Grissom Lift Station Memo for The Woodlans at McKinney C I'I'Y
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DENTON Water & Wastewater Utilities
901-A Texas St., Denton, TX 76209 • (940) 349-8200
Memo
To: Pritam Deshmukh
From: Stephen Moore, Senior Engineer
Rusty Willard, Water Rec Superintendent
Date: January 29, 2021
Re: New Grissom Lift Station for The Woodlands at McKinney
Overview
The Woodlands at McKinney development (Woodlands), a manufactured house
community, is a project in Development Services that will be connecting to Water
Reclamation's Grissom Lift Station (GLS) for sewer discharge from the community. The
Grissom Lift Station currently receives local flows as well as flows from the Lakeview Lift
Station, which collects all the flows from the Lakeview Ranch community and homes
located along Lakeview Blvd. The sewage flows through the collection pipes into the
wet well and fills it to a set point, and then the installed pumps automatically come on
and force the sewage out of the wet well. In the event of an emergency at the GLS, the
pumps stop working and all sewage flows collect in the wet well and will eventually
cause an overflow.
The developer's projections show a total of 112,000 gallons of sewage per day,
approximately 78 gallons per minute (gpm). The Grissom wet well is very small, and
only has a capacity of 248 gallons per foot of storage with approximately 5 feet of
storage, for a total storage of 1240 gallons. The current local flows are 23 gallons per
minute (gpm), plus 19 gpm from Lakeview, leading to 29 minutes of storage, which is
not enough of a response time. However, the response currently comes from the City
employee who lives (almost literally) across the street, so he can get there quickly.
However, he will likely be retiring in the next few years and we cannot assume the same
immediate response in the future.
Adding The Woodlands 78 gpm to the existing Grissom flows of 23 gpm and the
Lakeview flows of 19 gpm means that Grissom will be receiving a total of 120 gpm,
which means about 10 minutes of storage — clearly not enough time to allow staff to
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prevent an overflow. To get to the minimum storage time of 60 minutes (typical
response time for setting up backup generator and/or pump), another 6000 gallons of
storage will be needed.
Requirements
The developer shall design and construct a replacement lift station (LS) for the Grissom
Road Lift Station, following the City of Denton Water and Wastewater Criteria Manual
section 4.20 (Lift Stations). The replacement LS will be located at the existing site
unless the developer wishes to move it to a new location. The developer will provide or
purchase the land needed.
Requirements for the replacement Lift Station include:
1. All design and construction will be per the City of Denton Water and Wastewater
Criteria Manual. See section 4.20 for the Lift Station requirements.
2. Emergency storage of a minimum of 60 minutes (time 120 gpm, or 7,200 gallons) to
allow City staff to get to the site, diagnose problems, and fix them or connect a
temporary bypass. All storage must be within the wetwell.
3. The existing Grissom Lift Station will be abandoned, and all wasterwater will flow to
the new wetwell by gravity.
4. The developer will pay for all SCADA equipment, which will be provided and
installed by the City.
5. An emergency generator placed on-site and connected to the system.
6. Connection to Denton Municipal Electric (DME) if the Woodlands at McKinney
obtains service from them. Oncor currently provides the power to the Grissom Lift
Station, and reliability has been an issue. DME is expected to be the electrical
supply to The Woodlands at McKinney, which would put DME lines adjacent to the
Lift Station, and the City expects that connecting to the new DME lines will
significantly increase reliability.
If you have any questions or need further assistance, please feel free to contact me by
telephone at (940) 349-8086 or by email at Stephen.Moore@cityofdenton.com.
Sincerely,
Ste pkwwil Mamie/
Stephen Moore, P.E.
Senior Engineer, Water and Wastewater Utilities
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