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HomeMy WebLinkAboutSite Certifications - 04/24/20191218 W. ASH, STE. C, WINDSOR, COLORADO 80550 TEL. 970.674.3300 – FAX 970.674.3303 March 25, 2019 Mr. Wes Lamarque City of Fort Collins Stormwater 700 Wood Street Fort Collins, CO 80522 Re: Harmony Commons Lot 5–Site Certification Dear Wes, Please accept this letter as the Site and Drainage Certification for the Harmony Commons Lot 5 project. Survey of the site was completed on March 2, 2019 Northern Engineering. A site visit was conducted by Erika Schneider of Interwest Consulting Group on March 12, 2019. Photos of this visit are attached. My assessment is that the items constructed are in general conformance with the approved design. I have attached the as-built survey of the site. I have attached As-built drawings of the Storm System and Grading Plan and the Overall Site and Drainage Certification Form and Checklist. The site grading is finished and final landscaping for the site is nearly complete. Clean up will be completed once landscaping is complete and a final site visit will then be performed. We appreciate your time and consideration in reviewing this certification. If you have any questions or need additional information, please feel free to call at any time (970) 460-8471. Sincerely, Michael Oberlander, P.E., LEED AP Colorado Professional Engineer 34288 Accepted 4/24/2019 WL 4681 Lady Moon Drive B1806744 1/19 Page 1 OVERALL SITE and DRAINAGE CERTIFICATION Commercial, Multi-Family and Subdivision Certification Form and Checklist Project Name: Date: Building Permit Numbers: (Commercial or multi-family) Per the requirement in Fort Collins Stormwater Criteria Manual (FCSCM) Chapter 3, Section 3.0 to certify as- built construction to the approved drainage and grading plans, please fill in all applicable items in this Certification Form for Commercial, Multi-Family and Overall Single Family sites. NOTE: several items must be verified during construction. A copy of the approved grading plan must be submitted with the as-built grading plan. (As-built elevations must be written in red next to the approved elevations.) • Use “Yes” for items completed as described. • Use “N/A” for items that are not applicable to the site being certified. • If any blanks are “No,” attach an explanation referencing the item number below. Attach an explanation or description of the as-built condition for any items listed or for anything not listed but shown on the approved construction plans. Provide an as-built redline or Mylar drawing with the following: I. Water Quality and Quantity Detention Basin - FCSCM Ch. 6 and 7 For multiple detention basins on a site, provide the following for each basin separately: A. Volume: As-built topographic verification is attached at 1-foot (or less) contour intervals and volume verification calculations for the water quality capture volume and the 100-year detention storage volume. 1. Detention basin topography was prepared by a professional land surveyor registered in the state of Colorado. 2. Both proposed and as-built contours are shown on the same plan sheet (dashed lines for proposed and solid lines for as-built). 3. All critical spot elevations as shown on the approved construction plans have been verified and the as-built elevations are shown on the plan sheet. 4. Stage-storage-discharge tables are provided on a separate document. 5. Verification that designed drain time is in compliance with Colorado Revised Statute § 37-92- 602(8) is attached and has been uploaded to the Statewide Compliance Portal (tinyurl.com/COCompliancePortal) for approval. Uploaded documents must include: a. The cover sheet from the approved drainage report b. The stamped certification page from the approved drainage report c. As-built topographic survey d. Stamped certification page from the Overall Site & Drainage Certification e. PDF output from the Stormwater Detention and Infiltration Design Data Speadsheet 1/19 Page 2 B. Water Quality and Quantity Detention Basin Grading: Attached is as-built verification that there is a minimum 2% positive fall into the concrete trickle pans or flow-line(s) from all areas in the bottom of the detention pond. If there is a “soft pan” in the flow-line, all areas still must meet the minimum 2% grade requirement. 