Bass river is a salt water inlet in Beverly Ma
Could the calcium to magnesium ratio be off due to calcium chloride they use on the roads in the winter? The chloride level is high and the report saya it's due to road deicing as well as other contaminents but that might throw a lot of extra calcium into the water.
Does your report list an average and a range? I'd expect to see fairly large differences due to the seasonality if this were the case.