Indiana Farmstead Assessment for Drinking Water Protection
Site Evaluation
Why
is the site evaluation important?
The effects of farmstead practices such as pesticide handling or manure storage on groundwater depend on the physical characteristics of your farmstead site: soil type, geologic conditions and depth to groundwater. That's why evaluating the soils and geologic characteristics of your farmstead is an important step in protecting the groundwater you drink.
What's involved in completing this evaluation?
This evaluation has four parts:
-
1. Evaluating soil type and depth
- 2. Evaluating subsurface and geologic materials,along with
depth to groundwater
- 3. Determining overall site evaluation ranking (combining
parts 1 and 2)
- 4. Doing a farmstead diagram (optional)
Getting the information to complete parts 1 and 2 will require assistance from outside sources, such as your county NRCS or Extension office. How long this takes will vary depending on the information available in your county. Once you have the information in hand, though, it should take about an hour to complete the first three parts of Survey 11 (the farmstead diagram will take additional time).
If some of the information you need isn't readily available, instructions are included on how to proceed. The more information you can get, the better; some information is better than no information.
How do soils affect the potential for groundwater contamination?
Soil characteristics are very important in determining 1) how a contaminant breaks down to harmless compounds; and 2) whether it leaches into groundwater. Because most breakdown occurs in the soil; there is a greater potential for groundwater contamination in areas where contaminants move quickly through the soil.
Sandy soils have large "pore" spaces between individual particles, and the particles provide relatively little surface area for "sorption" or physical attachment of most contaminants. Large amounts of rainfall or excessive irrigation water can percolate through these soils, and can carry dissolved contaminants down through the soil and into groundwater.
Clay soils, on the other hand, are made up of extremely small particles that slow the movement of water and dissolved contaminants through the soil. Contaminants also stick tightly to clay surfaces. Even with clay soils, movement of water may be through rather large cracks (preferential flow) and treatment may be questionable.
While held securely to soil particles, contaminants are broken down by bacteria and reactions with minerals and natural chemicals in the soil. Most of this chemical and biological breakdown takes place in the loose, cultivated surface layers. Here the soil tends to be warm, moist, high in organic matter, well-aerated and with a higher microbial population.
Finally, soil organic matter is impor tant in holding contaminants. Soils high in organic matter provide an excellent environment for chemical and biological breakdown of contaminants--before they reach groundwater.
The natural purification capability of the soil is, however, limited. Under certain conditions, such as heavy rainfall, chemical spills or sandy soil, contaminants may leach below the soil. In such cases, the subsurface geologic material and the distance a contaminant must travel to groundwater are important factors in determining whether a contaminant actually reaches the groundwater.
How do subsurface and geologic materials affect the potential for groundwater contamination?
Glaciers receded from the nor thern two-thirds of Indiana just 20,000 years ago, relatively recent in geologic time. Soils in this part of the state were formed on loamy glacial till and course textured outwash overlying weathered bedrock. Soils in the southern third of Indiana were formed on older glacial deposits or directly on bedrock. The depth of surficial deposits across the state ranges from zero to hundreds of feet. These materials are called "unconsolidated deposits."
Aquifers are normally in sand and gravel in the unconsolidated deposits or in the bedrock beneath. Clayey or fine texture layers above the aquifer material help protect it from contamination.
Depth to groundwater is important primarily because it determines not only the depth of material through which a contaminant must travel before reaching an aquifer but also the time during which a contaminant is in contact with the soil. As a result, where soil and surficial deposits are fairly deep, contaminants are less likely to reach groundwater.
Bedrock geology influences groundwater pollution when the water table is below the bedrock surface. Sedimentary rocks have a wide range of permeability--from highly permeable fractured dolomite to nearly impermeable shales and crystalline formations. Movement of pollutants in fractured limestone or dolomite is unpredictable, and pollutants can readily spread over large areas. This would include areas with "sinkholes" which are common in par ts of southern Indiana. Where bedrock material contains significant cracks and fractures, the depth and characteristics of soil and surficial geologic deposits largely determine the potential for groundwater contamination.
A word of caution
As with the results of the previous 10 surveys, use the rankings from this survey cautiously. Many factors affect whether or not a contaminant will leach to groundwater. There is no guarantee that a "low-risk" site will be uncontaminated-- or that groundwater will become contaminated at a "high-risk" site. The type of contaminant involved, how you handle and store potential contaminants (such as pesticides and manure), the location and maintenance of your well, and many other factors can affect the potential for groundwater contamination.
