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Quality Control Sampling of Sand and
Rootzone Mixture Stockpiles
One of the most important aspects of putting
green construction is the rootzone. Whether the rootzone is composed
of straight sand or a mixture of sand and amendments, quality control
testing is recommended to ensure the rootzone material remains as
consistent as possible. This is accomplished by removing samples
from the stockpile and submitting those samples to an accredited
physical soil-testing laboratory for analysis.
The goal of the sampling and testing procedure is to monitor changes
in the rootzone material as it is produced. It is important to realize
that some change is inevitable. As sand is mined from a pit or from
a body of water, the physical make-up of the sand changes. Amendments
may also vary slightly from bag to bag or lot to lot. And, when
materials are blended, some variability is introduced through the
operation of the blending equipment. Good suppliers of sand, amendments,
and blending services can keep these variables to a minimum.
There is another major source of variability that can cause significant
discrepancies in the quality control testing efforts. Improper and/or
inconsistent sample collection procedures will introduce unwarranted
errors in the test results. Poor sampling procedures can result
in test results that make a good rootzone material appear to be
inconsistent and therefore of poor quality.
There are two levels of sampling and testing that should be carried
out. The first level should take place at the source where the sand
and amendments are produced. Samples should be collected and sent
to an accredited laboratory for analysis. The test results are then
provided to the person responsible for approval of the materials.
Sampling and testing several candidate materials is the best means
to identify the most appropriate and cost-effective products. The
laboratory will determine if the sand meets the green construction
criteria selected for the project. For example, if the USGA's Method
of Putting Green Construction is to be followed, the lab will analyze
the sand according to those criteria. Typically, the lab also will
add amendments to the sand in varying ratios to identify the best
mixture possible for the project. It is important to realize that
such amendments are added by hand in the lab, often from small stocks
they keep on hand. Later, when the rootzone mixture is produced
in bulk, blending will be accomplished by machinery. As a result,
when samples are collected from the blended stockpiles and compared
to the preliminary testing, the numbers are almost certain to vary.
The initial testing procedure should be used only to identify materials
that fall within the project guidelines.
The second level of sampling should occur throughout the actual
production of the rootzone materials so that mistakes due to handling
the material during mixing and transportation are detected. Collect
a sample from the first 200 tons produced and submit to the laboratory
for complete analysis. If the lab determines the sample meets the
requirements of the project (e.g. USGA Guidelines), the test results
become the target for all subsequent quality control testing. The
goal of all future rootzone material production is to match as closely
as possible the material in the first 200-ton pile. After the initial
200 tons, collect a sample for every 1000 tons of rootzone mix produced.
If less material is being used (for example, building only one green)
or if the material is inconsistent in its composition as indicated
by testing, sample every 500 tons or less.
Field sampling errors are almost certain to cause significant variability
in laboratory test results and can cause confusion, delay, and unnecessary
expense. It is imperative therefore, that stockpiles be sampled
in a manner such that the composite sample removed from each pile
represents the average properties of the entire pile. To do this,
a sufficient volume of material should be taken with each sampling
unit (a sampling unit is a core or auger of a given dimension) and
all sampling units should be collected to make a composite sample
(combining of sampling units) that are of equal volumes.
To better illustrate the importance of removing enough sampling
units, consider the science of polling during an election. If a
pollster queried only a few voters, there would not be a large enough
sample of the population to reasonably predict the outcome. While
the most accurate method would be to ask every single voter how
he or she voted, this is not feasible or cost-effective. The pollsters
utilize statistical analysis to determine how large a group of voters
must be interviewed to determine the likely outcome of the election
to a certain level of confidence. The greater the number of voters
interviewed, the greater the level of confidence there will be in
the poll. Similarly, the more samples that are removed from a stockpile,
the more accurately the test results will reflect the actual make-up
of the pile. This document recommends that at least 8 samples be
collected from each 1000-ton stockpile to achieve good results.
Field sampling procedures should be standardized for the duration
of the quality control testing program. ASTM D 75-97, Standard Practice
for Sampling Aggregate, offers some guidance regarding the best
method of sampling putting green rootzone mixture stockpiles. The
standard states, "If circumstances make it necessary to obtain samples
from a stockpile of coarse aggregate or a stockpile of combined
coarse and fine aggregate, design a sampling plan that will give
confidence in results therefrom that is agreed upon by all parties
concerned to be acceptable for this particular situation." There
are two very important statements in this quote from the standard.
First, a sampling plan must be established. Secondly, all parties
should agree to the plan.
The standard does not state exactly how the sampling procedure should
be designed. To meet this need, the USGA utilized the expertise
of university, industry and laboratory professionals to develop
the following procedure. All samples should be collected as detailed
in the following step-by-step procedure.
Produce a stockpile of approximately 1000 tons. The individual in
the photo is standing in front of a recently produced, 1000-ton
pile of rootzone sand. Assemble the necessary tools for sampling
the stockpile. These include a:
- clean, 5-gallon bucket
- rubber hammer
- shovel
- permanent marker
- 1-gallon zip lock plastic bags
- mailing labels and
- a large, non-permeable plastic tarp
The sampling tool is made from a 4-foot long piece of 2-inch PVC
pipe. To make sampling easier, one end of the pipe can be cut at
a 45-degree angle. A PVC "T" can be placed on the other end to make
it easier to push the pipe into the sand. Duct tape can be used
to mark the 2-foot sampling depth.
Collect a minimum of 8 samples to ensure an accurate representation
of the pile. Take samples at four equidistant points around the
pile, at 1¼3 and 2¼3 up the face of the pile, for a total of at
least eight samples.
Dig a hole into the face of the pile to prevent collection of any
of the sand from the surface of the pile. Expose an undisturbed
face of the pile into which the collection tube can be inserted.
When you first dig into the pile, material from above will usually
flow down the face into the area you are clearing. Keep digging
until the hole becomes stable. The shovel also works very well to
expose an undisturbed face. Make a vertical cut down into the face
just above the sampling point.
Insert the collection tube into the undisturbed face to a depth
of two feet. The tube should be inserted at a slightly upward angle
to prevent the sample from falling out when the pipe is removed.
Mark the collection tube to ensure uniform depth insertion. The
"T" fitting on the end of the two-inch, PVC pipe makes it easier
to push the pipe into the pile. In most cases, the pipe can be pushed
in by hand to the proper depth. In "tight" sand, a rubber hammer
may be needed to drive the pipe to the 2-foot depth.
Carefully remove the collection tube from the face of the pile.
Empty the sample from the tube into a clean, 5-gallon bucket.
Improper sample collection procedures will result in problems. This
sample is being collected incorrectly from the surface of the pile
rather than from within the pile. When this sample is tested, the
results will not represent the overall make-up of the stockpile.
Samples collected in this manner will be highly inconsistent from
test to test since the surface of the stockpile changes rapidly.
Samples collected from the surface of this pile can vary widely
from those collected from within the pile. Notice how the surface
of the pile has segregated due to wind and rain. As the finer materials
erode, the coarser materials accumulate on the pile surface. Test
results of a sample removed from this area would indicate a higher
percentage of coarse materials than actually exists in the pile.
After the eight samples are collected from the 1000-ton pile, the
5-gallon bucket should be about 1¼2 to 2¼3 full. (If a stockpile
larger than 1000 tons is sampled, the number of samples collected
should be increased proportionately. Thus, at least 16 samples should
be collected from a 2000-ton pile.)
Empty the bucket onto a clean, non-permeable surface. Thoroughly
mix the samples together by hand. The combined sample should now
be reduced to approximately 1 gallon to be sent into the laboratory.
This is accomplished by splitting the sample. The sample should
be shaped into a square so that it can be divided into quarters.
Divide the sample into equal quarters. Opposite quarters will be
removed from the sample and discarded. For example, if quarters
1 and 4 are removed and discarded, quarters 2 and 3 will be recombined
and mixed again. Another square is then formed. The process is repeated
until the sample is reduced to approximately 1 gallon.
Place the 1-gallon sample into a plastic, zip-lock bag. Label the
outside of the bag using a permanent marker. Record the pile number
and date of collection. Print the same information on a mailing
label and place the label on the outside of the bag. Place the sealed
and labeled bag into another plastic bag and seal it with duct tape.
This labeling and double-bagging procedure is important to ensure
the lab receives the sample intact.
With assistance from university and labortory scientists, the USGA
Green Section has identified the maximum amount of variation that
should be tolerated for key test parameters measured during quality
control testing. The following table details a variability percentage
for each parameter. This variability percentage is more accurately
referred to as the confidence interval and is used to establish
plus or minus values for each measured parameter. For example, assume
the laboratory test indicates a value for fine sand to be 10%. Using
the confidence interval percentage for fine sand of 15%, the acceptable
variance is 10% plus or minus 1.5% for an acceptable range for quality
control testing of 8.5 to 11.5%.
| Test
parameter |
USGA
Confidence Intervals |
| Fine Gravel |
50% |
| Very coarse
sand |
50% |
| Coarse sand |
10% |
| Medium sand |
10% |
| Fine sand |
15% |
| Very fine sand |
30% |
| Silt |
25% |
| Clay |
25% |
| Total Porosity |
10% |
| Air-filled
Porosity |
10% |
| Capillary Porosity |
10% |
| Saturated Conductivity |
20% |
| Percent Organic
Matter of Mix |
0.2* |
| *The
confidence interval for percent organic matter is not represented
as a percentage. Thus a reported value of 0.7% organic matter
could range from 0.5 -0.9 %. |
The following additional information can be found on the USGA's
web site at www.usga.org/green/coned.
Guidelines for a Method of Putting Green Construction
Accredited Physical Soil Testing Laboratories
ASTM Procedures Required for Laboratory Testing Putting Green Materials
(abstracts)
USGA Confidence Intervals for Quality Control Testing
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