CN-2013-00029-1.tif k
.- J
Allen Schoemaker °
To: BlakemanEngineering
Cc: Phil Green (Blair, NE); Rodney Storm; jane @littleblossomsblair.com; weidnerarch @cox.net;
sbassler @constructinc.com
Subject: Little Blossoms Day Care
Brad,
First of all thanks for the submittal of the calculations for the Little Blossoms Day Care here in Blair. However, the extent
of the calculations are not adequate. You failed to submit a breakdown of the areas for all of the new impervious areas
and using those areas to submit detailed calculations showing the increase in storm water runoff for each area. You
failed to provide the maximum discharge outlet size for the site showing the maximum size pipe outlet allowed to
restrict runoff to not exceed current runoff rates. Further you have failed to submit the requested charts you used for
calculating rainfall intensity for this project.
With all of this said I am going to approve the submittal assuming all of your calculations are correct and because the
development will not contribute substantially to storm water runoff and I do not believe there is a risk of flooding
neighboring properties. However, Blair will still hold Blakeman Engineering responsible for any miscalculations
submitted for this project. In the future any work submitted by Blakeman Engineering to Blair we will expect you to
comply with all requests and submittal formats for future projects you and your firm work on in Blair, Nebraska. If
submittals do not incorporate the requested materials for review, they will be rejected until they comply with the
required submittals. To make this process easier I sent you two examples of approved submittals and we suggest you to
follow those examples when making your submittal.
Please let me know if there are any questions.
Director of Public Works
City of Blair
402 - 426 -4191
r` R CcJ.b1air.ii .ti
Fri,23 Aug 2013 14:13:21
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Wed,21 Aug 2013 13:15:08
Allen Schoemaker
From: Blakeman Engineering [blakemanengineering @cox.net]
Sent: Thursday, August 08, 2013 5:02 PM
To: Allen Schoemaker
Subject: RE: Little Blossoms Day Care - Blair, N.E.
Attachments: Storm Water Report 08072013.pdf
Al,
We have received your comments dated August 7, 2013. There seems to be some confusion on your part as to how
storm water is being accounted for so we have simplified the calculations and split the site into just two basins and then
reanalyzed the each of those two basins into two more basins to verify our results. I have attached a revised storm
water management plan for this site which should clarify what the overall intent of the project achieves through the
storm water structures on the site. I also have personally addressed your review comments in this email to clarify some
issues that you seem to have with the overall design.
As far as to what the attached revised design addresses, it only adds in the rear roof areas that surface drain into the
grass swales that drain around the parking lot and it now accounts for all the grass swale basins in the design. In this
revised design I have adjusted the paved area C factor from 0.85 to 0.05 as you requested. I also have changed the C
factor for unimproved areas to 0.35 and grass areas to 0.20 as allowed by you in previous approved reports in lieu of the
constant C factor of 0.55 1 was using for all grass areas in my previous reports. This allowable pervious coverage C factor
of 0.2 and 0.35 was not mentioned in your comments but can be used based on your attachments for the City of Blair.
Also we have used the Blair, Nebraska rainfall graph for rainfall in lieu of the higher City of Omaha figures in the new
computations. This figure also lowers the detention requirements and storm sewer sizing. As a matter of interest we
also performed all the calculations using the City of Omaha rainfall graphs and those results are listed below as a matter
of future information for you.
Using the changes above significantly lowers the detention required as opposed to increasing it and allows for smaller
sewer structures and detention areas if we so chose to change them. In general by using all the site area to be
developed in the computations we get lower detention requirements than what was originally provided to you on the
building permit drawings. Even by using a Tc of 5 minutes in the revised design, which in reality is around 7 minutes on
this project, we still get a lower detention volume required.
Our initial building permit design used worse case scenarios for the 100 year event which made the parking lots the
most critical area to detain and most obvious for detention area use for this project. This is common practice in the
industry. Therefore by U5irig a C factor of 0.55 in our initial design a f lactor of saiety was built uiw our design and
accounted for the additional flows from the rear of the roofs and surface flows to the streets and inlets, As you can
clearly see that our initial design was more than adequate to meet the City requirements and the results are close to
what is really required by using the whole site as a study area.
In summary the following results are produced:
East half of site: Initial detention required (471 cf) Revised detention required (371 cf) Provided (473 cf)
West half of site: Initial detention required (505 cf) Revised detention required (363 cf) Provided (530 cf)
If we were to use the City of Omaha rainfall graphs and a Tc =5 min the detention required = Fast half (41S cf) West half
(453 cf) Still Ok.
