Do the cleanup levels for soil apply to concrete?

Yup. PCB's are nasty cancer causing materials.

You may use non-liquid materials such as concrete that were contaminated with PCBs $50 ppm provided the materials are decontaminated in accordance with a PCB disposal approval, or an applicable PCB spill cleanup policy, . The decontamination standard for concrete is <10 µg/100 cm² and requires that cleanup be initiated within 72 hours of the spill. If the state cleanup met these standards, you may continue to use the concrete. http://www.qjpcb.com/ Skype : wang.michelle35

definitely not a television question
commercial or residential ?
If clean up was done to state regs that concrete is good for any use
just in case
define contaminated
hazardous , carcinogenic ,nuclear, bio hazard
solid concrete slab poured post 1986 will have reo
if sound condition can be used, painted over, carpeted .sealed , tiled.what ever
if cracked up due to demolition
still ok to use for land fill or other rubble type back fill

it can be done as most what is termed "marble" products is polished concrete
talk with a masonry business as to how it is done but from what I have seen it will be a lot of "elbow" work with out power tools

You can try white vinegar with at least 5% acetic acid mixed with 1 tablespoon of dish washing liquid and table salt. Do not add water. Mix and use a spray bottle to disperse. I've used this method to kill weeds between concrete. I've never applied it to my lawn as it will kill off the grass as well. The acid and salt will draw out the moisture from the plant and the dish washing liquid will keep the solution on the leaves longer. Good luck.

I would take the soil back down to below the dpc level and scrape away the crumbling mortar and see how far it goes back. If it`s more than half the width of the wall I would seriously consider taking the wall down and rebuilding. If not, just re-point.

Sewer gases can contain explosive methane. This issue should be fixed as soon as possible.

Either replace the soil or pour some concrete in to stop it.

If this is on top or below (soffitt) If the cracks are movement or shrinkage when poured you can cut with Diamond grinder in a V type and then patch with a epoxy and sand fillers.If they are bigger you can use a repair motar .Your local hardware should have these in basic form.

Depending on how many pipes you have connected in the run from the toilet to the concrete pipe, I would replace all of it with plastic pipe and a new soil pipe if I could find one, if not put the plastic in the soil pipe and pour a concrete patch to fix the hole. Without seeing what you have there, it is hard to say for sure. But cast iron is not used much these days and a job to fix, cut, seal, repair, most are replaced. Hope this helps.