Geotech Report 05 23 2023

SOR CONSULTING ENGINEERS, INC. Garden Homes Report No. 23-C-17 Subsurface Stormwater Management System Page 5 West Orange, NJ hydraulically restrictive, high water table and shallow bedrock presence, the area C is not suitable for stormwater infiltration design. HDPE D (TP-D1, TP-D2): The area is presently a wooded site. Topographic data provided to us indicate that ground surface elevations range from approximately +576 feet to +580 feet. The preliminary bottom of HDPE system is set at + 570 feet. The subsurface conditions revealed in the test pits performed for this study encountered 8 to 12 inches of topsoil/vegetation. The topsoil was underlain by clayey soil and extended to a depth of 2 feet below the surface. The clayey soil was underlain by silty gravelly sand (loam material) extended to the maximum depths explored, 9 to 16 feet. TP-D2 encountered bedrock at 9’ below the surface. Groundwater seepage was encountered at depths of 6 to 10 feet below the surface. Laboratory tube permeameter testing performed on the silty gravelly sand stratum (loam material) resulted in permeability rates of 0.62 to 2.64 inches per hour (K2 to K3 soils). We recommend that the stormwater management system be hydraulically connected to these materials found at a depth of 2 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. HDPE E (TP-E1, TP-E2): The area is presently a wooded site. Topographic data provided to us indicate that ground surface elevations range from approximately +582 feet to +590 feet. The preliminary bottom of HDPE system is set at + 586 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 2.5 to 3.0 feet below the surface. The clayey soil was underlain by brown silty gravelly sand (loam material) extended to the maximum depths explored, 12 to 14 feet. Groundwater seepage was encountered at depths of 7 to 9 feet below the surface. Laboratory tube

ain by brown silty gravelly sand (loam material) extended to the maximum depths explored, 12 to 14 feet. Groundwater seepage was encountered at depths of 7 to 9 feet below the surface. Laboratory tube permeameter testing performed on the silty gravelly sand stratum (loam