The purpose of the pretreatment program is to regulate businesses and industries to ensure that toxic chemicals that can upset the water reclamation process, or pass through the reclamation facility to harm fish in the river, do not enter the sanitary sewer collection system. Federal law requires the pretreatment program.
Bacteria carry out the water reclamation process. These are living organisms that can be poisoned by some types of chemicals. If the treatment bacteria are killed, the reclamation process cannot be completed and improperly treated wastewater is released into the Arkansas River. This condition is called an 'upset' of the treatment process.
There are other types of chemicals that do not harm the treatment bacteria. This means the treatment bacteria will not remove them. Those chemicals can travel through the water reclamation plant and kill fish in the Arkansas River. This condition is called a 'pass-through.'
More details about the pretreatment process are available on the Reclamation Facility page.