SITE INFORMATION AND CORRESPONDENCE

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STAFF REPORT INTRODUCTION On 10 July 1985, the City of Stockton was issued a complaint proposing a $50,000 administrative civil liability for discharging wastes in violation of discharge requirements. On 19 and 20 June, these violations resulted in the death of an estimated 5,000 catfish in the San Joaquin River in close proximity to Stock- ton' s treatment plant outfall . This staff report provides the background information and conclusions which led to the issuance of this administrative civil liability complaint. BACKGROUND The City of Stockton operates a Regional sewage treatment plant which serves the domestic and industrial wastewater disposal needs of greater Stockton. In 1979, a major construction project was completed which improved the secondary treat- ment capability and added tertiary treatment capability. Secondary improvements included plastic media trickling filters. The City has 615 acres of ponds, which average 6'deep, which provide further treatment beyond secondary. The capacity of these ponds is 1 .2 billion gallons, or approximately 50 days of flow at 25 mgd. Tertiary treatment facilities are comprised of dissolved air flotation, multi-media filters, and continuous pH and chlorine residual monitoring capa- bility. The facility is operated to provide tertiary treatment during critical periods of the year. During the balance of the year, secondary treatment is provided. The plant effluent is discharged to the San Joaquin River between Burns Cutoff and French Camp Slough. The effluent flow averages 29 mgd and ranges seasonally from 22 to 34 mgd. Current requirements were adopted for this plant in Septem- ber 1980 in Board Order No. 80-116 (see Attachment A) . Stockton chose to discharge to the San Joaquin River in lieu of land disposal at the time a grant was available to construct new facilities. The City installed tertiary facilities to protect the beneficial uses of the San Joaquin River and the delta. The San Joaquin River and the South Delta provide a critical source of drinking water (the California Aqueduct and the Delta-Mendota Canal ) , and are widely used for recreation such as fishing and waterskiing. At times during the year, the San Joaquin River, at the point of waste dis- charge, experiences very low flows and flow reversals. The City of Stockton's discharge, during these times of low flow, makes up a large percentage of the flow of the River. The Board' s requirements, therefore, prescribe stringent effluent limits of 10 mg/l for BOD and suspended solids during the summer (low flow) season, to protect beneficial uses. When the dissolved oxygen level in the river falls below 5 ppm, the City is required to achieve this 10/10 require- ment. The year-round effluent limitation of 0.02 mg/l residual chlorine Is established to protect fish resources because chlorine is acutely toxic to fish at low concentrations. In addition, the permit prescribes an effluent pH range from 6. 5 to 8. 5. A pH less than 6.5 has a deleterious effect upon fish and aquatic life. r-7—