Geotech Report 02 12 2024

SOR CONSULTING ENGINEERS, INC. Garden Homes/West Essex Highlands, Inc. Report No. 24-C-02 Subsurface Stormwater Management System Page 4 West Orange, NJ 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 provide a unform separation layer and infiltrative surface to minimize the transmission of fines and possible soil clogging. Basin (TP-11 to TP-20): The area is presently a wooded site. Topographic data provided to us indicates that the ground surface elevations range from approximately +541 to +548 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 6 to 10 inches of topsoil/vegetation. The topsoil was underlain by clayey soil and extended to depths of 2 to 3 feet below the surface. The clayey soil was underlain by reddish brown silty gravelly sand and extended to the maximum depth explored, 5 to 10 feet. Groundwater seepage was encountered at depths of 5.5 to 9 feet below the existing ground surface. Laboratory tube permeameter testing performed on the silty gravelly sand stratum (loam material) resulted in permeability rates of 0.62 to 2.02 inches per hour (K2 soils). However, silt loam encountered at TP-16 and 17 resulted in permeability rates less than 0.2 inches per hour (hydraulically restrictive zone). We recommend that the stormwater management system be hydraulically connected to loam to sandy loam materials found at depths of 2 to 3 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 provide a unform separation layer and infiltrative surface to minimize the transmission of fines and possible soil clogging. Basin (TP-21, TP-22): The area is presently a wooded site. Topographic data provided to us indicate that ground surface elevations range from approximately +557 feet to +558 feet. The subsurface conditions revealed in the test pits performed for this study encountered 6 inches of

ided to us indicate that ground surface elevations range from approximately +557 feet to +558 feet. The subsurface conditions revealed in the test pits performed for this study encountered 6 inches of topsoil/vegetation. The topsoil was underlain by clayey soil and extended to maximum depths explored. Basalt bedrock was encountered