HowTo – Sampling from monitor wells [95%]

Priority: high
Updating: mature

This HowTo applies when we bring our own pump and hose to sample from a monitor well or owner well that does not contain its own pump. Note that monitor wells are only at categorical sites, not long term sites.

Change log:

When	Who	Comment
2021 02 27	Sp17	First version derived from memory of monitor wells in Catskills. (There is also a written SOP from that project.)
2021 08 07	Sp17	Beginning to flesh this out. Most effort on field blanks, more detail about pumps and washing between samples.
2021 09 29	Sp17	Much progress toward a reviewable version.
2021 10 01	Sp17	Reformatted toward export in DOCX.
2021 10 14	Sp17	We have a working Solinst 102 well sounder, refine the coverage here about it. Also some additional submersible pump options.
2022 03 21	Sp17	Narrowed to two specific sampling pumps.
2022 04 06	Sp17	Cumulative update for the Geotech bladder pump.
2022 05 17	Sp17	Cumulative update for the Masterflex peristaltic pumps, prior to first sampling trips this week.
2022 08 18	Sp17	Cumulative update based on experience with sampling several sites.
2022 09 28	Sp17	Cumulative update based on experience with sampling 20 monitor wells.
2023 04 26	Sp17	Cumulative update based on 1-2 rounds of sampling per every monitor well.
2023 05 24	Sp17	Add that we sample from certain owner wells in the same way as monitor wells.
2023 06 21	Sp17	convert to Markdown.

1. Objectives

Obtain representative samples from monitor wells or owner wells not having pumps.
Obtain field measurements of well water.
Record field data.

2. Quality assurance considerations unique to monitor wells

Collect samples representing the ground water system outside the well (purging), not water that has been in the well bore for a while.
Do not cross-contaminate between sites or consecutive samples during the trip.
Collect occasional trip field blanks to use in quality control evaluation.

3. Equipment needed

(See also the HowTo: Sampling road trips that covers equipment used across multiple sites of different kinds. That list is best for loading checklist, this is more detailed.)
Peristaltic or submersible pumps. Submersible needed for wells deeper than about 20 feet.
- Our Geotech air powered submersible bladder pump can lift to 200 ft. The air compressor runs off 12V battery.
- We have two peristaltic pumps: Masterflex L/S® Portable Sampling Pump; 115/230 VAC from Cole-Parmer. These pump at a higher rate than the bladder pump and can be used to about 20 feet of depth. These are charged with a 12VDC power brick.
Sampling hoses. These must be washed with deionized water before the trip (best when returning from prior trip) and held in new or rinsed ziplock bags until used in the field.
Meter to measure depth from well datum to groundwater. (“Sounder”).
- We have a Solinst model 102 meter with a 30m cable. It has marked graduations every centimeter and unmarked graduations at millimeters.
- There are other means to measure water levels in a well than the Solinst sounder. Please use a method accurate to the nearest 3 cm.
Rinsable open top container to take field measurements.
Cleaned 5 gallon paint bucket to carry deionized water for washing. With lids. Dedicated. Can also use plastic gallon jugs.
Container to carry deionized water to draw field blanks from (if doing field blank on this trip). Dedicated. Gallon jug from distilled water or spring water is OK for this.
Recommended: Tarps to lay clean equipment (submersible pump, hoses) on in the field. Bring several on the trip. These are sections of painters’ plastic dropcloths. Wash them with water and carry folded in ziplock bags after each trip. Rinse during the trip if they become soiled.

4. Expendable supplies needed

(See also the HowTo: Sampling road trips that covers supplies used across multiple sites of different kinds.)
Deionized washwater in containers dedicated to deionized or distilled water. Volume of water to bring depends on number of monitor wells to be visited per trip.
Extra deionized water in a separate container for drawing field blanks, when used. After the last field blank of a trip is drawn the remainder may be used for washwater.

5. First step onsite: Purging the monitor well

(Note: we are not sampling for volatiles. Thus we take no precautions against losing vapor.)

Move supplies and equipment from vehicle to sampling location

We recommend that a washable plastic tarp, such as used by painters, be used to hold field equipment, hoses, and sample containers to keep from soiling them. This is set up before purging begins.

Begin a paper field log entry for the sample and location. Date and time.
The first measurement is depth to water level, before purging begins. Also measure the total depth of the well and the height of the datum above ground periodically; these should be fairly stable.
We measure pH, temp, conductance periodically while purging. The pump expels water into a small measuring container which overflows to waste.
Measure parameters continuously in the measuring container. (Rinse this container with deionized water before the trip and optionally after each sample is completed; rinse with the sample water initially. This can be the same container used for measuring at wells with embedded pumps.) Record values with times (at least the conductance) every 2 minutes or so and evaluate stability.
- Note that temperature will be affected by the hose temperature, measurement container temperature, and sunlight. The meter compensates its pH and conductance values for temperature thus a temperature unrepresentative of groundwater is OK for these parameters.
Purging is completed when the conductance and optionally pH parameter values are stable in consecutive readings. Stability indicates that water standing in the well casing has been replaced by nearby groundwater. Highlight the final values in logbook to use as representative of the sample results for these parameters.
We should pump out up to three casing volumes of water. This can be calculated as
- (depth of well bottom below datum - depth of water surface below datum as measured before purging)*pi*well radius squared*3.14159 = volume to draw.
- Terminate purging and proceed to sample drawing if the meter readings do not stabilize by three casing volumes.
To speed field activity, a table could be prepared for each well indicating how much volume is needed as a function of the depth from datum to water surface.

a. Field measurement values: temperature (optional), specific conductance, pH, depth from datum to water level.

Water level is the initial value before purging, in case the well is slow to refill.
The others are the final values at the end of purging.
These are recorded in the field logbook, including the times of last measurement to the nearest 5 minutes. Temperature data are unreliable because of hose and meteorology effects, thus a low priority.

Special case: If a well refills too slowly to draw a complete sample within one hour due to low transmissivity, such as from a partially clogged screen or very low water table, it is fine to dewater it completely and come back the following day to draw the sample. In such case, make fresh measurements with meter during the sampling time, either before or after drawing the sample. Make provision for overnight revisits in trip scheduling.

Special case: We have a spring, a tile access box, and a large-diameter owner well at three sites. It is impossible to purge these because of the large volume in the well. We let it suffice that we want to draw enough water from these to flush the sampling hose, and stabilize the meter readings.

6. Second step onsite: Drawing the sample

Labels should be on containers before filling to ensure that they adhere; ideally attach them before the trip. Remove caps and protect from contamination. Make any manual changes to label, especially the date and time of sampling, before label gets wet; use a pen compatible with the waterproof laser label type so that wetting the container does not wash off the markings. Uniball Jetstream pens recommended.
For each container of the sample:
- With the pump still running after purging, put the outflow hose into sample container and fill partly, cap, shake then dump.
- Fill container, cap. Allow 10% air space for expansion during freezing.
Make a field log entry of the ending time of the sample and any special conditions existing at the location and time of the sample.
Put containers into ice chest in vehicle. Generally the bottles of a sample should be bagged together in a ziplock.

7. Third step onsite: Field cleaning of monitor well sampling apparatus

This is done between consecutive sites to avoid cross contamination of samples; note that since we are passing a large volume of well purge water through a hose before drawing a sample, the hoses are not cleaned between samples at the same site.

pH/temperature/conductance meter: Rinse probe and cable with deionized water; spray bottle, or dump a little from a jug.
Submersible pump and hose: Wash and brush exteriors with potable water, then pump deionized wash water at least two hose + bladder volumes.
Peristaltic pump and hose: Pump does not require cleaning. After each use of a given hose, pump a half gallon of deionized wash water through hose, and wipe exterior of the intake hose with paper towel moistened with deionized water.
Depth to water meter (well sounder). Wipe able with paper towel moistened with deionized water.
Clean while equipment is still wet from prior sample. Do not allow liquid inside the hose to evaporate to dryness before cleaning.
Clean hose carrying bags with deionized water before and optionally during trip: put some water in the bag, zip closed, shake, dump.
ToDo: check against the USGS field methods recommendations for organics sampling.

Note: If deionized cleaning water is exhausted during a trip, commercial distilled water may be purchased at a supermarket. Cost is on the order of $1 per gallon.

8. Optional field blank

The objective is to determine if there is carryover pesticide content in a sampling pump or hose following standard rinsing between samples.

In general the field blank is done at a site after the last field sample from a site and after the apparatus (including hoses) has been field cleaned following the last sample. We operate the sampling pump using as the source some Cornell deionized water. There is a dedicated container of deionized water to draw from, of a shape to fit the submersible pump and its short intake hose. (Peristaltic pump simply immerses the tip of a longer hose thus container can be shallow.)

We capture the sample as usual (rinsing container as specified above) into accustomed containers. The blank uses the same container type and is preserved along with the field samples from the same trip, i.e. chilled on ice while on the road and frozen in lab, thawed to make aliquots, etc. Record date and time of collection on the container labels and in the field logbook.

There can be a companion “lab blank” of only Cornell deionized water from tap into a sample container. This should be made from the blank water carrier just before the field blank is drawn, so that it may be compared against the field blank as an indicator of incomplete washing between samples.

There is no need to clean the interior of the apparatus used for the field blank after the blank because you have just pumped deionized water through it, same as the washwater. Do a supplemental cleaning of the exterior of hose and pump if the hose was on grass or soil – you want the pump and hose ready for the next actual sample.

9. Field log entries (per well per visit)

This will use a paper field logbook. The paper logbook is confidential so it can contain exact sites visited.

Sample site and well ID. Date. Who is sampling.

Initial water level below well datum. Date and time of measurement.

Purge beginning time. Table of readings of pH/temperature/conductance as purging continues. Indication of why purging stopped (either stable readings, 3 casing volumes exceeded, or completely dewatered a slow refilling well).

Sample time. Use the end of the last bottle filling.

Any exceptional site conditions, for example disturbances of the well cap or seal.

Any repair or other follow-up needs.

Details of field blank if collected: location, date, time, meter readings.

References: USGS field methods handbook. National Field Manual for the Collection of Water-Quality Data (NFM) (usgs.gov)