Valley R Center-CS 890815DUNAWAY ASSOCIATES, INC.
8804704
August 15, 1989
/
Mr. Russ¢l Doyle, P.E.
City En~neer
CITY O~ COPPELL
P.O. ~x 478
Cop~rll, 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, run parallel to Belt
Line Road, pass under the newly installed 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
flowline = 435.31
coming from existing
manhole at 0.33%.
Existing bottom edge of
10' x 6' RCBC = 434.73
I
Page Two
Mr. Doyle
Job No. 8804704
August 16, 1989
Summary
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 was constructed 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 i0' 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 apprQved construction plans resulting in a ±0.05 pipe separation
at 10' x 6' RCBC crossing.
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,
SKL/rel
cc: Scott Morway
Rick Walker
Howard Pafford
Steve Gotham
Larry Davis
Mike Robertson