As you can see the initial design and permit set of drawings adequately accounted for all storm water releases from the
site. Below I have addressed your comments in case they were not addressed in the report and this email for your
convenience.
1
Wed,21 Aug 2013 13:15:29
= It appears that the new building was left off of the calculations for new impervious area. Please include the new
building in your calculations. All that is shown is for pavement. Pavement and building are both included in the "paved
area" numbers. We verified all basin area acreages and found all areas accounted for.
° The coefficient you used for pavement is0.85. The requirement for coefficient for pavement is0.95. Usin8this
higher coefficient increases the difference runoff to 5.12 cfs per my calculations. Please recalculate and resubmit with
the new calculations. We have changed the factor to 0.95. The overall runoff is actually less using corrected pervious
coverage C factors from your approved reports and charts. (See comments above)
a Please submit a copy of the time ofconcentration. By clear observation the Tcis less than 5 min and the rainfall
graphs go no lower than 5 rnin. If we were to use the swales around the building as the controlling Tc they provide a Tc
of 6.6 min with a lower rainfall rate. For worse case in our computationsvve showed that aTcof5min controlled the
design so therefore the detention areas are slightly oversized still from our initial design.
° Please show all calculations supporting your numbers within your report, All calculations have been provided on
all reports and drawings submitted asis the case again here.
° Please show the calculation for maximum discharge pipe size. You show a12" pipe but is this the right diameter
of pipe for the required detention? 12 inch is correct as the flow is not just dependent of the size of the pipe but also the
slope of the pipe. No change required of pipe sizes.
" 1 am concerned you are planning on using the new curb for the detention but as I have shown above there is
going tobe more storm water that needs tobedetained. | will need you to show how the additional storm water water
will not overtop the new curb or the inlets will need to be moved to the middle of the parking area. Revised calculations
show this is not a concern and not required.
As you see the revised computations still verify and yield results that meet and/or exceed all the storm water
requirements for your City even using your required changes.
We believe this information meets your burden of proof and look forward to doing our next project in the City of Blair.
Brad
Brad Blakeman, P.E.
Blakeman Engineering
1O4Z3 Hansen Ave.
Omaha, 0EG8124
402.933S777
bt
Fromm: Allen Schoemoker[maikomrs@d.b|air.ne.ua
Sent: VVadnesdey, August 7, 2013 3:54 PM
To:BlakemanEngineahng
Cc: Phil Green (Blair, NE)
Subject: RE: Little Blossoms Day Care-Blair, N.E.
Brad,
Thanks for sending me the latest version of the storm water management plan for the Little Blossoms Daycare you
developed. Unfortunately I cannot grant approval of the report you submitted due to the following deficiencies:
* It appears that the new building was left off of the calculations for new impervious area. Please include the new
building in your calculations. All that is shown is for pavement.
* The coefficient you used for pavement isO.85. The requirement for coefficient for pavemen1isO.95. Using this
higher coefficient increases the difference runoff to 5.1.2 cfs per my calculations. Please recalculate and
resubmit with the new calculations.
2
\8/8d Aug 2013 13:15:29
0 Please submit a copy of the time nfconcentration.
w Please show all calculations supporting your numbers within your report.
m Please show the calculation for maximum discharge pipe size. You show e 12" pipe but is this the right diameter
of pipe for the required detention?
0 1 am concerned you are planning on using the new curb for the detention but as I have shown above there is
going tobe more storm water that needs tobedetained. | will need you to show how the additional storm
water water will not overtop the new curb or the inlets will need tobe moved to the middle uf the parking area.
Please contact me with any questions. I have once again attached a sample report from another development project in
Blair that you are free to use as a template for this project.
Director of Public Works
City of Blair
402-426-4 19 1
Fromm:BlakemanEngineehng
Sent: Monday, August 05, 2013 11:02 AM
To: Allen Schoemaker
Subject: RE: Little Blossoms Day Care-B|air, N.E.
Al,
Attached report again for your information.
Please notify Building Permit officials to release building permit for Little Blossoms.
Any further or additional comments or questions should be directed atme.
Brad
Brad Blakeman, P.E.
B|akennenEngineerin8
I04Z3 Hansen Ave,
Omaha, NE 68124
402.933.5777
From: Allen Schoemaker
Sent: Tuesday, 3uk/30, 2013 9:25 AM
To: B|akennanEngineering; Howard Wolfe
Cc: Phil Green (B)air, NE)
Subject: RE: Little Blossoms DayCana'B|air, N.E.
