Stormwater E-magazine, September 2008 edition
Accountability in comprehensive sampling
By Lanse Norris
“Water is the one substance from which the earth can conceal nothing; it sucks out its innermost secrets and brings them to our very lips.”
—Jean Giraudoux
What Comprises Comprehensive Sampling?
Since the early ’70s, Cobb County, GA’s municipal in-stream monitoring efforts have evolved into a program that conducts sampling across 21 sub-watersheds at 93 chemical sites per quarter, 24 macroinvertebrate sites per year, 24 habitat assessment sites biannually, and 24 fish sites every five years. Sites were selected considering land use, proximity to industries, and stream confluences of representative reaches.
The chemical data generate a water quality index (WQI) score derived from comparing the value for any parameter of interest with values for the same available parameter from sampling results recorded throughout the Atlanta region. The index itself is a value between 0.00 and 1.00, with 0.00 representing the best value in the database for each parameter. Table 1 shows the Cobb Stream Monitoring Program chemical data for an actual site with each parameter and applicable scores. The aggregate WQI for the site is calculated as the numeric average of the available WQIs shown.
Biological sampling produces macroinvertebrate and fish data, which are scored on an index of biotic integrity (IBI). Habitat assessments are scored on a standardized form following state of Georgia Environmental Protection Division (EPD) protocol.
A Cobb County Water System Watershed Monitoring Program Annual Report is published containing all of the chemical, biological, and habitat data collected; many permits addressing surface waters impacted by wastewater discharge, stormwater, point and non-point sources are maintained by the data. In the report, narratives for each site summarize a year’s worth of changes to the stream channel, riparian zone, and watershed itself as personnel wade upstream and drive through the watershed on the way to each site.
How Comprehensive Is It?
Ions in the Stream. Chemical monitoring parameters and methods are long-established water-quality standards prescribed by the approved 20th edition of Standard Methods for the Examination of Water and Wastewater (Clesceri et al. 1998) and are implicit in environmental regulatory sampling like National Pollutant Discharge Elimination System (NPDES) wet-weather ambient trend monitoring. Cobb County Stream Monitoring personnel take extra measures to ensure accuracy and integrity. For example, rather than rely on precarious dissolved oxygen (DO) meter readings, Winkler titration method dissolved oxygen samples are “fixed” in the field for more consistent and accurate analysis by Cobb’s Georgia Association of Water Professionals certified wastewater laboratory. Quality-control samples are collected at the first site for a given stream, and all samples are collected mid-depth in representative flow when possible and preserved in the field before transportation to the laboratory. Field notes supporting chemical sample characteristics are made concerning weather, degree of flow, color, odor, and turbidity.
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