Site Evaluation

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Site Evaluation

Why is the site evaluation important? • What's involved in completing this evaluation? • How do soils affect the potential for groundwater contamination? • How do subsurface and geologic materials affect the potential for groundwater* contamination? • Part 1: Evaluating the Soil on Your Farmstead • Part 2: Evaluating Subsurface and Geologic Materials on Your Farmstead • Part 3: Combining Your Farmstead's

Why is the site evaluation important?

How farmstead practices affect groundwater depends in part on the physical characteristics of your farmstead site: soil type, bedrock characteristics, and depth to groundwater. That's why evaluating the soils and geologic characteristics of your farmstead is such an important step in protecting the groundwater you drink.

What's involved in completing this evaluation?

This evaluation has four parts:

Part 1: Evaluating your soil type and depth
Part 2: Evaluating subsurface and geologic materials, along with depth to groundwater
Part 3: Determining your overall site evaluation ranking (combining parts 1 and 2)
Part 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 Natural Resources Conservation Service (NRCS) or Extension office. How long this takes will vary depending on the availability of the information in your county. Once you have the information, though, it should take about an hour to complete the first three parts of Work Sheet #9. The farmstead diagram will take additional time.

If some of the information you need isn't readily available, the work sheet contains instructions on how to proceed. The more information you can get, the better; but some information is better than no information. The definitions on the last page may help you better understand some of the words that are used.

How do soils affect the potential for groundwater contamination?

Soil characteristics are very important in determining how a contaminant breaks down into harmless compounds or moves through soil and into the groundwater. Because most breakdown occurs in the soil, there is a greater potential for groundwater contamination in areas where contaminants are able to move quickly through the soil.

Sandy soils have large spaces between individual soil particles, and the particles provide relatively little surface area for attachment of most contaminants. Large amounts of rainfall can move through these soils and cause dissolved contaminants to move rapidly 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.

While held securely to soil particles, contaminants are broken down by bacteria, other soil organisms, and by reactions with minerals and natural chemicals in the soil. Most chemical and biological breakdown takes place in the loose, cultivated surface layers, where the soil tends to be warm, moist, well-aerated, and high in organic matter. Soil organic matter is also important in holding contaminants. Soils high in organic matter provide an excellent environment for chemical and biological breakdown of these contaminants.

The soil's natural purification capability is limited. Certain conditions, such as heavy rainfall and chemical spills, may exceed the soil's purification capacity, allowing the chemical to move through the soil relatively quickly. 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?

Depth to groundwater is important because it determines two important factors: (1) the thickness of material through which contaminants must travel before reaching the local aquifer and (2) the length of time contaminants are in contact with the soil. Other factors being equal, the greater the thickness of material above the groundwater, the less chance of contamination from the ground surface.

Bedrock geology influences groundwater pollution when the local aquifer is below the bedrock surface. Movement of contaminants in fractured rock is difficult to predict, and pollutants can travel as far as one mile from their source. Where bedrock material contains significant fractures that are in contact with the local aquifer, the thickness and characteristics of the soil above the fractures largely determine the potential for groundwater contamination.

*Groundwater = local aquifer = the most shallow water-bearing strata that is used as a water source for human and/or animal consumption.

A word of caution

As with the results of the previous 8 work sheets, use the rankings from this work sheet cautiously. Many factors affect whether or not a contaminant will get into the local aquifer. 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, the location and maintenance of your well, and many other factors can affect the potential for groundwater contamination.

Part 1: Evaluating 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 most county offices of NRCS or Extension Service.

Step 1: Start by locating your farmstead on the aerial photos in the soil survey, note the soil mapping unit indicated on the photo, and look up information related to that soil in the written sections of the soil survey report.

If you have more than one soil mapping unit on your farmstead, rank each soil individually (up to 3) using this work sheet.

These rankings describe soil in native, undisturbed conditions. If your farmstead soil has been altered by human activities, such as clearing, tilling, or ditching, contact your county Extension agent or your NRCS office for assistance.

Don't skip any parts of the work sheet. If you are not familiar with using soil surveys, you may need help completing Part 1. Ask your county Extension agent 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, or organic matter content.
The classification of the soil series, including family, subgroup and order. Soil surveys published before 1965 will not include the soil classification. You'll have to get this information from your county Natural Resources Conservation Service office.

Step 2: Determing Soil Characteristics: With the information in hand from Step 1, you are now ready to rank your soil(s) according to seven characteristics.

For each of the seven characteristics highlighted 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: The soil survey says that the texture of one of your soils is a clay loam. Your score for that characteristic would be 8. Enter your scores for up to 3 soils in the spaces indicated.

For characteristics 1-6a that follow, consult the soil profile description and text, and the soil mapping unit text in the "Description of the Soils" section of your county soil survey.

