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Pre-Drill/Post-Drill Water Sampling: What do my results mean?

Context Corner Edition 6 examines water sample results.

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By Carrie Crumpton, CNX Vice President of Environmental Strategy


As we initiate our Radical Transparency program to expand the information we are providing to the community on residential drinking water quality, both before and after drilling, we wanted to get some important information out about drinking water analysis. We are committed to helping residential water source owners to not only understand the condition of their drinking water supply, but also find resources to evaluate, rehabilitate, and find appropriate treatment solutions for pre-existing water quality challenges. So let’s explore some of these aspects in this edition of Context Corner, starting with:

Hey Carrie, why is an environmental service company contacting me to collect water samples?

As a gas operator, we utilize independent third-party consultants to collect residential drinking water samples (pre-drill samples) from nearby water supplies prior to the start of drilling a new gas well. ​

What is the purpose of collecting the water samples?

We do this to establish a baseline for water quality in an area ahead of development. We follow the specific state regulatory or technical guidance guidelines but are taking that several steps further by collecting multiple samples, up to a year in advance, to gain a detailed understanding of water quality in an area. Additionally, we also take post-drill water samples for approximately one year after drilling has been completed to ensure the drinking water source was not adversely impacted by our well development activities. You are being contacted so that you are aware of the legal requirements and to establish suitable, convenient times to come collect these samples. ​ ​

Where do you collect the samples from?

We are collecting water samples from private residential drinking water supplies (wells or springs utilized for drinking water, animal husbandry, or other residential use) within a state prescribed radius of a proposed well location (in Pennsylvania this is 2,500 feet, but varies state to state). ​

The samples will be collected directly at the water source. This means that the sample will be collected before it goes through any type of treatment system. ​ ​ ​ ​

When does this sampling take place?

The pre-drill water samples will be collected before the drilling of the well has started. In accordance with our new initiatives for our unconventional well development, we will endeavor to collect four pre-drill samples. Typically, we try to schedule the first pre-drill sample to be collected one year before drilling starts, with additional samples taken seasonally (around every three months). There will also be four post-drill samples taken. The first post-drill water sample will be collected after well development has been completed, and additional samples will be collected approximately every three months. ​

Why are you collecting multiple samples?

We’ve heard from our communities and residents that they want clear information related to human health and natural gas development. Drinking water quality is a critical concern, and CNX is committed to providing data where we can and helping residents understand the best practices and steps that can be taken to ensure supplies are meeting safe drinking water standards.

Additional samples provide more data. Additional data can provide a comprehensive picture as to the condition of your water supply. Of course, water quality from private water wells can vary significantly from area to area. Water-bearing zones can contain naturally occurring contaminants, bacteria, and naturally occurring methane. And these conditions can change throughout the year. There are normal fluctuations that occur in water supplies due to changing seasons and a variety of other factors, including the construction and maintenance of the water wells themselves, that can impact water quality. Additional samples help us capture that information and can provide insight into the various factors that could impact your water quality. ​ ​

So now for the most important question: How do I read my sample results? ​ What does this analysis show?

The quick answer is that by looking at your results and knowing how to compare those results to the applicable safe drinking water standards, you can identify if your water is okay to drink. It can show if your water supply may have some creepy critters or chemical contaminants in it.


We are talking about micro-organisms here. Specifically, we are talking about coliforms. ​ Coliforms in water are bacteria that are typically found in the environment and primarily in the feces of humans and animals. They may not cause illness by themselves, but they indicate that the water could be contaminated by harmful organisms (pathogens). Some types of coliforms, such as E. coli, can cause serious disease. Typically, total coliforms are found in water sources that have been influenced by surface water and in human or animal waste. Unfortunately, studies show that millions of people in rural areas in the U.S. do not have reliable access to safe drinking water and are often exposed to microbiological contaminants through improperly treated drinking water.

