Field Equipment for Sample Collection and Analysis

Field Equipment – Sample Collection and Analysis

Field Teams

Field sampling teams make the rounds to each sampling site on a regular basis (weekly, biweekly,

monthly) and collect one or two water samples. Often one sample is preserved with an acid

addition and the other is refrigerated or kept on ice. Additionally, while at the site, team mem-bers

often measure temperature, dissolved oxygen, pH, electrical conductivity and more using a

multi-probe apparatus. They may also measure water depth at a reference site, so that a rating

curve can be used to calculate flow. Depth is also a parameter that can be simultaneously mea-sured

by some multi-probe instruments.

Automated Samplers

Automated samplers pull up water from a stream or lake and fill a sample container at regular

intervals that are determined either by time ("time-weighted") or by flow volumes ("flow-weighted").

ISCO manufactures automated sampling devices which can be managed manually or

programmed to start collecting samples when flow rates increase (e.g., during "flushing" events).

This latter feature is especially important where the role of storms needs to be determined,

because runoff after long dry periods is generally more polluted than runoff later in the event.

Some units are refrigerated so microbes don’t affect the quality of the sample before analysis.

Often the combination of automated samplers and continuous monitoring equipment can be used

to advantage in the field (see case study from Georgia, above).

Continuous Monitoring in the Field

Equipment for these applications is improving rapidly. Selecting monitoring equipment is an

investment that needs to provide credible, reliable data for the long term. Overall ruggedness is

very important. In addition, ask yourself or the equipment manufacturer’s sales representative

these questions:

1. How stable are the sampling probes? Does the calibration "drift" up or down over

time, so they have to be calibrated frequently? For any given multi-probe system, the

parameter that drifts most rapidly determines the maximum allowable time between field

visits for recalibration.

2. How sensitive is the probe to the parameter? Many waters have low concentrations of

potential pollutants during all or part of the year, but the concentrations are still

important for determining loads. Some chemical probes are stable over time but cannot

accurately detect the low concentrations necessary for continuous monitoring.

3. Which sensors need to be self-cleaning to yield accurate reliable results? For example,

self-cleaning probes and Rapid-Pulse DO technology can reduce the need for

maintenance. That allows less frequent visits to the sites, lowers labor costs and

increases reliability.

4. Is the equipment energy-intensive? Equipment that requires stirrers or auxiliary

pumps typically demands battery packs that make the instruments more unwieldy to

carry, and more expensive. Having to change batteries frequently can require too many

visits to the sample site for maintenance – a costly practice.

5. How can I collect, manage and manipulate the data? If values are collected and stored

every 15 minutes to one hour, this produces huge quantities of data. The data storage and

data analysis software must be efficient, user-friendly, and allow rapid interpretation of

results.

Common parameters that meet Criteria 1 and 2 above include pH, temperature, electrical conduc-tivity/

salinity, and dissolved oxygen. More recently, stable probes have been developed for

turbidity, chlorophyll, ammonium and nitrate. In some cases, such as ammonium, the chemical

sensitivity may be too poor for use in many natural waters, but the probes work well in sampling

applications in enriched systems like wastewater or industrial discharge. However, with rapid

improvements in technology, more parameters will be refined to the point where Criteria 1 and 2

will be met.