When the "professor" lifts the cut slab, the edges are clearly NOT cut. When concrete is cut, the cross-sections of the aggregate stones are visible with the cement between them forming a smooth surface with parallel curves that match the saw blade's diameter. This one shows a rough surface of cement.
The premise is that removal of excessive amounts of sand, both widening the river and making it deeper, will cause the water to speed up. This is incorrect. A wider river runs slower than a narrower river. The same is true for the depth.
When the 'Professor' is cutting the concrete, he is using a 14 inch blade. This would only cut about 6 inches into the concrete. When he lifts the block, it is at least 12 inches thick. This would require at least a 36 inch blade and saw that would be too big to be hand-held.
Gay says that the river sand stops heavy metals from being leached out of the ground. But rivers can't lift heavy metals out of their beds; heavy metals precipitate out of rivers into their beds. Disturbing the bed by siphoning sand stirs up those sediments containing heavy metals, re-introducing them into the flowing water. A hydro-geologist wouldn't make that mistake.
Sherlock says the supply of sand is finite, but it's the most-common substance in the Earth's crust. A company from India wouldn't need to pay for permits, impact studies, & trucks in the US when they could mine it (legally or not) much more-easily & -profitably closer to India.
When the "Professor" is shown cutting the concrete slab, he is pulling the saw towards himself when he should be pushing it in the opposite direction. One can also see how the concrete has already been cut, so pulling the saw backwards through an already cut slab serves no purpose.
The "professor" is shown using a gasoline-powered abrasive chop saw, but the sound is from an electric circular saw cutting wood.
Sherlock spends several minutes working to open the garage door. When he succeeds, the sound of a heavy mechanical latch is heard. But the next shot reveals only a doorbell-type button.
Marcus says the RF chip in the bracelet identified the company. But a passive repeater chip only returns a number - not text. The software of the antenna reading the chip has to recognize & react to the chip's number. Simply reading the number out of the chip wouldn't directly identify who bought the bracelet.
Troy says that Salinger decided to open-source the MERMA technology, making Lauren's points in the project worthless. He then suggests that others whose inventions were incorporated in MERMA might have been angry about her stealing from them. But since her theft hadn't been publicized yet, and since Salinger's decision had; they would have been angry at Salinger for the same reason she was - not at Lauren.
The MERMA is shown deploying a floating absorbent ring, and is described as cleaning the oceans. So there would be no need for it to measure heavy metal concentrations since it could never process enough water to affect those levels in any salt-water body.
At the beginning of the episode, Lauren Wexler is found embedded in the concrete. While the murderer is fingered, it's never explained how Lauren ended up in the concrete.
Sherlock says there is no signage in the video to identify the site of the MERMA test. In the next sentence, he says which county it's in, before visiting it.
The construction foreman says he has to watch that the "Professor" knows how to use a chain hoist. But he's using an electric cable winch. A chain hoist is hand-powered, and makes a distinctive rattle as the chain passes through the sheaves.
Troy tells Watson he doesn't own a car. Later, she & Sherlock refer to his lying about the contents of the garage, even though there actually was no car in the garage. So he didn't lie about that. He only lied about knowing Lauren.