This page at Level 2 elaborates on sampling and analysis methods outlined in Level 1.

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2.3 Sampling and analysis (Level 2)

2.3.1 Sampling from monitor wells

Note that none of the target analytes are volatile at environmental concentrations after application thus we are not concerned about loss of vapors during sampling.

We use battery-powered peristaltic pumps to draw water from wells. We use polyethylene and silicone hoses with thick walls so that suction does not collapse the hose. The polyethylene ensures that there is minimal sorption of any dissolved chemicals inside the hose during sampling; the short silicone hose segment endures thousands of pinches by the peristaltic pump. A few field measurements (using a Hanna electronic meter and a water depth sounder) are done while sampling from a monitor well.

A ==> monitor wells sampling HowTo page (Level 3) explains how to operate the pumps and make measurements in the field.

We begin pumping to purge the well to make sure that we withdraw groundwater just entering the well being sampled, not water that has been sitting in the well for a while. (Water in the well is much more open to the atmosphere than water in the aquifer or soil, thus the chemistry may change, and the inside surface of the well is different from what water encounters in gravel, sand or soil thus the microbial community may differ.) We pump the well while measuring temperature and specific conductance in an overflowing cup at the pump outlet hose. Stability of these parameters is a clue about fresh groundwater entry.

It is important to clean hoses between samples so that there is no carryover of liquid or particulates from the prior sampling point to the current sampling point. We clean the inside of the hose by pumping through at least a half gallon of deionized water, and we wipe down the outside of the hose with a clean paper towel moistened with deionized water. We store the hoses in bags when not attached to the pump, and we change bags between trips. As another way of ensuring that the current sample is not influenced by prior uses of the hose or the cleaning water, the purging process for the current well pumps through plenty of current well water.

While most of the wells sampled in this way were installed by Cornell, in a few cases we use this same equipment and approach with a well owned by the cooperator that does not have its own pump.

2.3.2 Sampling from owner wells

We draw samples from taps in most cases. We allow the owner’s pump to run for a few minutes to make sure that we are getting fresh groundwater rather than water sitting in plumbing for days or longer. An owner well that has been used actively in recent days does not need much of this kind of purging, one that has been idle needs longer.

The usual field measurements are done while sampling from an owner well, except that depth to groundwater can usually not be measured and we don’t measure conductance and temperature while letting the pump run before filling the sample containers.

There is a ==> specific HowTo page (Level 3) for sampling wells that have their own pumps.

2.3.3 Sampling from groundwater-fed ponds

A pond may be sampled by dipping in a container or using a peristaltic pump and hose. When a hose is used, it must be cleaned inside and out with deionized water after each sample, as in groundwater well sampling. Purging is not relevant. We rinse the container with sample water before filling it.

The usual electrochemical field measurements are done while sampling from a pond.

There is a ==> specific HowTo page for technical details of pond sampling.

2.3.4. Sampling from lakes

Most lake sampling is done with a transparent Kemmerer sampling cylinder that allows sampling from a specific depth range. This device can also be used for sampling deep inlets or outlets. Inlets and outlets can also be sampled with a peristaltic pump and hose, as for ponds. The Kemmerer is used from a boat, a long dock, or a bridge.

Volunteers have portable meters for measurements in field. Cornell samplers use the usual Hanna meters.

There is a ==> specific HowTo page for details applicable to Cornell SWL personnel’s sampling. (CSLAP sampling reference).

2.3.5. Sample preservation until analysis

The chemical content of a sample can change between when the sample is collected and when it is analyzed, thus we must preserve samples following lab guidance and professional standards. The NYSDEC pesticide lab has always recommended freezing and has confirmed the longevity of known pesticide concentrations for various durations of frozen storage. Until freezing a day or two after the samples are collected, the samples are chilled in insulated containers or refrigerators. The lake volunteers use their home freezers, and Cornell SWL has commercial refrigerator and freezers.

Aliquots (small sub-samples) for analytical work should be made before first freezing, or frozen samples can be thawed to make them later. We strive to thaw a minimum number of times and only for as long as needed to make the aliquots. We make aliquots for cations before first freezing, since they can be stored in a refrigerator instead of frozen. Since the samples arrive a few at a time and some analyses are months away, we sometimes defer making the rest of the aliquots (for alkalinity, anions, and pesticides) until the first of these analytical procedures, or shipment to the NYSDEC lab, is imminent. In 2024 we began to make all aliquots upon first arrival of Cornell-collected samples at Cornell, thus avoiding a first thawing of a field container. (Lake samples taken by volunteers arrive frozen thus do require a single thawing.)

The detailed cation aliquot acidification protocol is in a ==> HowTo page (Level 3), and sample storage is in another ==> HowTo page (Level 3).

2.3.6. NYSDEC lab analysis: pesticides and breakdown products

The NYSDEC lab routinely analyzes many samples for the State’s pesticide regulatory and enforcement program, for many different pesticides. The lab is very well equipped and staff highly experienced, and the data quality are the most reliable of any measurements in the project.

Many of the lab’s tests on water samples are performed with a liquid chromatograph coupled with a tandem mass spectrometer (Deeper). Analytes are tested in groups having common preparation steps. The machine can typically determine concentrations down to 0.1 or 0.01 micrograms per liter (μg/L) reliably in water samples, the level depending on the analyte and the sample batch.

2.3.7 Field measurements: water level

We use Solinst “sounders” to measure where the water table is below the rim of the Cornell monitor well, and when possible an owner well.

Model 102 Model 102 mini
Solinst model 102 sounder Solinst model 102 mini sounder

These meters work by making a sound and flashing a LED when a weighted probe tip on their cable touches water. The user raises and lowers the probe in the well to zoom in on where the sound first begins. The cable is graduated in millimeters above the probe tip, and holding it against the rim of the well establishes how far down the probe tip is below the rim.

We call the well rim (without well cap) elevation the datum, a reference point. The distance of the datum above or below the land surface can be measured, allowing converting the depth-below-rim value to depth-below land surface.

A monitor wells sampling HowTo page (Level 3) covers operation of these devices.

2.3.8. Field measurements: chemical and physical

We measure pH, temperature, and specific electrical conductance (EC) using handheld meters by Hanna Instruments.

Low range (0-3999 μS/cm) High range (>4 mS/cm)
Model 98129 Model 98130 Hanna 98129 or 98130 meter picture

These meter models are identical except for the 98129 reporting in microsiemens (μS/cm), topping out at 3999 μS, and the 98130 reports in millisiemens (mS/cm). We have one site whose EC is typically above the maximum 3999 value of the 98129, sometimes above 5 mS/cm on the 98130. These meters report specific conductance which is expressed as if the water temperature were 25 degrees C. (Conductance increases with temperature.)

We immerse the meter in a cup containing water drawn from the well, pond, or lake. While purging a well, we let water flow through the cup with the meter immersed and observe changes in the quality of water being brought up. When the measurements stabilize, particularly temperature and specific conductance, that is an indicator that the pumping is drawing in fresh groundwater instead of water that has been sitting in the casing for a while.

While we do measure temperature of the sample, we do not consider the data to be representative because sun or air on the surface may raise or lower the temperature of a sampling hose compared to the temperature of the water being tapped. Also for owner wells there can be influences on temperature caused by piping and pumping that make the sample water temperature different from groundwater temperature. Fortunately, the pH and specific conductance measurements are automatically adjusted from whatever temperature occurs in the sample water, always referencing to a conctant temperature.

A detailed ==> HowTo page (Level 3) covers meter operation.

2.3.9 Cornell lab measurements: anions, alkalinity, cations

These secondary analyses all provide context for the pesticide measurements.

Anions

We measure four anions: nitrate NO3-, sulfate SO4-2, phosphate PO4-2, and chloride CL- using an ion chromatograph (IC). Cornell SWL staff operate the Dionex IC as guests at a USDA lab facility on the Cornell Ithaca campus.

This is covered in a ==> HowTo page (Level 3).

Alkalinity

Combined with pH, alkalinity tells us carbonate (CO3-2) and bicarbonate (HCO3-) anion concentration.

We measure alkalinity with a handheld Hanna HI775 freshwater alkalinity meter, using a ~12 mL aliquot. We measure lab pH in the aliquot before transferring the liquid into a vial for the alkalinity meter. Hanna provides a calibration checking liquid. The full procedure is in a HowTo.

These measurements were discontinued after 2023 due to limited utility.

Cations

An analytical chemist colleague at the same USDA lab on the Cornell campus where we do anion testing analyzes samples for a range of cations such as sodium and calcium. The procedure is described in a ==> HowTo page (Level 3).

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Last updated 2025-01-07. sp17 AT cornell.edu