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 5 West Orange, NJ trap water. Laboratory tube permeameter testing performed on the silty gravelly sand stratum (loam material) resulted in permeability rates of 0.95 inches per hour (K2 soils). We recommend that the stormwater management system be hydraulically connected to these materials found at a depth of 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 provide a unform separation layer and infiltrative surface to minimize the transmission of fines and possible soil clogging. Basin (TP-46 and TP-47): The area is presently a partially wooded site. Topographic data provided to us indicate that ground surface elevations range from approximately +574 feet to +578 feet. The subsurface conditions revealed in the test pits performed for this study encountered 15 inches of topsoil/vegetation. The topsoil was underlain by clayey soil and extended to a depth of 4 feet below the surface. The clayey soil was underlain by reddish brown silty gravelly sand (loam material) extended to the maximum depths explored, 5 to 8 feet where bedrock was encountered. Groundwater seepage was encountered at depths of 5 to 8 feet below the surface immediately above the bedrock and considered trap water. Laboratory tube permeameter testing performed on the silty gravelly sand stratum (loam material) resulted in permeability rates of 0.99 inches per hour (K2 soils). We recommend that the stormwater management system be hydraulically connected to these materials found at a depth of 4 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.