1. Low Flow: Choose one of the following detention basin low flow options as applicable: a. Turf swale for low flow path in detention basin. There is a minimum 2% grade in the flow-line(s) of the detention basin. The flattest as-built grade is . b. Concrete pan for low flow in detention basin. There is a concrete pan installed that meets the grades as shown on the approved construction plans. (Show as-built spot elevations.) c. Soft pan for low flow in detention basin. • Verify and document the soft pan material gradation, trench width and depth - to be verified during construction by engineer. Picture documentation is preferred or engineer’s statement of visual inspection and compliance. (Choose one below.) o There is a soft pan with an underdrain installed that meets the design on the approved construction plans. (Show the underdrain grades, bedding material, geotextile, spot elevations, bends, cleanouts, etc.) o There is soft pan installed without an underdrain but there is a type A or B soil. The soil type must be documented by supplying verification from a registered professional geotechnical engineer. NOTE: Spot elevations are to be within 0.2 ft. +/-. 2. Side Slopes: The as-built side slopes of the detention basin have been calculated and are shown. Indicate the side slope with an arrow and a numerical value (e.g., 6.25:1). The maximum slope allowed is 4:1. Small areas of 3:1 may be acceptable, but slopes steeper than 3:1 must be stabilized or re- graded. Provide documentation if a variance was granted for steeper slopes during the design process. 3. Spillway: The following items must be field verified: a. The location of the spillway is indicated on the as-built plan. b. The width of the spillway is indicated on the as-built plan. c. The elevation(s) of the spillway is shown on the as-built plan. d. A concrete ribbon defines the location and grade of the spillway. e. There is downstream scour protection in the spillway as per the construction plans. Indicate type: (riprap size “D50” gradation and bedding type, geotextile, buried riprap with inches of bury, etc.). f. There are no obstructions in the spillway, such as trees, bushes, sidewalks, landscape features, rocks, etc. 1/19 Page 3 4. Outlet Structure: a. The orifice plate for the approved release rate is installed with the correct size and location of the orifice. b. The orifice plate for the water quality outlet is installed with the correct hole size, number of rows and columns of holes. c. The bottom hole on both the water quality and quantity outlets are at the bottom of the plate so no water ponds in front of the plate. d. The well screen is the correct material and is installed as shown on the construction plans. e. 100-year overflow grate elevation is . (Elev. A on detail D-46) f. The top elevation of the water quality capture volume is . (Elev. B on detail D-46) g. Overflow grate is made of the correct material, has the correct bar spacing, is hinged at the top and bolted at the bottom. h. The bottom of the outlet box has no obstructions or misalignments that will cause it to retain runoff water and is sloped at 2% towards outlet. II. Channels/Swales - FCSCM Ch. 8, Sec. 2.0 and Ch. 9, Sec. 5.0 A. Capacity: The as-built capacity of all the major channels and swales has been verified. They meet or exceed capacity requirements shown in the approved drainage study for this project. 1. All swales are located within the drainage easements as shown on the construction plans. 2. Longitudinal slopes and side-slopes (cross-sections) have been verified. Design criteria requires longitudinal slopes of 2% min. (on vegetated swales) and side-slopes no steeper than 4:1. If these criteria are not met, the certification engineer will write a justification and propose mitigation for each instance or have the issues corrected. If variances to these criteria have previously been approved and are shown on the construction plans, no justification is needed. 3. As-built spot elevations on channels/swales are shown that correspond to spot elevations shown on the approved construction plans. 4. All permanent erosion control measures are installed as shown on the approved construction plans (e.g., drop structures, riprap, TRMs, etc.). (Include pictures and verification of the materials used as part of this verification.) 5. All pans, curbs, storm pipes or other appurtenances appropriately tie into each other in the system. (Pictures at tie-in points suggested.) 