SS9402-CN 950328CITY COUNCIL MEETING:
AGENDA REQUEST FORM
March 28, 1995
ITEM
ITEM CAPTION:
SUBMITTED BY:
TITLE:
Consideration and approval of an amendment to the contract with HDR Engineering, Inc. for the
design of Grapevine Creek III, IV and Bethel Road Sanitary Sewer Improvement~. #SS 94-02 and
authorizing the Mayor to sign. ~ z~-~:~-.,~ ~ .~ ~ ~,,-t'~ /~ / ' d__.
DATE
/
Assist~t City Manager/City Engineer INITIALS
STAFF COMMENTS:
See attached memo.
STAFF RECOMMENDATION Approval X Denial
EXPLANATION:
Based on the potential immediate cost savings and the anticipated long term cost savings, staff
recommends approval of the change in the contract with HDR Engineering in the amount of
$17,600.
BUDGET AMT.$ AMT. EST.$ +/- BUD:$
FINANCIAL COMMENTS:
Funds are available in CIP for this amendment.
FINANCIAL REVIEW:~
Agenda Request Form - Revised 1/94
CITY MANAGER
REVIEW:
MEMORANDUM
To:
From:
Mayor and City Council
Kenneth M. Griffin, P.E., Assistant City Manager/City Engineer
Consideration and approval of an amendment to the contract with HDR
Engineering, Inc. for the design of Grapevine Creek III, IV and Bethel Road
Sanitary Sewer Improvements #SS 94-02 and authorizing the Mayor to sign.
Date: March 20, 1995
On November 8th, 1994, the City emered into a contract with HDR Engineering for engineering
services associated with the design of three major sanitary sewer lines as shown on our Master
Plan. During conceptual and preliminary design phases of the portion of the sewer line adjacent
to Denton Tap north of Bethel Road, it became apparem that the City was going to have a
difficult time installing a sewer line on the east side of Denton Tap Road. It was our opinion
that it was necessary to be on the east side so we could replace an existing 8" sewer line and
provide service to the existing developmem on the east side. However, because of the potential
construction problems, we decided to investigate whether or not the existing 8" sewer line
beneath the north bound lanes on the east side of Denton Tap Road would be adequate to handle
the flow that would be left on that line if we constructed the new sewer line on the west side.
After checking maintenance records on the 8" line and TVing the line, it was determined that
the line would be adequate once we removed the flow from Shadow Ridge and any development
on the west side of Denton Tap off of the 8" line. With that information, we began looking at
alternative locations of the proposed 12" sanitary sewer line. The optimum location is on the
west side of Demon Tap Road, away from the developed areas. However, to stay entirely on
the west side we need to cross Grapevine Creek. One of our goals was not to have aerial
crossings because of long term maimenance. We then investigated whether or not a siphon
would work. Siphons are used in other cities and is an acceptable sewer design (see sample
siphon design included).
Because we will be installing the sewer line in a location which has not been surveyed and
because we will be designing two siphons which were not anticipated it is necessary to revise
the contract. The cost of the revision also includes various other changes which were necessary
to save large trees west of Denton Tap (behind the Burch Addition).
While this is an up from cost to the contract, the City should realize a very quick savings. That
savings will be due to not having to remove and replace existing driveways, landscaping,
sidewalks, monument signs, etc. on the east side and boring beneath Denton Tap Road to get
from the east to the west side. In the long term, the City will realize savings on the project due
to not having to maintain two aerial crossings. Aerial crossings tend to catch debris and create
erosion in the creeks. Also, any damage to the piers need to be repaired so that the integrity of
the sewer line is not compromised.
Based on the potemial immediate cost savings and the anticipated long term cost savings, staff
recommends approval of the change in the contract with HDR Engineering in the amount of
$17,600 and authorizing the Mayor to sign.
6-11. INVERTED SIPHONS
An inverted siphon is a section or' sewer constructed below the
hydraulic gradient due to some obstruction and operates under pres-
sure. The term depressedse~'er is actuall.~ more appropriate, since no real
siphon action is involved. Usually, two or more pipes are needed for a
\~')epressed sewer
la)
Inflow_ ~.
~- Excess flow 1
Minimum flow
~ Flows exceeding
Excess flow z plus
Minimum flow
Inlet structure
Section ~-.~
FiG. 6-7. Sketch of an inverted siphon or depres~d
siphon in order to handle flow variability. Normally the water-surface
elevation at the entrance and exit to a siphon is fixed. Under these con-
ditions the hydraulic design consists of selecting a pipe or pipes which will
carry the design flow with a head loss equivalent to the difference in en-
trance and exit water-surface elevations. A transition structure is gener-
ally required at the entrance and exit of the depressed sewer to properly
proportion or combine the flows.
