HomeMy WebLinkAboutSite Certifications - 10/20/1997AIRES
ASSOCIATES
September 23, 1997
Mr. Basil Harridan
City of Fort Collins Stormwater Utility
235 Mathews Street
Fort Collins, Colorado 80522
Re: 'Jefferson Commons drainagecertifcation
.Dear Basil,
STORMWATER
RECEIVED
SE%P 2 4 1997
In response to your letter to me dated August 26, 1997, we had the contractor regrade
Detention Ponds 170 and 172 in order to achieve the detention storage volumes specified in
our drainage report for the Jefferson Commons PUD. The contractor was successful in grading,
the'ponds to match the construction drawings. As we discussed during our phone conversation
on September 19, 1997, the as -designed ponds (shown on the construction drawings) do not
provide the detention storage volume specified in the approved drainage report. I have
included volume computations for the as -designed ponds as well as the as -built ponds for your
review.
I have also provided an annotated as -built grading plan for your review. This plan shows
numerous as -built spot elevations at significant topographical locations throughout the site.
Finally, I've included plots showing all of our as -built survey information for the project. It is
somewhat difficult to read, but provides more information than would be practical to write down.
Please call me if you need additional information or need clarification on the information
provided 'in this correspondence.
Sincerely,
wen Ayres & Associates, Inc:
Scott Queen, P.E.
Civil Engineer
SQ:sp
Enclosure
cc: Todd Barrick, JPI, without enclosures
Owen Ayres & Associates, Inc.
Engi nee rs/Scientists/Su rveyors
3665 JFK.Parkway, Building 2, Suite 300, P.O. Box 276460, Fort Collins, CO 80527 HAMD-9221TR
(970) 223-5556, Denver Metro (303) 572-1806, FAX (970) 223-5578 34-0431 :00
Printed on recycled paper _ -
Water Utilities
Stormwater
City of Fort Collins
Mr. Scott Queen
Owen Ayres and Associates, Inc.
3665 JFK Parkway, Building 2, Suite 300
P.O. Box 270460
Fort Collins, Colorado 80527
August 26, 1997
Re: Jefferson Commons Drainage Certification
Dear Scott:
Stormwater received your letter dated August 13, 1997 concerning the drainage
certification of the Jefferson Commons detention ponds. Certified grading plans of the
ponds as well as certified site grading plans were not included, but are needed for review.
Please submit a set of plans showing all pertinent as -built information, including survey
elevations.
According to your letter, detention pond volume calculations showed that all of the ponds
are undersized. These ponds must be re -graded so that their design volumes are met.
Please feel free to call with any questions you may have.
Sincerely,
Basil Hamdan
Stormwater Utility, City of Fort Collins
cc: Todd Barrick, JPI
235 Mathews Street • P.O. Box 580 • Fort Collins, CO 80522-0580 • (970) 221-6589 • FAX (970) 221-6239
STORMWATER
RECEIVED.
IAVMS AUG 15.1997
ASSOCIATES
August 13, 1997
Mr. Basil Harridan
City of Fort Collins Stormwater Department
235 Mathews Street
Fort Collins, Colorado 80522
Re: Jefferson Commons Drainage Certification
Dear Basil,
On July 21 and August 5, 1997, we surveyed the three detention ponds on the Jefferson
Commons site to determine the as -built volumes. Additionally, on August 5, 1 walked the site to
determine if the drainage patterns followed the design patterns and to verify that storm drainage
facilities were in place.
All the drainage facilities are in working order and provide proper drainage for the site. This fact
was substantiated by the flood of July 28, 1997.. According to Grant Etheridge (JPI site
superintendent), none of the.buildings were flooded during that event. The large detention
pond (Pond 144) was overtopped, resulting In flow just south of Building 6 into the parking lot.
Our survey showed that all of the building first floor elevations are within 0.05 feet of the design
elevation.
The volume of Pond 144 is 1.10 ac-ft, compared to a design volume of 1.13 ac-ft. While the
low flow outlet design calls for a 3-inch outlet pipe, a much larger pipe (6-inch probably) was
installed. Todd Barrick was notified that an orifice plate with a 3-inch orifice would be required;
as of August.12, 1997, it has. not been installed. As such, the low flow -releases from the pond
will exceed'th"e design flows. -
The volumes of Ponds 170 and 172 are well below the design.volumes. The design volume of
Pond 170 is 0.05 ac-ft while the, as -built volume is 0.03 ac-ft. The design volume of Pond 172 is
0.13 ac-ft and the as -built volume is 0.07 ac-ft. Volume calculations for the detention ponds are
included in this letter for reference...
The Plum Creek channel has been graded according to design and functioned properly during
the above -mentioned flood. The box culvert conveyed the floodwaters without overtopping.
The grouted riprap pad at the east boundary of the site held up during the flooding without
problem.
Riprap pads have been, placed at the storm drain pipe outfalls in Plum Creek, but I did not see
any riprap at the other.outfalls (such as at the two inflow points to Pond 172) as shown in the
design.
If you have any questions or need clarification, please call at your earliest convenience.
Sincerely `
jwjAyre�§;SAssociates, Inc..
ueen, PIE
Civil Engineer :
Owen Ayres & Associates; Inc
Engineers/Scientists/Surveyors HAMD-8B.LTR
3665 JFK Parkway, Building 2, Suite 300, P.O. Box 270460, Fort Collins, CO 80527 34-0557.00
(970) 223-5556, Denver Metro (303) 572-1806, FAX (970) 223-5578
Printed on recycled paper
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