HomeMy WebLinkAbout2005-02-07 BRAA Ltr to OPH Re Plan Review-Storm Wter & Traffic IssuesJA Bonestroo r-) West Hi 36 w St. Paul, MN 55113
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Februar 7, 2005
Mr. Eric Johnson
Cit Administrator
Cit of Oak Park Hei
14168 Oak Park Blvd., P.O. Box 2007
Oak Park Hei MN 55082-2007
Re: Wal-Mart Expansion
Plan Review- Storm water and Traffic Issues
BRA File No. 55-04-000
Dear Eric:
We have reviewed the storm water modelin storm sewer calculations, and Traffic Stud
for the proposed Wal-Mart expansion as submitted, on Januar 12, 2005, b McCombs,
Frank Roos and Associates, Inc. Followin are our comments and/or recommendations.
Existin Pond (EX-P A)
1. To meet the re of the Brown's Creek Watershed District ( BCWD )
followin the ioilowin pararneters were chan on the existin pond.-
Z:)
a. In the 100 y ear event, the Hi Water Level (HWL) of the existin pond
will be raised from 937.09 to 939.48. The existin pond does have the
stora capacit for the increased water level.
b. In the 100 y ear event, the peak dischar from the pond will decrease from
5.50 efs to 3.94 cfs.
c. The existin outlet structure will need to be fitted with an 8" orifice to
limit dischar to pre-expansion rates.
n St. Paul, St. Cloud, Rochester, Willmar, MN A Milwaukee, Wl ■ Chica IL
Affirmative Action Opportunit Emplo and Emplo Owned
Z. Submit the details for the modifications to the existing outlet structure. It is
recommended that the S "orifice not be placed directly over the existing pipe.
3. The proposed plan currently shows raising the Normal Water Level (NWL)
from 933.3 to 933.65. It is recommended that the NWL remains the same.
The existing flared end discharging into the pond from the main parking lot is
at 932.9. By maintaining the existing NWL the amount of water in this storm
sewer system will be minimized.
4. The pipe run from EXSTMH 1 to the FES should be considered as pond
storage, rather than storm sewer conveyance.
5. In the 1.5 year event the pond should be modeled using the starting elevation
at the NWL.
Central Pond (2P)
1. It appears the HydroCAD model used the 1.5 year event to determine the wet
volume required for the pond. This was accomplished by setting the outlet
high so the discharge would be zero. However, in all the other models the
NWL. was set at 937.00. The 1.5 year event should be modeled using the
NW of 937.00.
2. Provide details of the outlet structure.
South Pored OP
1. It appears the HydroCAD model used the 1.5 year event to determine the wet
volume required for the pond. This was accomplished by setting the outlet
high so the discharge would be zero. However, in all the other models the
NWL was set at 940.45. The 1.5 year event should be modeled using the
NWL of 940.45.
2. The South storm sewer conveyance system discharges into the pond at an
elevation of 93 8.12. This is 2.3 3' below the NWL. As a result the system is
backed up with water to STMI-116. Design changes must be made to
eliminate the backed up storm water in the system.
3. Provide details of the outlet structure.
4. Place the outlet structure at a location that is easily accessible for
maintenance.
General Storm water Comments
1. BCwD story water runoff rules for this area are being met downstream via the
City of Stillwater's Trout Stream. Mitigation Program, through a Cooperative
Agreement between the Cities of Stillwater and Oak Park Heights and the
BCwD. As such, BCwD volume control rules do not need to be met on this site.
However, plans and storm water calculations shall be submitted to the BCwD for
their review.
2. To prevent erosion, it is recommended that rip rap be placed at all flared end
sections that are discharging into a pond.
Traffic Stud
1. Probably the most important item missing from the study is the absence of
existing volume data at the existing access points along Norell. Avenue. The
preparer chose to assume data rather than do some counts at the access points.
2. The future volumes that they have projected for the two access points along
Norell Avenue have not been analyzed with regard to the left turn queues
(southbound) into the site. The 290 vehicles turning left to the site, from Norell at
the north access, may well "backup" into the through lane. The future left turn
lane storage is only 90 feet (approximately) in length which is quite short. The
analysis should be amended to include such calculations. It is recommended to
conduct existing peak period counts at both drives. It may be advisable to
consider a reconfiguration of the proposed fuel station so that the left turn storage
can be lengthened.
3. It is recommended to conduct a count at the existing store access points during the
Saturday peaks which, historically, are higher than the weekday peaks. The
existing data can than be used to project the future data at these locations and
analyses undertaken to determine if the storage length will be a problem at the
nortn access and to determine if the south access may require an exclusive left
turn lane.
4. The City should be advised that the queing for northbound Norell, at TH 36, does
sometimes backup into the Norelll60 intersection and this situation will become
a bit more prevalent in the future. This was pointed out in the traffic study. The
future levels of service for the Norell/60 intersection will degrade to "F" in the
2007 time period. The study did not offer any recommendations as to how this
can be mitigated. The City needs to be aware of that situation...
A more comprehensive review of all issues will be conducted when final development
plans are submitted. If you have any questions or require additional information, please
contact me at (651) 604 -4788 or Dennis Yostler at (651) 604 -4815.
Sincerely,
BONESTROO, R.OSENE, ANDERLIK & ASSOCIATES, INC.
Karen S. Erickson, P.E.
cc: Judy Holst, Finance officer
Tom Ozzello, Public Works Director
Jim Butler, Building official
Scott Richards, City Planner
Mark Vierling, City Attorney
:Kathy Widin, City Arborist
Erik W. Miller- McCombs Frank Roos & Associates
DMP, DDH, File --- Bonestroo & Associates
K :1551 55040001 Work Iil ProgresslJoluison _KSE ^walmartstormwaterpondand sewer.doc