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Genesis and function of pore structures formed in saprolite by Mike Vepraskas, NCSU, Soil Science.

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Presentation on theme: "Genesis and function of pore structures formed in saprolite by Mike Vepraskas, NCSU, Soil Science."— Presentation transcript:

1 Genesis and function of pore structures formed in saprolite by Mike Vepraskas, NCSU, Soil Science

2 Veins in saprolite

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

4 Objectives Review typical k sat changes with depth Discuss water movement through saprolite matrix Review research on quartz veins and water movement

5 No BC or CB and shallow Cr K sat Depth Cr

6 No BC or CB and sandy C K sat Depth Sandy C Cr

7 BC or CB with no mixed mineralogy K sat Depth BC

8 BC or CB with mixed mineralogy K sat Depth BC Bt ???

9 How does water move through the saprolite matrix?

10 K sat profile – C2 horizon K sat (cm h -1 ) Depth (cm) C2 CB C2 C1 Bt C3

11 Veins and structure in C

12 Water conducting fractures in mineral grains

13 Fracturing of mineral grains due to biotite weathering

14 Water movement between mineral grains in C2 High K sat

15 Photo of dye in C2

16 K sat profile – CB horizon K sat (cm h -1 ) Depth (cm) C2 CB C2 C1 Bt C3

17 Veins and structure in CB

18 Clay plugging in CB

19 Clay plugging of pores in CB or BC Clay in pores Low K sat

20 K sat profile – Bt Horizon K sat (cm h -1 ) Depth (cm) C2 CB C2 C1 Bt C3

21 Clay skin on ped face in Bt horizon

22 Illuvial clay in pores in Bt horizon

23 Water movement in Bt horizon Low to high K sat Peds

24 Quart veins and water movement

25 Photo Quartz vein

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

27 Schematic of field experiment

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

29 Illustration of Br concentrators with depth across ponded area

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

31 Results KeKe DrainfieldVeinMatrix cm/day

32 How to field identify conducting veins

33 Look for clay or Fe/Mn in voids and between fragments

34 Observe infillings

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

36 If pore fillings are hydrothermal then veins are probably plugged very deeply

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

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.

39 Where does the water go and how fast?


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