3721 OAKES AVE EVERETT MEMORIAL STADIUM 2018-12-21

P 1 engineeringlc t underdrain grass outfield has been considered as 100%grass,along with the other non- underdrained grass portions of the infield. Below is a summary of the existing and proposed areas used in the WWHM model for the comparison of the 100-year peak flows.Refer to Figure 4—Existing Conditions and Figure 5— Proposed Conditions,which show a layout of the project areas and drainage system. Table 1—Existing Areas Surface Type Square Feet Acres Cinder Surfacing 23,192 0.533 (modeled as 100%impervious) Compacted Dirt Infield 11,691 0.268 (modeled as 100%impervious) Impervious Surface Total 34,883 0.801 Existing Grass Field (non-underdrained) 12,606 0.289 (modeled as 100%grass) Underdrained Grass Outfield 68,714 1.578 (modeled as 100%grass) Pervious Surface Total 81,320 1.867 Total Existing Area 116.203 2.668 Table 2—Proposed Areas Surface Type Square Feet Acres Green Underdrained Synthetic Turf 83,419 1.915 (modeled with WWHM porous pavement element) Brown Underdrained Synthetic Turf 31,812 0.731 (modeled with WWHM porous pavement element) Infield Mix Surfacing (modeled as 100%impervious) 972 0.022 Total Proposed Area 116,203 2.668 Below is a summary of the 100-year peak runoff rates for both the existing conditions and the proposed conditions using WWHM with 15-minute time steps. A complete copy of the WWHM output is included in Appendix B of this report. Table 3—100-year Peak Runoff Rates 100-year Existing Condition Peak Flow Rate 1.47 cfs 100-year Proposed Condition Peak Flow Rate 0.82 cfs Difference in 100-yr Peak Flow Rates -0.65 cfs As shown above,in comparing between the existing conditions and the proposed underdrain synthetic turf field there is not an increase in flows greater than 0.15 cfs for the 100-year peak flow. Therefore,flow control(MR7)will not be required for the project. LPD Engineering, PLLC Page 6 Everett Memorial Stadium Baseball Field Replacement Storm Drainage Report, September 15, 2017