SITE INFORMATION AND CORRESPONDENCE

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City of Stockton 1.� 5 - 13 December 2000 Pretreatment Compliance Audit City should review and improve its practice of monitoring and inspecting private companies who use special permits to discharge to sanitary sewer manholes. LOCAL LIMITS The present pH limitation for local limits is defined by City Health and Safety Code Section7-089.16 as between 5.0 to 10.0. In March 2000 the City issued and Emergency Order to the SNs of Sewage Collection System 7. The Order requires SNs to maintain a discharge of pH 7.5 or higher on a monthly basis allowing for an overall range of pH of 7.0 to 12.0. The Order was enacted to elevate the overall pH in System 7 to prevent biological production of sulfide gases, which in turn damage the collection system and potentially endanger the public health. The Order was not previously discussed with the Regional Board nor was a copy of the Order forwarded to the Regional Board at the time of its issuance. According to 40 CFR 403.18(b)(2), changes to the pH local limits is a non-substantial program modification. As such the City is required to notify the Regional Board at least 45 days in advance of the change pursuant to 40 CFR 403.18 (d)(1). The Emergency Order was still in effect at the time of our inspection. .During the interview with the Technical Services Supervisor and the Senior ECO there was considerable discussion regarding the adequacy of local limits. Specifically, State inspectors inquired about the hydrogen sulfide levels in Collection System 7 which have been difficult for the City to control. The City indicated that high sulfate concentration wastes streams result in the production of hydrogen sulfides which are the underlying cause of corrosive damage of Collection System 7. There are presently no local limits on sulfides or sulfates. The City is required by 40 CFR 403.5(b)(2) to limit discharges that will cause corrosive structural damage and by 40 CFR 403.5(b)(7) to limit pollutants that result in the presence of toxic gases, vapors or fumes within the POTW in a quantity that may cause acute worker health and safety problems. The purpose of developing and implementing local limits is to protect surface and ground water quality, the wastewater treatment plant and collection system, worker.health and safety, and sludge quality. The current local limits filed by the City with the Regional Board were not modified during the revision of the existing NPDES permit. The City should coordinate its local limits development with Regional Board staff and the revision of the NPDES permit. When the local limits are considered acceptable by Regional Board staff, they should be brought before the City Council for adoption. The adopted local limits are then publicly noticed and brought before the Regional Board for incorporation into the City's pretreatment program. Requirements: The City shall send a technical report to the Regional Board, which describes the necessity of the Emergency Order. The presence of excessive sulfates that convert under biological activity to sulfides appears to be the underlying cause of damage to the Sewage Collection System 7. This damage potentially