3003 W CASINO RD BLDG 40-58 2025-07-25

} I 111 Design Criteria The following criteria were considered in the post-development analysis as set forth by the City of IEverett: - Maintain the permitted runoff to each of the Powder Mill Gulch detention systems and the I underdrain system by maintaining the runoff areas and impervious coverage's established in the 1991 EIS Report and as modified for the Boeing Office Project for Buildings 40-87 and 40-88. la - Account for any displaced pervious area within each of the 3 basin outfalls. Post-Development Summary The post-development sub-basin and impervious areas were compared to the existing condition for Sub-basin A, Sub-basin B, Sub-basin C, and Sub-basin D. The total areas and impervious percentages for Sub-basin A, Sub-basin B, and Sub-basin C do not exceed the existing condition. The pervious area 1 lost in Sub-basin D is mitigated to Sub-basin 57m within the same drainage area discharging to Powder Mill Gulch Detention Pond. The remaining sub-basins from the 1991 EIS Report were evaluated to maintain permitted impervious I coverages within the permitted basin areas. These sub-basins were permitted for 100% impervious coverage, with the exception of Sub-basin 38, Sub-basin 59, and Sub-basin ::= which account for 1.4 I AC of required pervious area as shown in the existing condition summary table. Sub-basin 59, Sub- basin 57, and Sub-basin 88B currently provide a total of 1.4 AC of pervious landscaping and fall within the same basin outfalling to Powder Mill Gulch Detention Pond.1.0 AC of pervious area has been Ireassigned to Sub-basin 59 and Sub-basin 57, while Sub-basin -will continue to maintain 0 AC of pervious area. Q,4. 1 The following table summarizes the pervious/impervious relationship in the post-development condition for these sub-basins within the project limits: (Refer to Exhibit 5 for an EIS Report sub-basin location map for the post-development condition. Refer ato Exhibit 4 for a sub-basin location map for the post-development condition) I I I I 1 4 I