Something else to think about. They use wyoming bentonite under pits, lagoons, landfills, road construction, etc. because it forms an impermeable barrier to keep water from going through. Also in road construction, lime is inncorporated to help with water movement. Lime is also used to get rid of smells in mass burial sites and was used a lot in Vietnam.
A layer of bentonite incorporated with lime may help. Lime can be had at fertilizer stores, farm supplies, and concrete companies among others. Bentonite is used as drilling mud and can be bought from drilling mud companies in bags and their are probably other sources.