Valley R Center-CS 890815ENOINEER$ · PLANNERS · SURVEYORS . ,0 INTERNATIONAL PLA~A · TOWER [I - SUITE 636 RT WORTH. TEXAS 78109 · (817) 731.0~36
DUNAWAY ASSOCIATES, INC.
8804704
August 15, 1989
Mr. Russell Doyle, P.E.
City Engineer
CITY OF COPPELL
P.O. Box 478
Coppell, Texas 75019
RE:
8-inch Sanitary Sewer
10' x 6' RCBC Crossing
Valley Ranch Center (VRC)
Dear Mr. Doyle:
As requested by Howard Pafford this afternoon, I am sending the City of Coppell the
following explanation for the conflict at referenced sanitary sewer/storm drain
crossing and a list of possible construction alternates.
The proposed 8-inch sanitary sewer main (Line "SA")which parallels Belt Line Road
was designed as part of the Valley Ranch Phase iV - Water and Sanitary Sewer Plan
(Approved March 4, 1988).
Said proposed 8-inch sanitary sewer main is to connect and flow to an existing
T.R.A. manhole near Valley Ranch Center's northwest corner, ~un pa~aliel Lo Belg
Line Road, pass under the newly instal]ed Dallas County 10' x 6' RCBC at Valley
Ranch Center's northeast corner and stub out to provide future sewer service for
property east of Valley Ranch Center. The following is a summary of design and
existing data pertaining to Line "SA":
Line "SA" Station
Design Existing
Elevation Elevation Comment
0+00 - Existing TRA Manhole 431.90
8" = 433.04
Existing manhole invert
= 431.69
0+25.79 - Existing Manhole 431.98 433.26
6+46.90 - Edge 10' x 6' RCBC 433.96 --
Proposed 8-inch
flow]iue = 435.31
coming from existing
manhole at 0.33%.
Existing bottom edge of
10' x 6' RCBC = 434.73
Page Two
Mr. Doyle
Job No. 8804704
August 16, 1989
The 8-inch connection at manhole station 0+00 was constructed by the Mobile station
contractor 1.14 feet higher than designed and the invert elevation of manhole
station 0+25.79 wac conetructed the Mobile station contractor 1.28 feet higher than
designed. The Dallas County 10' x 6' RCBC was constructed approximately 0.13 feet
lower than designed. An 8-inch sewer line that extends from existing 0+25.79
manhole and clearly passes under 10' x 6' RCBC must lie on a ~0.11%.
Construction Alternates
(Based on limited knowledge of available sewer service and flow characteristics of
properties east of Valley Ranch Center)
Reconnect 8-inch to existing manhole 0+00 at invert flowline 431.90 and
reconstruct manhole 0+25.79 to invert flowline to 431.98. Install remainder of
Line "SA" per approved construction plans resulting in a ±0.05 pipe separation
at 10' x 6' RCBC crossing.
O
Construct line "SA" from Station 0+25.79 to Station 6+01.90 at a minimum 0.33%
from the existing manhole 0+25.79 to service Valley Ranch Center only. Trinity
River Authority, City of Coppell, or Dallas County install sewer service
across Belt Line Road from eastern property's northwest corner to existing
33-inch on north side of Belt Line Road.
o Install siphon under 10' x 6' RCBC.
o Punch 8-inch sanitary sewer through 10' x 6' RCBC.
Due to a critical construction schedule, please respond to this issue as quickly as
possible. Thank You.
Sincerely,
emke
SKL/rel
cc: Scott Morway
Rick Walker
.~Howard Pafford
Steve Gorham
Larry Davis
Mike Robertson