Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Yes, anywhere close to the delta or river from about Pittsburg west can get some salt.
East of that (Brentwood, Oakley...) the main problem is nitrates from farming. Friends outside of Knightsen had a well that tested 20 ppm NO3 with GH and KH off the scale (Actually I quit testing at 20 drops).
I am glad you are having your well tested for mercury. The old miners sure worked over those foothills! My Aunt and Uncle had a place in Gold Run where it used to be a pretty good sized mountain. Got placer mined down to a valley. They only quit when the springs kept filling up the place they were working.
My Aunt and Uncle's well had really good water for a few years, then got really bad. Very high in minerals, though I do not know if they ever had it tested. They just quit drinking it.
Test kits age.
Look at the code or lot number (whatever they call it)
The last 4 digits refer to the date of manufacture.
.... 0413 for example is April of 2013.
Many tests are OK for up to 5 years:
High Range pH,
Freshwater pH(low range)
PondCare Salt Level
Some go bad by 3 years:
PondCare Wide Range pH,