If-clause condition 3 (would have -- had)

[Schwartz]

Error Idenification :

If smaller amounts of pesticide would have been used by the farmers. The streams around Joplin would not now be so polluted.

The correct answer (incorrect grammar one) is would have --->had.
It said 'If-clause condition3' in solution but I think it isn't fit condition3.
need more explanation please.

[Esl_Expert]

Hello Schwartz,

Your sentence is basically a variant of a type 3 conditional.

When you talk hypothetically about something that happened in the past, you normally use the past perfect form of the verb in the IF-clause. I have written two sentences for you. The first one talks about what was real in the past, and the other talks about what was not real:

Past fact, and past result (real):
- I did not remember his name, so I did not say hello.

To talk about that same past situation hypothetically, you can use a standard type 3 conditional. Everything in the following sentence refers to the past:

Type 3 conditional (unreal past):
- If I had remembered his name, I would have said hello.

The difference in your sentence is that there is a reference to a hypothetical past (in the IF-clause) with a hypothetical result in the present. In addition, the verb in your IF-clause is in the passive voice rather than in the active voice:

- If smaller amounts of pesticide had been used by the farmers, the streams around Joplin would not now be so polluted.

_________________________
“In order to shake a hypothesis, it is sometimes not necessary to do anything more than push it as far as it will go.”

[Schwartz]

why it isn't this way :
If smaller amounts of pesticide had been used by the farmers, the streams around Joplin would have not now been so polluted.

[Schwartz]

Anyone knows?