MIL-HDBK-1022A
12.3.2.2 Double Bottom With Concrete Layer and New Steel
Bottom. Clean and repair the existing tank bottom, install a
liner on top of the existing tank bottom, pour 4 to 6 inches
(100 to 150 mm) of fiber reinforced (low slump mix - typically
3,000 psig (21 000 kPa)) concrete over the liner and existing
bottom, shape the concrete to provide adequate slope, and
install the new steel tank bottom on top of the concrete.
Slope the concrete towards a sump and form with a series of
grooves along the top surface to collect any product which may
leak through the new bottom. Slope the channels to a
collection point with a pipe extending to an observation well.
Provide concrete with an alkalinity of 13 or higher.
12.3.2.3 Double Steel Bottom. Clean and repair the existing
tank bottom, place a structural support system on top of the
existing tank bottom, and install the new tank bottom. Design
the structural support system to prevent excessive deflections
resulting from loads on the primary (new) tank bottom. Allow
for an interstitial space between the two tank bottoms to
detect and collect any product from a leak. Purge the
interstitial space between the two bottoms with nitrogen to
remove the oxygen, thus creating a non-corrosive, non-
combustible environment. The elimination of condensation and
oxygen within the space provides cathodic protection for the
upper (new) bottom. Provide leak detection with sensors which
can detect pressure changes within the space. A pressure
increase results from a leak in the upper tank bottom as
product enters the space. A decrease in pressure indicates a
leak or steel failure has occurred in the lower tank bottom.
12.3.2.4 Single Bottom With Liner. Remove the existing tank
bottom and prepare the sub-base for bearing capacity. Place
sand layer on the sub-base to support the primary tank bottom,
install a liner with a slope to a center liner sump, place a
minimum 12-inch layer of sand on top of the liner, and install
a new tank bottom on top of the sand layer. The liner sump is
the collection point for any leaks from the bottom and
consists of a drain pipe leading to an observation well. An
alternative method is to use tell-tale slotted PVC or
stainless steel pipes in accordance with Standard Design AW
78-24-27. Provide cathodic protection by sacrificial anodes or
impressed current close to the liner to allow maximum
clearance from the new tank bottom. Install adequate numbers
of a cathodic protection reference cells between the two
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