Stormwater Management Report 03302026

Client: Gomes Management Project: 525 Northfield Avenue, West Orange, NJ Page: 6 Date: 09/03/2024 GROUNDWATER: Groundwater was encountered in only two borings B-6 & B-8 below existing grade surface as follows: Depth to Depth to Boring Boring Groundwater Groundwater Number Number (feet) (feet) B-1 - B-5 Hole collapsed at 9'-2" B-2 Hole collapsed at 7'-5" B-6 11'-1" B-3 Hole collapsed at 7'-2" B-7 - B-4 Hole collapsed at 4'-4" B-8 8'-9" It should be noted that groundwater level will fluctuate due to variations in rainfall or other factors not evident at the time of our investigation. SEASONAL HIGH WATER TABLE: Signs of black mottling was noted at 6 feet depth in only boring B-7, indicating SHWT below 6 feet. CONCLUSIONS: 1. Groundwater was encountered at 11'- 1" in B-6 and at 8'- 9" in B-8 below existing grade surface. Consequently, we anticipate that groundwater management during construction will be critical. 2. Signs of black mottling was noted at 6 feet depth in only boring B-7, indicating SHWT below 6 feet. 3. Fill was noted in top 2'-6" in boring B-1, in top 4' in B-2/2A, in top 4'-11" in B-3, in top 5" in B-4, in top 2' in B-5/5A and in top 9" in B-8. Below fill, the majority of the on-site soil consists of silt with trace f/c sand &trace f/m gravel. The onsite soil will be suitable as structural fill. Depending upon the time of the year when the actual construction takes place, drying of excavated sandy soil and aeration may be required to reduce the moisture content. In-situ moisture content of soil varied between 5.5 % to 14.2 %which is

ction takes place, drying of excavated sandy soil and aeration may be required to reduce the moisture content. In-situ moisture content of soil varied between 5.5 % to 14.2 %which is generally considered moist. 4. The following parameters should be used for seismic design of the building in accordance with IBC-2021 ASCE 7-22: Description Parameter Recommended value Mapped Spectral Acceleration for short periods: Ss 0.27 Mapped Spectral Acceleration for 1-sec period: S, 0.05 Site Class: C Very dense Soil &Soft Rock 5 percent damped Design spectral response Sos 0.18 acceleration at short periods: 5 percent damped Design spectral response So, 0.043 acceleration at 1-sec periods: The following parameters should be used for seismic design of the building in accordance with IBC-2018-ASCE 7-16: