Evansville Water &amp; Sewer : Deerfield Lift Station elimination &amp; relief sanitary sewer
Creators: name: Ferguson, Mitchell
name: Pepper, Alex
name: Walls, Brayden
Publisher: name: Unknown
Year: 2018

description: To reduce overall costs in which the taxpayers of Vanderburgh County are responsible
for and to reduce environmental liability, Evansville Water and Sewer Utility (EWSU) has been
evaluating the possibility of decommissioning many of the 94 sanitary sewer lift stations that
they maintain. EWSU has asked for an analysis of a sanitary sewer lift station in service on the
north-side of Evansville. This lift station, referred to as the Deerfield lift station, is located west
of U.S. HWY 41 along E. Mt. Pleasant Rd. The Deerfield lift station currently services the
Deerfield and Copperfield subdivisions, receiving inflow from the subdivisions' 140 homes. If
decommissioned, a gravity-fed sanitary relief sewer system would be implemented to intercept
the station's peak inflow of 174,506 gallons per day. The topography of the project area presents
unique challenges in designing such a system. Particularly, the relief system would cross under
the bed of Little Pigeon Creek. Compliance of pipe coverage specifications (3.0 feet) forces the
sanitary relief system design to reach depths above 20 feet. Due to the lack of an interceptor
sewer to connect to, a lift station was needed to discharge the waste water from Copperfield and
Deerfield subdivisions. Recently, Commonwealth Engineers Inc. has been designing a new
sanitary interceptor that will end west of HWY 41 at the HWY 41/HWY 57 intersection. This
gives EWSU a new target to discharge the wastewater handled by the Deerfield lift station. This
presents a unique situation because the lift station needs to be rebuilt soon. With that being said,
this project thoroughly considered two project alternatives, (1) rebuild the lift station to keep it in
service, or (2) decommission the lift station and implement a gravity-flow sanitary relief system.
The project team took a variety of steps to determine the most appropriate course of action. First,
a topographic survey was conducted to obtain data that would create a representative model of the existing surface. The survey included the immediate site surrounding the lift station, cross
sections of Little Pigeon Creek, as well as the existing surface along two possible routes for the
relief system. As requested, the survey data was used to create a full set of plans for two sanitary
relief system designs. Design components include: (1) Known lift station inflow data was
provided by EWSU and used to determine a portion of the volumetric flow rate the relief system
would handle. (2) Anticipated volumetric flow rates and density factor values were chosen using
the EWSU Water and Sewer Design Manual according to the current zoning status (industrial) of
the undeveloped properties of which the system would be constructed in. (3) Pipes were sized,
using Manning's equation, to commercially available sizes using calculated flow rates. A
peaking discharge factor was determined (factor determined to be 4) and applied before
calculating minimum and maximum flow velocities. Designs achieve minimum velocity of 2 feet
per second and do not exceed maximum allowable velocity of 15 feet per second. (4) Two route
and layout alternatives for a relief system were analyzed. The two routes were determined by
considering environmental and economic impacts along with construction feasibility. Routes
were compared with each other to recommend the best route alternative. Design plans include
plan and profile views of all pipes and structures within each alternative. (5) Specification and
Detail sheets were developed. Typical detail drawings can be found at the end of each set of
plans. The specifications can be found in the front-end bid documentation provided along with
this report. With the two full designs completed, a project cost estimation was completed.
Estimation software was utilized in order to provide the most accurate cost estimation possible.
Route alternative 1 is estimated to cost $1,725,342.20 while the second route alternative is
estimated to cost $1,845,872.21. This suggests, of the two, route 1 is the best alternative economically, however, it encroaches on the city right-of-way along E. Mt. Pleasant Rd. This
means that if the city decided to widen Mt. Pleasant Road in the future, EWSU would be
responsible for relocating the sewer main. This makes route 2 the more feasible option. Finally, a
financial analysis of the lift station was conducted. The analysis considered the cost to rebuild
the station. This cost, along with operational and maintenance costs, were projected into the
future. In a graphical approach, this data was plotted against the projected cost of the sanitary
relief system. This allows EWSU to see when (in years) the cost of the two alternatives would
meet (the break-even point). This break-even point occurs before 40 years (2 lift station life
cycles). This is not as soon as was expected. However, replacing the lift station with a gravity
sewer would increase the possibility of land development and new customers, along with
relieving the utility of the environmental liability that a lift station and force main pose. If EWSU
decides to eliminate the Deerfield lift station in the future, the recommended design would be
design 2. This is due to right-of-way encroachment of design 1.