How to use a semicolon

Don't. That used to be my tact on semicolons. Why bother getting it wrong, I will just craft my sentence(s) in a fashion that does not lend itself to the old crotchety punctuation that I only use to make winking smiley faces in texts.

Well that is a pretty ignorant thing to do. My colleagues us "semis" and I always assume they are using them in the correct fashion. To that I say no more! I have ESL colleagues that depend on my to make sure their English is correct. For example:
"The nature of penalty under s.75.21 as a surcharge on stumpage also support absolute liability; there is no defence of due diligence in respect of stumpage payable on the excess volume s.103 of the Forest act."
Is this correct? I need some help.

1. Use a semicolon between closely related independent clauses not joined a coordinating conjunction. When related independent clauses appear in a sentence they should usually be linked together with a coordinating conjunction (and, but, or, nor, for, yet, so). These words signal that there is a relationship between the two clauses. If the clauses are related and if the relationship between them is clear without a conjunction, you can use a semicolon instead.

* I got into an accident; the car was damaged badly.
* I remember the incident well; it happened in 1983.

Semicolons are often used to correct comma splices, which is what happens when we connect two independent clauses with a comma when there is no coordinating conjunction:

* I was late to class today, there was no parking.

This sentence contains a comma splice. While the instinct in correcting comma splices is to use a semicolon here, simply adding a coordinating conjunction would correct the comma splice:

* I was late to class today because there was no parking.

One common mistake is to use words like “however” or “therefore” as coordinating conjunctions. However, they are not. When connecting two independent clauses with a comma and a word like “however” or “therefore,” you can either divide the sentence into two sentences, or use a semicolon, which can be used to connect two independent clauses without a coordinating conjunction.

If you are unsure whether to use a comma or semicolon, check if both sides are independent clauses, or what can stand on their own as sentences. If both sides are independent clauses, you either need a semicolon or a coordinating conjunction. If only one side is an independent clause, and the other is a dependent clauses, use a comma.

If you are unsure whether to use a semicolon or period, think about why you want to join the two ideas together in the first place: should they be in the same sentence or in separate sentences?

2. Use a semicolon between items in a series of items that already contain commas:

* Some of her favorite deserts are chocolate cake, the kind with cherries on top; banana splits, without any nuts; and rice pudding, but only if it is made without raisins.
-University of Maryland

So taking my new-found knowledge I think my colleague was attempting to fix a comma splice with a semicolon. I would change the sentence to read (also correcting the spelling):
"The nature of penalty under s.75.21 as a surcharge on stumpage also support absolute liability because there is no defense of due diligence in respect of stumpage payable on the excess volume s.103 of the Forest Act."

Straight up. Tell me I'm wrong.