HomeMy WebLinkAboutMONTAVA PUD - ODP180002 - MONTAVA SUBMITTAL DOCUMENTS - ROUND 3 - STORMWATER-RELATED DOCUMENTSJanuary 21, 2019
Jaclyn Michaelsen
ICON Engineering, Inc.
7000 South Yosemite Street, Suite 120
Centennial, Colorado 80112
Re: Anheuser- Busch Mix-Used Development
Martin/Martin, Inc. Project No.: 17.0946
GENERAL COMMENTS AND RESPONSE
C1: The proposed SWMM model has been reviewed and the following comments pertain to the EPA
SWMM model:
C1a: Pond 430 is now flooding/overtopping. Please adjust the modeling so that the 100-year flow
is contained within the pond.
R1a: Martin/Martin has verified that the attached model does not show Pond 430 overtopping.
C1b: Pond 429 has been added into the model with the latest submittal. This pond is
overtopping. Please adjust the modeling so that the 100-year flow is contained within the
pond.
R1b: Martin/Martin has verified that the attached model does not show Pond 429 overtopping.
C1c: There is no flow coming out of pond 429. Is this meant to be a retention pond?
R1c: Martin/Martin has verified that the attached model shows an outflow of 390 cfs for Pond
429
C2: The impacts to the AB Pond (425) seem minimal. The water surface elevation decreases from
Existing Conditions to Proposed Project. It is recommended to continue to evaluate this pond to
ensure no negative impacts from the proposed development.
R2: Noted. Martin/Martin will continue to evaluate this pond as development progresses.
C3: The proposed improvements have been added into the L&W unsteady HEC-RAS model by ICON. The
improvements reduce the peak flow in Cooper Slough (downstream of the Larimer and Weld Canal)
from 734 cfs to 670 cfs. There is room for design adjustments during the other design stages.
However, the final design should be rechecked with the Larimer and Weld Canal unsteady HEC-RAS
model to ensure that the flow downstream does not increase with the development.
R3: Noted. Martin/Martin will continue to evaluate impacts to the L&W as development progresses.
Anheuser- Busch Mix-Used Development
January 21, 2019
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C4: It is recommended that the proposed improvements be fine-tuned during final design to ensure that
flows into Cooper Slough remain similar to existing conditions during higher frequency runoff events
such as the 2- through 10- year events. This task was not performed by either ICON or
Martin/Martin at this time.
R4: Noted. Martin/Martin will provide detailed analysis for proposed infrastructure improvements as
development progresses.
C5: The onsite detention ponds were not checked with the proposed grading plans. The outlet
structures were also not verified. The pond rating curves and outlet structures will be verified with
the design submittal.
R5: Noted.
Please do not hesitate to contact me with any questions.
Sincerely,
Ryan Byrne, PE, CFM, LEED AP
Senior Project Engineer
H:\SCHLAGETER\17.0946-Anheuser-Busch Mix-Used Development\RECEIVED\2018.12.28 PUD 2nd Comments - Final\17_0946_Jan_21_2019_R0_CR.docx