low fl ow sampling LOW FLOW SAMPLING -THE COMPLETE GUIDE
What is Low Flow Sampling? Collecting and testing water samples is all well and good when the water is on the surface, but what happens when you want to collect samples that are located underground?
With low fl ow groundwater sampling, you can accurately and effectively monitor water located in aquifers underground. The aim is to collect water samples underground accurately while ensuring no outside factors end up impacting the water, and in turn, the collected data.
These samples are then used by scientists, environmentalist agencies and similar outfi ts that can use data surrounding the quality of the water to inform others or make decisions. The practice for this method of sampling groundwater is meticulously implemented as not to disturb the sample and to give an accurate picture of the water’s overall quality.
Low fl ow sampling will monitor different aspects of the water in order to determine its overall
quality.Most often it will look for changes in pH levels, dissolved oxygen, electrical conductivity and temperature.
However, some groundwater samples may look into other characteristics of water quality. This is all done with a set of specialised water quality measuring equipment, of which there are a number of variations available.
The Difference Between High Flow and Low Flow Sampling
The difference between high fl ow and low fl ow sampling can be seen in the equipment used and the rate at which water is extracted from the ground. These differences are related as different equipment is needed to get water out of the ground quickly.
High fl ow sampling will use bailers to extract water from the ground at a faster rate. This method purges signifi cant amounts of water compared to low fl ow sampling. Low fl ow sampling will analyse the water quality by obtaining smaller amounts of water at a rate below 500 milliliters per minute. It does this using a probe that captures the water and uses sensors to take readings.
The criticism of high fl ow sampling revolves mostlyaround its ability to contaminate the samples and reduce the accuracy of the sample readings. The higher pumping rates cause a mixing of the water with other chemicals and materials, making the likelihood that the sample is not an accurate representation of the groundwater.
The wellhead of the bailer used in high fl ow sampling may also cause contamination and even aeration of the sample may occur. Other criticisms surround the amount of water wasted when extracting samples and the potential for this to cause issues for wildlife and nearby residents.
As a result, low fl ow sampling has overtaken the uses of high fl ow sampling. In contrast to high fl ow sampling, it boasts many advantages, including:
AP-2000
Equipment Necessary for Low Flow Sampling
Whatever you’re measuring or testing, your low fl ow sampling project will involve purging the water underground ata steady rate. This is done to ensure there is less disturbance to the site during the purging procedure, as conducting the process too quickly could negatively impact sample results.
To purge the water, you will need a low fl ow sampling pump. There are many different types of pumps on the market, so you will need to make sure you select the one that best fi ts your needs.
For reference, the size of your borehole will have a large impact on the type of pump you will need. For example, Inertial pumps are suitable for boreholes that are 10mm in diameter or above.
While the size of the borehole will be your main consideration, there are other factors that may infl uence your decision. Some pumps are fully automatic, while others require manual pumping throughout the purging process. The costs of various pumps will also likely be an important consideration, so be sure to explore all your options before settling on your chosen low fl ow sampling pump.
Purged water is not much help unless you have the equipment necessary to conduct your required tests on the samples, which is why a water quality measurement device is so important.
Leveline IET September / Ocotber 2019
www.envirotech-online.com Groundwater Well
What you intend to measure will play a large role in which water quality measurement device you select, although many devices are able to measure multiple parameters at once to help streamline the process.
Our very own AP range of devices, including the AP-2000, are able to monitor all of the most common testing parameters, with the option to attach additional sensors as needed.
Careful monitoring of the water being purged and collected is vital for effective low fl ow sampling. To help measure the drawdown and levels of the water underground, you will need a form of water level measurement device.
The most simple to use of these devices is a Heron water level meter. They can be used to easily and quickly measure water levels and is available in both static mode, which is used for measuring the depth of water, as well as drawdown mode, which is more suited for low fl ow sampling.
Alternatively, Leveline loggers allow users to collect water level data automatically and store the data in its internal memory. Made from titanium and with a 500,000 data point memory and 10 year battery life, the Leveline range of water level loggers are moresuited for longer term monitoring but are still suitable for shorter term projects as well.
Finally, you will need tubing to help connect all the necessary parts
• Purging of less water so less is wasted • No wastwater is left behind
• Does not empty wells and cause soil to mobilise • Requires less time to complete.
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