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Chandler Martin May 12,2000 Page 2 The CSD is also concerned about the project's impact on an already overloaded local and rural storm drain system(roadside ditches)just north of I-205 in the vicinity of the intersection of Mountain House Parkway and Grant Line Road. The streets in this area have been observed to flood during heavy rains. Nearby home sites may have also been impacted. Even though you may impose a restriction of pre-development storm runoff maximum flow rates on the project, the total volume of runoff to the area north of I-205 will definitely increase. This increase could add to the flooding problem currently being experienced. Quality of Storm Water Runoff: On January 11, 2000, based on their concerns about not wanting to degrade the water quality of the Delta, the San Joaquin County Board of Supervisors,through Board Order No.B-00-52, instructed the CSD staff to prepare standards for addressing water quality control that will be applied to the design of all storm drainage facilities within the Mountain House community. Pursuant to this order the CSD is presently securing the services of an engineering consultant to help in the preparation of the standards. It is possible that the standards established by the CSD will be very similar to the Phase 2 NPDES standards soon to be imposed by the State of California. The CSD interprets the Board order to mean that the standards eventually developed should apply to all developments inside and outside the Mountain House community within San Joaquin County that contributes storm water runoff to the community storm water disposal system. Therefore,the CSD feels that the proposed project should be subject to the same storm water quality standards. Recommendations: Because of our concerns noted above,the CSD recommends that you place the following conditions on any approval the County may give to the subject project: 1. The project storm drain disposal system be designed in manner that the storm water maximum flow rate from the watersheds south of I-205 not increase the peak flow rates within the Mountain House community above what is indicated in the CSD master plan. Imposing this condition will allow the CSD's master plan to remain unchanged, and increasing trunk pipeline sizes will not be necessary. 2. The project storm drain disposal system be designed and constructed in a manner that will ensure compliance with the storm water quality standards soon to be prepared by the CSD and proposed for adoption by the Board of Supervisors. To meet this requirement,the applicant will need to provide a report that identifies all the primary potential pollutants that may be added to the storm water runoff as a result of their project.