Q19 - When permits for the discharge

[WaltGrace1983]

This is a necessary assumption question so we have to find the core, evaluate any gaps in logic, and then go into the answer choices with that in mind.

Chemical discharging permits are given on estimate of the effect of the dilution of the chemical
→
Waterway is protected against being adversely affected by chemicals

We have a really strong conclusion here, which is great for NA questions! So what is going on here? Well honestly I think the argument is just kind of weak, especially in the premises. There are definitely gaps in logic but the first thing we notice is the gap in the general argument. The argument is talking about how permits are given on the basis of an estimate of how the chemicals affect the water. It doesn't really give us anything to work with here. There is no mention of any effects, which just makes it for an odd premise. From this, it concludes that the water is completely protected from being all adverse effects by the chemicals. Whoa! I notice the gap here: this argument is assuming dumping these chemicals into the water in accordance with the permit is alone sufficient to protect the water! Well what if the chemicals harm the fish and the fish are necessary for water? I don't really know how the answer choice is going to be phrased but I know that I have an understanding of what it might possibly be about which, for NA questions, may be all that you want!

(A) looks really good off of the bat! We have "relatively harmless chemicals" as they are being dumped in accordance with the permit. Then it goes on to say that they don't combine to harm the water. Well this definitely seems necessary. Let's negate it and see what happens:

"Relatively harmless chemicals do interact with each other and form harmful compounds."

Oh that looks REALLY good! This really makes the premise-conclusion link weak. Let's look at the other ones but I think I got the right answer.

(B) This is all about speed of the water, speed of the dispersion, etc. However, what do we know about speed and how it relates to the relative harmfulness of chemicals? In short, we don't know anything. Maybe having a slow moving flow with slow dispersion is perfectly sufficient to ensure that these chemicals are harmless. I will eliminate this for simply being not necessary.

(C) The word "no" is a big red flag here. Does it absolutely need to be true that all chemicals are able to be discharged into the water? Well no, this doesn't need to be true at all. If we negate this, it doesn't really hurt our argument one bit because we are talking about the chemicals that are able to be discharged - no other ones.

(D) Let's say they do discharge the entire quantity that the permits allow. Well isn't that the point of the permits?! The permits are telling you what is safe. The argument is saying that, because the permits say that it is safe (this is more or less implied but for argument's sake I'll say that this actually is what the argument is saying), then it actually is safe. We know nothing about quantities of chemicals and, for all we know, quantities don't mean an thing!

(E) Should be evaluated in terms of human health only? Where did that come from?! We can eliminate this easily due to scope issues.

So there you have it. (A) is the correct answer choice.

[NoahS986]

Are we supposed to assume that these chemicals are initially "harmless" or that the dilution process renders them as such? That specific detail made me identify (A) as Out of Scope, given that nothing in the passage alludes to their basic toxicity.