Part 1. Evaluation the soil on your farmstead
To complete your soil evaluation, you will need a copy of your county's soil survey report. This report is available at county offices of the Cooperative Extension Service, Natural Resource Conservation Service (NRCS) or Soil and Water Conservation District (SWCD).
Step 1. Start by locating your farmstead on the detailed soil
map sheets (those with an aerial photo background) in the soil
survey,note the soil map unit indicated on the photo and look
up information related to that soil in the written survey
report.
Don't skip any parts of the survey. If you are not familiar
with usinga soil survey, you may need help completing Part
1. Ask your county extension educator or your NRCS specialist
to help you find the following information:
*Location of your farmstead on the map and aerial
photographs provided in the soil survey report.
*The soil mapping unit and soil series from the
legend provided in the soil survey report.
*The soil series and/or soil mapping unit, including
the profile description as well as any other
information in the report regarding depth to bedrock,
depth to water, organic matter or organic carbon
content.
Step 2. With this information in hand, you are ready to rank
your soil according to seven characteristics. For each of the
seven characteristics in the left column, find information
about your soil in the soil survey. Then, match your soil
description to the description in the middle column to
determine your score in the right column. (For example, if the
soil survey tells you that the surface texture of your soil is
a clay loam, your score for that category would be 8.) Enter
your score in the space indicated.
Soil Characteristics
1. Texture of surface
(A horizon or upper 6-10 inches)
loam, silt loam, sandy clay loam, silt.............. .9
clay, silty clay, clay loam silty
clay loam, sandy clay........................ 8
loamy very fine sand, very fine
sandy loam, loamy fine sand,
fine sandy loam ............................. 4
sand, loamy sand, sandy loam,
organic materials, and all
textural classes with coarse
fragment class modifiers
(such as "gravelly loam") ................... 1
Score ________
2. Texture of subsoil
(the most clayey B horizon)
clay, silty clay, sandy clay, silt ...................10
sandy clay loam, loam, silt
loam, clay loam, silty clay loam ............. 7
loamy very fine sand, very fine sandy
loam, loamy fine sandy, fine
sandy loam ................................... 4
sand, loamy sand, sandy loam organic
materials, and all textural classes
with coarse fragment modifiers
(such as "gravelly loam") .................... 1
Score _________
3. Organic matter
(A or Ap horizon; or upper 6-10 inches)
If the surface texture is muck or peat,
or soil is less than 20 inches to bedrock 1
OR
If your soil does not fall into the above groups,
obtain the following information either from a soil
test report for your farmstead, or from the Physical
and Chemical Properties table in the soil survey,
or from your NRCS office.
-----------------------------------------------------------
Organic Organic Score
Matter (%) Carbon
-----------------------------------------------------------
high (4-10%) 2.32-5.8 10
medium (2-4%) 1.16-2.32 7
moderately
low (1-2%) 0.58-1.16 5
low (.5-1%) 0.29-0.58 3
very low
(less tahn 0.5%) less than 0.29 1
(lower your score by on elevel if the soil mapping unit
description in the soil survey indicates moderate or severe
erosion, unless you take organic matter or carbon from soil
test results.)
Score _________
------------------------------------------------------------
4. pH-Surface
(A horizon)
6.6 or greater 6
less than 6.6 4
Score _________
5. Depth of soil solum
(In the "Classification of Soils' section of a soil survey. It is
often in the text below the profile description.)
greater than 60 in. 10
40-60 in. 8
30-40 in. 5
less than 30 in. 1
(lower your score one level when rock is present at 30-40
inches below the soil surface. Consult the profile
description in the soil survey report to learn about depth to
rock. you may wish to subtract the inches of the surface
erosion from the depth to dedrock.)
Score _________
6. Permeability of the slowest subsoil horizon
(In the table of "Physical and Chemical 2 Properties of Soils" of
your county soil survey.)
