Geotech Report 05 23 2023

SOR CONSULTING ENGINEERS, INC. Garden Homes Report No. 23-C-17 Subsurface Stormwater Management System Page 4 West Orange, NJ provide a unform separation layer and infiltrative surface to minimize the transmission of fines and possible soil clogging. Basin B (TP-B1, TP-B2): The area is presently a wooded site. Topographic data provided to us indicates that the ground surface elevations range from approximately +544 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 12 inches of topsoil/ vegetation. The topsoil was underlain by clayey soil and extended to depths of 4 to 5 feet below the surface. The clayey soil was underlain by brown silty gravelly sand and extended to the maximum depth explored, 13 to 15 feet. Groundwater seepage was encountered at depths of 8 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 0.89 to 1.12 inches per hour (K2 soils). We recommend that the stormwater management system be hydraulically connected to these materials found at depths of 4 to 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 provide a unform separation layer and infiltrative surface to minimize the transmission of fines and possible soil clogging. HDPE C (TP-C1, TP-C2): The area is presently a wooded site. Topographic data provided to us indicate that ground surface elevations range from approximately +558 feet to +560 feet. The preliminary bottom of HDPE system is set at + 557 feet. The subsurface conditions revealed in the test pits performed for this study encountered 12 inches of topsoil/vegetation. The topsoil was underlain by clayey soil and extended to depths of 3.5 to 4 feet below the surface. The clayey soil was underlain by silty gravelly sand (loam material) extended to depths of 5 to 5.5 feet. Basalt bedrock was encountered beneath the loam material. Groundwater was encountered at depths of 4.0 to 4.5 feet below the surface. Due to the presence of clayey soils which is