Friday, August 13, 2010

Surveying for MEC’s

Our country and our military have a long history of
disposing of things they don't want in the water.  This has
included unexploded ordinances (UXO), or the newer term for the same
things, Munitions of Concern (MEC).  Through our combination of
applicable skills and navy contracts, the company I work for (Tetra
Tech) has worked its way into the niche of attempting to find these
underwater munitions at and around past and present military
installations.  This might sound more dangerous that it really is.  In
reality it is extremely unlikely that I will ever even see an MEC that
has not been certified as inert.  My job is to use the applicable
geophysical tools to find these munitions.  Our number one tool for this
job is the Marine Gradiometer Array (MGA), or as we like to call it,
"Maggie".  Maggie is a a custom built array of magnetometers designed
to be towed behind our survey vessel on the surface and at depths up
to 120ft.  This system measures perturbations in earth’s magnetic field
to detect iron bearing objects. If you were an easy client, you would
say "Wow that sounds great, how about you come survey at our
facility." If you were a smart client, you would say  "Now wait a
second... so your saying it you can't actually tell the difference
between a crab pot and a bomb, or a anchor and a torpedo?"  It is true
that Maggie has her limitations, but that is what specially trained UXO
divers are for.  At this point being able to tell the difference
between an MEC and a scrap of metal is the holy grail of our work.
From what I can tell so far in this industry, remediation of
underwater munitions is often initiated by having a few of them wash
ashore.  At our current survey location we are adjacent to a public beach
in extremely shallow water, so shallow in fact that we had to flip
Maggie upside down and use surfboard to reduce the draft.  At one
point while surveying there was only about a foot and a half of
water beneath or jet boat.  The photo I have attached shows Maggie
upside down on the surf boards, in-tow behind the jet boat.  The tall
mast above the MGA holds the GPS so we can accurately position the


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