The radius of influence of a combined method of in situ air sparging and soil vapor extraction in the intertidal sediments of Gomso Bay on the west coast of South Korea

Abstract

Background: In situ air sparging (IAS) was undertaken at sites in the tidal flats of Mandol and Hajeon, on the west coast of South Korea, to estimate variations in the radius of influence (ROI). Results: The Mandol core sample consisted of sand and muddy sand 1.6-3.4 Phi (average 2.3 Phi) and contained water (average 15.10 %). The Hajeon core sample consisted of muddy sand, sandy silt, and muddy sandy gravel 1.31-4.44 Phi (average 3.11 Phi) and contained water (average 19.77 %). These sites differ in their sedimentary and geochemical characteristics. At the Mandol site, no H2S or combustible gas was detected during a 48-h sampling period, except for some volatile organic compounds (0.1-2.0 ppm) at the monitoring well during the initial 30 min. At the soil vapor extraction wells, CO2 and O-2 varied by 850 ppm (690-1540 ppm) and 0.5 % (20.4-20.9 %), respectively. At the Hajeon site, CO2 and O-2 varied from 580 to 1250 ppm and 20.6 to 20.9 %, respectively, during the 48-h sampling period. Conclusions: At the Mandol site, an oxygen concentration of 20.6 % was assumed as the effective concentration, and the ROI was estimated to be 128.0 cm. However, at the Hajeon site the ROI was estimated to be 85.7 cm. The smaller effective ROI at the Hajeon site was likely caused by the thin aquifer and thin screens of the sparing well. This estimated ROI show that the remediation effectiveness varies greatly as a heterogeneities and anisotropies in the porous sediments. Besides, injection pressure, flow rate, pulsing or continuous mode, and the range of intrinsic permeability for most important characteristic of sediment (soil) type impacted the ROI. Therefore, the IAS method is more effective at a pervasive air flow sediments such as Mandol, which consists of sand and muddy sand than at a channelized site such as Hajeon.