HomeMy WebLinkAbout18-3998 ExM Engineers reviewH:\ORNO\C13115486\z-18-3999_Brackets Point\Southways_PrePlatReview-1_2018-01-09.docx
January 9, 2018
City of Orono
Attn: Jeremy Barnhart
2750 Kelley Parkway
Orono, MN 55356
RE: Preliminary Plat Application 18-3999
Southways Addition
Engineering Review #1
Dear Jeremy:
As requested, I have completed an engineering review of the documents submitted for the above
referenced project. In addition, Adam Edwards has provided comments for inclusion with this review.
We offer the following observations, comments, and recommendations for your consideration:
1.0 GENERAL:
1.1 Stormwater management for the site to meet regulatory requirements is proposed through use
of wet retention basins. The following should be considered regarding the proposed system:
a.Volume control and water quality measures must be provided as well to meet NPDES
requirements. Plans should be revised to include volume reduction equal to 1” of runoff
from the new impervious surface. If infiltration is considered infeasible, other methods of
volume reduction must be considered. It appears that there are sufficient areas high
enough above the water table to provide localized filtration practices or amended soils.
Also, the overall estimate of Total Suspended Solids (TSS) and Total Phosphorus (TP)
from proposed improvements must be reduced from pre-project conditions. Calculations
detailing volume control and water quality compliance must be submitted for review and
approval. If the applicant pursues a design with less than the normally required infiltration
volume, sequencing of design to provide treatment to maximum extent practical must be
provided.
b.An Outlet Control Structure (OCS) that provides skimming must be installed on the wet
retention ponds in order to keep floatables in ponds. The following should be considered
regarding OCS design:
i.The inlet pipe from the pond to the OCS should be submerged with back slope from the
OCS to the pond to facilitate maintenance. The normal water level should be
controlled by a weir in the structure or the outlet pipe. The inlet pipe should be one
nominal size larger than the outlet pipe to limit flow control and turbulence at the pond
interface.
ii.A sloped rim should be utilized, per City Standard Details, with the bottom of the rim
placed at the predicted 100 year high water level.
iii.A trashguard should be installed on the outlet pipe.
c.Wet retention basins must provide a minimum 1800 cubic feet per acre of drainage area.
The stage-storage curves for permanent pools must be submitted for review to verify
Resolution Exhibit C
Preliminary Plat Application 18-3999
Southways Addition
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adequate storage is provided.
d.A minimum 8’ wide access bench along the top of the berm should be provided all the way
around the pond to allow for inspection of outlets and future maintenance.
e.The stormwater management plan should be revised as necessary to meet all requirements
and resubmitted for review prior to Final Plat approval to ensure adequate siting is
available for required facilities.
1.2 The condition of Bracketts Point Road to remain should be reviewed by the City and Contractor
prior to any work, and the existing condition should be documented with pictures. After
completion of work, the street should be reviewed for damage, and the Contractor should be
required to repair any damage deemed to be caused by site work.
1.3 Work within public right-of-way must be coordinated with the Public Works Department.
Contractor must provide a minimum 48 hour notice prior to any work being performed. Notes
should be revised accordingly.
1.4 Final Plans must include a Storm Water Pollution Prevention Plan (SWPPP) that meets NPDES
requirements. The plan should include a rock construction entrance, perimeter silt fence, inlet
protection, and ditch checks in swales. For specific requirements, refer to the following link:
https://www.pca.state.mn.us/sites/default/files/wq-strm2-68a.pdf
1.5 A Demolition/Removals Plans should be included with Final Plans to ensure items slated for
demolition are removed as proposed and required. The Removals Plans should include items
north and south of the site to make the street connections.
1.6 Per the meeting of December 20 th with the City, it is the City’s understanding that the developer
wishes to install a pressure system with lift station in lieu of what is depicted in the current plan
set. A revised sanitary sewer plan must be submitted for review prior to final development
approval. The plat should be revised to provide sufficient room for the lift station; including
wet well, control panel and back-up generator; via the road ROW or a utility easement. The
final design must conform to City standards and should include all pertinent City details.
1.7 The development will require the city to increase the capacity of Lift Station #9 which receives
the sewage from the development area. The lift station is being remodeled/ rehabilitated this
coming year. Larger pumps sized to handle the increased demand from the development is
expected to add $1000 to the lift station projected. That difference should be borne by the
developer.
1.8 For the sewer line designated to be abandoned all pipes must be removed or filled such that no
subsurface voids remain. For sanitary manholes designated to be abandoned, the covers, rings,
castings and any other structure must be removed to a minimum of 4 feet below the
surface. The remaining structure must be backfilled to ensure no subsurface voids. This work
should be indicated on the Final Removals Plan.
1.9 The applicant will be required to obtain Minnehaha Creek Watershed District (MCWD)
approval and permitting. A copy of any approvals or permits required should be submitted
prior to Final Plat approval.