6. The minimum freeboard is provided for all channels and swales as shown on the approved construction plans or as identified in the approved drainage study. (Show the freeboard provided on the cross-sections as on the construction plan set or attached as separate documentation.) 7. The low flow portion of all channels or swales is clear of obstructions. (No landscaping, trees, shrubs, sod, etc. infringe on the low flow portion of channels or swales.) 1/19 Page 4 III. Storm Pipes (aka storm drains) - FCSCM Ch. 9, Sec. 4.0 A. Storm Drain Pipe Capacity: The as-built capacity of all pipes installed on this project has been verified and meets or exceeds the capacity requirements shown in the approved drainage study for this project. 1. All storm drain pipe sizes and materials have been verified and are in conformance with the approved construction plans. (Indicate on the plan and profile sheets that they have been verified.) Material and size substitutions must be approved prior to installation. If a pipe size or material was changed during construction, the certification engineer must attach the approval documents or supply them with this certification. Approval documents must include a calculation documenting the capacity equivalency (equal or greater) of the substituted size. 2. The longitudinal slope of the pipe is as shown on the approved construction plans. The acceptable minimum slope is 0.4%. All slopes flatter than the designed slope on the construction plans must be justified with capacity calculations on an attached sheet. 3. The as-built invert elevations have been verified and are shown on the plan and profile sheets of the approved construction plans. B. Storm Drain Pipe Installation Requirements: All pipes are installed in accordance with the approved construction plans and construction specifications. 1. The minimum cover requirements for all pipes have been met as shown on the approved construction plans. These will be called out in critical locations. 2. All encasements and clearances as specified on the approved construction plans have been met. 3. Any specific joint types or construction methods specified on the approved construction plans have been met. (List on a separate sheet and attach to this certification.) IV. Concrete Pans - FCSCM Ch. 8, Sec. 2.0 A. Construction/Installation: All concrete pans have been constructed in accordance with the approved construction plans. 1. The concrete pans are the correct size/width as shown on the approved construction plans. 2. The longitudinal slopes of the pans are as shown on the approved construction plans. The certification engineer must justify or mitigate longitudinal slopes less than the minimum of 0.4% unless a flatter slope was approved and is shown on the approved construction plans. Provide mitigation or justification by separate document. 3. The cross-section of the pan is as shown on the construction plans. (Specifically, the pan cross- section is “V” shaped and meets the side slope shown on the detail.) 4. The concrete pans are a minimum of 6 inches thick without reinforcement and a minimum of 4 inches thick with a minimum of 6X6-W14xW14 reinforcement per detail D20B and D20C. (Provide documentation of the reinforcement used if different than shown on the details or on the approved construction plans.) 5. The spot elevations shown on the concrete pan(s) have been verified and are shown on the as- built drawings. 1/19 Page 5 V. Storm Drain Inlets - FCSCM Ch. 9, Sec. 3.0 A. Construction/Installation: All storm drain inlets have been constructed in accordance with the approved construction plans and construction specifications. 1. The size and type of inlets are consistent with the inlets shown on the approved construction plan. Indicate by writing “Verified” on each inlet on the plan sheet or list on a separate document the inlet number(s), type and size (length). If the inlet installed is other than the one on the approved construction plan detail sheet, provide the name and source of the detail with justification for equal or better capacity. 2. The size of the inlet opening is consistent with the approved detail. (Check height and width.) 3. The elevation of the grate (if applicable) is at the elevation shown on the street profile or as indicated by a spot elevation on the construction plans. 