If sampling performed by an IU indicates a violation, the IU must notify the director within twenty-four hours of becoming aware of the violation. The IU shall also repeat the sampling and analysis and submit the results of the repeat analysis to the city within thirty days of becoming aware of the violation. Where the city has performed the sampling and analysis in lieu of the IU, the city must perform the repeat sampling and analysis unless it notifies the IU of the violation and requires the IU to perform the repeat analysis. Resampling is not required if: