PRELIMINARY ASSESSMENT OF GRAIN-SIZE DISTRIBUTION USING SEDIMENT SAMPLES COLLECTED FROM THE RECENTLY EXCAVATED TRENCHES, YORK COLLEGE, QUEENS, NEW YORK CITY

A sedimentological study was conducted at five specific sites in the vicinity of the York College campus, borough of Queens, New York City. These newly excavated sites with depth ranging from 6 feet to 20 feet, became available as the city undertook the vigorous step of replacing the old storm/sewer drainage pipes to meet the potential demand of excessive discharge due to extreme-weather-related events and the rapid construction of high-rise buildings. It is becoming part of an increased urbanization project to accommodate offices and housing in close proximity to York College.

In addition, the JFK Redevelopment project also necessitated greater excavation to enable sub-soil testing to ensure geotechnically sound bedrocks for constructing high rise buildings. Sediment samples were collected from different depths, encompassing 0-6 feet, 8 feet, 9 feet, 10 feet, and 20 feet. Initial investigation into the sediment exhibited significant heterogeneity with respect to grain sizes, featuring a wide range of particles from very fine gravel to coarse sand. The coarser fractions, represented by the very coarse sand and gravel, played a substantial role in textural classification of analyzed excavated sediments - which led to non-uniformity throughout the depth profile. Relying on published reports on surficial geology, detailed statistical analysis of numerous graphs and tables led to the determination that the analyzed samples can be attributed to originate from a Wisconsinan glacial environment that largely affected all the five boroughs including Queens and Long Island in the recent past. The observed patterns indicate grain size distribution to be a bimodal type.

In summary, the standard deviation (SD) analysis reveals that higher values tend to have more randomness. The 0-6 ft sample, likely affected by anthropogenic fill material, demonstrates higher variability (SD = 3.40). In contrast, the 17 ft sample exhibits lower variability (SD = 1.20), while the SD values of the 8 ft, 9 ft, and 10 ft samples (around 1.9) indicate somewhat similar deviations, likely influenced by their uniform depositional environment, primarily glacial and devoid of anthropogenic fill.