Grain size of bed sediment surface samples from south San Francisco Bay, California, summer 2020

The grain-size distributions of samples were determined in the USGS Pacific Coastal and Marine Science Center sediment lab. Approximately 20 g of sediment was subsampled and 10 mL of 30 percent hydrogen peroxide was added to remove organic material in the sample. The sample was heated at 250 degrees C to remove any remaining hydrogen peroxide and was placed in an ultrasonic bath to liberate the fine fraction. Subsequently, the sample was centrifuged for 1.5 hours to remove soluble salts. Samples were funneled through a 1-mm and a 63-um sieve to separate the gravel (greater than 1 mm), sand (63 um to 1 mm), and mud (less than 63 um). The sand and gravel fractions were dried in an 80-degree C oven and weighed. Five mL of sodium hexametaphosphate was added to the mud fraction and a 20 mL aliquot was taken from a 1 L graduated cylinder to determine the weight of the mud. The particle-size distribution of the mud and sand fractions was analyzed separately using a Beckman Coulter LS 13 320, and the gravel, sand, and mud results were integrated into a single grain-size distribution for each sample. Where used, phi sizes are equal to the negative log base 1 of millimeter size.