A recent nationwide analysis of U.S. Census and U.S. Environmental Protection Agency (EPA) Safe Drinking Water Act (SDWA) data identified Appalachia as one of the U.S. regions with the highest rates of water quality violations and numbers of households without complete plumbing1. Many states, including Pennsylvania, do not regulate private water wells, and standard best practices for construction, maintenance, and treatment aren’t always applied to ensure well installation isn’t contributing to water quality issues.

For drinking water, the EPA has recommended that ideally there should be no coliforms present in drinking water.


Certain elements or chemicals can sometimes be introduced into ground water through various surface activities. At certain levels, some of these chemical contaminants (such as iron and manganese) are not so much of a health concern, but instead more of a nuisance. Other chemical contaminants may have health effects if they are consumed for many years. ​

CNX follows the technical guidance provided by state regulatory agencies to develop the list of parameters we test to monitor for and protect against impacts from oil and gas operations. Your results will compare these parameters to the EPA list of the Maximum Contaminant Levels (MCLs) for drinking water. MCLs are basically the highest level of a contaminant that is recommended in drinking water. ​ ​

The full list of MCLs can be found here: Maximum Contaminant Level (MCL) chart, but to illustrate what this may look like, we have provided an example table below. If you are going to be drinking this water, you want your drinking water results to be below the MCLs. ​

You may notice that some of the chemical contaminants in your water sample results are not listed on the MCL chart. These chemical contaminants do not have MCLs, but they are listed because they may help an investigator to identify what has caused a change in a water supply. For example, conductivity is typically in the range of 0-1200, but if there is a significant increase in this number, that may indicate that there has been an influx of minerals into your water supply. If that’s the case, this may show up as an increase in the amount of sodium, total dissolved solids ("TDS"), and/or calcium, so we would begin analyzing those numbers as well. This additional data can be crucial in determining what is causing changes to a water supply and the effect of those changes on any health concerns such drinking water may pose. As mentioned earlier, additional data can provide a better picture as to the condition of your water well. ​ ​

After your water has been sampled, CNX will review your water sample results and send you a copy for your records. CNX compares your water sample results to the MCLs. Then the water sample results will be compared to previous samples (if any) that were taken from your water supply. CNX will be looking for any MCL exceedances or fluctuations between the samples. Exceedances and large fluctuations will be flagged and evaluated, and any exceedances and/or large fluctuations identified in post-drill results will initiate an investigation by the CNX Environmental Team and/or your state regulatory agency. As part of the investigation, CNX and/or your state regulatory agency may request to take additional samples. ​

Results from your water analysis may vary in appearance, depending on the laboratory. However, you can expect to receive a package of information with the lab results regardless of the lab utilized. These can be several pages in length and include a lot of information about your water quality and all the quality assurance and quality control (QA/QC) requirements the labs must follow. When reviewing your results, please note that there is a summary page that compares your results to the MCLs. An example is provided below and demonstrates how your results may be flagged if they exceed primary or secondary drinking water standards.

Results noted in bold on this page signify an exceedance of a drinking water limit and treatment measures should be taken.
Results noted in bold on this page signify an exceedance of a drinking water limit and treatment measures should be taken.

If you have any questions for CNX about your water sample results, you may E-mail directly to radicaltransparency@cnx.com and someone will respond to the request via communication of your indicated preference.

To further demonstrate our commitment to the communities where we live and work, the CNX Foundation plans on establishing a program to provide grant/funding opportunities to help community members more effectively evaluate the condition of their private water wells and water quality, and secure water well maintenance and treatment options. ​ As part of our Appalachia First vision and our commitment to making tangible, impactful, and local investment, we are committed to establishing resources to assist on this front. ​ Stay tuned for more information on this and other exciting community initiatives being led by the CNX Foundation.


Additional resources:


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A CNX news hub highlighting all aspects of our Appalachia First vision. Subscribe for insights on energy innovation, advocacy, and community engagement across the region.