Vistas of C SL-CS 960729 DOWDeY, ANDERSON AND ASSOCIATES, INC.
CIVIL ENGINI:ERS
16250 DALLAS PARKVVAY SUITE 100
DALLAS, TEXAS 75248
(214) 931-0694 FAX (214) 931-9538
July 29, 1996
Mr. Mike Matin
Assistant City Engineer
City of Coppell
255 Parkway Blvd.
Coppell, Texas 75019
WASTEWATER COLLECTION SYSTEM
SERVICE A~A "F"
(N. OF DENTON C~EK)
Dear Mike:
We have carefully evaluated the Sanitary Sewer Trunk Main System for the area south of the
proposed S.H. 121 Bypass, north of Denton Creek and west of Denton Tap Road. The trunk
main that will service the above defined area is a Sewer Line C, as designed in our construction
plans for Vista Properties.
We propose to construct 848 linear feet of 12" main from an existing manhole to the west right-
of-way of Denton Tap Road. When we began exploring the alignment and depths, it appeared
that if we relayed approximately 2200 linear feet of 10" main, we could lower the end point of
Line C (Station 8+48) by 4.0 vertical feet, however, at Station 7+58, an existing Dallas Water
Utilities 30" water main would cause interference.
Realistically, we could only lower line "C" by 2.0 vertical feet to allow 12" of cover over the
D.W.U. 30" main. I spoke with Mr. Steve Hardy of D.W.U. last week. He was very
much opposed to lowering their main unless it was a last resort. Even if D.W.U.
was agreeable, the lowering of the main is complicated by the timing of our
construction, being a water peak demand situation for the Town of Flower Mound.
Attached is a proposed schematic of potential grades for a system west of Denton
Tap Road, so that you can evaluate the depth. The following design elements were
considered.
a) Minimum velocity of a main (2.0 fi/s)
b) Manhole spacing equal to or less than 500 feet
c) Pipe friction (N=0.013)
d) Minimum curvature of trunk main
e) The FEMA 100 year water surface establishing future site elevation
f) The floodway location determined by FEMA
g) The City of Coppell aerial topography
h) The proposed alignment of S.H. 121 Bypass
i) Property ownership
I have shown on the attached map two alignments west of a proposed subdivision
named Magnolia Park. The length of 12" main through the proposed City Park
adjacent to Magnolia Park is 2445 linear feet. The flow line of the proposed 12"
sanitary sewer trunk main at the southwest corner of said Magnolia Park is
459.80+. At this location, the system can break into two distinct alignments.
The first alignment would follow the future floodway limit. Near S.H. 121 the
main would result in an elevation of 467.05+, assuming a 12" main at 0.20%.
The alternate alignment could extend from the above mentioned main immediately
west of Magnolia Park, extend 1400 linear feet north to the proposed S.H. 121
bypass thence parallel to said bypass, westerly to a point near the existing S.H.
121. This elevation would be 467.80+ assuming that this alternate line was a 12"
main at 0.20%.
In summary, if we leave the plan as designed, the extended alignment allows for
flexibility west of Magnolia Park assuming that the affected developer raises
his property from the floodplain. If he so chooses not to maximize reclamation,
the alternative alignment adjacent to the proposed bypass would have adequate
cover from natural ground.
If you have any question, please do not hesitate to contact me.
Sincerely,
William A. Anderson, P.E.
WAA/ldt