3700 FEDERAL AVE PORTABLE 6 JACKSON ELEMENTARY 2025-08-07

JACOBSON N U LTINI ENGINEERS Section 1 - Project Overview Jackson Elementary School is located at 3700 Federal Ave in Everett. The elementary school is spread over four separate parcels with a total of 5.04 acres owned by Everett School District (see Figure 1-Existing Conditions). The project site is bound by Charles Avenue to the north, Federal Avenue to the east, an undeveloped City owned parcel to the south, and Tulalip Avenue to the west. The project will be pursuing a major replacement in the near future, however as a "make- ready" project this drainage memo is specifically for the relocation of classroom portables and with additional new portables to be installed in the summer of 2024. The two northern parcels located immediately north of Charles Avenue (parcel numbers 00605000601101 and 00605000400700) are currently used as a parking lot with approximately 43 parking spaces on 0.56 acres. The existing school building parcel (parcel number 00605000500000) is immediately south of Charles Avenue and is 2.57 acres in size. The undeveloped Edwards Avenue right-of-way serves as a separator between the existing school building parcel and the adjacent parcel to the south. The southern parcel (parcel number 2905300030260) currently serves as the school's playfield with an area of 1.9 acres. The highest point of Jackson Elementary School is at the southwest corner with an elevation of 348 feet. The lowest point of the site is at the northeast corner with an elevation of 306 feet. In general, the site topography slopes from the southwestern corner to the northeast corner with an elevation change of approximately 42 feet. A Level-1 downstream analysis was performed for 1/4 mile downstream of the site and is included in Section 2 of this report. Table 1.0: Existing Land Cover Conditions Impervious Area Pervious Area Grass Field with Total Area (sf) Parcel (sf) Sub-Drain (sf) Parcel A 10,982 6,007 - 16,989 Parcel B 4,678 2,727 - 7,405 Parcel C 83,262 26,094 - 109,356 Parcel D 26,968 24,938 35,200 87,106 Total 125,890 59,766 35,200 220,856 The project is located in a drainage basin that is served by a combined storm/sewer system. Projects draining to a combined sewer system are not required to meet the same stormwater management standards as projects that drain to separated stormwater systems. However, the stormwater performance criteria for the project will require that stormwater discharges match the existing site discharge durations for the 10-year to 100-year peak flow. Additionally, the 25-year and 100-year peak runoff rates from the proposed conditions must not exceed the existing runoff rates for the same design storms. As the primary contributor to the generation of stormwater runoff, impervious surfaces are described in detail in this report with the ultimate effective impervious area matching the existing condition and therefore the combined sewer criteria will be met by this project. 255 S.King Street,Suite 800,Seattle,WA 98104 I 206.426.2600 I JACOBSONENGINEERS.COM