SOP EM-14 Page 1 of 10

Collection of Groundwater Samples 

Revision: # 3 Replaces: 2/19/14 Effective: 9/3/19

1. Purpose and Scope: Groundwater samples are collected to measure the concentration of

pesticide in the subsurface environment. This SOP describes how to collect, transport, and store

groundwater samples from shallow environmental monitoring wells. Often the monitoring wells

sampled by the Program will be a component of an environmental site investigation not

associated with APHIS activities. Monitoring wells are different in many ways from potable

wells used as drinking water sources and the procedures for collecting a water sample are also

different. If the well being sampled is a potable well, contact the Environmental Compliance

Team at (301) 851-2345 for instructions and equipment requirements. Any instructions on water

sampling and documentation found in the Environmental Monitoring Plan (EMP) for the

Program supersedes instructions contained in this SOP.

Environmental monitoring wells provide access to the unconfined aquifer, also called the water 

table, for sampling and measurement of hydraulic characteristics. Monitoring wells are typically 

a plastic pipe composed of slotted (screen) and solid (riser) portions. Typically four or two inch 

diameter plastic pipe is installed into a larger diameter (eight to twelve inch diameter) vertical 

hole. The area around the plastic pipe (annulus) is filled with filter sand adjacent to the screen. 

The annulus is sealed with manufactured clay (bentonite) at the riser and cemented to the 

surface. The top of the plastic pipe will be sealed with a removable compression cap. Access to 

the plastic pipe is usually protected by either a small manhole or a steel standpipe. Proper 

maintenance of the bolt down manhole lid gasket, and the compression cap inside the manhole, 

are important to protect the subsurface environment from the intrusion of sediments and surface 

water into the well. A schematic of a typical below grade well is presented in Figure 1.

To ensure the water sample collected from the well is representative of the current subsurface 

conditions, stagnant water resting in the plastic pipe and the annulus filled with filter sand should 

be purged and allowed to recharge. The procedure to calculate the volume of water that should 

be purged from the well and measurement of other aquifer characteristics is described in detail in 

Section 3. 
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Collection of Groundwater Samples 

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Figure 1 - Below-grade environmental monitoring well.
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Collection of Groundwater Samples 

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2. Supplies Required: To request sampling supplies, contact the monitoring supplies 

coordinators, Lisa Mosser (305) 278 4902, or Richard King (305) 278 2905, Center for Plant 

Health Science and Technology, Miami, or email the Environmental Monitoring Supplies 

Checklist to lisa.k.mosser@usda.gov or richard.a.king@usda.gov.

 (for address see SOP EM - 17, Packaging and Shipping of Samples).

2.1 Hammer, screw-driver, pry-bar, socket set

2.2 hand operated bilge pump and sponge 

2.3 water level indicator

2.4 field log book and environmental monitoring forms (APHIS Form 2060) 

2.5 calculator and SOP EM-14 Collection of Groundwater Samples

2.6 disposable weighted bailers (1.5 x 36 inch for two inch diameter wells and 3.0 x 

36 inch for four inch diameter wells)

2.7 cotton “jersey” work gloves and nitrile gloves

2.8 nylon rope (3/8 inch thick) and string

2.9 plastic buckets (five gallon) with lids

2.10 pH and temperature meter

2.11 conductivity (specific conductance) meter with a range of 0.0 to 19.99 

millisiemens (mS)

2.12 1 gallon, collapsible plastic "cubitainers"*

*NOTE: cubitainers may introduce material that will interfere with the analysis

of some compounds. Please check with CPHST when ordering supplies. If the

pesticide to be analyzed is among those that might be affected by the cubitainer,

then the laboratory will supply glass containers instead.

2.13 sodium sulfate (pre-packaged five gram vials) †
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Collection of Groundwater Samples 

Revision: # 3 Replaces: 2/19/14 Effective: 9/3/19

2.14 sulfuric acid (in a plastic squeeze bottle) †

†

NOTE: most pesticides used by PPQ are stable in acidic water. However, check 

with the CPHST- Biloxi when ordering supplies to determine that the acid and 

buffer specified herein are correct for the pesticide being sampled. If not, the 

laboratory will provide alternate materials and instructions for stabilizing the 

sample.