4. The as-built invert elevations of all pipes entering and leaving the inlet are shown on the plan and profile sheets within construction tolerance of 0.2 feet. If substantially different, provide justification and capacity calculations to show the capacity is not affected or propose mitigation. 5. The as-built size of the inlet box is as shown on the construction plans or an explanation or justification is attached. 6. All Type C, R, 13 and 16 inlet covers are stenciled or stamped with the following designation (or an equivalent): NO DUMPING – DRAINS TO POUDRE RIVER. VI. Culverts - FCSCM Ch. 9, Sec. 4.0 A. Construction/Installation: All culverts have been constructed and/or installed in accordance with the approved construction plans and construction specifications. 1. All culvert sizes have been verified as indicated on the as-built construction plans as correct. 2. The culvert material type for all culverts installed is as on the approved construction plans and is indicated on the as-built plans. 3. The as-built invert “in and out” elevations have been verified and are indicated on the as-built construction plans. 4. The culvert headwalls or wing walls have been installed as shown on the approved construction plans. Headwalls or wing walls may be needed in the as-built conditions onsite if the slopes adjacent to the culvert are greater than 4:1. Please note areas needing stabilization in the certification narrative. An alternative to consider is a turf reinforcement mat (TRM). VII. Sub-Drains A. Construction/Installation: All sub-drains shown on the construction plans have been installed in accordance with those plans and the construction specifications. Sub-drains installed with the sanitary sewer are to be verified on the sanitary sewer plan and profile sheets of the construction plans. (NOTE: Indicate any sub-drains installed after the plans were approved on the as-built plans.) 1. The size of the sub-drains are as approved on the construction plans and are indicated on the as- built plans. 2. The type of sub-drain, in particular the perforated and non-perforated sections of the drain, are as indicated on the approved construction plans. 1/19 Page 6 3. The cover requirements per the construction plans are provided. 4. The cleanouts have been installed at the locations shown on the construction plans and are accessible for cleaning. (Cleanouts can be buried a maximum of 6 inches deep with their locations marked.) 5. The backfill materials for sub-drains are as shown on the approved construction plans. (This includes the type, depth and width.) 6. The geo-textile liner completely wraps the sub-drain and the permeable backfill material unless shown otherwise on the approved construction plans. (Sub-drain pipe wrapped in a sock filter material is accepted only if approved prior to installation.) VIII. Curb Cuts A. Construction: All curb cut openings are constructed in accordance with the approved construction plans and construction specifications. 1. The size (width) of the curb cut opening is as shown on the approved construction plans. 2. The curb cut openings tie into a downstream swale, pipe, or other appurtenances with a smooth transition and there no obstructions such as riprap or sod impeding the flow downstream of the curb cut. IX. Sidewalk Culverts & Chases A. Construction/Installation: All sidewalk culverts have been installed at the locations shown on the approved construction plans. 1. The size (width and length) of the culverts are as shown on the approved construction plans. 2. The cover plate is a minimum 5/8-inch galvanized plate bolted to a galvanized angle iron per the detail shown on the approved construction plans or per the City’s detail. 3. The sidewalk culvert invert “in and out” elevations have been verified and are indicated on the as-built plans. 4. The sidewalk culvert opening is as shown on the approved construction plans or per the City’s detail. 5. There is a smooth transition both on the inlet and outlet ends of the sidewalk culvert with no obstructions such as riprap or sod impeding the flow into or out of the sidewalk culvert. X. Site Grading - FCSCM Ch. 8 A. Construction: All common open spaces have been graded in accordance with the approved construction plans. 1. The grading on all common open spaces bordering private lots has been verified as correct and the as-built rear lot corner elevations have been shown on the as-built plans. 