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Please try not to be worried about ALS.
ALS is a very rare condition, and affects people generally older than you are. You have a very common reason for twitches in your leg -- that is the nerve root irritation by the disc herniation at L5-S1, which can affect the muscles down the leg, including the areas in the back of the calf, which is why you probably have felt those spasms down in the achilles tendon area (which is S1 nerve territory).
If you would have had ALS -- the twitching is associated with progressive weakness in the muscles -- which you obviously have not progressed in the past 8 years -- and so these twitches are not related to ALS.