2.15 sample cooler or insulated shipping container from the laboratory 

2.16 one gallon resealable plastic “freezer” bags

2.17 15 to 20 pounds of ice (double bagged and sealed with clear packing tape), or 

frozen blue ice packs, per cooler 

2.18 five to ten gallons of distilled water

2.19 dish detergent or cleaning product supplied by the laboratory 

2.20 dish brush 

2.21 paper towels

2.22 duct and clear packing tape 

2.23 overnight courier service shipping labels and account numbers 

2.24 55 gallon drums (for temporary storage of purge or decontamination water)

2.25 indelible markers 

2.26 100 foot measuring tape or surveyor’s measuring wheel 
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Collection of Groundwater Samples 

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3. Preparation of the monitoring well:

3.1 Identify and document the exact location of the monitoring well. Measure the 

location of the well relative to three or more fixed features on site (utility poles, 

street curbs, fuel dispenser islands, other monitoring wells). Check your work 

area for possible hazards and environmental concerns. Ensure that vehicular 

traffic is prevented from entering the work area immediately around the 

well. Wear all the appropriate personal protective equipment including eye 

protection and chemical resistant gloves.

3.2 Remove the manhole cover or standpipe lid. Manholes lids are often bolted (9/16 

inch socket) down and may need to be pried up with a screw driver. Remove 

gross amounts of sediment from the lid gasket if present. If surface water is 

present inside the manhole, use a hand operated bilge pump or sponge to remove 

the water, until it will not flow into the plastic pipe protected by the compression 

cap. Remove the compression cap. 

3.3 Determine the volume of water in the well (plastic pipe) by measuring the height 

of the water column and multiplying by the gallons per foot. Use the water level 

indicator to measure the depth to water (DTW) and the bottom of the well or total 

depth (TD) from the top of the plastic pipe. Note that the water level indicator 

measures depth in decimal feet (hundredths) so the measurement hatch marks are 

not in inches. Subtract DTW from TD to get the water column height (CH) in 

feet. Multiply the CH by the gallons per foot for the well diameter (WD) to 

determine the well volume (WV). A four inch diameter well will hold 0.67 

gallons of water per foot of CH. A two inch diameter well will hold 0.17 gallons 

of water per foot of CH. Record the well information in the field book and 

prepare a purge water data table. An example table is presented in Table 1. 

Prepare and maintain the sample documentation as described in Section 6 (i.e. 

APHIS Form 2060). 
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Collection of Groundwater Samples 

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Table 1 – Example well purge water data. 

Site Name: Public Works Well Identification: MW1 Date: Sept-30-09

WD (inches) TD (feet) DTW (feet) CH (feet) Gal./foot WV (gal.)

4 30.0 14.35 15.65 0.67 10.5 

Purge start

time

Purge stop

time

Amount 

purged (gal.)

Sample 

identification

Sample time Recharge 

DTW (feet)

09:30 09:55 31.5 PW-9/30-MW1 10:15 18.3 

Measurements pH Temperature (◦F) Conductivity 

(mS)

Turbidity

Initial 5.76 61.0 865 Moderate 

1st WV 5.88 58.9 848 Moderate 

2nd WV 5.90 56.3 856 Moderate/slight 

3rd WV 5.85 55.9 851 Slight 

Sample 5.80 55.8 855 None 

Comments: Well purged and sampled with disposable bailer. Light yellow brown turbidity cleared up while purging. 

Compression cap needs to be replaced. Joe Consultant (BSC Inc.) was on site and collected split samples.