1/19 Page 7 2. The as-built contours for “overlot grading” are shown on the as-built construction plans for all common open spaces, tracts, outlots, etc. If not in compliance, please attach a narrative describing the situation for noncompliance and when it may be corrected. An escrow for overlot grading may be required. (NOTE: Residential Lot Grading Certification is a separate process from this Overall Site Certification. It is understood that residential lots will be brought to final grade once the foundation is backfilled so they may be lower than the plan shows at this Overall Site Certification stage.) 3. All turf reinforcement mats (TRMs) have been installed as shown on the approved construction plans and the slopes are stabilized. XI. Permanent Erosion Control BMPs - FCSCM Ch. 9, Sec. 7.0 A. Construction: All permanent erosion control BMPs have been installed per the approved construction plans. 1. All riprap has been installed in the locations and sizes indicated on the approved construction plans. 2. All fabric has been installed in the locations and sizes indicated on the approved construction plans. a. All fabric was installed per the details on the approved construction plans. XII. Post-Construction Site Cleanup - FCSCM Ch. 3, Sec. 2.0 A. Construction: All construction debris and obstructions of any kind have been removed from drainage paths. 1. All construction debris has been removed except in staging area(s). 2. All ruts have been smoothed out in all construction areas. 3. All areas needing reseeding have been identified and future stabilization goals have been coordinated with the Erosion Control Inspector and in accordance with FCSCM Vol.2 Chapter 12. Note the area needing stabilization in the narrative. XIII. Certification of LID and Water Quality Facilities - FCSCM Ch. 7 A. Attached are the During Construction Inspection Checklist for Low Impact Development (LID) and other items to be verified during construction, along with pictures and other required documentation. XIV. Certification of Other Permanent BMPs A. The construction of other permanent BMPs not specifically addressed in this certification is in accordance with the approved plan. This may include grade control structures, rundowns, bridges, stream access/improvements, etc. Please specify other permanent BMPs included on this site: 3-21-19 Proposed Detention Pond - Stage/Storage LOCATION:LOT 5 PROJECT NO: COMPUTATIONS BY: MPO DATE: 4/3/2018 V = 1/3 d ( A + B + sqrt(A*B)) where V = volume between contours, ft3 d = depth between contours, ft A = surface area of contour SAND FILTER SUMMARY TABLE-ASBUILT SURVEY 3-8-19 Surface Incremental Detention Total Stage Area Storage Storage Storage (ft)(ft2)(cu-ft) (cu-ft) (cu-ft) TOP SAND FILTER 11.0 431 11.5 1600 477 477 WQ OVERFLOW 12.0 2328 976 0 1453 12.5 2560 1222 1222 2675 FLOOD CONTROL 13.0 3387 1482 2703 4157 13.5 3600 1746 4450 5903 SPILL OVER WALK 13.7 3800 740 5190 6643 LID VOLUME REQUIRED = 1,204 cu-ft LID VOLUME PROVIDED =1,453 cu-ft DETENTION VOLUME REQUIRED = 2,545 cu-ft DETENTION VOLUME PROVIDED = 2,703 cu-ft Q100 RELEASE RATE = 5.7 cfs Sand Filter Stage Storage - POND 3-8-19 AB.xls 3130 Verona Avenue • Buford, GA 30518 (866) 888-8479 / (770) 932-2443 • Fax: (770) 932-2490 © Nyloplast Inlet Capacity Charts June 2012 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 Ca p a c i t y ( c f s ) Head (ft) Nyloplast 2' x 3' Curb Inlet Diagonal Grate Inlet Capacity Chart High Hood Setting (8.47" Curb Setting) Low Hood Setting (4.47" Curb Setting) Mid Hood Setting (6.47" Curb Setting) Scenario: Base Title: Harmony Commons, Lot 5 x:\...\appendix\3-21-19 inlets to sf.stm 03/26/19 09:09:45 AM Interwest Consulting Group © Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 USA +1-203-755-1666 Project Engineer: Interwest Consulting Group StormCAD v5.5 [5.5005] Page 1 of 1 P-2P-1 I-1 O-2O-1 I-2 Calculation Results Summary Title: Harmony Commons, Lot 5 x:\...