1. Texture of surface
(A horizon)

loam, silt loam, sandy clay loam, silt

Score
9

clay, sandy clay, silty clay, clay loam, silty clay loam

Score
8

loamy fine sand, loamy very fine sand, fine sandy loam, very fine sandy loam

Score
4

sand, loamy sand, sandy loam, organic materials, all "O" horizons, and all textural classes with coarse fragment class modifiers - such as "gravelly loam"

Score
1

Your Score(s)

__________
soil #1

__________
soil #2

__________
soil #3

2. Texture of subsoil - B horizon. If there is no B horizon, consider the character of materials within approximately 2 feet below the A horizon.

clay, sandy clay, silty clay, silt

Score
10

sandy clay loam, loam, silt loam, clay loam, silty clay loam

Score
7

sand, loamy sand, sandy loam, organic materials, and all textural classes with coarse fragment modifiers - such as "gravelly loam"

Score
1

Your Score(s)

__________
soil #1

__________
soil #2

__________
soil #3

3. pH-Surface
(A horizon)

6.6 or greater. The A horizon description will include one of the following terms: neutral, mildly alkaline, moderately alkaline, or strongly alkaline.

Score
6

less than 6.6. The A horizon description will include one of the following terms: slightly acid, moderately acid, or strongly acid.

Score
4

Your Score(s)

__________
soil #1

__________
soil #2

__________
soil #3

4. Depth of soil solum (The depth of A and B horizons, minus inches of surface layer erosion noted in soil survey description)

greater than 60 inches

Score
10

40-60 inches

Score
8

30-40 inches

Score
5

less than 30 inches

Score
1

Your Score(s)

__________
soil #1

__________
soil #2

__________
soil #3

5. Soil drainage class

well drained

Score
10

well to moderately well drained

Score
7

moderately well drained

Score
4

somewhat poorly, poorly, and very poorly drained; somewhat excessively and excessively drained

Score
1

Your Score(s)

__________
soil #1

__________
soil #2

__________
soil #3

6. Permeability of subsoil horizon

6a. If your soil series description indicates that bedrock is found within 20 inches of the surface, or if bedrock is present in the soil mapping unit within 40 inches of the surface, use the following ranking:

bedrock at 20-40 inches

Score
3

bedrock within 20 inches

If this does not apply then go to 6b.

Score
1

6b. For soils other than those listed in 6a, look in the "family" column of the "Classification of Soil Series" table in your soil survey. To determine permeability of the subsoil horizon, use the particle-size class in this column and find the rank for it below. If there is more than one particle-size class listed, such as "fine silty" over "sandy," choose the underlying material, such as "sandy." If your soil survey was published before 1965, see your NRCS specialist for assistance.

moderately low, low to very low (fine, very fine, clayey, clayey-skeletal)

Score
10

moderate (fine loamy, fine silty, coarse silty, loamy-skeletal)

Score
8

high (sandy or sandy-skeletal, coarse loamy)

Score
3

very high (coarse sand, fragmental, sandy; or psammentic suborder)

Score
1

Your Score(s)

__________
soil #1

__________
soil #2

__________
soil #3

7. Organic matter content in Ap horizon or 0-6" depth from surface

7a. If the soil survey "Classification of Soil Series" table classifies your soil series as Histosols, Aquic suborder, or Lithic, Aquollic and Aquic subgroup, use the ranking score of "1." (These are organic soils, wet soils, or soils with less than 20 inches of material over bedrock.)

7b. If your soil does not fall into the above groups, obtain the organic matter percentage from a soil test report for your farm, the chart of "Soil Properties Significant to Engineering" found in some soil surveys, or your county NRCS office. You can find the soil order for your soil series in the "Classification of Soil Series" table.

Organic matter

Soil order

Score
10

high (4-10%)

Mollisols

Score
10

medium (2-4%)

Score
8

moderately low (1-2%)

Alfisols

Score
5

low (0.5-1%

Inceptisols, Entisols, Ultisols

Score
3

very low (less than 0.5%)

Score
1

Your Score(s)

__________
soil #1

__________
soil #2

__________
soil #3

Step 3:

Add your seven scores together
for each soil ranked.

TOTALS

__________
soil #1

__________
soil #2

__________
soil #3

Step 4: From the box below, find your score in the listed ranges in the left column. Then identify your soil's "potential to protect groundwater" and find the rank number assigned to your score.

Total Score	Soil's Potential to Protect Groundwater	Rank
51+	Best	4
41-50	Good	3
31-40	Marginal	2
0-30	Poor	1

Step 5:	Enter rank number(s) here	SOIL #1 RANK
		SOIL #2 RANK
		SOIL #3 RANK

Step 6: Understand your soil(s) rankings.