3.4 Purging four inch diameter monitoring wells requires the lifting of a bailer 

(approximately 1 gallon = 8.3 pounds) from depths varying from 10 to 40 feet 

many times. Protect your hands from rope burns and blisters that result from 

handing saturated rope with thick gloves. A pair of cotton “jersey” gloves 

covered with a pair of nitrile gloves works well. Change both pairs of gloves 

often when they become saturated and torn, respectively. Secure an end of the 

rope to the bailer using a bowline or multiple tight square knots. Lower the bailer 

to the bottom of the well and secured the above ground portion of rope to an 

appropriate object (e.g. bucket handle) after a generous amount of additional slack 

has been laid out. 

3.5 Rapidly remove the bailer from the well and pour a small aliquot of water from 

the top of the bailer into a clear vessel for measurement of the aquifer 

characteristics. Record the measurements in the field log book including the 

purge start time. Pour the remaining contents of the bailer into a five gallon

bucket. Purge the calculated well volumes (WV) ensuring the last bailer-full of 

each volume has submerged to the bottom of the well. Record the aquifer 

characteristics by measuring an aliquot of water from the last bailer removed for 

each well volume. 

3.6 Before, during, and after purging the well volumes, several aquifer characteristics 

should be measured to determine if the water sample is representative. Measure 
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Collection of Groundwater Samples 

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the pH, temperature, and conductivity (specific conductance) of the first water 

drawn from the well, and at the completion of each of the three well volumes 

purged. This data should be measured when the sample is collected once the 

groundwater has recharged into the well. In addition, the turbidity should be 

visually estimated when the aquifer characteristic measurements are collected. 

Turbidity can be characterized as:

• Heavy – water opaque and sediment settles rapidly to the bottom of the vessel,

• Moderate – water opaque little or no sediment settling apparent,

• Slight – water is transparent,

• None – water is clear of turbidity but may still have discoloration.

3.7 Some wells may not recharge at a rate that will allow three well volumes to be 

purged. This will be apparent when the bailer does not completely submerge at 

the bottom of the well. When this condition occurs the purging is complete. 

Record the aquifer characteristics, the total amount of water removed and the 

purge stop time. After purging is complete allow the well to recover to static 

conditions prior to collecting the sample and final aquifer characteristic 

measurements. 

3.8 Dispose of the purge water in a manner appropriate for the monitoring well that is 

being sampled. In most cases the wells up-gradient from the sources of 

contamination being investigated will be selected for sampling. Unless otherwise 

instructed pouring of apparently clean (i.e. no chemical odors or sheens) purge 

water onto nearby landscaped areas is acceptable. Dedicated 55 gallon steel 

drums may be present on site for use as temporary storage containers. Follow the 

instruction of the facilities management or their representative concerning the 

disposal of purge water. 

4. Collecting a Groundwater Sample:

4.1 Prepare the sample cooler or an insulated shipping container provided by the 

laboratory by removing any expired shipping labels and tape. Fill one gallon 

resealable “freezer” bags half full with ice and expel the excess air before sealing 

the seams. Seal each of the ice bags into another one gallon resealable bag and 

adhere clear plastic tape along both sides of the top seam to ensure the seal 

remains closed. In general the cooler should have equal amounts of ice to water 

samples by weight. Therefore a laboratory supplied insulated shipping container 

with three water samples in 1 gallon cubitainers will require 20 pounds of ice in 

four to six double-bagged pouches. More detailed instructions on how to pack 
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Collection of Groundwater Samples 

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and ship the water samples to the laboratory are described in SOP EM-17, 

Packaging and Shipping of Samples. 

4.2 To prevent introducing turbidity into the sample, gently lower the bailer into the 

well water and collect the water sample from the top of the water column. 

Measure the aquifer characteristics at the time when the sample was collected and 

record data including the sample time in the field log book. 

4.3 Remove the cap and inflate the cubitainer by exhaling into the opening of the 

cubitainer. 

4.4 Fill the cubitainer from the top of the bailer while ensuring as little turbidity as 

possible is transferred from the bailer. Depending on the volume of water 

required for analysis, this step maybe repeated many times, therefore sampling 

only the turbidity free water in the top half of the bailer is prefered. 

4.5 Check the pH of the sample, adjust if necessary, and add the stabilizer. See 

Section 5 of this SOP for instructions. 

4.6 Collapse the cubitainer containing the stabilized sample to expel most of the air 

and screw on the cap securely. 

4.7 With the indelible marker label the sample container with a unique identifier that 

will allow the sample to be matched to its documentation. Sample labels provided 

by the lab will not adhere to the container if it is wet, so the unique identifier 

should also be written on the container. Seal the labeled container in a resealable 

plastic bag with the blue copy of the APHIS Form 2060 in another resealable 

plastic bag and expel the excess air. 

4.8 Place the sample in the cooler to keep it chilled until it can be transported from 

the field and placed in a freezer for storage until shipping. 

5. Adjusting pH and Stabilizing a Water Sample:

5.1 Measure and record the pH of the water using the pH meter or by dipping one end 

of a strip of pH paper into the sample. 

5.2 Stabilize the water sample by adding three sodium sulfate vials to the water 

sample container. Cap the sample container and mix by inverting the container 

until the sodium sulfate is dissolved. (NOTE: most pesticides used by PPQ are 
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Collection of Groundwater Samples 

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stable in acidic water. But check with CPHST when ordering supplies to 

determine that the acid and buffer specified herein are correct for the pesticide 

being sampled. If not, the laboratory will provide alternate materials and 

instructions for stabilizing the sample.)

5.4 If the pH of the water sample is greater than 5, add three to five drops of sulfuric 

acid to the sample. (NOTE: Sulfuric acid can cause chemical burns. Flush skin 

with water if exposure occurs. Reference the Material Safety Data Sheet provided 

by CPHST with this chemical.) Mix the acid and water, and measure the pH 

again with a fresh piece of pH paper or the pH meter. Repeat this step as until the 

pH of the water sample is about 5. 

5.5 Record the final pH measured in step 5.4. 

6. Documentation:

6.1 Complete an APHIS Form 2060 for each water sample. 

6.2 Record all observations in the field log book (see SOP EM-12, Using a Field Log 

Book) as described in Section 3.3 of this SOP. Describe difficulties encountered 

during the sample collection and potential sources of cross-contamination (i.e. 

poorly maintained monitoring well, surface water infiltration, nearby land-use 

practices). For groundwater samples, be sure to record the soil type, ground 

cover, and the topography of the treatment site. For all samples, include GPS 

coordinates and a sketch of the sample location and its relation to the treatment 

site and any sensitive site(s) in the vicinity. The sketch should include an 

approximate scale and a North arrow. Annotated aerial photographs, 

topographical maps, or photographs of the site in addition to the sketch are useful. 

6.3 Retain the pink copy of Form 2060 for your records and distribute the remaining 

copies as specified in the EMP.

7. Decontamination:

7.1 Before moving to another site all the equipment that came into contact with the 

well pipe and water must be cleaned to prevent the cross contamination of other 

groundwater monitoring wells. Disposable bailers and ropes should be 

decontaminated and reused until they become permanently soiled or have 

chemical odors. Bailers can be cleaned by repeatedly submerging the ball checkvalve in a bucket half full of a soapy solution. If needed scrub the outside of the 
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Collection of Groundwater Samples 

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bailer with a brush to remove residual material. Wash the parts of instruments 

that contact groundwater or the monitoring well pipe taking care not to submerge 

display screens or sensitive electronics. Rinse equipment with distilled water 

from a gallon jug or spray bottle. Catch the rinse water in a bucket and dispose of 

it in an appropriate manner. Allow the equipment to air dry or wipe the surfaces 

with paper towels. 

7.2 Follow the storage and equipment care instruction provided by the equipment 

manufacturer. Equipment, instruments, and supplies should be stored in sealable 

containers (e.g. large plastic storage bins) to prevent contact with common 

workplace or automotive chemicals.

8. Packaging and Shipping:

8.1 Package and ship the water samples to the laboratory as described in SOP EM-17, 

Packaging and Shipping of Samples.