I agree with digdirt. It doesn't look like it but it still MIGHT be pressure treated, but it's doubtful that any poisonous chemicals are in high enough concentration to be of danger. Keep in mind, even an apple has arsenic in them! :) Here's my suggestion: take one of the boards and put a bottomless pot on it (like say an empty milk carton with the bottom cut out, or even a styrofoam cup.) Plant a few seeds in the pot of cucumber and beans. They will be your canary-in-the-coal-mine testers. Cukes and beans are very sensitive to chemicals, so if they croak shortly after sprouting they are probably being poisoned. If they live ...the wood is okay to use.

Most danger from the "bad" arsenic treated lumber would be it's effect on handling it...be it direct contact or it degraded parts coming in contact with the soil. As far as plants go...it's a non-issue. It's more of a human health issue. If you're afraid of it...wear gloves, minimize direct contact with the wood, itself...wash harvested produce. Almost all of the danger of it is going to be found on residues outside of the plant, not within the plant. Most people don't bother with replacing it unless it's so old it's degrading/flaking away. If it's intact the biggest risk is going to be surface residues on the wood, itself. You could always put a layer of waterproof coating or some other type of paint/coating/covering (like tiles) over the wood, but it too will degrade over time.

The old CCA PT wood was known to leach Arsenic especially as it got older and because of that and that children could get that Arsenic on their hands and potentially lick if off is why that CCA PT wood was banned some years back. You must make direct contact with the wood and any Arsenic that would be washed off the wood and into the soil will accumulate near those posts, it does not migrate far in the soil and plants usually do not uptake enough to make them hazardous to you.

I don't totally understand your design. You have a layer of wood not in contact with the soil? Why do you need this layer if it's not containing soil? There is absolutely no problem using PT wood to build raised beds. The PT wood these days is treated with a copper based preservative and not the arsenic based compounds used several years ago. Even then, it was shown in several studies that the arsenic hardly traveled away from the wood. Other studies have shown that crops planted in arsenic-containing soil did not contain arsenic in their fruit. So crops like tomatoes were fine. Leafy vegetables absorbed the arsenic but not in huge quantities. Copper doesn't have the toxicity of arsenic so you are absolutely fine. I'm guessing that too much copper in the soil would lead to some noticeable problems with your plants so you would know if copper was leaching into the soil. If you are building some large raised beds, it's pretty much a guarantee that there will be no copper contamination beyond a certain distance from the wood and that distance would be very short (a few inches at most).