Collecting Water Quality Samples

Methodology and Parameters

Why do we collect water quality (“WQ”) samples? There are a variety of reasons, such as, to identify the baseline quality of water, determine what type of treatment may be needed for the intended uses, monitor possible contaminants, and track changes over time to name a few.

At Lytle Water Solutions, LLC we follow standard field protocols that follows procedures established by the U.S. Environmental Protection Agency. Of utmost importance in collecting groundwater samples is that the samples collected are representative of the groundwater aquifer and that the samples are collected, stored, and delivered to the analytical laboratory in a manner to not contaminate the samples.

Ground water sampling includes the following procedures:

First, is the initial cleaning of the sampling equipment. Bailers and pumps are disassembled, cleaned, and rinsed with either de-ionized or steam-distilled water and reassembled. This decontamination procedure also needs to be followed between sampling of subsequent wells.

Another important consideration, if multiple wells are being sampled and the data are being collected to evaluate potential contamination, the well sampling should be sequenced such that the least contaminated wells are sampled first and the most contaminated wells are sampled last. In that way, with that sequencing and the decontamination procedures, it minimizes the potential for cross-contamination.

Next, the water level is measured to establish the casing volume. A water level meter is used to measure from the top of the casing to the bottom of the well and to the water level, which provides both a total depth and a static water level in the well. The water column from the static water level to the total depth of the well, coupled with the casing diameter, is used to provide the casing volume. The casing volume is used as an initial measure of the minimum volume of water that needs to be purged to obtain a representative water quality sample.

To make this evaluation, the casing volume is multiplied by three and a constant that is dependent on the casing diameter to provide the required minimum purge volume. An example of this equation based on 2-inch well casing is provided below. The purge volume is pumped from the well to provide a representative sample of groundwater from the saturated zone. It is important to remove any stagnant water from the casing, as well as the gravel pack surrounding the well, to obtain representative results from the water sample.

(37.1 ft-23.1 ft)x3x0.16 gallons/ft (for 2-inch casing)= 6.72 gallons to be purged

Water quality meter reading.

Purging

Collected, labeled, water quality samples.

While the well is being purged a water quality meter is used to monitor field parameters to evaluate when the parameters have stabilized, which is an indication that aquifer water is being pumped. These parameters can include pH, specific conductance, temperature, oxidation-reduction potential, and dissolved oxygen. At least four consistent readings (<10% variation) for a minimum of two casing volumes is typically used as an indicator that the parameters have stabilized, and the well is ready to be sampled. If the field water quality parameters have not stabilized after pumping a minimum of 3 casing volumes, then pumping should continue until these parameters do stabilize.

Once the field parameters have stabilized, it is important not to contaminate the samples as they are placed into containers for storage and shipment to the laboratory. Nitrile gloves are required safety equipment for sampling to reduce the possibility of contamination of the sample and your skin. If multiple wells are being sampled, a fresh pair of gloves are used for each well to prevent cross-contamination problems. Dedicated sampling bottles are provided by the laboratory conducting the analyses for the sample collection, and the number and types of bottles will vary depending on the parameters being analyzed. Some may contain preservatives.

The bottles are labeled in the field with the project name and number, well name, date, time collected, and initials of the sampler. Similarly, a Chain of Custody (“COC”) form is provided by the laboratory and must be filled out accurately by the sampler prior to submitting the samples. The COC is maintained in the possession of the sampler until the samples are delivered to the laboratory.

Once collected, the bottles are placed in a dedicated cooler with ice to preserve the specimen until it reaches the laboratory. The samples must arrive at the lab within the required holding time, which varies based on the analytical tests to be performed, from the sampling time to prevent sample degradation. Upon arrival, the cooler temperature will be checked by the laboratory technician to ensure proper preservation of the samples. The COC will be checked, and both the sampler and the lab technician will sign the form to transfer custody of the samples to the lab. The lab will analyze the samples and provide results once they all are available.

A future blog will discuss some of the common means to evaluate water quality results. If you have the need to develop a water quality monitoring program or need assistance with water quality sampling, please contact LWS (303-350-4090, lws@lytlewater.com) or email any of our team members listed below.

Dan Rowe, E.I. dan@lytlewater.com

Marlena McConville marlena@lytlewater.com

Ben Bader ben@lytlewater.com

Bruce Lytle, P.E. bruce@lytlewater.com