Holdfast Training Services Trial Blog

In my last blog entry I mentioned Acid Sulphate Soils or ASS.  I have been put in charge of the safe disposal of the ASS.  Not only does this help me cover the sustainable development piece for CPD but, more importantly allows me the opportunity to talk ASS whenever I want.

A heap of ASS.  Note at the time these stairs were the only egress and the black smudges/ooze.

So what are acid sulfate soils? Here comes the Science…

Acid sulfate soil is the common name for soils that contain metal sulfides. In an undisturbed and waterlogged state, these soils may pose no or low risk. However, when disturbed or exposed to oxygen, acid sulfate soils undergo a chemical reaction known as oxidation. Oxidation produces sulfuric acid which has led to these soils being called acid sulfate soils.

How and where are acid sulfate soils formed?

Acid sulfate soils are formed by bacterial activity in waterlogged conditions when there is no or little available oxygen.

Naturally occurring bacteria convert sulfate (dissolved salt) from seawater, groundwater or surface water into sulfide (another type of compound that contains sulfur). This sulfide reacts with metals especially iron in the soil sediments or water column, to produce metal sulfides (the main components of acid sulfate soils). In order to convert the sulfate into sulfide, the bacteria also need a source of energy provided by organic material such as decaying vegetation.

So what I hear you say!

Well we have just dug up a lot of this soil, exposed it to air then added a good downpour of monsoon rain onto it and left it there to get really nice and acidic.  Essentially any water we pump out has to be treated like sulfuric acid and needs to be neutralised.  So you can imagine my joy when the bloke came to pump it out this morning then proceeded to let it leak out of his truck on the way to the disposal site.

For Damo!

This will be where the lime is added once the water tank has been moved.  

The Water holding tank is in the top right hand corner of the picture and needs to be moved to the corner of the excavation to avoid stressing the wall.