SITE INFORMATION AND CORRESPONDENCE 1980-1999

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H. Monitoring Of Effluent Discharged To Dredger Cut. Settleable Solids (SS) -The Tentative permit proposes a grab sample conducted daily. In reviewing other POTW data,we have noticed a tendency to collect a single sample early in the morning, generally at low flow conditions. How many sample results have the Regional Board received that were collected at 10 PM during the high evening flow period? This test is easily performed by the Discharger. We believe that sampling should be conducted twice each day (once on day shift and once on evening shift, on a rotating hourly basis). For example,if the morning sample was collected at 7 AM,the following day the sample would be collected a 8 AM. This sampling schedule would ensure monitoring throughout the entire discharge period. The Regional Board has established an effluent limit for settleable solids of 0.1 mg/l. Whenever sampling results show that suspended solids exceed 0.1 mg/l, the Discharger should be required to have the composite sample collected for that day analyzed for zinc, lead and cyanide. It is reasonable to require sampling when an exceedance indicates possible upset condition at the facility. This additional sampling would not be required when SS solids are maintained below 0.1 mg/l,. In reviewing data from other POTWs,we believe there is a clear correlation between metal concentrations and increased suspended solid concentrations in the effluent. We believe that sampling for zinc,lead and cyanide should also be conducted any time the total suspended solid concentration exceeds the daily maximum concentration established by the Board in this permit. We note that sample hold time for metals is six months. We do not believe it difficult for the Discharger to hold one liter of composite effluent until the TSS results are completed. The Discharger currently is required to sample for TSS daily. These tests are conducted in-house. If there are no exceedances, additional testing would not be required. I. Receiving Water Monitoring. The Tentative Permit states that effluent discharges are prohibited when dissolved oxygen concentrations in Dredger Cut are less than 5 mg/l. However,the Discharger is only required to sample dissolved oxygen in Dredger Cut weekly. This sampling frequency is inadequate to ensure compliance with the 5 mg/1 prohibition. DeltaKeeper patrols have observed extensive chemical weed eradication efforts by the California Department of Boating and Waterways in Dredger Cut. Dissolved oxygen levels frequently plummet following application of chemicals for weed control. DeltaKeeper is also informed that several dairies are regularly and illegally discharging dairy wastes into these waters. Dairy wastes cause additional oxygen demand and are likely to move through the system as a slug. Consequently, it is important to have continuous dissolved oxygen data to determine when dissolved oxygen levels fall below 5 mg/1. DeltaKeeper,Tentative NPDES Permit,Lodi, 17 December 1999,Page 13.