HomeMy WebLinkAboutSite Certifications - 08/15/2016 (2)1
MVG Morningstar Senior Living – October 22, 2015 (Date of site visit)
March 31, 2016 (Updated)
Interwest Response in Blue Bold Italics. Updated comments in Bold Red Italics.
COMMERCIAL, MULTI-FAMILY AND SUBDIVISION
CERTIFICATION CHECKLIST
Please fill in all applicable items in this Certification Form for Commercial, Multi-Family and
Overall Single Family sites. A copy of the approved grading plan must be submitted with the as-
built grading plan.
Use “OK” for items checked or actual numbers for items verified/surveyed in the field.
Use “N/A” for items that are not applicable to the site that is being certified.
Please provide an As-Built Redlined or Mylar drawing showing the following:
Note: >>>> During the site visit there were several items noted that require remediation.
1) At the north pond there are two (2) concrete drain pans that discharge to the pond
bottom. However, each pan has been stopped short of the bottom of the pond and
there is a vertical drop at the end of each pan. We recommend the use of ScourStop or
a similar erosion control matting application at the end of each pan to prevent long
term degradation of the pond bottom from the cascading water. The contractor chose
to installed riprap at the end of each concrete pan in lieu of the ScourStop. While less
aesthetic than the ScourStop would have been, the area is now well protected from
erosion at the ends of the pans.
2) At the south pond it was noted that the two (2) gravel dry wells noted on the
approved plans were not installed within the limits of the pond. It is our professional
opinion that these dry wells are not needed in this particular application as the site
drainage and grading does in fact meet the intent of the Low Impact Development
(LID) Code. The basin to this pond is made up of rooftop and open space areas only.
No vehicular drive areas contribute to the pond thus minimizing the addition of most
pollutants from those areas. Also, this pond is fed by a long flat grass lined swale that
runs along the southern boundary which will provide LID infiltration along the
meandering swale. The location of the pond immediately adjacent to the building also
meets the intent of treating the runoff near the source and the Extended Detention
Basin (EDB) will provide a level of infiltration during the settlement drawdown period
as noted by Urban Drainage. Therefore, we request that this certification be approved
without the installation of the gravel dry wells.
3) At the south pond the emergency spillway has been disturbed as part of the final
landscaping operations. Previous reviews of the spillway indicated that it had been
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constructed in accordance with the design; however, at the time of the most recent
site visit it was noted that the spillway will require reconfiguration prior to final
acceptance. The spillway has been reconstructed and the updated elevations verified
to be in conformance with the pond design criteria. See attached updated calculations
and detail sheets.
4) At the south pond it was noted that the bottom of the pond has two low areas where
water was ponding prior to reaching the outlet structure. The contractor is aware of
this condition and will fine grade the pond bottom to ensure positive drainage to the
outlet prior to the final seeding operation. The two low areas have been filled in and
the pond bottom shaped to flow to the outlet structure as designed.
5) At the southeast corner of the building the exterior grades do not drain away from the
structure to the extent recommended on the Geotechnical Report in order to protect
the foundation from potential damage from drainage. The site contractor has
indicated a desire to improve this condition and will work with the Civil Engineer and
Landscape Architect to develop a solution to this drainage condition including the
addition of roof drain extensions to discharge the roof water farther from the building
foundation. Roof drain extensions have been added around the building to direct
water farther away from the building foundation. In the southeast corner a new
swale has been constructed just beyond the planting bed area that will direct the
water north and away from the building.
A. Detention Facilities Certification
1. Pond Certification
• Provide Topographic Records and Volume Verification Calculations – The as-built
survey and pond calculations are attached. Based on the information provided,
both ponds achieve the required design volumes for WQCV and the 100 year storm.
• Provide Pond Cross-Sections and Spot Elevations (especially @ Pond Embankment
and Pond Flow Line) – Spot elevations are provided on the survey and are in
general conformance with the design grades.
• Positive Fall to Pan (if applicable) – N/A
• General Pond Grading including all Side-Slopes – OK
• Invert Elevation – OK (with the exceptions noted above)
• Forebay Construction and Elevation – N/A
• Spillway Weir (Location, Elevation, Height, Opening Width) – OK. The north pond
spillway bottom was noted to be 8 feet wide as opposed to the 13 feet noted on
the drawings. Updated weir calculations were performed to verify that the 100
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year storm will be contained within the emergency spillway with approximately 3
inches of freeboard remaining to the top of berm.
