Sampling is a Key to Better Onsite System Performance

As effluent regulations tighten and advanced systems take off as an onsite solution, you’ll need to sharpen your wastewater sampling skills.

Last month we discussed a requirement for some Iowa homeowners to provide samples or sample results to prove performance of their discharging onsite systems. In the future, sampling will be a more integral part of service calls, and there will be more emphasis on providing access in systems for monitoring and maintenance. Here are additional aspects of sampling that need to be considered.

First, a sample must be obtained from the right location in the system to provide the needed information. Sampling locations are usually at the inlet or outlet point of a treatment component.

These samples can be defined as influent (inlet) and effluent (outlet) samples.

FIND THE RIGHT LOCATION

For example, an influent sample to the aeration chamber of an ATU would be collected from the outlet of the trash tank. Even though this sample could be called an effluent sample following primary treatment in the trash tank, an effluent sample notation is generally reserved for a sample taken from the final component of the treatment train, so in this case the outlet of the ATU.

Influent samples are usually collected from the various internal components of the treatment train to determine the influent wastewater characteristics. This information aids the service provider in diagnosing, troubleshooting or mitigating the system.

Effluent samples collected following a final treatment component are often taken for the purpose of diagnostic evaluation or compliance monitoring.

The sample must be representative of the wastewater that needs to be sampled. It must be done using an analytical method that can be reproduced by another person. Documentation must be provided and the results must be accurate so sample analysis is defensible and the samples collected should be useful in meeting the objectives of the sampling or monitoring program.

TYPES OF SAMPLES

Two types of common samples for purposes of evaluating system performance are grab samples and composite samples. A grab sample is one taken from one point in time. It is important to understand what the sample is for and when to take the sample to be most helpful in troubleshooting. It may be necessary in some cases to take a series of samples over time to give the best picture of what is happening.

Composite samples are multiple samples taken at one point, then combined in one sample to give an average picture over the course of a day or some other time frame. Taking a sample from a trash tank ahead of an ATU — or a septic tank ahead of treatment trenches — would give you a composite sample collected over time from the source of the wastewater.

Some typical locations to determine performance include sampling from a pump tank to evaluate a pressure distribution system, a gravity system from the outlet of the septic tank, and proprietary units wherever the manufacturer recommends. As a service provider, many times you will be taking samples from the outlet of the device in question because this provides a view of the wastewater entering the next component.

CHECK THE LAB

It is important to know ahead of time where the sample will be analyzed and talk with lab staff about any special handling requirements, and the time frame needed to analyze and provide accurate results. Another reason is to make sure the test they run will give you the answer you need in the units you need. So talking with them about expected ranges in value and where the samples are coming from is very important. Select a lab that practices standard methods and is state-approved or accredited. Results from a nonaccredited lab may not be accepted by regulatory agencies or stand up if there is some type of court challenge.

How the sample is collected, stored and handled is important to ensure it provides the desired information. A number of different sampling tools include long-handled dippers or containers, Sludge Judges or dipsticks. Pay attention to the type of container necessary for the specific purpose of the sample. For example, different types of collecting devices work if you are pulling the sample from a tank, but sometimes a vacuum pump or some other type of device might be necessary if you are collecting the sample from a small sampling tee. No matter what the device, they must be clean to prevent cross contamination of samples. To avoid cross contamination, the device must be cleaned with distilled water between samples.

The type of sample container will be specific to the type of tests needed. For the most part, the container can be polyethylene or glass, but there are some exceptions. For example, samples that will be analyzed for fats, oils and grease (FOG) must be in a glass container because a strong preservative is used and plastic bottles will break down. Often, the lab will provide a container for the sample. Since many samples look similar, make sure they are clearly labeled with at least the sample number. Label the container ­— not the cap — with something that is waterproof. Lastly, make sure the container is watertight. You don’t want to lose the sample and you don’t want melted water in the ice chest to leak into the sample, diluting it.

SIZE OF SAMPLE

The amount of sample needed is dependent on the test or tests being performed. Typically, the rule of thumb is a quart. Check with your chosen laboratory to find out how much sample will be necessary. Some testing only requires a small amount of sample, while others need more. Typically, the more tests being run on the sample, the more volume will be needed. Also, the cleaner the sample, the more sample needed. To be on the safe side, fill the container given for sample collection.

These are just some of the aspects to consider if you need to take samples from systems you are maintaining or troubleshooting. We will revisit sampling in other articles in the future.



Discussion

Comments on this site are submitted by users and are not endorsed by nor do they reflect the views or opinions of COLE Publishing, Inc. Comments are moderated before being posted.