0.06 to 0.6 in./hour 10
0.6 to 2.0 in./hour 8
2 to 20 in./hour 3
greater than 20 in./hour 1
Score __________
7. Natural soil drainage class
(In the "Map Unit Descriptions" or Classification of Soils.)
well drained 10
moderately well drained 4
somewhat poorly drained, poorly, and very
poorly drained; somewhat excessively
and excessively drained 1
Score ___________
Step 3. Add your seven scores together
TOTAL SCORE _____________
Step 4. In the box below, find your score in the listed ranges in the
left column. Then identify your soils "potential to protect
groundwater" and find the rank number assigned to your score.
-------------------------------------------------------------------------
Total Score Soil's potential Rank
to protect groundwater
-------------------------------------------------------------------------
>51 Best 5
41-50 Good 4
31-40 Marginal/Good 3
21-30 Marginal 2
0-20 Poor 1
-------------------------------------------------------------------------
Step 5. Enter this rank number here:
SOIL RANK: ______________
Step 6. Understand your soils ranking.
A soil with more than 50 points (ranking 5) probably is a
deep, medium or fine textured, well-drained soil which
contains 4-10% organic matter. Potential contaminants move
slowly through the soil, allowing them to become attached to
soil particles. Sunlight, air and microorganisms then have
time to break down the contaminant into harmless
compounds. The groundwater contamination risk level is low.
A soil with a score less than 20 (ranking 1) is probably a
coarse-textured, (sandy) extremely well-drained soil with less
than 1% organic matter. Such a soil would enable most
contaminants to move rapidly down toward the water table.
Overall, the higher your ranking number, the more likely that
your soil conditions will help to reduce the risk of
groundwater contamination from farmstead practices.
Part 2: Evaluation subsurface and geologic materials on your farmstead
This part looks at the subsurface and geologic materials blkb beneath your farmstead's soils. Completing the survey will give you a much clearer picture of your site's potential for preventing pollutants from reaching groundwater.
For example, the soil evaluation might have indicated a moderate potential for protecting groundwater. However, if the soils are fairly shallow and lie over fractured bedrock, the potential for groundwater contamination at the site is probably higher than indicated by the soil evaluation alone.
This part requires only two items of information: your site's subsurface geologic material and depth to groundwater. Unfortunately, information on subsurface geologic material as well depth to water, is often difficult to obtain.
*It is sometimes available from the soil survey report, although this differs from county to county.
*You may also obtain this information from your well construction report or those of neighboring farms.
*You can find additional information from other well construction reports. Some Indiana river basins have reports published by the Indiana Department of Natural Resources (IDNR). These are generalized maps, though, and may not accurately reflect the depth to groundwater or direction of flow at your farmstead.
*If there is a published geological report for your county it may show the type of geologic material in your area.
Try not to skip any steps in this part. Ask your county extension educator or NRCS specialist to help you gather the information and provide assistance in completing Part 2.
If the information for this part is not available, though, you may skip to Part 3. The instructions will tell you how to proceed without it.
Step 1. Find the information you need--from soil surveys, well construction reports or geological survey reports--to identify: the geologic materials beneath your farmstead and depth to groundwater. Step 2. Match the information on your site's geology to one of the descriptions in the left column below. (You will be choosing only one description from the entire table that follows.) Step 3. When you have chosen the description that best matches your site's geology, read across to the right until you get to the appropriate "depth to groundwater" for your site and circle that score for your farmstead. For example, you may determine from your well constructor's report that geologic material beneath your farmstead consists of 30 feet of coarse-textured, unconsolidated material over fractured limestone bedrock, and that depth to groundwater is 15 feet. Looking down the left column to find your category, and then going across to the right, you see that your rank is "1". --------------------------------------------------------------------------- Geologic Material Depth to Groundwater 0-30 ft. >30 ft. --------------------------------------------------------------------------- Loam, clay loam, glacial till, loess deposits, fine textured lakebed deposits 3 4 Sandy loam till, interbedded with sands and gravel 2 3 Coarse texture, sand and gravel outwash 1 1 Fractured limestone bedrock, sink holes present 1 1 Sandstone, shale bedrock 3 4 ---------------------------------------------------------------------------- Step 4. Enter your circled number here: Subsurface Rank __________ Step 5. Understand your subsurface and geology ranking. The table below shows what your rank means. --------------------------------------------------------------------------- Rank Subsurface Potential Level of Risk to Protect Groundwater --------------------------------------------------------------------------- 4 Best Low 3 Good Low/moderate 2 Marginal High/moderate 1 Poor High --------------------------------------------------------------------------- A ranking of "4" shows that the subsurface material has small pore spaces, groundwater is at least 10 feet from the soil surface, and the risk of groundwater contamination is low. A ranking of "1" indicates a material with large pore spaces that allow contaminants to move downward easily, increasing the risk of groundwater contamination. In highly fractured rock or in very coarse-textured, unconsolidated materials (e.g. sands, gravels), the depth to groundwater doesn't seem to matter because some contaminants will flow through the pore spaces with very little slowdown. Overall, the higher your ranking number, the more likely that your farmstead's geologic conditions and depth to groundwater will help to reduce the risk of groundwater contamination from farmstead practices.