• Placement and size of riprap or alternative permanent erosion control measures –
OK
• Orifice Plate and/or Water Quality Outlet Structure Installation – Confirmed in the
field and installed correctly per drainage design – OK
• Water Quality Capture Volume (Volume Required, Volume Provided and Water
Surface Elevation) – OK
• Berm and Embankment Compaction Level – OK per the contractor, not observed by
Interwest
• Subsurface Media for Water Quality Ponds and Swales – OK per the contractor, not
observed by Interwest
2. Swales
• Location (are they within easement?) – The southern grass lined swale was
installed in the location noted on the plans; however, it is was not intended to be
located within a drainage easement
• Dimension and Cross-Section Verification – The grass lined swale was not designed
to a specific cross section nor were volume calculations provided with the Drainage
Report. The intent of the swale is to convey runoff from the south end of the
building to the pond in the southwest corner of the site while keeping the
meandering sidewalk from being inundated during minor storm events. Interwest
has reviewed the as-built grades of the swale and has determined that it meets the
intent of the design.
• Longitudinal Slopes and Side-Slopes – OK
• Spot Elevations – OK
• Permanent Erosion Control Measures (drop structures, riprap, lining) – N/A
• Tie-in to Storm Lines, Pans, Curbs, or other appurtenances – N/A
• Required Minimum Freeboard, Provided Freeboard – N/A
• Landscaping Infringement on Flow Line? – No infringements were noted
3. Pipes
• Size and Type – OK
• Slopes (As-Built and comparison to 0.4% Minimum) – OK
• Pipe Capacity Calculations (if slopes are significantly altered from design) – N/A
• Invert Elevations – OK
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• Installation and Backfill – OK per the contractor, not observed by Interwest
• Cover – OK
• Encasement and Clearance from other nearby utility lines – OK
• Joints Type and construction – OK per the contractor, not observed by Interwest
4. Concrete Pan Channels
• Size – OK
• Slope– OK. A drop structure was added to the southern pan within the northern
pond. This drop has been deemed to be compliant with the design now that riprap
has been added to minimize the velocity and erosion potential.
• Cross Section – OK
• Thickness – OK per the contractor, not observed by Interwest
• Elevations – OK, with exceptions noted above
5. Inlets
• Size and Type – OK
• Size of Opening (or name of Standard Detail used) – OK
• Grate Elevation – OK
• Invert Elevation – OK
• Box Size – OK
6. Street Cross-Pans
• Size – OK
• Type – OK
• Grade – OK
• Elevations – OK
• Cross-Sectional Depth – OK per the contractor, not observed by Interwest
• Tie-in to Curb and Gutter – OK
7. Culverts
• Size – N/A
• Type – N/A
• Invert Elevations – N/A
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• Headwalls or Wing Walls – N/A
8. Sub-Drains (Pervious Pavers)
• Size – OK
• Type (Perforated/Solid) – OK
• Cover – OK
• Backfill – OK per the contractor, not observed by Interwest
• Geo-Textile Liners – OK per the contractor, not observed by Interwest
• Clean-Outs – OK
9. Curb Cuts
• Size – OK
• Tie-in to Swale, Pipe or other appurtenances – OK
B. Certification of Grade Elevations Adjacent to Drainage Facilities:
•••• Minimum Opening Elevations – OK
•••• Top of Foundation Elevations – OK
•••• Comparison to 100-year Water Service Elevations – OK
•••• Comparison to Freeboard Elevations and Base Floodplain Elevations – BFE – N/A
C. Certification of Erosion Control Measures:
The project is now substantially stabilized. The contractor noted that several rock socks
were remaining to be removed as directed by the city erosion control inspector.
