Geotech Report 05 23 2023

SOR CONSULTING ENGINEERS, INC. Garden Homes Report No. 23-C-17 Subsurface Stormwater Management System Page 3 West Orange, NJ of higher ridges formed by intruding magma of Jurassic age. Locally, glacial till deposits can be found deposited directly by glacial ice during the Wisonsinian glaciation. The bedrock underlaying the site is composed of a Jurassic aged basalt formation called the Preakness Basalt, a fine to coarse grained basalt that composes the second Watchung Mountain. Surface Features: The entire property is currently moderately to heavily wooded and contains some areas of rock outcrops. Large boulders are scattered throughout the site. Several areas identified as wetlands traverse the property in a general northeast to southwest orientation. Surface grades throughout the site reportedly range from a high of Elevation +630 feet in the extreme northern section to Elevation +530 feet along the townhomes. STORMWATER MANAGEMENT SYSTEM DESIGN CONSIDERATIONS Basin A (TP-A1, TP-A2): The area is presently a wooded site. Topographic data provided to us indicates that the ground surface elevations range from approximately +542 to +546 feet. The preliminary bottom of basin elevation is set at + 540 feet. The subsurface conditions revealed in the test pits performed for this study encountered 8 inches of topsoil/ vegetation. The topsoil was underlain by clayey soil and extended to depths of 2 to 2.5 feet below the surface. The clayey soil was underlain by brown silty gravelly sand and extended to the maximum depth explored, 13 feet. Groundwater seepage was encountered at depths of 7 feet below the existing ground surface. Laboratory tube permeameter testing performed on the silty gravelly sand stratum (loam material) resulted in permeability rates of 0.64 to 1.39 inches per hour (K2 soils). We recommend that the stormwater management system be hydraulically connected to these materials found at depths of 2 to 2.5 feet. The system should be designed in accordance with the NJDEP Stormwater BMP Manual based on the specific measured permeability rates in each area. We also recommend that the infiltrative surface be covered with a geotextile filter fabric or properly graded soil/aggregate filter material to