A soil with more than 50 points (ranking #4) probably is a deep, medium- or fine-textured, well-drained soil which contains 4 to 10 percent 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 of 30 or less (ranking #1) is probably a coarse, sandy, extremely well-drained soil with less than 1 percent organic matter. Such a soil would allow 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: Evaluating Subsurface and Geologic Materials on Your Farmstead

This part looks at the subsurface and geologic materials beneath your farmstead's soils. Completing the work sheet will give you a much clearer picture of your site's potential for keeping pollutants out of groundwater. For example, the soil evaluation might have indicated a moderate potential for protecting groundwater. However, if the soils are fairly thin 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 two items of information: (1) your site's subsurface geologic material and (2) depth to the local aquifer. Unfortunately, information on subsurface geologic material, as well as 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 can also obtain this information from your well construction report. If the well installer filled out the report correctly and submitted it to the Arkansas Geological Commission, it is on file at the state office (3815 West Roosevelt Road, Little Rock, Arkansas; telephone 663-9714).
You can find additional information from other well construction reports in your area, hydrogeological reports, and groundwater flow maps for some counties, which are also available from the Geological Commission. These are generalized maps, though, and may not accurately reflect the depth to groundwater or direction of flow at your farmstead.
Published geological reports may show the type of geologic material in your area.

Try not to skip any steps in this part. Ask your county Extension agent or NRCS personnel to help you gather the information and provide assistance in completing Part 2.

Step 1: Find the information you need - from the soil survey, well construction reports, Geological Commission reports, or Extension and NRCS personnel to identify (1) the geologic materials beneath your farmstead and (2) depth to local aquifer.

Step 2: Match the information on your site's geology to one of the descriptions in the table that follows. You will be choosing only one description from the entire table.

If your well construction report describes more than two types of geologic material below 5 feet, ask for help in filling out this section from your county Extension or NRCS office.

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 local aquifer" for your site and circle that score for your farmstead.

For example, you may determine from your well construction report that geologic material beneath your farmstead consists of 30 feet of coarse-textured, unconsolidated material over fractured bedrock, and that depth to local aquifer 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."

Subsurface Geology Table
Geologic Material (more than 5 feet below ground)	Depth to Local Aquifer (in feet)
	0-10	11-30	31-50	More than 50
Fine-textured materials (more than 45' of materials) silt, clay or shale	3	3	4	4
Unweathered and unfractured metamorphic, igneous, limestone or sandstone	2	2	3	4
Medium- to fine-textured, unconsolidated materials over fractured bedrock
33-45' of materials	2	2	3	3
21-32' of materials	1	1	2	3
6-20' of materials	1	1	2	2
0-5' of materials	1	1	1	1
Coarse-textured, unconsolidated materials over fractured bedrock
33-45' of materials	1	1	2	2
21-32'of materials	1	1	1	2
0-20' of materials	1	1	1	1
Sand and gravel (more than 45' of materials)
greater than 12% silt or clay (sorted)	1	1	2	2
less than 12% silt or clay (sorted)	1	1	1	1
Karst, highly permeable or fractured rock (more than 45' of materials)	1	1	1	1

There may be other situations that do not fall into the above categories (such as unconsolidated materials over limestone/shale/sandstone sequence). Determining a ranking for such situations requires a judgment call.

Step 5:	Enter rank number(s) here	SOIL #1 RANK
		SOIL #2 RANK
		SOIL #3 RANK

The table below shows what your subsurface geology ranking means.

Rank	Level of Risk of Groundwater Contamination
4	Low
3	Low/moderate
2	High/moderate
1	High

A ranking of "4" shows that the subsurface material has the best potential to protect groundwater. This 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 poor potential to protect groundwater. Its large pore spaces allow contaminants to move downward easily, increasing the risk of groundwater contamination. In highly fractured rock or in very coarse-textured, unconsolidated materials, 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 keep pollutants from moving down to groundwater.

Step 1: Transfer your boxed rankings from the soil evaluation (Part 1, step 5,) and the subsurface/geologic evaluation (Part 2, step 4) to the boxes below:

Soil #1 Rank
Soil #2 Rank
Soil #3 Rank
Soil #1 Subsurface Rank
Soil #2 Subsurface Rank
Soil #3 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 from step 1 on page 11, written in the correct sequence of "soils rank-subsurface rank," and circle the sequence in the following table.

LEVEL OF RISK
Low Risk (Rank 4)	Low-Moderate Risk (Rank 3)	High-Moderate Risk (Rank 2)	High Risk (Rank 1)
1-4	1-3	2-2	1-1
2-3	3-2	4-1	1-2
2-4	4-2		2-1
3-3			3-1
3-4
4-3
4-4

Step 3: Look above the sequence you circled to find your risk level and your ranking. (For example, if your numbers are 3-2 "soils rank-subsurface rank," your site is in the low-moderate risk column and your ranking is 3.)

Step 4: Enter your combined ranking here. (If you calculated more than one soils ranking, calculate a combined ranking for each soils ranking.)

Combined Ranking #!
Combined Ranking #!
Soil #3 Rank

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. Its subsurface conditions will also keep contaminants from 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 not affect your drinking water. Both site characteristics and your management practices are of equal importance.

Your three site ranking numbers (soils ranking, subsurface ranking, and combined ranking) will be used again in Work Sheet #10. If you have more than one soil on your farmstead, you will need to transfer individual soil rankings and combined rankings to Work Sheet #14. It will be especially important for you to complete Part 4 of this work sheet if you have more than one soil on your farmstead, so that you can match particular site concerns with each farmstead activity.

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