Genesis and function of pore structures formed in saprolite by
Mike Vepraskas, NCSU, Soil Science Slide 2 Veins in saprolite Slide
3 Focus of past research Identify materials suitable for on-site
wastewater treatment and disposal suitable means k sat > 0.4 cm
day -1 Determine if quartz veins conduct water quickly Identify
horizon properties that allow prediction of restrictive k sat Slide
4 Objectives Review typical k sat changes with depth Discuss water
movement through saprolite matrix Review research on quartz veins
and water movement Slide 5 No BC or CB and shallow Cr K sat Depth
Cr Slide 6 No BC or CB and sandy C K sat Depth Sandy C Cr Slide 7
BC or CB with no mixed mineralogy K sat Depth BC Slide 8 BC or CB
with mixed mineralogy K sat Depth BC Bt ??? Slide 9 How does water
move through the saprolite matrix? Slide 10 K sat profile C2
horizon 0 100 200 300 400 00.511.522.53 K sat (cm h -1 ) Depth (cm)
C2 CB C2 C1 Bt C3 Slide 11 Veins and structure in C Slide 12 Water
conducting fractures in mineral grains Slide 13 Fracturing of
mineral grains due to biotite weathering Slide 14 Water movement
between mineral grains in C2 High K sat Slide 15 Photo of dye in C2
Slide 16 K sat profile CB horizon 0 100 200 300 400 00.511.522.53 K
sat (cm h -1 ) Depth (cm) C2 CB C2 C1 Bt C3 Slide 17 Veins and
structure in CB Slide 18 Clay plugging in CB Slide 19 Clay plugging
of pores in CB or BC Clay in pores Low K sat Slide 20 K sat profile
Bt Horizon 0 100 200 300 400 00.511.522.53 K sat (cm h -1 ) Depth
(cm) C2 CB C2 C1 Bt C3 Slide 21 Clay skin on ped face in Bt horizon
Slide 22 Illuvial clay in pores in Bt horizon Slide 23 Water
movement in Bt horizon Low to high K sat Peds Slide 24 Quart veins
and water movement Slide 25 Photo Quartz vein Slide 26 Questions
about quartz veins 1.Do quartz veins and fractures in saprolite
conduct water 2. How can non-conducting veins be separated from
conducting veins in the field Slide 27 Schematic of field
experiment Slide 28 Procedure Pond water over saprolite that has a
vein to measure K Apply dye to stain flow paths Apply Br- salt for
a specific time period and measure depth of penetration to estimate
K Slide 29 Illustration of Br concentrators with depth across
ponded area Slide 30 Estimated K K e = -D T ( H/Lw) K e = Estimated
K D = Depth of Br penetration = Water content T = Time Br applied
H/Lw = Hydraulic gradient Slide 31 Results KeKe
DrainfieldVeinMatrix cm/day 141214 544 292634 Slide 32 How to field
identify conducting veins Slide 33 Look for clay or Fe/Mn in voids
and between fragments Slide 34 Observe infillings Slide 35 Pore
fillings and coatings Spaces between gravels in veins are filled
with clay or Fe/Mn minerals These materials restrict water flow
through veins All veins and fractures studied had materials in
pores or gravels Slide 36 If pore fillings are hydrothermal then
veins are probably plugged very deeply Slide 37 Conclusions Water
conducting voids in saprolite are: Spaces between mineral grains
Channels made by organisms Veins and fractures conduct water at
rates similar to the saprolite matrix Veins do not impede flow Clay
and oxide minerals plug pores in fractures and veins No unplugged
features were observed Slide 38 Conclusions The saprolite (C
horizon) usually had a higher k sat than the BC horizons BC
horizons formed under well developed Bt horizons Water flow through
C horizon occurs between mineral grains (like sand) BC horizons
have a low k sat values when spaces between grains are filled in.
Slide 39 Where does the water go and how fast?
