funny, maybe its a california thing, but at the county dump, haz mat material can be brought by and disposed of with an appointment and up to certain quantities at once. All you need to do is show your d.l. that you are from that county. also, some of the local fire departments accept some and will dispose of it then.....they don't want to fight a fire at your home\shop with these chemicals in there.
Even our local transfer stations will take the stuff but you have to pay a fee and make appointment....check into it.
J-LC Landscaping & Maintenance Gardening
C-27 CA. Contr# 770044