Gateway BP(1.4)-CS011012 (2)'-Il Halff Associates
ENGINEERS · ARCFIfrlsCTS · SCIENTISTS
PLANNERS ° SURVEYORS
October 12, 2001
AVO# 19266
8616 NORTHWEST PLAZA DRIVE
DALLAS, TEXAS 75225
(214) 346-6200
FAX (214) 739-0095
City of Coppell
Department of Engineering & Public Works
255 Parkway Boulevard
P.O. Box 478
Coppell, Texas 75019-4409
Attn: Mr. Kenneth M. Griffm, P.E.
Gateway Business Park, Lot 1R
Haverty's Drainage Improvements & Exchange Circle Reconstruction
Construction Plan Review Comments
Dear Mr. Griffin:
The following are revisions made to our drawings for Haverty's Drainage Improvements
and Exchange Circle Reconstruction per your comments sent on September 24, 2001.
Sheet DA-1
1. Please provide detailed calculations showing the beginning time for your drainage
calculations associated with line '.4' and line 'B '. Typically the beginning time of
concentration is 10 minutes.
Storm drainage calculations are shown on Sheet DA-1. Both Line A and Line B
have been revised to show a beginning time of concentration of 10 minutes.
Sheet STM-1
1. I am concerned about constructing a drainage system and then having 14field
connections to that system in the future. Is it possible to install all or some of the
stub-outs now? .4re you proposing to build the parking lot and buildings as shown ? If
so you shouM provide the stub-outs for the drainage connections.
Three stub-outs for future pipe connections to Line A have been added and are
noted on Sheet STM-2. The proposed building layouts could change.
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lll
· ,, Halff Associates
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ENGINEERS · ARCHITECTS · SCIENTISTS
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October 12, 2001
Page 2
2. The abandonedportion of the 60" RCP and the 33" RCP near station 19+00 on Line
'A ' should be removed, not plugged and left in the ground
The abandoned portions of the 60" RCP and 33" RCP will be filled with low
strength grout as noted on Sheet STM-1.
You're proposing to tie into an existing 12" stub-out for an 8" sanitary sewer. Please
be advised that the 12" stub-out is a clay pipe installed in 1981. It is doubtful that it
is in an acceptable condition, therefore you should remove the existing 12" V.C.P.
sanitary sewer and install your proposed 8" directly to the existing manhole in
Freeport. With some slight modification of the proposed 8" sanitary sewer, it is
possible you could eliminate the need for the two onsite manholes. There would still
need to be some repair work to the existing manhole in Freeport caused by the
removal of the existing 12" V. C.P. sanitary sewer stub-out.
We have revised the sanitary sewer plan to show the proposed 8" PVC to be
installed inside the existing 12" V.C.P. The annular space will be grouted.
4. A headwall should be provided on the proposed 6x5 RCB.
A headwall has been added to the proposed 6x5 RCB on Line B, as noted on
Sheet STM-1. A headwall detail has been added to Sheet STM-3.
Sheet STM-2
1. The hydraulic grade line needs to be lowered from approximately station 9+73 to
station 20+68. The hydraulic grade line as proposed in that location is at the existing
ground. I am unsure whether the ground will be cut or filled for future paving
operations, however, it is not good engineering practice to design the hydraulic grade
line at or above the proposed ground. Also, the hydraulic grade Hne at that elevation
more than likely will cause water to come out of the proposed manhole at station
16+86. Lowering the hydraulic grade line will more than likely necessitate larger
pipe sizes.
The ground line was shown incorrectly on the first submittal and has been
adjusted to reflect the correct elevations. The hydraulic grade lines for Line A
and Line B are below the existing ground elevation throughout the length of the
pipe, shown on Sheet STM-2 and STM-3.
III
--- Halff Associates
Ill
ENGINEERS · ARCHITECTS · SCIENTISTS
PLANNERS · SURVEYORS
October 12, 2001
Page 3
Sheet STM-3
1. Please provide the slope of the existing 60" RCP in Freeport which you are
connecting line 'B' to.
The slope of the existing 60" RCP has been added to Sheet STM-3.
If you have any questions or need additional infoiniation please call me at (214)346-
6249.
HALFF ASSOCIATES, INC.
Marty S. Paris, P.E.
Project Manager
cc: Robert McCann, Catellus Development Group