A) as the amount of both tainted soil and industrial polluters continue to drop
"the amount of tainted soil" and "the amount of industrial polluters". If we open the parallelism you can see that " the amount of industrial polluters" is wrong because "polluters" is countable
B) as the drop continues in both the amount of industrial polluters and tainted soil
From a parallelism perspective; you would see "in [the amount of polluters]" and "in [tainted soil]". It would be better to have "tainted soil" followed by "the amount". Also the "number of polluters" suits better because "polluters" are countable
C) as the amount of tainted soil and the number of industrial polluters continue to drop
CorrectD) with the continually decreasing amount of tainted soil and the number of industrial polluters
Though usage of "with" is not completely wrong here it may trick a reader to think that "chance" decrease together with "the amount of soil...".
Also notice that it would be more concise and less ambiguous to compare two actions; "chances" decrease because "amount of tainted soil" decrease. However, here, the option conveys the following meaning; "chances" decrease because of "some amount of tainted soil".
E) with the amount of tainted soil continuing to decrease along with the number of industrial polluters
Similar issue in D