Geo-Pollution Science, Medical Geology and Urban Geology
Vol.2

No.3

2006

ContentsReview
72

Understanding of elemental migration properties in geological environment-A case of low permeability unconsolidated clayey sedimentary layerHidekazu YOSHIDA

Report82

Distribution of “Uwagasu”, Spoutiong Natural Gas, in Kujyukuri Plain, Boso Peninsula, Central
Japan – Geo-environmental Survey for Uwagasu －Osamu KAZAOKA, Takashi KAZATO, Yutaka KASAHARA and Takashi KUSUDA

News92

Understanding of elemental migration properties in geologicalenvironment-A case of low permeability unconsolidated clayey sedimentary layerHidekazu YOSHIDA
Nagoya University Museum, Material Research Section, Nagoya, 464-8601 Japan

Abstract
Understanding of elemental migration in sedimentary strata is a critical issue to clarify for the long-term safe
utility of deep underground environments e.g.CO 2 storage, LPG (Liquefied Petroleum Gas) storage and Nuclear
Wastes Disposal as well as for the remediation of polluted subsurface rocks and sediments. In the consolidated
hard rocks, behavior of elemental migration can be controlled mainly by distinguishable geological structures
relevant to groundwater flow such as faults and fracture(s) network and by the surrounded hydraulic potentials.
In order to elucidate the role of these features, many kinds of in-situ and laboratory experiments with numericalmodeling studies have been applied. On the other hand, for the unconsolidated sediments, it is however little
known the major feature to control the elemental migration due to undistinguishable complex heterogeneity ofphysical properties influencing groundwater permeability and chemical characteristics of composed minerals that
affect on the chemical retardation such as sorption capacity. Here, as an example, it is therefore focusing on thecharacterizing methodology of elemental migration behavior in unconsolidated clayey sediments in order toenforce the further studies and developments necessary to provide confidence for the future safe utility ofunderground environments as well as for the urgent issues of geo-pollution facing in our society.

Keyword: Elemental migration, Geological environment, Unconsolidated clayey sediments

Distribution of “Uwagasu”, Spoutiong Natural Gas, in Kujyukuri Plain,
Boso Peninsula, Central Japan– Geo-environmental Survey for Uwagasu －Osamu KAZAOKA, Takashi KAZATO, Yutaka KASAHARA and Takashi KUSUDA
Research Institute of Environmental Geology, Chiba

3-5-1, Inagekaigan, Mihama-ku, Chiba City, 261-0005 Japan

Abstract
The Kanto sedimentary basin occurred in Green Tuff movement at the Miocene and developed in Island Arc
movement since the Pliocene. In this sedimentary basin, It consists of Miura Group, Kazusa Group, ShimosaGroup, Kanto loam formation, Alluvial formation and Artificial formations in ascending order. Methane isincluded in Miura Group, deposited from the Miocene to the early Pleistocene, and Kazusa Group, depositedfrom the late Pliocene to the early Pleistocene. These Groups accumulated mainly in deep sea.
Large quantity of high purity methane is included particularly in groundwater and strata of Kazusa Group.
Kazusa Group distributes in subsurface in central part of Boso Peninsula. The natural gas which spouts up into
the air, is used for house fuel since late Edo era in Otaki Town, eastern Kazusa region. The natural gas has beencalled “Uwagasu” there. On this account, large quantity of watersorble natural gas has been taken by deep wells insouthern part of eastern Kazusa region after the World War II. In central part of Kujyukuri region thewatersorble natural gas has been pumped up recently, too. Distribution of the “Uwagasu” increases in central partof the Kujyukuri region. The crops have die at the sites where the “Uwagasu” blowing off. In addition, a gasexplosion was generated in Iwashi Museum, museum for sardine, in Kujyukuri Town in summer, 2004. On thisaccount, distribution of the Uwagasu was surveyed in central part of the Kujyukuri region. The result is asfollows.
A great deal of the Uwagasu is observed from Fukutawara, eastern part of Togane City, to Seinagoya, easternpart of Oami-Shirasato Town. Methane gas of several cube meters per second spouts out in the irrigation ditch in
the “Area Ⅰ” of Fukutawara - Seinagoya district. In addition, the “Uwagasu” spouting zones extend to thewest-northwest direction along Kita-Goya river. In Kujyukuri district, several Uwagasu zones extend tonorth-northeast direction. The largest zone, from Shinsei to Suijinyama through Katakai, is 4 km in length and0.2 – 0.5 km in width. The Iwashi Museum is in this zone. The crops often die at the Uwa-gasu.
In the future it is necessary to examine the change of location and the quantity of spouting gas of the “Uwagasu”
every year. Further the mechanism of the “Uwagasu” must be going to be probed in each site. Accordingly the“Uwagasu” will be used effectively and safely. These information is important for urban planning.

Key Words: Uwagasu, Natural Gas, Kujyukuri Plain