The minimum flow in a siphon must be great enough to prevent
deposition of suspended solids. Normally, velocities less than 3 ft/sec are
unsatisfactory. When the siphon is required to handle flows which vary
considerably during any 24-hr period, it is customary to provide two or
more pipes. A small pipe is provided to handle the Iow flows; inter-
mediate flows may be carried by the smallest pipe and a larger pipe. Max-
imum flows may require the use of three or more pipes. By subdividing
the flow in this manner, adequate cleansing velocities are assured for all
flow magnitudes. The entrance transition structure is designed to properly
channel the flow into the various pipes. Figure 6-7 illustrates a typical
transition structure.
REVISED 12" DESIGN LOCATION
(8" S.S, IN DENTON TAP TO REMAIN)
n
BETHEL
I
12" DESIGN LOCATION
(RELOCATE 8" S.S. IN DENTON TAP)
LIMITS OF 8" S.S. TO REMAIN
WITH REVISED DESIGN LOCATION
E
BETHEL RD.
PROPOSED SIPHONS
E]
20.
Citizen's Appearances (Student).
Jonathan Smith, 306 Pecan Hollow Drive, addressed the Council concerning minimum
size housing in Coppell.
Diane deWahl, 1919 Redwood Trail, commended the Mayor and City Manager for an
outstanding job with the Students in Government program and commendation was also
given to the participating students.
The Students in Government portion of the agenda ended at this time.
A short recess was held at this time.
21. Citizen's Appearances.
There were no citizens signed up to speak under Citizen's Appearance.
CONSENT AGENDA
22. Consider approval of the following consent agenda items:
A. Minutes of: March 14, 1995.
Be
Consideration and approval of granting a variance to the Sign Ordinance to
allow the Lions Club of Coppell to hang banners publicizing a Pancake
Breakfast for April 1, 1995, on poles provided along Denton Tap Road from
March 29 through April 3, 1995, and waiving all applicable fees.
Ce
Consideration and approval of granting a variance from Section 10-8-4 of the
Coppell Sign Ordinance to allow a temporary construction sign advertising
the coming of a new business for the property located on the east side of
MacArthur Blvd., south of Sandy lake Road, across from the intersection of
MacArthur and Starleaf.
Consideration and approval of an amendment to the contract with ItDR
Engineering, Inc. for the design of Grapevine Creek HI, IV and Bethel Road
Sanitary Sewer Improvements//SS 94-02 and authorizing the Mayor to sign.
ge
Consideration and approval of Birdsong Addition, F'mal Plat, Lot 1, Block
A, located east of MacArthur Boulevard, north of DeForest Road.
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Consideration and approval of Primrose School of Coppell, Final Plat, Lot
2, Block A, located at the southwest corner of Parkway Boulevard and
Heartz Road, just east of City Hall.
Consideration and approval/rejection of aH bids associated with Bid
#Q 0195-05, for the lighting of athletic fields at Coppell Middle School and
Pinkerton Elementary School.
He
Consideration and approval to award Bid Q-0195-06 to Bush Landscaping,
Inc. for the purchase, planting, staking, and protection of trees at Andrew
Brown, Jr. Community Park West and City Hall, in the amount of $26,065.
Consideration and approval for awarding of Bid Q-0195-03 for temporary
staff services to SkiltCtaff (Secretary, Executive Secretary, Accounting Clerk,
Sr. Accounting Clerk) and Manpower (Receptionist, Library Aide, General
Clerk I and H, Data Entry Clerk, Sr. Data Entry Clerk, Light Industrial,
Maintenance Worker, Meter Reader).
Mayor Pro Tem Robertson moved to approve Consent Agenda Items 22 A, B, C, D, E, F, H
and I and to reject all bids on Consent Agenda Item 22 G. Councilmember Sheehan seconded
the motion; the motion carried 6-0 with Mayor Pro Tern Robertson and Councilmembers
Alexander, Sturges, Watson, Reitman, and Sheehan voting in favor of the motion.
23.
Consideration to appoint one member from an educational environment to the
Keep CoppeH Beautiful Committee.
Steve Goram, Director of Information and Customer Services, made a presentation to the
Council. Mayor Pro Tern Robertson moved to accept the resignation of Kim Geddie and
advertise to fill the vacancy on the Keep Coppell Beautiful Committee. Councilmember Sheehan
seconded the motion; the motion carded 6-0 with Mayor Pro Tem Robertson and
Councilmembers Alexander, Sturges, Watson, Reitman, and Sheehan voting in favor of the
motion.
24. A.
Accept the resignation of Richard Diekman the Vice Chairman of the
Telecommunications Board.
Appoint a replacement to the Telecommunications Board, the term to
expire October, 1995.
Councilmember Reitman moved to accept the resignation of Richard Diekman, the Vice
Chairman of the Telecommunication Board. Councilmember Sturges seconded the
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