Upgrades
to Pump Up Water Plant's Capacity
Treatment process at Indiana facility maintained
throughout project
by Craig Barner
Getting pumped has been important during the $56.9 million
upgrade of the wastewater treatment plant in Lafayette, Ind.
Even during construction, water received from city sewers
has continued to move through pipe in the 30-acre facility
before being discharged into the Wabash River after treatment,
said John Dettman, project manager for Indianapolis-based
Bowen Engineering Corp., the general contractor on the project.
The requirement is a demanding one. Between 16 and 22 million
gallons of water is processed in the plant every day.
Meantime, 26 different structures in the facility are being
renovated or newly constructed, said Mike Kesler, project
superintendent for Fort Wayne, Ind.-based Hagerman Construction
Corp., the concrete contractor.
Maintaining water quality was especially tricky when systems
were bypassed, Dettman said. Provisional systems were occasionally
set up while components went offline for a week or more for
replacement or renovation.
For instance, pumps were put in place for three weeks while
the existing effluent pump station was demolished and built
anew. This job included constructing a junction box, building
gates and valves for it and connecting the entire structure
to a 60-in.-diameter pipe.
"In essence, we were taking a chunk of pipe, plugging
it here, plugging it there and pumping [water] while we did
the work in the middle," Dettman added.
Another time, water was bypassed for a week from a primary
settling tank while it was renovated.
Since the project started in July 2001, including during bypass
operations, water discharged from the plant was still required
to meet stringent state requirements on the levels of bacteria,
suspended solids and similar measures.
"The city hasn't had one violation since we started,"
Dettman said.
Expanding Plant Capacity
The project was implemented because the plant has neared the
limits of its capacity, said Brad Talley, water pollution
control superintendent for Lafayette's Water Pollution Control
Department. Indeed, a significant upgrade had not been done
on the facility since 1954.
The facility's capacity will more than double, Talley added.
The treatment process is relatively typical but complex. Water
comes into the facility from Lafayette's combined sanitary
and storm sewer system, and four 250-horsepower pumps drive
it into the headworks so treatment can begin. "Water
comes in with dirt, grit, sewage, garbage - anything that
can fit down a manhole," Dettman said.
Coarse screens remove the biggest contaminants, such as tree
stumps, aluminum cans or even bicycles. The effluent is passed
through fine screens, which sift the still large impurities,
and fine-screen washers.
Grit collectors, the next station, remove sand, gravel and
stone.
Solids are still in the effluent as it enters the primary
settling tanks, despite the sifting processes already completed.
The solids settle on the tank bottoms as sludge, and the sludge
goes to digesters. There, biological agents consume the waste
matter, and the effluent goes in another direction.
"It (the effluent) is a lot cleaner now than when it
came into the plant," Dettman said. "You got a lot
of settled sludge out of it, and you've got your grits and
big materials out."
The effluent falls over several weirs and enters aeration
tanks, where diffusers on the bottom blow air to keep beneficial
biological agents alive. The effluent still has sewage in
it, despite the previous sloughing off of the sludge.
"There are different bugs in different areas that do
different things," Dettman said. Like the digesters,
the agents consume the sewage.
Next, the increasingly clean effluent enters the final clarifiers.
Like the primary tanks, solids in the water, now very small,
settle on the bottom.
Through gravity, the water goes over weirs into a chlorine-contact
tank because Indiana requires chlorination from April 1 through
Nov. 1. The water is dosed and leaves the plant.
Methane gas, a byproduct, is produced during the digestion
processes and has to be dealt with, Dettman said.
The gas can either be burned away or routed to boilers, some
of which can run on methane. The gas is purified and fired
to produce hot water, which can heat buildings on site.
"The city can potentially save money by using what they're
producing anyway," Dettman said.
Systems Added, Renovated
The project called for many system components to be added
or renovated, including:
The headworks facility, which is new, contains two coarse
screens, three fine screens and two grit collectors.
A new primary settling tank, which was put up and joins
the four existing tanks.
Two aerating tanks were added, and the four tanks on-site
were renovated. Three blowers were added to the treatment
system.
Four 90-ft.-diameter clarifiers, which were constructed
while the existing 70-ft.-diameter clarifiers were scheduled
for renovation.
A new sludge-thickening building with two thickeners, one
for digested sludge and the other for waste sludge.
A new chlorination building, which doubled the capacity
for this process.
Besides the pump station, other new structures include process
pipe, an administration building, vehicle storage building,
maintenance building and warehouse space.
"We added more volume to their existing process and we
added new things to their existing process," Dettman
said.
Fighting the River
The site location near the river presented difficulties.
Two floods have occurred since the start of the project,
Dettman said. Though the deluges did not go over the levee
protecting the site, they did cause the groundwater to rise.
Numerous systems were used to dewater the land, including
deep wells, pumps and well points, but they provided only
limited efficacy due to the high water table and the composition
of the soil, Dettman said. It includes silt, sand, clay,
gravel seams, fill and even plain garbage.
"I could drill a hole 30 to 40 ft. in the ground with
a pump, and in one day it'd be slurping air," he said.
"It was the nature of the ground - it would not give
up water."
One flood occurred while the headworks facility was under
construction, causing work to fall behind schedule. Time
was later recouped, and the schedule was back on track.
Adding to the soggy condition is a hillside from which water
runs off and down into the site, Hagerman Construction Corp.'s
Kesler said.
The area's unstable nature resulted in more than 400 cast-auger
piles being laid as foundations, Dettman said.
Coordination among the team members was important in the
intricate project.
Hagerman alone had 20 subcontractors and suppliers in its
contract package, Kesler said. The company scheduled frequent
foreman's meetings, and a schedule was produced every three
weeks to keep on track.
Bowen also called superintendent's meetings, which helped
plan the 26,000 cu. yds. of concrete that was laid, Kesler
said. Flexibility was needed, because both pumping and crane
and bucket were used to move material.
Pollutant Levels Down
Some of the new systems are online, and work is expected
to finish in June.
Already, the project has borne fruit in terms of the quality
of water discharged from the plant, the Water Pollution
Control Department's Talley said. "Since we put the
new plant online, we're sending out half the stuff to the
river we used to," he added.
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