Map. The easement is a minimum of 15 feet past the top of bank and abuts the ingress/egress easement along the drive extension for access. 18. Based on concerns raised by the HCSO and the Carmel Engineering Department, please revise the drainage report to include calculations for a downstream analysis of the proposed receiving system for the discharge from the site. The analysis should verify the required and provided capacity of the swale at the outfall of the detention outlet and of the receiving regulated drain storm sewer system. Also, peak flood elevations should be analyzed within the receiving swales in comparison to the eastern adjacent development (invert elevation of the detention outlet appears to be higher than spot grades at the property line and within the adjacent parking lot). And lastly, the condition and flow characteristics of the receiving swale should be analyzed. Outlet pipe has been added to release within the near vicinity of the 30 inch RCP pipe of the W.R. Fertig legal drain (shown on Grading Plan C.401 and Storm Sewer Plan and Profile C.409). After discussing with the HCSO, since we are discharging immediately adjacent to the 30” RCP pipe of the regulated drain, no further downstream analysis is required. Also, we are substantially reducing the discharge when compared to the existing conditions. Mr. Gregory J. Ilko, P.E. December 12, 2013 Page 7 19. In review of the existing drainage conditions on site, it appears that the project area currently drains south/southeast to the adjacent off-site detention pond. Depending on the results of the downstream analysis requested in Comment #18, this off-site detention pond may be a more adequate receiving system for the detained site discharge. It will need to be verified that the approved drainage calculations for the off-site pond accounted for this watershed area, and that the detention facility is sufficient to handle the project’s detained flow prior to approval. Also, additional coordination should be completed with the HCSO and the Carmel Engineering Department for this scenario prior to approval. Upon review of the drainage report for the existing pond to the south, and the existing site topography, it was determined that the pond was not designed to receive flow from our project site, not does it receive flow in the existing conditions. Currently, runoff from the existing site bypasses the existing pond and heads east towards the W.R. Fertig Regulated drain. The proposed design maintains this drainage pattern. Outlet pipe has been added to release within the near vicinity of the 30 inch RCP pipe of the W.R. Fertig legal drain (shown on Grading Plan C.401 and Storm Sewer Plan and Profile C.409). Per the Hamilton County Surveyor’s Office, this legal drain has a restricted release rate designated. This release rate was used in the revised drainage calculation and can be found in the revised Drainage Report. If you have any questions or need clarification on any of these comments, please feel free to contact me at our office (317) 547-5580. Very truly yours, American Structurepoint, Inc. Ross L. Nixon, PE, LEED AP Project Manager RLN: