Geotech Report 04 04 2024

SOR CONSULTING ENGINEERS, INC. Garden Homes/West Essex Highlands, Inc. Report No. 24-C-11 Subsurface Stormwater Management System Page 4 West Orange, NJ silty gravelly sand at TP-42 and extended to the maximum depth explored, 4 feet. Bedrock was encountered below the sandy or clayey soil at depths of 4 to 5 feet. Groundwater seepage was encountered at depths of 4 to 5 feet below the existing ground surface on top of bedrock and determined to be trapped water. Laboratory tube permeameter testing performed on the silty gravelly sand stratum (loam material) resulted in permeability rate of 0.95 inches per hour (K2 soils). However, silt/clay loam encountered at TP-43 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 materials found at a depth of 2 feet (TP-42). 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. Test Pit 43 encountered clayey soil underlain by bedrock and not suitable for stormwater infiltration. Basin (TP-44 and TP-45): The area is presently a wooded site. Topographic data provided to us indicate that ground surface elevations range from approximately +570 feet to +574 feet. The subsurface conditions revealed in the test pits performed for this study encountered 6 to 10 inches of topsoil/vegetation. At TP-44, the topsoil was underlain by clayey soil and extended to maximum depths explored. Basalt bedrock was encountered beneath the clayey material at a depth of 2 feet. Groundwater seepage was encountered above the bedrock and considered trap water. Due to the presence of clayey soils which is hydraulically restrictive and shallow bedrock presence, the area is not suitable for stormwater infiltration design. At TP-45, the topsoil was underlain by clayey soil and extended to a depth of 2.5 feet below the surface. The clayey soil was underlain by silty gravelly sand (loam material) and extended to the maximum depths explored, 8 feet. Bedrock was encountered

and extended to a depth of 2.5 feet below the surface. The clayey soil was underlain by silty gravelly sand (loam material) and extended to the maximum depths explored, 8 feet. Bedrock was encountered beneath the loam at a depth of 8 feet below surface. Groundwater seepage was encountered at depths immediately above the bedrock and considered