The Government will be announcing national guidelines this week for oil industry waste farms - known as landfarms.
A year ago the Parliamentary Commissioner for the Environment urged the Government to intervene on the farms saying they posed a risk to New Zealand's reputation as a safe producer of food and a working group was established to investigate.
There are about a dozen oil industry waste farms in Taranaki, where oil industry waste is mixed with soil and then pasture sown.
Microbes in the soil break down the petro-chemical contaminants in the waste over time - a process known as bioremediation.
Until now, grazing of livestock on active landfarms, before bioremediation of the oil industry waste is complete, has been permitted.
Censored documents released to Radio New Zealand by the Ministry for Primary Industries show the working group was at one point considering guidelines that would have continued to allow this.
However the working group later said that while it believed the food safety and animal welfare risks of doing this would be low, it was too costly to prove it.
The working group's key finding was that animals and crops should be kept off the oil industry waste farms until the waste is fully bioremediated.
The national guidelines are due out on Wednesday.