Persistence of LNAPL sources and relation to risk

Conference · Wed Dec 31 04:00:00 EST 1997

OSTI ID:569949

Huntley, D; Beckett, G D ^[1]

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1. San Diego State Univ., CA (United States)

Light non-aqueous phase liquids (LNAPL), such as fuels, are the source of much soil and groundwater contamination. Though the mobility of LNAPLs is limited in many environments, dissolved-phase components, such as benzene, can produce groundwater plumes that are more mobile than the LNAPL source. Research over the past several years, however, has suggested that natural biodegradation of many of these dissolved-phase components can limit potential health impacts. A simplified release and degradation scenario has four phases: (1) release of the LNAPL and downward movement through the vadose zone, (2) arrival of LNAPL at the water table and growth of a dissolved-phase plume, (3) a pseudo-steady-state condition where mass removal of dissolved-phase components by biodegradation keeps pace with the rate of dissolution from the LNAPL source, and (4) contraction of the dissolved-phase plume as the LNAPL source is depleted. Analytic approximations are available to estimate stages (2) through (4), allowing evaluation of plume spreading, longevity, and related environmental risk. These analyses show that the period of time where the dissolved phase plume is growing to a pseudo-steady-state condition is very small compared to the duration of most LNAPL sources, and that the downgradient extent is generally less than about 200 feet. Therefore, the risk to receptors, as measured by the maximum down gradient extent of dissolved phase plume, is generally unrelated to the longevity of the LNAPL sources. The maximum down gradient extent of the NAPL plume is determined almost entirely by the groundwater velocity and the biodegradation rate. Only in the case of NAPL plumes with minimal mass is the down gradient extent of the dissolved phase impacted by the volume of the NAPL. Regulatory agencies and industry should therefore separately consider the risk factors related to the LNAPL (mobility, mass, and solubility) and those related to the dissolved-phase generated by the LNAPL.

• OSTI ID: 569949
• Report Number(s): CONF-971116--
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
BIODEGRADATION
ECOLOGICAL CONCENTRATION
ENVIRONMENTAL TRANSPORT
GROUND WATER
HYDROCARBONS
PLUMES
REMEDIAL ACTION
RISK ASSESSMENT