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`+1 City of Stockton and County of San Joaquin Page 80 NPDES Permit CAS0083470 Response to Comments MS-14 and MS-18, are in the same general vicinity and both discharge to Mosher Slough. Due to the similarity of monitoring data from these two residential basins and the fact that they both discharge to the same receiving water, this monitoring program requires monitoring of MS-14 only along Mosher Slough" This accounts for the reduction in urban discharge monitoring stations. Additionally, the reduction in wet weather monitoring accounts for an increase dry weather monitoring. The level of monitoring in the Tentative Order is the minimum level deemed adequate by Regional Board staff to demonstrate compliance with permit prohibitions and receiving water limitations. Consequently, we will not increase any monitoring at this time. 56. Comment: (DK Comment 8(c) [incorrectly marked as 8(b)])Monitoring Program, Receiving Water Monitoring, C: We concur with the Permit's receiving water monitoring requirements, with several additional recommendations. Mosher Slough,the Calaveras River and Duck Creek flow from outside the urban area through the City of Stockton before their confluence with the San Joaquin River. It would be appropriate to require that these three waterways be sampled before they enter the urban area and concurrently sampled as they leave the urban area to isolate pollutant loading attributable to urban runoff. We also recommend that the number of sampling events be increased from two to three. Response: The purpose of receiving water monitoring is to determine if MS4 discharges are causing or contributing to exceedances of water quality standards, and to track water quality trends over time. Monitoring of upstream sources (i.e., outside the urban area) is only required if exceedances of water quality standards occur and the cause is in question. If Regional Board staff and the Permittees concur that, based on urban discharge monitoring data,MS4 discharges caused or contributed to the exceedance(s),then upstream monitoring is not required. 57. Comment: (DK Comment 9) The Permittees Have Failed to Implement Existing BMPs. Attached as Appendix "A," and included within as a part of these comments, is an assessment of the failure of the Permittees to implement their present BMPs. Response: Comment noted. 58. Comment: (DK Comment 10)PCBs Have Bioaccumulated and Caused Toxicity in Smith Canal Sediments. Attached as Appendix "B,"and included within as a part of these comments, is the report titled Preliminary Assessment of the Bioaccumulation of PCBs and Organochlorine Pesticides in Smith Canal sediments, G. Fred Lee&Assoc. Response: Comment noted. 59. Comment: (DK Comment 11) Wisconsin Has Instituted Numerical Performance Standards.