(a) Effective January 1, 1989, commercial users as identified under Section 937.12 and all industrial users determined by the City to have waste of a strength in excess of normal sewage shall be subject to an extra strength surcharge. The surcharge, by class of user, shall be established by comparing the average strength concentration for that class of user with the normal strength sewage and using the unit cost of treatment of the excess strength.
The steps to be followed in computing surcharges are as follows:
(1) Estimate the total billable flow volume per calendar year;
(2) Estimate the total volume of BOD or COD, ammonia, suspended solids and PO4-P which are expected to be received in the treatment plant per calendar year; and
(3) Estimate the total volume of BOD or COD, ammonia, suspended solids and PO4-P which would have been received if all of the billable flow volume had been at the strength of normal sewage.
Data needed as a basis, but not available to estimate the volumes described in paragraphs (a)(1) to (3) hereof, may be estimated by the City in the most practical manner possible.
The surplus elements of extra strength shall be attributed to each nonresidential class based on strength difference.
(b) The cost of treatment plant operation and maintenance attributed to each element of extra strength shall be determined, and from the estimated items described in subsection (a) hereof the unit cost of treatment shall be computed, for the following extra strengths:
(1) A surcharge for BOD or COD of a strength in excess of normal sewage, in cents per pound;
(2) A surcharge for suspended solids of a strength in excess of normal sewage, in cents per pound;
(3) A surcharge for ammonia of a strength in excess of normal sewage, in cents per pound; and
(4) A surcharge for phosphates of a strength in excess of normal strength sewage in cents per pound.
(c) For each specific significant industrial user service connection, the strength of the oxygen demand shall be either the BOD or COD test method as determined appropriate by the City. The extra strength oxygen demand shall be computed with the strength and rate which produce the higher charge, but not with both the BOD and COD rates.
(d) Using the unit cost of treatment for each element of strength, the cost of a class of user or of an individual user shall be computed. A strength level may be used which is below the normal strength for a given element of strength which may offset a higher element of strength. However, no class of user or individual user shall be charged a rate below the normal strength rate.
(e) For the purpose of reporting on bills, the combined surcharge may be expressed as a factor determined by dividing the unit cost of treatment for a specific waste by the unit cost for normal strength waste.
(Ord. 86-41. Passed 2-19-86.)