Environmental Engineering Reference
In-Depth Information
3. At the location where the IRIS tubes were installed, an estimation of the level of
the ground water table should be obtained by digging a small hole to a depth
slightly greater than the depth to the water table and allowing it to equilibrate in
the hole.
4. At the location where the IRIS tubes were installed, Eh should be measured
using five replicate Pt electrodes at depths of 12.5, 25, and 40 cm. A stainless
rod should be used to make pilot holes for the electrodes to the specified depths.
First the five electrodes should be placed at 12.5 cm and measurements made.
Then the pilot holes should be deepened and electrodes placed at 25 cm and
measurements made a second time. A third set of measurements should be made
after electrodes have been placed at 40 cm. Because electrodes will not remain in
the field between the two measurement dates, the reference electrode does not
need to be placed within a salt bridge. Rather, a small amount of water should be
added to the soil surface (if not already saturated) and stirred to make a paste,
into which the reference electrode should be placed. The reference electrode
should be situated within 25-75 cm of the location of the Pt electrodes.
5. Using either the push probe, a spade or an auger, samples should be collected
from depths of 12.5, 25 and 40 cm so that pH can be determined at the same
depths where Eh was measured.
6. Using either soil on cores removed when making pilot holes for IRIS tubes or
soil collected with a spade or auger, apply a few drops of alpha-alpha dipyridyl
dye at various depths in the soil to see whether there is a positive reaction to the
dye, indicating the presence of Fe
2+
.
7. Make a brief soil description at the location where the IRIS tubes were installed
making special note regarding whether or not the soil meets any of the approved
field indicators of hydric soils (USDA-Natural Resources Conservation
2010
).
8. After approximately 4 weeks have elapsed, on the date when the IRIS tubes are
extracted and examined, you should again make measurements of Eh, pH and
water table height, and evaluate whether the soil gives a positive reaction to the
alpha-alpha dipyridyl dye.
Part 2: IRIS Data Collection and Analysis
1. Four weeks after the IRIS tubes were installed, they should be extracted from the
soil. Adhering soil can be removed by rinsing with very gentle brushing
(as needed) under a stream of water, and then placed aside to dry.
2. Quantification will be accomplished using the mylar grid method (Rabenhorst
2012
)because this method is more accurate and more reproducible than visual
estimations (Rabenhorst
2010
). A 15 cm by 6.7 cm grid containing 390 50 mm
by 51 mm sectors should be printed on transparent mylar sheet so that it can be
wrapped around an IRIS tube and held in place using rubber bands (Fig.
7.11
).
3. The Technical Standard (National Technical Committee for Hydric Soils
2007
)
requires that paint be removed from 30 % of the IRIS tube within a 15 cm zone