Part 3. Combining your farmstead's soil and subsurface geologic rankings
Combining the rankings from parts 1 and 2 will provide you with a good overall ranking of your farmstead site's potential to prevent pollutants from moving down to groundwater.
Step 1. Transfer your boxed rankings from the soil evaluations (Part 1, page 7) and the subsurface/geologic evaluation (Part 2, page 9) to the two boxes below: Soil Rank ________ Subsurface Rank _________ Step 2. The table below shows the overall level of groundwater contamination risk associated with your farmstead site conditions. Find your two numbers written in the correct sequence (soils rank-subsurface rank, for example 4-2) and circle the sequence. ------------------------------------------------------------------------ Level of Risk Low Low-Moderate High-Moderate High (Rank 4) (Rank 3) (Rank 2) (Rank1) ------------------------------------------------------------------------ 1-4 2-3 1-3 1-1 2-4 4-2 3-2 1-2 3-3 5-1 2-1 3-4 2-2 4-3 3-1 4-4 4-1 5-3 ------------------------------------------------------------------------- Step 3. Look above the sequence you circle to find your risk level and your ranking. (For example, if your numbers are 2-3, your site is in the low-moderate risk column and your ranking is 3.) Step 4. Enter your combined ranking and level of risk here. Combined Ranking _________ Level of risk ____________ Step 5. Understand your combined ranking. In general, a site with a combined ranking of 4 (low groundwater pollution risk) will have a soil with a good capacity to hold and break down contaminants before reaching the water table. Under certain conditions, however, such as spills, poor management and heavy rainfall, contaminants may reach groundwater. On the other hand, if you carefully manage a site with a combined ranking of 1 (high groundwater pollution risk), you may still protect your drinking water. Both site characteristics and your management practices are of equal importance.
Part 4. Learning more about your site
Sketching a diagram of your farmstead can provide useful information to help you understand how the physical layout and site characteristics of your farmstead may contribute to-- or lessen--the effects of possible contaminants reaching your drinking water.
The diagram can show the location of well, septic drainfields, manure storage areas, direction of groundwater flow, surface water, buildings and other activities that may contribute potential contaminants. Along with the soil and subsurface evaluations, the diagram will help point out aspects of your farmstead that may present a hazard to your drinking water.
Step 1. Begin by looking at the sample diagram on page 13.
Step 2. Diagram your farmstead on the blank grid provided on page 14. Include all of the following that apply to your farmstead:
*all buildings and other structures (home, barn, machine shed) *well and abandoned wells *septic systems (tank, dry well, absorption field and/or ditch) *barnyard/livestock yard *manure storage (temporary and permanent) *fuel storage tanks (above and underground) *pesticide and fertilizer handling and storage *silage storage *milkhouse waste disposal systems (tank, field and/or ditch) *farm dumps *vehicle maintenance areas *liquid disposal areas You can use the same diagram to indicate surface water (ponds and streams), directions of land slope, groundwater flow and different soil types found around your farmstead. Generally, groundwater follows surface topography and moves downhill towards surface water. Step 3. Use your diagram to note which activities or structures on your farmstead have a greater likelihood of allowing contaminants to reach groundwater. This information should help prepare you to make better decisions about your farmstead activities and structures and how they might be affecting your drinking water. The following is just given as an example farmstead Diagram.
It is the policy of the Purdue University Cooperative Extension Service, David C. Petritz, Director, that all persons shall have equal opportunity and access to its programs and facilities without regard to race, color, sex, religion, national origin, marital status, parental status, sexual orientation, or disability. Purdue University is an Affirmative Action employer. This material may be available in alternative formats. 1-888-EXT-INFO.
