Optimal Corrosion Control Treatment (OCCT) is in place whenever the value of the 90th percentile sample result, minus the value of the highest entry point sample result, equals less than the Practical Quantitation Level (PQL) [90th percentile sample - Entry Point Sample = <5 ppb]. Any supply which meets the calculation for optimal corrosion control for two consecutive six month sampling periods is required only to submit water quality samples. Based upon these samples, the Agency will establish water quality parameter ranges by Special Exception Permit (SEP), and will reduce the number of sampling sites for both faucet and water quality samples to the reduced monitoring schedule. This schedule will remain in place until eligible for further reduction or unless the Action Level is exceeded.
Once a supply has either met the OCCT formula for two consecutive sampling periods or has installed corrosion control treatment, been deemed to have optimized corrosion control by the Agency and completed follow-up monitoring, the Agency will specify water quality parameters by Special Exception Permit (SEP). The Agency establishes minimums or ranges initially to accommodate temperature fluctuations and changes in water quality, and will adjust those levels as needed upon its own volition or upon request of the public water supply. Only those water quality parameters which are adjusted for purposes of corrosion control will be established. Other water quality compliance parameters, such as trihalomethane and CT requirements, will be taken into consideration when parameter minimums or ranges are established.