Following up on this series on what can be kept confidential, we have arrived at the conclusion that under the Clean Water Act all effluent data must be revealed to the public and cannot be kept confidential. Effluent data pertains to pollutants, and by reference to USC Title 33 § 1362 (6), a pollutant is defined as follows

(6) The term “pollutant” means dredged spoil, solid waste, incinerator residue, sewage, garbage, sewage sludge, munitions, chemical wastes, biological materials, radioactive materials, heat, wrecked or discarded equipment, rock, sand, cellar dirt and industrial, municipal, and agricultural waste discharged into water. This term does not mean
(A) “sewage from vessels or a discharge incidental to the normal operation of a vessel of the Armed Forces” within the meaning of section 1322 of this title; or
(B) water, gas, or other material which is injected into a well to facilitate production of oil or gas, or water derived in association with oil or gas production and disposed of in a well, if the well used either to facilitate production or for disposal purposes is approved by authority of the State in which the well is located, and if such State determines that such injection or disposal will not result in the degradation of ground or surface water resources.

So, the definition applies to basically everything that is discharged. Now,  (B) above exempts materials injected into the subsurface for hydrofracturing, BUT not after it is pulled back out and subsequently discharged to surface waters.  In my view, it is  neither the letter, nor the intent, of this definition to keep from public knowledge everything that people need to know about what is discharged into waters as under the Clean Water Act.

Some complications might exist if one is referring to waters that are not under the Clean Water Act, which may need to be looked at further.  Such complications arise if one is looking at wetlands or subsurface areas which are not clearly associated with surface waters.