How would hydrochloric acid would change the pH of creek water?

I am doing a lab in Environmental science. It involves having 3 coke bottles filled with creek water, 2 of them also consisting creek sediment. I drop about 4 drops of hydrochloric acid everyday. The purpose of the lab is to see if the acid will evaporate from the bottle or if the sediment 'sucks' the acid from the water. I believe my results are wrong. Does anyone know what should happen?How would hydrochloric acid would change the pH of creek water?
the ph of creek water (a salty substance) is high on the alkaline scale, hydrochloric acid with a ph of about 1-2 would basically neutralize the new mixture made possibly leaving it slightly acidic dependent on the concentraction of the creek waterHow would hydrochloric acid would change the pH of creek water?
i believe the sediment is slightly basic and the hcl is acidic so the sample with sediment should have a more neutral ph