MGP NAPL interception with organophyllic 

media: flow-through column test results

Abstract

Flow-through column tests were conducted to support the remedial design for a former manufactured gas plant in New York State, USA. LNAPL and DNAPL exist at the site, and some neutrally buoyant NAPLs may be present. The column tests found that neutrally buoyant MGP NAPL can be intercepted in the presence of flowing water using a mixture of organically-modified clay and anthracite (i.e., organoclay). Four test columns were separately packed with coarse sand [control], granular activated carbon [GAC], organoclay, or coke breeze, respectively. Potable spring water was pumped through the columns in closed-loop, recirculation mode at a rate consistent with expected full-scale application. Site-specific LNAPL and DNAPL were mixed to produce NAPL with a density of approximately 1.00 g/mL. This NAPL was injected into each column, and the columns were pumped for 25 days achieving a minimum of 22 000 water pore-volume exchanges. The post-test sorbent media were dissected and each interval was assessed for the presence of visible NAPL, response to UV light, and production of a sheen upon contact with water. All of the post-test sand, GAC, and coke breeze produced a positive UV light response and sheen. In contrast, none of the post-test organoclay produced a visible sheen, not even the portions of organoclay that contained a visible NAPL residue. In spite of the relatively rapid water flow rate, the organoclay resisted NAPL migration and sheen production, proving more effective than the other test media as a passive NAPL interceptor permeable to water.

Key words: coal tar, column test, sorb, sorption, NAPL, organoclay

© 2007 EPP Publications Ltd

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Article code 744