Water and Pollution Control Department

Purpose of the Pretreatment Program

The Clean Water Act of 1977 required wastewater treatment facilities with design flows greater than five million gallons per day to have and implement a non-domestic wastewater pretreatment program. The City of Ames Water Pollution Control (WPC) Facility has an average wet-weather design capacity of 12 million gallons per day. The purpose of having a pretreatment program is to protect the treatment facility from wastewater components that may
pass through the treatment facility untreated into the receiving stream; in this case, the South Skunk River; inhibit the treatment facility’s processes, many of which are biological; contaminate the resulting biosolids or wastewater effluent; reduce the ability of the treatment facility to recycle and reclaim wastewater and biosolids from the treatment system; (The WPC Facility recycles its biosolids by land-applying them as soil conditioners for trees and agricultural crops.) cause damage to the municipal sanitary sewer system; or potentially cause harm to workers in the sanitary sewer system.
The City’s pretreatment program implementation has four elements as follows:
Contracting for wastewater treatment Issuing wastewater discharge permits Monitoring wastewater parameters Enforcing corrective action to permit violations
The Contract for Wastewater Treatment is generally valid for 20 years and specifies the conditions for non-domestic wastewater treatment. The Non-Domestic Wastewater Discharge Permit is valid for no more than five years. It specifies the wastewater parameters and concentrations or masses of those parameters that a non-domestic user may discharge to the sanitary sewer. It also specifies the parameters, frequencies, and locations for monitoring of the non-domestic discharges. Sampling and analysis of the wastewater is done according to the permit and can be performed by either the non-domestic facility or the City Water/Wastewater Laboratory. In either case, the City is required by law to do verification monitoring of the wastewater discharges. Enforcement actions are taken only in cases of permit violation. In most cases, issuing Notices of Violation (NOV) is the only enforcement action needed prior to the correction of the permit violation. The City has pretreatment coordinators, who are also responsible for evaluating requests for discharging chemicals or liquids other than normal household wastewater to the sanitary sewer (Special Discharge Requests).