PrepTest 158

We are looking for an answer choice that describes this arrangement, in order from top to bottom: (1) Surface; (2) (300 meters); (3) Impermeable rock; (4) WELL: Permeable rock strata with salt water; (5) (1,800 meters). This answer choice is hard to follow, but does it describe that?

Let's break it down. This answer choice says it should be 300 meters or more beneath the surface, so elements (1) and (2) are met. It then says there's a layer of impermeable rock "below which there are no permeable layers." This mixes up elements (3) and (4). We know element (4), permeable rock, is beneath element (3), impermeable rock. So, there does have to be a permeable rock layer beneath the impermeable layer.

Question Type:
Minor Point/Must Be True

Strategy Overview:
Refer to notes or what you highlighted/underlined to locate where the passage discusses the "ideal" characteristics for an underground area suitable for deep-well injection, and refer to the relevant part of the passage as needed to find that answer choice that must be true

Answer Anticipation:
This is the fourth consecutive question that asks us to identify a specific piece of information. However, this time, the question stem asks us to find which answer choice "most accurately describes" the ideal characteristics of an underground area suitable for deep-well injection. When the question stem uses modifiers like "most likely" or "most accurately," the answer probably won't restate something from the passage. Instead, answering the question will likely require us to draw a connection between a few different pieces of information.

Like Questions 4, 5, and 6, this is asking a very general question about deep-well drilling. So, part of the correct answer is likely to come from the first paragraph since that provides the most background information. In the fourth through sixth sentences, the author explains that wells are drilled into “permeable rock strata that are already saturated with salt water" located "at least 300 meters" deep, so they're beneath “any aquifers that contain drinkable water (P1, S4-6).

While we're reviewing the first paragraph, we might notice the reference to "the best conditions" at the beginning of the second paragraph. This should remind us of the "ideal conditions" brought up by the question stem. This sentence tells us that the best conditions involve injecting waste into rock strata that are "separated by impermeable rock strata from aquifers containing drinkable water (P2, S1). We know these aquifers are above 300 meters, so the ideal conditions of an underground area would be rock strata with salt water, located 300 meters or more beneath the surface, with a tight seal of rocks in between the salt water strata below and any drinkable water aquifer above. The first paragraph also clarifies that the permeable rock strata with salt water shouldn't be more than 1,800 meters deep, since drilling that far would be too expensive (P1, S7). In other words, we're looking for:

——Surface——
Possible aquifers
(300 meters)
Impermeable rock
[WELL: Permeable rock strata with salt water]
(1,800 meters)

Answer Choice Explanation:
We are looking for an answer choice that describes this arrangement, in order from top to bottom: (1) Surface; (2) (300 meters); (3) Impermeable rock; (4) WELL: Permeable rock strata with salt water; (5) (1,800 meters). This answer choice is hard to follow, but does it describe that?

Let's break it down. This answer choice says the site should be 300 meters or more beneath the surface, so it satisfies elements (1) and (2). It also says the well should be in a layer of permeable rock. This satisfies element (4). And it says there should be a layer of impermeable above the layer of permeable rock, so element (3) is also met. This answer choice doesn't specify that the site should be no deeper than 1,800 meters, but the description is otherwise spot on. Therefore, this is the correct answer.

Key Takeaway:
The passage didn't make it very easy to understand where the ideal site for deep-well injection is relative to permeable and impermeable rock strata, drinkable and salt water, and 300 and 1,800 meters. And the answer choices certainly weren't easy to understand. When the language gets tricky, we must have as clear an anticipation as possible. Actually drawing a quick diagram, as we did in the Answer Anticipation above, can only help you make sense of the answer choices.

We are looking for an answer choice that describes this arrangement, in order from top to bottom: (1) Surface; (2) (300 meters); (3) Impermeable rock; (4) WELL: Permeable rock strata with salt water; (5) (1,800 meters). Does this answer choice describe that?

Nope. This answer choice says that the area is well will contain rock strata that extend from the surface to a depth of 300 meters. So, this doesn't satisfy element (2) — we know the well will need to be lower than 300 meters. It also doesn't satisfy element (4), as we know the site will need to contain permeable — not impermeable rock strata. These issues make (C) incorrect.

We are looking for an answer choice that describes this arrangement, in order from top to bottom: (1) Surface; (2) (300 meters); (3) Impermeable rock; (4) WELL: Permeable rock strata with salt water; (5) (1,800 meters). Does this answer choice describe that?

No. This answer choice says the site is less than 300 meters deep, violating element (2). According to the passage, the well will need to be lower than 300 meters so the waste won't touch any aquifers.

We are looking for an answer choice that describes this arrangement, in order from top to bottom: (1) Surface; (2) (300 meters); (3) Impermeable rock; (4) WELL: Permeable rock strata with salt water; (5) (1,800 meters). Does this answer choice describe that?

Not at all. This answer choice says the site will be more than 1,800 meters deep, violating element (5). The passage states that the well should be less than 1,800 meters deep. Therefore, this answer choice is incorrect.