Brad,
Wed,21 Aug 2013 13:15:29
Please send the report.
Al
4
Wed,21 Aug 2013 13:15:29
LITTLE BLOSSOMS DAYCA"
1221 DEERFIELD BLVD.
BLAIR, NE
July 30, 2013
PRO
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The site is currently a vacant lot covered with grass. The proposed development will be a small daycare
building with a parking lot taking up less than half of the current vacant lot.
The site requires storm water runoff for the 100 year storm event for the proposed development must not
exceed the current 100 year runoff. The lot site is approximately 3.80 acres in size.
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SITE MAP
LOT B4 OF DEERFIELD ADDITION '..
A REPLAT OF LOT 4, OF DEERFIELD, AN ADDITION TO THE CITY OF BLAIR
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INLET UNTIL SITE IS STABILIZED -1
PRO"ADE IN[ET PROTECTION TO OWNERS SATISFACTION vo
ADDLE OR APPROVED SYS
AWATER POLLUTION PREVENTION PLAN/ LEGEND EXISTING CONTOUR
ROSION CONTROL EL,2��� �WPP�P) _1276_ PROPOSED CONTOUR
30'-0" -- X — SIL FENCE
TOTAL ACRES; 3.80 EXISTING PERVIOUS COVERAGE = 3-80 cc RUNOFF 100 YEAR F-VENlj-*
SUB BASINAREAS AREA FUTURE PERVIOUS COVERAGE = 2,95 CC EXISTING LOT = 180 cc
A - 0,30 ac LOSS OF PERVIOUS COVERAGE == 0,85 cc PRE DEVELOPED C = 0.55
B — 0.26 ar POST DEVELOPED C = 0,61
RESTRIDGE DR. C - 0.08 ac TIME OF CONCENTRATION < 5 MIN FOR A�l- AREAS PRE DEVELOPED RUNOFF = 31.6 CIS
GRADING DISRURBED AREA = 2.85 cc POST DEVELOPED RUNOFF = 35.0 cis
GRADING UNDISTURBED AREA = 095 cc DETENTION REQUIRED
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LITTLE BLOS.'z
LD. PVC WATER LINE. SEE ARCHITECTURAL 4 FOR EXACT BUILDING DI
5 FEET BEHIND BACK OF CURB � F.F.E.
TER UTILITY. CONTRACTOR MANHOLE (VERIFY EXACT BUS
\TION. RIM=1090.00 a.
l.E.= 1085.00 ` ```�.,, ARCHITECT BEFORE
/ - PARKING LOT 100 YEAR
DETENTION AREA, TYP.
,• --450 C.F. OF STORMWATER DETENTION
STORAGE. DEPTH LESS THAN 6"
-BASIN (AA
AREA INLET/ DETENTION STRUCTURE
RIM = 87.40 _ ri
\ I.E. - 82.40 /
C E STORAGE = 80 G.F.
C.F. OF
STORMWATER
-TAP EXIST. DETENTION - BASIN�B
AREA INLET STORAGE.
DEPTH LESS AREA IN[
THAN 6" RIM = 81
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12' I.D. ADS "N -12" STORM SEWER-- -' AREA INLET
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TOTA SITE STORM DETENTION ANALY
A. O VERALL SITE - ( YEA EVENT
EXISTING CONDITIONS
SURFACE ACRES C Tc PEA FLO
GRASS 3.80 .55 5
PAVED 0.00 0
TOTAL 3.80 .55 5 31.6 cfc
PROP OSED CONDITIONS:
SU RFACE ACRES C Tc PEAK FLOW
GRASS 2.95 .55 5
PAVED 0.85 .85 5
TOTAL 3,80 .61 5 35.0 cfe
INCREASE OF 3.4cfc THEREFOR DETENTION REQUIRED.
DETENTION PROVIDED: BASIN A BASIN I3
DETENTION STRUCTURE/ INLET: 80 c.f. 68 c.f.
ON SITE PARKING AREA: v 45 c .f, 405 c.f,
TOTAL DETENTION PROVIDED = 530 0, 473 c.f.
TOTAL DETENTION REQUIRED = 505 c.f. 4710.
(TOTALS INCLUDE ADDITIONAL REQUIRED DETENTION FOR
ENTRANCE DRIVE DRAINAGE TO STREET)
DESIGNER/ ENGINEER/ INSPECTOR
BLAKEMAN ENGINEERING
BRAD BLAKEMAN
10423 HANSEN AVE.
OMAHA, NE 68124
402- 033 -5771 '
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