BC Hydro has finally replied to questions that were posed back in October. You can decide if they answered sufficiently.
The questions were as follows:

What is the cost to put in a sub-station (which can be 230kV or whatever is necessary) off the 500kV line beside the capacitor station (or in another more convenient area)  vs the required upgrades to the 100 Mile House sub-station to accommodate the increased demand?
Has this cost been presented to the Taseko Mining Corporation for them to compare what it will cost them?

What about the long term power demands for the Vavenby Valley. The pipeline is looking at requiring more power, where will this come from? Will this branch off the 100 Mile House sub station or the is the Mica Creek line a more suited interconnect for both demands?

The reply is this:

BC Hydro is performing technical studies to identify options for supplying electricity to Taseko’s proposed Yellowhead Mine that is located near Vavenby. We must ensure that all customers receive power that is safe, reliable, and cost-effective.

The interconnection process for transmission voltage customers involves technical studies which are currently underway at Taseko’s request. To date, these studies indicate that connecting the Yellowhead Mine from the 100 Mile House substation with a dedicated 230 kV transmission line is the most technically feasible and suitable option.

We also assessed the possibility of supplying the mine by connecting the Mica 500 kV transmission system to the North Thompson 138kV system. The proposed new connection point would have been near the Seymour Arm capacitor station, however, this option presents significant challenges, including:

Increased risk to the reliability of the 500kV bulk transmission system (which services many areas of the province).
 

A new substation to step down from 500kV to regional transmission voltage.
 

To meet system reliability requirements, there would be a requirement for a double-circuit transmission line from the Mica 500kV system to the North Thompson system.
 

This would result in substantially higher costs, a substantial portion of which would be borne by BC Hydro ratepayers.
 

Relative to the 100 Mile House option, the alternative of supplying Yellowhead from the Mica 500kV system would be several multiples of cost higher, with a greater proportion borne by the BC Hydro ratepayer.
 

Schedule delays due to additional planning, design, and construction requirements.
In contrast, a dedicated line from the 100 Mile House substation is technical feasibly without increasing risk to the 500 kV transmission system. This solution is also estimated to cost considerably less than the Seymour Arm alternative, minimizing financial impact on BC Hydro ratepayers while maintaining system reliability.

Please note that Taseko is responsible for building, operating, and maintaining its dedicated line. BC Hydro’s role is to ensure the chosen solution meets our standards for safety, reliability, and cost-effectiveness.

A system impact study for the 100 Mile House option is currently in progress, and results will be shared with Taseko Mine upon completion.

We trust this clarifies BC Hydro’s position regarding early planning for power supply to the proposed Yellowhead Mine.

On the surface the answers are vague but give some insight into the decision making process. However, there are still some things that don't add up. Let's see if we get answers to the following questions:

I understand that the current North Thompson line 1L210 (138kV), is barely adequate for the current needs of the region. Can you confirm this?

If that is the case, what are the plans for expanding that to compensate for the increase in temporary and permanent workers for the mine, as well as the expansion of the communities because of this? 
Will all of that be powered by the proposed transmission line from 100 Mile House that Taseko is responsible for installing and maintaining?
Will the 100 Mile House line and sub-station be able to deal with that additional load in a stable and reliable way if that is the intent?
 
If this is not the plan, and you are looking at expanding or upgrading the current 138kV line? 
If yes, then why not upgrade it so the mine can use it as well and share the costs with Taseko? A solution that would use existing right of way and infrastructure. 

I understand BC Hydro's concerns about the stability and reliability of the Mica Creek 500kV line. However, I see that there is already a 69kV line coming off that generator station. So if there was no concern in adding that line, why is there a concern in adding a line to Taseko?
These lines have safety systems in place to prevent issues from affecting the source and the rest of the line. 
 
What has changed since 2013? when BC Hydro stated that the Mica Creek line was the preferred choice for supplying more power to that region? 
Below is the article link to that statement from 2013, I had to use the web archives to find it because for some reason the newspaper no longer has a record of it.
https://web.archive.org/web/20240221214845/https://www.clearwatertimes.com/news/bc-hydro-tells-clearwater-council-more-power-not-necessary-5687575