Physical properties of oil-particle aggregate (OPA)-containing sediments

Abstract

Sediments composed of oil-particle aggregates (OPAs) have unique physical characteristics. These in situ deposited sediments develop at locations where a continual or nearly continual discharge of nonaqueous phase liquids (NAPLs) have occurred, or are occurring through time. The NAPL discharged into the surface water body interacts with suspended particles in the water column. The particles adhere to the suspended NAPL, which generally is in the form of a bead, and produce a discrete aggregate. As the aggregate grows in response to additional particle adherence, the density of the unit increases and deposition occurs. The resulting sediment consists of a collection of discrete OPAs that form a network with small pores, where oil is tightly bound and/or contained. Porosity, water content, and dry bulk density measurements indicate the sediment formed by OPA deposition is physically unique. Although the sediment consists of a very open pore structure, the pore openings are relatively small, typically being less than 5 microns in diameter. These small pores inhibit fluid movement. Results of physical property testing suggest the OPA structure is retained upon deposition. Although the sediment contains NAPL, this original OPA structure inhibits the oil beads from coalescing, which would enable NAPL flow.

NAPL mobility of OPA-containing sediments

“…Previous studies (Johnson et al, 2018) of these sediments indicate indicated the IDN sediments consist of an open porous structure composed primarily of submicron size pores. The majority of the fluids within the pore network are retained within these small pores.…”

“…In contrast to upland-based soils, the pore network of IDN sediments is more open, as reflected by higher porosity values. IDN sediment porosity values typically range from 50% to 80% (Johnson et al, 2018). The higher porosity reflects the deposition of the particles from the surface water and the absence of any significant compaction.…”

“…Physical property measurements (Johnson et al, 2018) indicate the Site 1 sediment consists of a relatively open structure that is water filled. Specifically, porosities range from approximately 40% to 70% of the total sediment volume, while measurements of dry bulk density average 1.0 g/cm3 (varying from approximately 0.7 to 1.5 g/cm3).…”

Exploring the effects of microalgal biomass on the oil behavior in a sand-water system

“…Suspended particulate matter and aggregates of detritus, living organisms and inorganic matter known as marine snow, play an important role through the adsorption of hydrocarbons and the association of dispersed oil droplets Passow and Ziervogel 2016). The particles less than 2 μm with the capacity to bind hydrophobic compounds dominate free surface of natural waters, leading to a significant amount of oil sedimentation via agglomeration (Johnson et al 2018). 87-98% of spilled oil may change to ''particulate'' form, either incorporated into suspended particulate matter aggregates or as particulate free oil globules (Johnson et al 2018).…”

“…The particles less than 2 μm with the capacity to bind hydrophobic compounds dominate free surface of natural waters, leading to a significant amount of oil sedimentation via agglomeration (Johnson et al 2018). 87-98% of spilled oil may change to ''particulate'' form, either incorporated into suspended particulate matter aggregates or as particulate free oil globules (Johnson et al 2018).…”