I am contemplating putting several raised beds atop a large gravel bed. I am worried that herbicide or other chemicals have been put on the gravel previously. Can I "wash" the gravel or place something over it before I place my boxes? Thanks so much!!!!

Conventional raised beds sometimes recommend putting a layer of cardboard down first and then putting the bed on top of that. A barrier like the cardboard is recommended especially in urban areas where lead may be present in the soil. You can "rinse" the gravel if you feel compelled but that will wash away some of the chemicals to the surrounding area.

ShellyS said:I am contemplating putting several raised beds atop a large gravel bed. I am worried that herbicide or other chemicals have been put on the gravel previously. Can I "wash" the gravel or place something over it before I place my boxes? Thanks so much!!!!

Shelly. How deep will your raised beds be, and what will you be growing in them? If vegetables, then the concerns would be different from ornamentals. I don't think "washing" would help much because presumably the gravel gets washed every time it rains. It's a difficult question to answer without knowing what kind of herbicide or other chemical might have been used there. Are you suspicious because there are no weeds?

Another consideration would be if there is plastic sheeting under the gravel bed that prevent weed/vegetative growth. If so, this has to be removed first. Just a thought.

Yeah, I doubt seriously washing will help. Do put down at least an inch of cardboard, the depth of the raised bed depends on what you need to plant. Something like a tomato needs at least the depth of soil of a 5gal bucket, and a few inches more. Your bed will drain just fine with the cardboard under it, and the plant wont get access to anything in the gravel.
PS- most herbicides/pesticides remain in the soil for at least 3 years...roundup glysophates are there for a lot longer time period.