Actually, I've noticed, if you find areas that are tainted, the taint is usually high enough that those extra-taint plant thingies spawn and taint the area even further, so in theory the taint is just going to get worse and worse...
BUT, instead, if you keep your distance, and let it alone, the taint will spread around the neighbor chunks, lowering the original value to something like 50% or less. THAT's when you go in, find every single taint-spouting thing in it and break it with whatever tool you can. After you do that, the taint will remain high enough for tainted ground, grass and mobs, but it will not increase since the plants themselves don't spawn until 60% or so taint I think.
EDIT: Now, on a different note, I'm starting my nuclear power plant project. By that I mean I want to build a "real" nuclear plant, which of course uses IC2 stuffs in it, but is also a big stupid building. I'm modeling it after Chernobyl, so far I got a stack which looks like this:
The "reactor room" looks like this:
I've been very careful to place all the reactors (plus all 4 extra chambers) inside a single chunk, all the wiring is going to be under it, I'll also place the RP2 computer in the basement, the monitors themselves can be outside the chunk I guess since they're just for user I/O, so no funny business of the reactor blowing up because some chunk didn't load.
Anyway, I plan on making the turbine hall and everything, except obviously there is no such thing... so I guess I'll just model one out of stone and/or iron and place maybe a MFSU in it. Whatcha think?
(BTW I'm doing this in creative mode, then I'm using the Buildcraft blueprints to transplant them into my survival map using finite materials).
EDIT2: Oh, another thing: I noted that while some guides/wiki tell you to make a 2-block thick cube of reinforced stone around the reactor, everything in a 5x5x5 cube around the reactor has a chance of turning to lava (including reinforced). That means once it explodes, that "thin" part of the wall won't protect anything, it will leave a thin line of destruction in that direction (like some sort of deathray laser). So the best idea is to try to leave the 5x5x5 cube centered on the reactor empty if possible, then make the cube outside that.
Now, then only way to turn off a reactor with 4 chambers is with a red torch under it... and you're supposed to fill every block around it with water, so you have to do something like this: the floor, with a hole in the middle, and the reactor over it:
Then you can wire under it like this:
This also has the fortunate side effect of reversing the redstone power. So when it loses power for whatever reason, the torch actually turns on and the reactor stops. (unless the torch burns or melts, in which case... tough luck.