If they are referring to levels of Arsenic, ppb would not surprise me as most Arsenic salts are not very soluble or they tend to react to form insoluble salts, on the other hand drinking water with 100's of ppb of Arsenic has been seen to give health problems. As this is discharging to sea, the risks are minimal.
The EA usually are on the ball, so it would have to be with good reason to doubt their results. One reason to test the water independently would have been to persuade the EA to do their own tests, if they are already doing so and disclosing results hopefully this will answer your concerns.
There are 2 issues really: Are their dangerous levels of Arsenic in the water? Is there something that is killing off marine life near to the adit outlet ?
If possible you need to gather evidence (photos) to send to the EA (and maybe CWF) to show there is an effect on nearby marine life.
For interest, if you are able to get a sample of the white deposit (which is unlikely to be Arsenic), I might be able to do a crude analyses on it (ie Elements etc) assuming the EA haven't laredy done this.
However from the video it looked like it was on a rather dangerous outcrop of rock.
I guess if there is a problem here which later has consequences and the EA don't discover it or ignore it they would be in big trouble later, so they have nothing to gain by hushing anything up or ignoring it.
Is it safe to come out of the bunker yet?