Figure 9. Based on observed breaks in the landscape, the second step is to place pins where major changes in soil conditions are likely to exist.
Since soils are three-dimensional entities, their vertical extent and arrangement of horizons must be examined to understand how they will behave in treating and dispersing wastewater.
A number of auger borings and other exposures, such as soil pits, are needed to examine the soil variability on the site. A soil pit is the best form of exposure for description and evaluation of the soil that is proposed as a treatment site.
Site and soil evaluation is a five-step process.
Collect background information on the site before making a visit. By knowing what soil conditions are likely to be found at a site, the site visit can be conducted in an efficient manner. Familiarity with available information will save valuable field time. Figure 5 is a guide to help in recording background information.
Soil surveys are the most useful information source on expected site and soil conditions. The following sequence provides a general approach for gaining useful information from a published soil survey:
Soil survey maps will also show the location of nearby streams, drainage ways and wetlands.
Plat maps and titles should be examined to identify the property lines, rights of way and easements. These maps or documents may also indicate past or present structures and other improvements or disturbances to the site.
Local utilities should be contacted to mark the location of underground service lines. Drainage districts may need to be contacted about the location of subsurface drainage mains.
Property owners, past property owners and long-time neighbors should be consulted about past land uses. Try to find out if parts of the property have been excavated or filled, and if artificial surface or sub-surface (tile) drainage has been installed. Buried tanks or cisterns may be present or have been present on the property. The history of fences, driveways or tree plantings (for example, old orchards) helps to eliminate surprises when making a field visit.
Figure 9. Based on observed breaks in the landscape, the second step is to place pins where major changes in soil conditions are likely to exist.
Make a visual assessment of the landscape at the site. Mark with pins or flags the major breaks in slope. Figure 9 shows the pin placement at a proposed site. Look for evidence of seasonal springs, wet areas and drainage ways. The vegetation at the lot is a good indication of soil conditions. Table 2 lists some olants that may indicate wet or well drained areas. Be especially watchful for dead vegetation, which may indicate a change in drainage patterns or the disposal of toxic substances. Make note of features that may predispose the site to increased risk of pollution, including the location of nearby wells, ponds, lakes and streams.
Table 2. Plants that grow in wet areas and in well drained soils.
| Well Drained | Poorly Drained | Wet Soils | |
|---|---|---|---|
| American holly | Mountain laurel | Box elder | Cattail |
| American beech | Pitch pine | Green ash | Rush |
| Black walnut | Red oak | Highbush blueberry | Sedge |
| Black Oak | Red pine | Pin oak | Skunk cabbage |
| Black locust | Shagbark hickory | Red maple | |
| Basswood | Sugar maple | River birch | |
| Cherry | Sweet birch | Redosier dogwood | |
| Chestnut oak | Sassafras | Silver maple | |
| Crab apple | Tulip poplar | Swamp white oak | |
| Eastern white pine | Virginia creeper | Spicebush | |
| Flowering dogwood | White oak | Silky dogwood | |
| Hazelnut | White ash | Sweet gum | |
| Lowbush blueberry | Sycamore | ||
| Willows | |||
Figure 10. Using a soil probe, soil is examined on either side of the pins to confirm soil differences. Pins are moved as necessary.
Estimate the extent of each soil type at the site. Using the marked breaks in slope as a guide, use a soil probe to look for obvious changes in soil type. The notes on the mapped soil series and associated soils act as a guide to interpret the soil probe findings. Soil probes are useful in identifying changes in features with depth and area as shown in Figure 10.
Since soil probes, with their small diameter, cause little soil disturbance, dozens of observations can be made quickly, without damaging the site of a wastewater treatment system. Soil probes, however, give a limited assessment of the soil and its properties. By themselves, soil probes only help outline the extent of each soil type at the site.
Figure 11. Detailed descriptions of the identified soil types on the lot are generated from several soil cores. Soil is lifted out of a small hole with a spade or auger and placed on the ground in order. Evaluator observes and notes color patterns, texture, structure and consistence of each soil horizon.
Excavate the soil in small bore holes in different regions of the site to estimate the depth to a limiting condition and the soil’s permeability. Soil augers or narrow spades work well for this task. Carefully lift the soil out of a six-inch wide bore hole and place it, in order, in a line on the ground surface as shown in Figure 11. As the soil is removed from the bore hole, note the color, texture and structure of the soil layers on the soil description sheet (Appendix 1). Using the homework notes from the soil survey as a guide, look for evidence of limiting conditions by looking for:
The soil removed from the bore hole can give indications of soil permeability. Observe the size, shape and strength of soil aggregates (peds) being removed. Permeable soils will have well-developed structure. Massive or weak soil structure may serve as a limiting condition.
The following tools are useful for soil profile descriptions:
Using the information collected from several soil bore holes, indicate the most suitable location for the proposed system. Suitable sites should be marked on the plan and on the ground.
Figure 12. Confirmation of the soil to be used for wastewater treatment is made in a soil pit. An excavation, large enough for a person to safely stand in is made to enable the evaluator and the regulator to make detailed observations, in situ, of the soil in consideration. Since soil pits disturb the site for wastewater treatment, pits are excavated just outside the planned treatment area.
Figure 13. Location of soil pit excavations relative to proposed location of mound system.
Confirmation of soil permeability and depth to the limiting condition must be made before a final system design can be approved. This can best be done by excavating soil pits. Soil pits range from 3 to over 6 feet deep and are large enough for 2 people to stand in them to examine the soil profile (Figure 12).
Since soil pits disturb the site and can be expensive to excavate, they are the last step in site and soil evaluation. Using the proposed system location from step 4, site the soil pit or pits just outside of the possible wastewater treatment site as shown in Figure 13.
Instruct the backhoe operator not to drive on the proposed spot for the wastewater treatment system or to remove site markers when excavating the soil pits. Rope or fence off the open excavations to avoid accidents.
Color change in the soil profile is the most obvious feature evident in the soil pit. While standing in the soil pit, mark the easily recognizable horizon breaks. Large nails work well for this. Measure the depth to each horizon break and record them on the site and soil evaluation form. Write down on the soil description sheet the soil colors present in each soil horizon, using the alphanumeric symbols which stand for hue, value and chroma from the Munsell soil color book. Be especially alert to and carefully describe the presence of redoximorphic features, such as mottled colors.
Record other important soil and horizon features on the description sheet. Observations of the texture, structure and consistence of each horizon should be recorded. Also indicate on the description sheet the depth of root penetration and the nature of the horizon boundaries.
Complete soil descriptions on the appropriate form must be prepared for each distinct soil profile observed at the site.