Frequently Asked Questions
Can an empty reactor float out of the hole?
No. The steel reactor casing is grouted in place with cement. The reactor design includes a number of fixtures, including lifting lugs, guide shoes, grout lines,
and stiffening rings, which are welded to the outside of the steel casing. The weight of the casing and attached grout exceed the buoyant force of the empty reactor.
Even if the grout failed completely and behaved as sand backfill, then the reactor would still be restrained because it has a very large
surface area to volume ratio and a skin friction of approximately 150 to 200 lbf/ft2.
There is no foreseeable reason to empty a reactor and
provisions to do so are not included in the design. It can not be emptied accidentally. An operator would have to make a conscious effort to shut down the system,
drain the head tank, remove the head tank internals, and install a submersible pump in the bottom of the reactor to drain it.
What are the Long-term reactor maintenance requirements?
Over 30 years of operating experience with in-ground hyperbaric aeration reactors have shown that
long-term reactor maintenance requirements are minimal.
The reactor is, in effect, a tank. It has no moving parts. There are multiple air lines,
feed lines, and extraction lines to allow on-line repair in the unlikely event that internal parts are damaged by corrosion. All reactor designs allow the internals to be
removed through the top, and in a worst case scenario, an internal sleeve can be fitted without personnel working in the reactor shell.
In the past 30 years the only repairs required on previous generation in-ground hyperbaric aeration reactors have been due to pipe supports in the reactors wearing the
air lines or providing anaerobic pockets between the air lines and the hangers that caused crevice corrosion to penetrate the pipe wall. This problem has been
eliminated in the current reactor design by freely suspending the internal pipes from the top of the head tank thus eliminating pipe hangers immersed in the
The internals of a 20 year old reactor were recently tested with 100 psi compressed air and there were no leaks.
What is the expected life of the reactor shell?
A very long time.
The reactor wall is designed to withstand the grouting operation.
The wall thickness required to withstand the resulting external pressure far exceeds typical corrosion allowances chosen for equipment in this service. For example,
a ¾" wall would have a calculated linear pit corrosion life of approximately 125 years.
Corrosion has been measured on older reactors, now 20 to 25 years old, and was found to be approximately 0.006 in/year during the initial penetration of a pit.
However, the penetration rate may slow down over time if the microbes produce phospholipids which would protect the steel through biopassivation. This phenomenon is usually
observed in VERTREAT™ reactors.
Care is taken in the design to eliminate crevices and hence crevice corrosion. When two surfaces meet and
cannot be seal welded, an extra thickness of material is used. There are no pockets in the internal piping in the reactor.
Are in-ground reactors resistant to earthquakes?
Yes - more so than above-ground vessels, diked ponds and lagoons.
Earthquake analyses have been carried out for Pacific Rim installations including Japan, Alaska, British Columbia, and Washington state. In each case, it was found
that subsurface vessels are much more earthquake resistant than above ground vessels. These reports are available for review. California authorities did not require this
analysis to be carried out because they have obtained extensive data from off-shore oil wells.
During the placement of 2 VERTREAT™ reactors
in California in 1999, a force 7 earthquake occurred approximately 50 miles from the site. One reactor was in place and an uncased drilled hole was open prior to placement
of the second reactor casing. No damage was sustained during the earthquake even though there was substantial ground movement.
Can the reactors leak?
It is highly unlikely that a reactor would leak, and if one did leak, the consequences would be minimal.
Because of the high void fraction in the reactor, the effective specific gravity of the material in the reactor is much lower than that of the surrounding ground water.
Except in locations with an unusually low water table, ground water would tend to leak into the reactor in the unlikely event that a leak developed. If material did leak
out of the reactor, the escaping material would be treated effluent and biomass, which are relatively innocuous.
A reactor leak test can be
easily performed by shutting down the reactor and observing the level change over a 24 hour period.
Which geological formations are suitable for installation?
Almost all. Depending on the local geological conditions, techniques commonly used by the mining, tunneling, construction, or oil drilling industries are used. Reactors have been
placed in numerous geological formations varying from water saturated silt deposits to hard rock. Before excavation begins, a core hole is run in the vicinity of the
proposed reactor. The core hole data allow selection of the appropriate excavation method and design of cutting tools. They also allow accurate determination of the
In water saturated silt, a ring of freeze holes is constructed around the proposed reactor bore hole. The ground is frozen to form
a 2 to 3 ft thick ice wall around the bore hole and the material contained within the ice wall is excavated.
In sedimentary rock and
aggregate deposits, reactors up to approximately 18 ft in diameter can be placed using a reverse circulation rotary drill.
In very hard
rock or for large diameter reactors, mining techniques are preferred.
How difficult is it to find a driller capable of drilling large diameter shafts?
NORAM has identified several highly qualified drillers in North America,
some of which have experience drilling 18’ diameter shafts over 1,000 ft deep, through hard and soft rock. NORAM will assist prospective clients to evaluate core hole data
and identify suitable drilling methods and drillers.
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