Answer:
The total change that will likely occur in 2 years is  mg/L
 mg/L        
Step-by-step explanation:
Given : The first year, they found the chloride concentration changed by  mg/L .
 mg/L . 
It is estimated that the chloride concentration will change  mg/L the next year.
 mg/L the next year.
To find : What is the total change that will likely occur in 2 years?
Solution :
The chloride concentration changed by  mg/L in first year.
 mg/L in first year.
The chloride concentration will change  mg/L the next year.
 mg/L the next year. 
The total change that will likely occur in 2 years is
 
 
 
 
 
 
 
 
In a mixed fraction -  mg/L
 mg/L