Wiil use treated wood posts, will sink in ground , 42inches, my question is - can the standard "treated" 6x6 wood posts available at any Lowes or Home Depot be used for this????
It depends on what retention the 'treated' posts are treated to, and what the treatment is.
Lots of misuse of the word 'treated', as anything can be called a 'treatment'.
Best to have a marine treatment for posts in the ground, and I think that is .6#/cuft compared to a 'std' treatment of .4#/cuft. Something like that anyway.
There are landscape timbers that are called 'treated' that have little to no treatment. Reason is that they are all heartwood, and the heartwood of most species of wood will not take a treatment. True, they were in the treating cylinder, but nothing was injected into the wood.
Even 6x6 timbers only are treated in the sapwood, and the heartwood center is untreated because there was no acceptance of the chemical. Same goes with treated wood of any description. However, the heartwood does have some natural resistance to decay, so in one sense, it doesn't need the same protection as the sapwood. (Heartwood can usually be identified by its darker color in the 'center' compared to the ring of sapwood around it, which is usually lighter color.
Best to ask for the treatment specs at Lowes or Home Depot.