Composition B (Comp B) detonation residuals pose environmental concern to the U.S. Army because hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), a constituent, has contaminated groundwater near training ranges. To mimic their dissolution on surface soils, we dripped water at 0.51 ml/h onto individual Comp B particles (0.1-2.0 mg) collected from the detonation of 81-mm mortars. Analyses of the effluent indicate thatthe RDX and 2,4,6-trinitrotoluene (TNT) in Comp B do not dissolve independently. Rather, the relatively slow dissolution of RDX controls dissolution of the particle as a whole by limiting the exposed area of TNT. Two dissolution models, a published steady-flow model and a drop-impingement model developed here, provide good agreementwith the data using RDX parameters for time scaling. They predict dissolution times of 6-600 rainfall days for 0.01-100 mg Comp B particles exposed to 0.55 cm/h rainfall rate. These models should bracket the flow regimes for dissolution of detonation residuals on soils, but they require additional data to validate them across the range of particle sizes and rainfall rates of interest.

a b s t r a c tLive-fire military training can deposit millimeter-sized particles of high explosives (HE) on surface soils when rounds do not explode as intended. Rainfall-driven dissolution of the particles then begins a process whereby aqueous HE solutions can enter the soil and groundwater as contaminants. We dripped water onto individual particles of TNT, Tritonal, Comp B and Octol to simulate how surface-deposited HE particles might dissolve under the action of rainfall and to use the data to verify a model that predicts HE dissolution as a function of particle size, particle composition and rainfall rate. Particle masses ranged from 1.1 to 17 mg and drip rates corresponded to nominal rainfall rates of 6 and 12 mm h À1. For the TNT and Tritonal particles, TNT solubility governed dissolution time scales, whereas the lower-solubility of RDX controlled the dissolution time of both RDX and TNT in Comp B. The large, low-solubility crystals of HMX slowed but did not control the dissolution of TNT in Octol. Predictions from a drop-impingement dissolution model agree well with dissolved-mass timeseries for TNT, Tritonal and Comp B, providing some confidence that the model will also work well when applied to the rainfall-driven, outdoor dissolution of these HE particles.Published by Elsevier Ltd.

Cenozoic tectonic evolution of the Japanese rifted continental arc‐trench system is reflected in the detrital modes of sand and sandstone deposited in forearc and backarc basins sampled by the Deep Sea Drilling Project. At present, the Japan arc is divided into two segments along a complex plate boundary where the Izu‐Bonin Ridge intersects the Japan arc, creating two triple junctions, in front of and behind the ridge. Southwest of the Izu‐Bonin Ridge, quartzofeldspathic Cretaceous forearc sediments were uplifted and recycled into Tertiary forearc deposits in response to strike‐slip movement associated with backarc spreading in the Shikoku basin. Quaternary forearc sections record the first major influx of volcanic detritus to southwest Japan sites. Triple‐junction‐related deformation in central Honshu has produced sand of mixed volcanic/sedimentary provenance, which is funneled by the Suruga Canyon into the Nankai Trough along the southwest Japan margin. North of the triple junction, Oligo‐Miocene forearc sand compositions indicate Oligocene forearc uplift and volcanism, possibly related to initial backarc rifting and formation of the Japan Sea, and subsequent Miocene exposure of arc basement. In contrast, Pliocene and Quaternary forearc sand from northeast Japan is primarily volcaniclastic and documents uninterrupted arc volcanism. Within the backarc region, sand compositions vary from east to west across the Japan Sea. The Asian rifted continental margin and submerged remnants shed quartzofeldspathic sand into the western side of the basin, whereas the Japan arc sheds volcaniclastic sand into the eastern side of the basin.

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