Water Code § 8939
ARTICLE 3. Sacramento and San Joaquin Drainage District Refunding Act
Each of the semiannual installments upon each tract shall be based upon the original principal amount of the assessment on the tract less any deductions theretofore made by reason of any credits made upon the tract pursuant to the provisions of Chapter 556 of the Statutes of 1919, and shall continue to be so based until such time as the principal and interest of the assessment on the tract are paid in full.