e-journal

An environmental screening model to assess the consequences to soil and groundwater from railroad-tank-car spills of light non-aqueous phase liquids

---

Abstract.
North American railroads transport a wide variety of chemicals, chemical mixtures and solutions in railroad
tank cars. In the event of an accident, these materials may be spilled and impact the environment.
Among the chemicals commonly transported are a number of light non-aqueous phase liquids (LNAPLs). If
these are spilled they can contaminate soil and groundwater and result in costly cleanups. Railroads need
a means of objectively assessing the relative risk to the environment due to spills of these different materials. Environmental models are often used to determine the extent of contamination, and the associated
environmental risks. For LNAPL spills, these models must account for NAPL infiltration and redistribution,
NAPL dissolution and volatilization, and remediation systems such as pump and treat. This study presents
the development and application of an environmental screening model to assess NAPL infiltration and
redistribution in soils and groundwater, and to assess groundwater cleanup time using a pumping system.
Model simulations use parameters and conditions representing LNAPL releases from railroad tank cars. To
take into account unique features of railroad-tank-car spill sites, the hydrocarbon spill screening model
(HSSM), which assumes a circular surface spill area and a circular NAPL lens, was modified to account for
a rectangular spill area and corresponding lens shape at the groundwater table, as well as the effects of
excavation and NAPL evaporation to the atmosphere. The modified HSSM was first used to simulate NAPL
infiltration and redistribution. ANAPL dissolution and groundwater transport module, and apumping system
module were then implemented and used to simulate the effects of chemical properties, excavation,
and free NAPL removal on NAPL redistribution and cleanup time. The amount of NAPL that reached the
groundwater table was greater in coarse sand with high permeability than in fine sand or silt with lower
permeabilities. Excavation can reduce the amount of NAPL that reaches the groundwater more effectively
in lower permeability soils. The effect of chemical properties including vapor pressure and the ratio of
density to viscosity become more important in fine sand and silt soil due to slow NAPL movement in the
vadose zone. As expected, a pumping system was effective for high solubility chemicals, but it was not
effective for low solubility chemicals due to rate-limited mass transfer by transverse dispersion and flow
bypassing. Free NAPL removal can improve the removal efficiency for moderately lowsolubility chemicals
like benzene, but cleanup times even after free NAPL removal can be prolonged for very low solubility
chemicals like cyclohexane and styrene.

Keywords:
NAPL
HSSM
Railroad-tank-car accident
Environmental consequence
Screening model
Hazardous materials transportation risk

---

Ketersediaan

Tidak ada salinan data

Informasi Detail

Judul Seri

Journal of Hazardous Materials

No. Panggil

-

Penerbit

London : Elsevier B.V.., 2009

Deskripsi Fisik

Journal of Hazardous Materials 165 (2009) 332–344

Bahasa

English

ISBN/ISSN

-

Klasifikasi

-

Tipe Isi

-

Tipe Media

-

Tipe Pembawa

-

Edisi

-

Subjek

LINGKUNGAN HIDUP

Info Detail Spesifik

-

Pernyataan Tanggungjawab

agus

Versi lain/terkait

Lampiran Berkas

Komentar

---

Anda harus masuk sebelum memberikan komentar