I'll bite. 

A quick Google search of the LCT suggests they prefer the upper Crowley and Pole Creeks. In fact, hybrid LC + rainbow trouts had to be killed (years ago) on the lower Crowley to protect the population of pure LCT in the upper. Examining the topo map, it appears that any runoff from TP joins the lower Crowley at Sentinel Rock, before it washes into the desert playa below. This may be why the BLM didn't look into this issue much. In the 1970s, when the LCT became endangered (1970) and then bumped down to threatened (75), there was other mining activities going on at TP and no mention of needing to curtail that for the trout. 

The water that washes into the playa, however, does appear vital to replenish the groundwater for the center-pivot irrigation in the valley below, near Orovada. Water is scarce and this is something that ranchers would be very attuned to protecting, for good reason! Sometimes, environmental reviews are used for reasons other than the environment (see California HSR).

All of this is just my guess...I'm more familiar with the desert just north of the border, in Oregon, than that area. Either way, though, I feel for the ranchers. Their patriarch appears to have passed away a few years ago, and I'm sure the family is concerned about their own future and the future of their ranch. Hope it can all be resolved to everyone's satisfaction.