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Gary M. Carlton Page 3 November 23, 1999 Total coliform counts should not exceed: a median of 2.2 MPN/100 ml for the last seven daily samples 23 MPN/100 ml in more than one sample in any 30-day period (samples should be collected on a daily basis) Turbidity should not exceed: a daily average of 2 NTU 5 NTU 5% of the time 10 NTU at any time (turbidity should be monitored continuously with a recording turbidimeter) Recommendations for Further Analysis Should the City and the RWQCB decide to address the above issues, we recommend undertaking the following actions: 1. The risk analysis model should be re-run using a range of ISPs. This will allow reviewers to assess the influence the assumption of a very large ISP has on the difference between Scenario 1 and Scenario 2. If the influence is large, a lower assumed ISP should be considered (e.g., an ISP based upon the number of boats registered in the Stockton area.) 2. Further sampling should be conducted to develop an actual virus reduction distribution provided by the treatment plant, which will allow the determination of the probable frequency of low reduction situations. We recommend the sampling program consist of daily samples (or an alternate frequency designed to provide a database of adequate statistical power), collected over a twelve-month period to allow seasonal variations to be documented. 3. The risk analysis should be re-run using the actual virus reduction distribution in lieu of the current 2-10 log range for virus reduction. 4. The study should examine two "worst case" scenarios: a) body contact recreation near the outfall, and b) body contact recreation anywhere in the affected receiving -waters, including near the outfall, by a sensitive individual. These results should be compared with the other three scenarios to determine whether there is a significant increased risk of infection.