Geotech Report 05 23 2023

SOR CONSULTING ENGINEERS, INC. Garden Homes Report No. 23-C-17 Subsurface Stormwater Management System Page 7 West Orange, NJ Basin G (TP-G1, TP-G2): The area is presently open land. Topographic data provided to us indicates that the ground surface elevations range from approximately +536 to +538 feet. The preliminary bottom of basin elevation is set at + 530 feet. The subsurface conditions revealed in the test pits performed for this study encountered 4 to 8 inches of topsoil/ vegetation. The topsoil was underlain by clayey soil and extended to depths of 1.5 to 4 feet below the surface. The clayey soil was underlain by brown silty gravelly sand and extended to the maximum depth explored, 15 to 16 feet. Groundwater or seasonal high groundwater was not encountered at the maximum depths explored. Laboratory tube permeameter testing performed on the silty gravelly sand stratum (loam material) resulted in permeability rates of 0.74 to 0.95 inches per hour (K2 soils). We recommend that the stormwater management system be hydraulically connected to these materials found at depths of 1.5 to 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. RECOMMENDED SERVICES It is recommended that Sor Consulting Engineers be provided the opportunity for a general review of the final design and specifications to assure that the stormwater management system recommendations are properly interpreted and implemented in the construction documents. We also recommend that controlled compacted fill and backfill operations as well as stormwater management system subgrades be observed by a geotechnical engineer from our firm. This is to ensure compliance with the recommendations contained herein and to address any changes in the subsurface conditions that were not disclosed by the test pits.