\appendix\3-21-19 inlets to sf.stm 03/26/19 09:08:58 AM Interwest Consulting Group © Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 USA +1-203-755-1666 Project Engineer: Interwest Consulting Group StormCAD v5.5 [5.5005] Page 1 of 2 ================================================================= Scenario: Base >>>> Info: Subsurface Network Rooted by: O-1 >>>> Info: Subsurface Analysis iterations: 1 >>>> Info: Convergence was achieved. >>>> Info: Subsurface Network Rooted by: O-2 >>>> Info: Subsurface Analysis iterations: 1 >>>> Info: Convergence was achieved. CALCULATION SUMMARY FOR SURFACE NETWORKS ________________________________________________________________________________________________________ | Label | Inlet | Inlet | Total | Total | Capture | Gutter | Gutter | | | Type | | Intercepted | Bypassed | Efficiency | Spread | Depth | | | | | Flow | Flow | (%) | (ft) | (ft) | | | | | (cfs) | (cfs) | | | | |-------|---------------|----------------------|-------------|----------|------------|--------|--------| | I-1 | Generic Inlet | Generic Default 100% | 0.00 | 0.00 | 100.0 | 0.00 | 0.00 | | I-2 | Generic Inlet | Generic Default 100% | 0.00 | 0.00 | 100.0 | 0.00 | 0.00 | -------------------------------------------------------------------------------------------------------- CALCULATION SUMMARY FOR SUBSURFACE NETWORK WITH ROOT: O-1 _______________________________________________________________________________________________ | Label | Number | Section | Section | Length | Total | Average | Hydraulic | Hydraulic | | | of | Size | Shape | (ft) | System | Velocity | Grade | Grade | | | Sections | | | | Flow | (ft/s) | Upstream | Downstream | | | | | | | (cfs) | | (ft) | (ft) | |-------|----------|---------|----------|--------|--------|----------|-----------|------------| | P-1 | 1 | 15 inch | Circular | 18.95 | 4.00 | 3.26 | 13.04 | 13.00 | ----------------------------------------------------------------------------------------------- ______________________________________________________ | Label | Total | Ground | Hydraulic | Hydraulic | | | System | Elevation | Grade | Grade | | | Flow | (ft) | Line In | Line Out | | | (cfs) | | (ft) | (ft) | |-------|--------|-----------|-----------|-----------| | O-1 | 4.00 | 13.00 | 13.00 | 13.00 | | I-1 | 4.00 | 13.75 | 13.04 | 13.04 | ------------------------------------------------------ CALCULATION SUMMARY FOR SUBSURFACE NETWORK WITH ROOT: O-2 Calculation Results Summary Title: Harmony Commons, Lot 5 x:\...\appendix\3-21-19 inlets to sf.stm 03/26/19 09:08:58 AM Interwest Consulting Group © Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 USA +1-203-755-1666 Project Engineer: Interwest Consulting Group StormCAD v5.5 [5.5005] Page 2 of 2 _______________________________________________________________________________________________ | Label | Number | Section | Section | Length | Total | Average | Hydraulic | Hydraulic | | | of | Size | Shape | (ft) | System | Velocity | Grade | Grade | | | Sections | | | | Flow | (ft/s) | Upstream | Downstream | | | | | | | (cfs) | | (ft) | (ft) | |-------|----------|---------|----------|--------|--------|----------|-----------|------------| | P-2 | 1 | 15 inch | Circular | 16.73 | 7.60 | 6.19 | 13.14 | 13.00 | ----------------------------------------------------------------------------------------------- ______________________________________________________ | Label | Total | Ground | Hydraulic | Hydraulic | | | System | Elevation | Grade | Grade | | | Flow | (ft) | Line In | Line Out | | | (cfs) | | (ft) | (ft) | |-------|--------|-----------|-----------|-----------| | O-2 | 7.60 | 13.00 | 13.00 | 13.00 | | I-2 | 7.60 | 14.07 | 13.14 | 13.14 | ------------------------------------------------------ ================================================================= Completed: 03/26/2019 09:07:49 AM Profile Scenario: Base Title: Harmony Commons, Lot 5 x:\...\appendix\3-21-19 inlets to sf.stm 03/26/19 09:10:38 AM Interwest Consulting Group © Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 USA +1-203-755-1666 Project Engineer: Interwest Consulting Group StormCAD v5.5 [5.5005] Page 1 of 1 Elevation (ft) Station (ft) Profile: Profile - 1 Scenario: Base -1+00 0+00 10.00 15.00 Sump: 10.25 ft Rim: 13.25 ft Label: I-1 Sump: 11.11 ft Rim: 13.00 ft Label: O-1 S: 0.006860 ft/ft Size: 15 inch L: 18.95 ft Dn. Invert: 11.11 ft Up. Invert: 11.24 ft Label: P-1 Profile Scenario: Base Title: Harmony Commons, Lot 5 x:\...\appendix\3-21-19 inlets to sf.stm 03/26/19 09:11:17 AM Interwest Consulting Group © Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 USA +1-203-755-1666 Project Engineer: Interwest Consulting Group StormCAD v5.5 [5.5005] Page 1 of 1 Elevation (ft) Station (ft) Profile: Profile - 2 Scenario: Base -1+00 0+00 10.00 15.00 Sump: 10.15 ft Rim: 13.57 ft Label: I-2 Sump: 11.13 ft Rim: 13.00 ft Label: O-2 S: 0.008368 ft/ft Size: 15 inch L: 16.73 ft Dn. Invert: 11.13 ft Up. Invert: 11.27 ft Label: P-2