1. Permanent BMP Measures:
•••• Permanent Vegetation (no more than 6” bare spots and weeds under control) – OK
•••• Riprap or alternative permanent erosion material - OK
•••• Riprap Bedding - OK per the contractor, not observed by Interwest
•••• Cut-Off Walls or Channel Drop Structures Cross-Sections – OK
•••• Sediment Basins – N/A
•••• Water quality ponds/Sand Filter/Bio Retention Construction and liners - OK
•••• Permanent Netting Mats or Blankets – N/A
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•••• Mulching and Seeding – OK
2. Temporary BMP Measures:
•••• Mulching and Seeding – N/A
•••• Temporary BMP Measures as shown on Erosion Control Plan – OK
D. Post-Construction Site Cleanup:
•••• Construction Debris Clean-Up – OK
•••• Smoothing of Ruts in all Construction Areas – OK
•••• Reseeding of all Areas Affected by Construction Activities – OK
E. Statement of Compliance:
This certification is signed and stamped and by signing this form the Engineer(s) attests that
they have inspected the site and to the best of their knowledge the as-built conditions of
the drainage facilities are as described in the above form and in the As-Built plans enclosed.
Failure to properly disclose all known information could result in the rejection of this
certification and prevent the release of any and all Stormwater Utility permit holds on
Building Permits and/or Certificates of Occupancy within this development.
F. Signature and Stamp by a Colorado Registered Professional Engineer
FOR SAUNDERS CONSTRUCTION
KING SURVEYORS
650 E. Garden Drive | Windsor, Colorado 80550
phone: (970) 686-5011 | fax: (970) 686-5821
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N:\2014476 ASB\DRAWING\2014476ASB.dwg, 1/4/2016 8:24:36 AM
EXTENDED DETENTION BASIN B (NW)
Proposed Detention Pond - Stage/Storage
LOCATION: MVG - Morningstar
PROJECT NO: 1173-105-00
COMPUTATIONS BY: MHM
SUBMITTED BY: INTERWEST CONSULTING GROUP
DATE: 10/23/2015
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
Surface Incremental Detention Total
Stage Area Storage Storage Storage
(Elev) (Ft^2) (Ac-ft) (Ac-ft) (Ac-ft)
62.80 0
63.0 160
64.0 2155 0.02 0.02
WQ WSEL- 64.5 3807 0.03 0.00 0.06
65.0 5458 0.05 0.05 0.11
66.0 7535 0.15 0.20 0.26
100-yr WSEL- 67.0 9287 0.19 0.39 0.45
SPILLWAY - 67.1 9871 0.02 0.42 0.47
TOP OF BERM - 68.1 0 0.08 0.49 0.55
Total Storage Req'd Storage
0.548 > 0.362
NORTH POND AS BUILT
Surface Incremental Detention Total
Stage Area Storage Storage Storage
(Elev) (Ft^2) (Ac-ft) (Ac-ft) (Ac-ft)
62.8 0
63.0 384 0.00 0.00 0.001
64.0 3427 0.04 0.04 0.039
WQ WSEL- 64.25 4201 0.02 0.06 0.060
65.0 6405 0.11 0.15 0.171
66.0 7795 0.16 0.31 0.334
100-yr WSEL- 67.0 9276 0.20 0.51 0.530
SPILLWAY - 67.02 9276 0.00 0.51 0.534
EXTENDED DETENTION BASIN A (SW)
Proposed Detention Pond - Stage/Storage
LOCATION: MVG - Morningstar
PROJECT NO: 1173-105-00
COMPUTATIONS BY: MHM
SUBMITTED BY: INTERWEST CONSULTING GROUP
DATE: 10/23/2015
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
Surface Incremental Detention Total
Stage Area Storage Storage Storage
(Elev) (Ft^2) (Ac-ft) (Ac-ft) (Ac-ft)
67.0 0
67.1 0 0.00 0.00 0.000
68.0 1223 0.01 0.00 0.008
WQ WSEL- 68.5 2433 0.02 0.03 0.029
69.0 3642 0.03 0.06 0.064
100-yr WSEL- 69.70 5386 0.07 0.14 0.136
SPILLWAY - 69.80 6078 0.01 0.15 0.149
TOP OF BERM - 70.80 0 0.05 0.20 0.195
Total Storage Req'd Storage
0.195 > 0.130
SOUTH POND AS BUILT
Surface Incremental Detention Total
Stage Area Storage Storage Storage
(Elev) (Ft^2) (Ac-ft) (Ac-ft) (Ac-ft)
67.0 0
68.0 1394 0.01 0.00 0.010
WQ SEL 68.7 3277 0.04 0.04 0.047
69.0 3946 0.06 0.07 0.106
100-YR WSEL 69.7 5408 0.07 0.18 0.180
SPILLWAY 69.71 5412 0.00 0.18 0.182