Environmental Engineering Reference
In-Depth Information
previous landowners indicate simple soil assemblage of one to a few types, then intensive sampling
may not be warranted. Most soil surveys describe the typical soil profile. Dig a couple of shallow
test pits to confirm that your site has conditions similar to those described in the soil survey. The
presence of certain indicator plant species can provide valuable clues as to the nature and extent
of soil conditions. If you have any suspicions that soil conditions may vary significantly with depth,
then dig several deep soil test pits to inspect the profile of the subsoil. This action is especially
important if you are relying on having your plants tap into the groundwater table. Old fields may
have been built up over time, and the subsoil structure may be unknown or dramatically different
from the surface. If changing the elevation of the surface is being seriously considered, then col-
lect soil depth data at the time of excavation. Evaluate the depth of sampling to ensure you obtain
a clear picture of the soil of your final grade elevation.
Through simple and relatively inexpensive tests, soil laboratories can provide significant in-
sights and offer expert advice for techniques to improve soil structure and plant viability. One
cautionary note, however: labs commonly provide information based on crop production rather
than native vegetation. References or local practitioners may be able to provide some assistance.
At the very least, be sure to have lab tests conducted for pH, salinity (EC), percentage of organic
matter content, texture, macronutrients and micronutrients, and any other chemicals that are
known locally to be of concern.
Leaving the surface at its present elevation also has its challenges. Abandoned fields and
recently used agricultural fields typically are nutrient rich from fertilizers and air quality fallout
and thus will promote weed growth over native species. Certain techniques, such as herbicide,
irrigation, and dry cycling, can manage the soil seed bank with varying results. One technique that
has been recently promoted in Great Britain and Denmark is soil inversion, in which the top three
feet of soil is flipped. This technique buries the weed seed bank below the subsoil, which has less
nutrients and permits native growth over weed species that thrive in nutrient-rich soils.
Hydrology.
Are streams present? What are the flow rates? Is there a nearby stream gauge from
which you can construct a hydrograph for the portion of the stream that runs through your site?
Do portions, or does all, of your site flood? If data are not available, can you determine the typi-
cal high-flow level (ordinary high-water line) by inspecting the banks or adjacent rocks and trees
for signs? Often, exploring off-site areas will be necessary to understand what is contributing to
drainages on your site. Changes in land use upslope may have an effect on your project site, so try
to determine whether there are plans for changes that would increase runoff, such as residential
or commercial development. Natural watercourses may be present on your site and can be read-
ily identified. However, if the site has been in agricultural production for some time, there may
be structures and landform changes installed to redirect the water to protect the fields. Careful
examination of the property perimeter upslope to locate signs of changes in water handling may
provide important results. You will need to decide how to address these features. Will changing the
watercourses back to their original path be compatible with your objectives?
If you suspect that flooding is a potential issue regarding project success, consult with locals
regarding the history of flooding on your project site. The occurrence frequency, duration, and
depth of floodwaters will affect your project. You should also consult a hydrologist who can help
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