First, don't worry about the flowers and frogs. If the health dept says food is okay then the amounts must be teeny tiny. Amending the soil is the best way to clean it up. The little critters that chomp on the organic matter will also clean out the impurities - to a point. I would layer the compost or organic matter on top and let the earth worms mix it in for you. That way any arsenic would be less likely to be tracked into your home by walking on it. It may help you to rest easier to realize that although arsenic sounds scary, there are many very toxic things that we use every day. Like table salt. So toxic it will sterilize the soil and it can also poison humans - but only in large amounts. Again, if the health department gives the green light for growing food, the amount of arsenic cannot be too high. Keep growing, Marianne Binetti