Environment Services technician Tanner Stein using the low flow to collect water samples from a ground water monitoring well in the Garrison Petawawa RTA. (Photo by N.McGregor)
A day in the life of Garrison Petawawa’s Environmental Technician Part 2: Field Work
Posted on Thursday, July 27, 2017
Last week began with a description of the preparation and planning prior to commencing environmental field sampling. This article will describe a typical day in the field while conducting groundwater sampling.
The sampling day begins after all the equipment and sample bottles have been loaded into the vehicle. The first stop is Range Control to confirm that the area that is being sampled that day is still clear of any military training activities, then off to the site to start sampling. The number of sampling locations scheduled for that day is based on the location, depths of the monitoring well and anticipated purge volumes.
Prior to sampling groundwater monitoring wells (MWs) it is important to review the MW installation log (screened interval, estimated depth of the groundwater) and reference the program to confirm what samples need to be collected. For continuity, where possible, all MWs are purged using a low flow method with a peristaltic pump. Low flow sampling supports minimal mixing of sediments from the bottom of the well and is recognized as a more accurate way of obtaining representative data. The objective of the low flow method is to remove water at a rate of less than 0.1 litre per minute as to not induce a drawdown in the well. Occasionally the ground water depth is too deep for this method and a manual hand purge is required.
After referencing the MW log and confirming the method of purging, a ground sheet is set out adjacent to the MW to minimize contact of the equipment with any potential contaminants on the ground surface. The MW cap is removed and, using a reel type measuring tape with a water indicator probe attached to the end, the water level and depth to bottom of the MW is measured. These measurements are used to calculate the volume of water to be removed from the well before sampling can take place. During the MW purging a multi-parameter meter (YSI) is used to record water quality variables such as pH, conductivity, dissolved oxygen and redox potential. Once these variables are stable within defined limits, sampling may occur.
Sample bottles are labelled and filled according to the parameter they are collected for. They are placed into coolers containing ice packs in the field before transferring into a fridge at the end of the day to await shipment. Field duplicates are collected at a specified number to meet quality assurance and control measures. All samples are then listed on a chain of custody, indicating the analysis required, which is shipped with the samples to the laboratory.
Field work typically consists of long days outside in all types of weather and the ability to adapt to interesting challenges that can arise. Come back next week to read a full description of what a monitoring well is and how it is installed.