Properties of sediment collected throughout the strategic placement of dredge material in south San Francisco Bay, California, 2023-2025

SEDIMENT COLLECTION. Sediment samples were collected at several stations in south San Francisco Bay, from a small vessel, using a custom build hand-operated push-core device that consisted of the push core “tube” secured onto a pole mount with an internal valve, the device was carefully lowered vertically off the side of the ship by hand, when the operator finished pushing the core into the bed, paracord attached to a lever on the value was pulled to close it, “capturing” the sediment, the device was carefully brought on deck and the core was dismounted and capped, this was repeated 3 times per station to obtain replicates. The two stations that were in and adjacent to the channel used a Gomex box corer that was then subsampled with three push cores (38 mm in diameter) when a sufficient amount of sediment was recovered. For each push core, the six uppermost subsamples were collected at 1 cm vertical intervals. The rest of the core was sampled at 2 cm intervals, except for two samples (P3B2-6 and P3B2-7), that were accidentally sampled at 2 and 1 cm intervals respectively. A couple of cores have a -1 cm sample depth, which means there was a feature protruding from what we defined as the sample’s (sediment bed's) surface, for example a small cluster of shells packed with mud protruding from the surface of the sample. Sediment samples were carefully extracted from cores by sliding core on top of an extruder, which pushed the sediment in the core upward, allowing us to section precise sample depths starting with the surface sample. Subsamples were placed into pre-weighed Whirl-pak bags.

A total of 687 samples were analyzed for bulk density by the USGS Pacific Coastal and Marine Science Center sediment lab. Dry bulk density was calculated with the formula: dry bulk density = (1 - porosity)* sediment density, where porosity is calculated as P = (water mass/water density)/[(water mass/water density)+(corrected dry sediment mass/sediment density)], water density is 1 g/cm3 and sediment density is 2.65 g/cm3. Local salinity readings were used to correct for the mass of salt in the pore water that was left behind during the drying process (salt mass = water mass * (salinity/1000)). The salt mass gets subtracted from dry sediment mass, to obtain the corrected dry sediment. Approximate salinity values were obtained from nearby time-series station that were deployed as part of this project or from USGS station 11162765 when no time-series station were available. The time-series data are available on this data releases' landing page.

GRAIN-SIZE ANALYSIS: A total of 438 samples (including occasional duplicates) were analyzed for grain-size. Grain-size analysis was conducted by the USGS Pacific Coastal and Marine Science Center (PCMSC) sediment lab using a Beckman Coulter LS 13 320 grain-size analyzer with an aqueous liquid module attachment. PCMSC procedures are modified from those described in Carver (1971) and Folk (1974, 1980). 5-50 grams of sediment was sub-sampled and at least 10 milliliters of 30 percent hydrogen peroxide was added and left for approximately 12 hours to remove organics. The samples were then heated to 250 degrees Celsius to remove excess hydrogen peroxide. Next, samples were placed in an ultrasonic bath to help disperse silt and clay (mud) from sand and larger-sized particles. Samples were then rinsed twice in deionized water with centrifugation to remove soluble ions. Subsequently, the samples were wet sieved with 1 millimeter and 0.063 millimeter sieves to segregate the combined gravel and coarse sand fraction (greater than 1 millimeter), sand (1 millimeter to 0.063 millimeter), and mud (less than 0.063 millimeter). Shells > 1 mm were visually identified and removed using forceps, during the sieving process, dried, and weighed. The coarse sand + gravel fractions were then dried, dry sieved at 1/4 phi intervals and weighed (Carver, 1971). The sand fraction was dried and weighed. The mud fraction was collected in a 1 liter graduated cylinder, 5 milliliters of at least 10 percent sodium hexametaphosphate (dispersant) was added, and deionized water was added to bring the total the volume to 1 liter. The mud + dispersant solution sat overnight to ensure complete dispersion and to observe if flocculation occurred. Subsequently, a 20 milliliter aliquot was extracted from the graduated cylinder and dried to obtain the mud fraction weight normalized to a 1-liter basis. The mud and sand fractions were analyzed separately via the Beckman Coulter LS 13 320 with the aqueous liquid module attachment. All size fraction data were compiled and converted by the PCMSC sediment lab pcSDSZ program (Penscil, 2015) to a grain-size distribution at 1/4 phi size intervals on a weight percent basis. pcSDSZ also calculated interpolated sizes and graphical statistics on a percent coarser basis (Folk and Ward, 1957; Folk, 1966; Folk, 1974, 1980; Inman, 1952; Trask, 1930, 1932) and moment measures (Collias and others, 1963; Jaquet and Vernet, 1976; Folk, 1980).

INTERPOLATED SIZES: Grain-sizes at select cumulative percentage values (D) were calculated by the PCMSC Sediment Lab software pcSDSZ version 1.71 on a percent coarser basis, which summed from coarse to fine bins. D values were interpolated between phi bins bracketing the specified D value. Grain-sizes were converted into units of millimeters (mm) using the formula mm=reciprocal of 2(exponent) phi or (phi=-log2(mm)). Interpolated grain-sizes at D50 are reported in phi and millimeter units.

CARBON ANALYSIS: A total of 202 (including occasional duplicates) samples were analyzed for percent carbon. Carbon analysis was performed by the PCMSC carbon lab employing a coulometric titration technique described in Engleman and others (1985) and UIC operating manuals for the UIC CM5200 autosampler furnace, the UIC CM5230 acidification module, and the UIC CM5017 coulometer. Total carbon (TC), total inorganic carbon (TIC), total organic carbon (TOC) and percent calcium carbonate (CaCO3) are reported as percent dry weight. Approximately 5 grams of sediment were dried in an 80 degrees Celsius oven. Samples were then pulverized, redried, and placed in a desiccator. For TC analysis, approximately 20 milligrams of the pulverized sample were weighed and wrapped in an aluminum capsule then combusted at 950 degrees Celsius in an UIC CM5200 autosampler furnace attached to an UIC CM5017 coulometer. The carbon dioxide (CO2) produced by combusting the sample was then converted to TC by the UIC CM5017 coulometer. For TIC, approximately 20 milligrams of sample were weighed and loaded into an UIC CM5230 acidification module attached to an UIC CM5017 coulometer. The samples were then digested in a perchloric acid solution, and the CO2 generated was measured and converted to TIC. Two analyses per sample were run and the results were averaged. TOC was calculated by subtracting TIC from TC. The TIC value was then multiplied by 8.333 (the molar stochiometric ratio of CaCO3 to C) to convert TIC to percent CaCO3.