1.10 The applicant will be required to obtain a General Construction Permit (NPDES) to discharge
stormwater associated with construction activity since more than 1 acre will be disturbed. A
copy of the permit should be submitted prior to any land disturbing activity.
1.11 The applicant will be required to obtain a Sanitary Sewer Extension permit from the Minnesota
Pollution Control Agency. A final copy of the permit should be submitted prior to
construction.
1.12 The applicant will be required to submit a Maintenance Agreement for all stormwater
management structures and facilities. The agreement should define maintenance
responsibilities following completion of project, specify types and frequencies of inspection
Preliminary Plat Application 18-3999
Southways Addition
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and maintenance activities, designate who will conduct inspection and maintenance activities,
and outline reporting requirements.
1.13 Clear drive lanes must be maintained on Brackets Point Road during construction. The
Contractor will have to exercise care during mobilization of equipment to not block traffic, and
parking for construction workers should be restricted to on-site only. The Contractor should
submit a Traffic Control Plan prior to any work. Access must be maintained to properties south
of site at all times. Plan should be approved by Fire Department and/or applicable emergency
services.
1.14 A final estimated cost of proposed improvements, matching approved plans, must be submitted
in order to determine the total Letter of Credit (LOC) amount. The LOC must be written to
150% of cost of improvements and submitted prior to any land disturbing activities. Estimated
costs should include grading, erosion control, utilities, street construction, vegetation
management, buffer establishment, temporary stabilization, and final stabilization.
1.15 Development grading, including the storm ponds and drainage ways, should be completed prior
to acceptance of the development and release of the escrow. In addition, a copy of MCWD
approval for the Stormwater Management system should be submitted prior to issuing any
Certificates of Occupancy.
1.16 Record drawings must be submitted upon completion of the project.
2.0 PRELIMINARY PLAT / SITE PLAN:
2.1 A Flowage and Conservation easement will be required over any wetlands to remain.
2.2 Drainage and Utility Easements should be provided as follows:
a.Over all stormwater management facilities used to meet regulatory requirements.
b.All swales and storm sewer providing drainage for multiple properties.
c.5’ along all side lot lines, unless adjacent to Development boundary.
d.10’ along all front lot lines, rear lot lines, and adjacent to Development boundary.
3.0 PRELIMINARY GRADING PLAN:
3.1 Perimeter erosion control should be installed by the Contractor and inspected by the City prior
to any other work. Contractor must provide a minimum 24 hour notice prior to inspection.
3.2 Facilities necessary to meet regulatory requirements should be installed and the site mass-
graded at the same time as street construction to ensure all drainage ways and watersheds are
constructed per the approved Stormwater Management Plan. If done piece-meal, coordination
of required stormwater management facilities can be difficult, and facilities required may be
forgotten during future construction.
3.3 Pond emergency overflows should be provided at the predicted 100 year high water level and
armored with Turf Reinforcement Mat (TRM).
3.4 Additional spots and revised contouring should be provided in several areas to ensure a
minimum 6” swale depth is provided for swales providing conveyance to wet retention ponds
per the approved Stormwater Management Plan. These spot elevations should be confirmed
with record drawings prior acceptance of development.
3.5 The grading adjacent to the road should be revised as necessary to provide a minimum 2’ depth
for the ditch in the rural section per the City Standard Detail or follow the curb line in the urban
section.
Preliminary Plat Application 18-3999
Southways Addition
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4.0 PRELIMINARY STREET PLAN
4.1 A minimum 15” culvert should be provided under driveways and roads to limit potential for
clogging.
4.2 Proposed curb should be indicated as B612 Curb and Gutter, and a detail should be provided with
Final Plans.
4.3 Bituminous pavement should be saw-cut to full depth at connection to existing to provide clean
match lines. Pavement at connection should match existing elevation and section. Final limits
should be coordinated in the field with the City prior to any demolition work.
4.4 Pipe characteristics should be provided for all proposed storm sewer and culverts (i.e. invert
elevations, diameter, length, slope, and material). Culverts under the roadway should be
concrete. Provide minimum 2’ cover.
5.0 PRELIMINARY LANDSCAPE PLAN
5.1 The Final Landscape Plan should include the following:
a.Types and locations of proposed restoration.
b.Abandoned road should indicated removal of pavement and restoration type.
c.De-compaction of existing soils under removed impervious surfaces with 12” ripping depth
prior to placement of topsoil.
d.Areas disturbed by sanitary manhole removal.
e.Restoration of the existing rain garden at the south street connection.
f.Trees should be located so as not to interfere with drainage. In rural section areas, trees may
need to be placed outside the right-of-way.
If you have any questions or comments, please contact me to discuss.
Sincerely,
Bolton & Menk, Inc.
Robert E. Bean, Jr., P.E.
Water Resources Engineer
CC: Adam Edwards, City of Orono