Depending on the size of the Fresh Snowfall you will need to put more or less Firesand into the mine. For areas with more snowfall you need less Firesand and areas with less snowfall you need more Firesand.
The 3 Fresh Snowfalls are in the area in and around (K-7). If you start at Conflux #05, and run northwest, you should come across all 3 (run more to the west to find the third one, right next to zone boss pop area).
When you check the Fresh Snowfall, it gives you the option to Load Firesand, Remove Firesand, Set the mine, or leave it alone. The mine will initially be at a random level and you will remove or load Firesand as needed (it is normal for it to take 1-5 times for the level to change when choosing either load or remove). Your Subniveal Mine has five different levels of Firesand:
1. "The chamber of the Subniveal Mine contains only a pinch of firesand..."
2. "The chamber of the Subniveal Mine contains a small lump of firesand..."
3. "The chamber of the Subniveal Mine is filled halfway with firesand..."
4. "The chamber of the Subniveal Mine is filled to the brim with firesand..."
5. "The chamber of the Subniveal Mine is overflowing with firesand..."
Baldric seeks to put an end to the avalanches that plague the survivors by triggering small explosions to disperse accumulated snow. Assist him in an experiment to determine the optimal quantity of firesand for the task.