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This article in JEQ

  1. Vol. 23 No. 1, p. 202-207
     
    Received: Jan 27, 1993


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doi:10.2134/jeq1994.00472425002300010031x

Quartz Vein Impact on Hydraulic Conductivity and Solute Transport through Quartz-Phyllite Saprolite

  1. J. P. Williams,
  2. M. J. Vepraskas * and
  3. M. T. Hoover
  1. Dep. of Soil Science, North Carolina State Univ., Raleigh, NC 27695.

Abstract

Abstract

Saprolite cannot be used for on-site wastewater disposal in North Carolina if it has quartz veins within 60 cm (2 ft) of the septic trench bottom, because it is believed such features could transmit raw sewage quickly to groundwater. A quartz phyllite saprolite was sampled to compare the saturated and unsaturated hydraulic conductivities between samples with and without quartz veins. The fine sandy loam saprolite had veins that were approximately 0.8 cm wide and comprised 0.2 cm2/cm2 of the sample's cross-sectional area. The mean saturated hydraulic conductivity values of 32 undisturbed cores with veins and 27 cores without veins were not significantly different (α = 0.10) and the geometric mean for a combined population was 0.85 cm/h. Unsaturated hydraulic conductivities for a soil water pressure head of −30 cm were also not significantly different between the two populations. Dye studies confirmed that water flowed both along the vein but also through the saprolite matrix. Examination of thin sections showed that pores within the vein were coated or plugged with Fe-Mn oxides that restricted the water movement through the vein. It was computed that a noninteracting solute would travel 60 cm in the vertical direction in 33 h when the saprolite was saturated, and in 88 h when the soil water pressure head was −30 cm. These results suggested the quartz vein would not transmit raw sewage fast enough to contaminate groundwater at the site.

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