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USGS scientists deploy SPMD and POCIS samplers to collect waterborne contaminants in Manoa Stream on Oahu, Hawaii.


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Chapter A6. Field Measurements

National Field Manual for the Collection of Water-Quality Data (TWRI Book 9)

6.6 Alkalinity and Acid Neutralizing Capacity

Revised By S.A. Rounds

This section of Chapter 6 is available as a pdf file:
6.6 Alkalinity and Acid Neutralizing Capacity (Version 4, dated 9/2012) [665 KB PDF]

Download a copy of Adobe Acrobat Reader for free.

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USGS Internal Note: Water-quality field forms, including PCFF, are available from the Field Forms page on the Office of Water Quality USGS-only Web site.


Alkalinity (determined on a filtered sample) and Acid Neutralizing Capacity (ANC) (determined on a whole-water sample) are measures of the ability of a water sample to neutralize strong acid. Alkalinity and ANC provide information on the suitability of water for uses such as irrigation, determining the efficiency of wastewater processes, determining the presence of contamination by anthropogenic wastes, and maintaining ecosystem health. In addition, alkalinity is used to gain insights on the chemical evolution of an aqueous system. This section of the National Field Manual (NFM) describes the USGS field protocols for alkalinity/ANC determination using either the inflection-point or Gran function plot methods, including calculation of carbonate species, and provides guidance on equipment selection.


Alkalinity and acid neutralizing capacity

6.6.1 Equipment and supplies

6.6.1.A Maintenance, cleaning, and storage

6.6.2 Calibration and standardization

6.6.3 Collection and processing

Surface water


6.6.4 Measurement

6.6.4.A Titration systems and procedures

Digital titrator

Buret titrator

6.6.4.B Inflection point titration method

6.6.4.C Gran-function plot method

6.6.5 Calculations

6.6.5.A Alkalinity or ANC

6.6.5.B Carbonate-speciation equations for samples with pH < 9.2

6.6.5.C Computer-program analysis of titration data

6.6.6 Troubleshooting

6.6.7 Reporting

Selected references


 [Back] Return to Chapter A6 Contents Page

 [Back] Return to Field Manual Table of Contents

Section 6.6 Archived Versions:

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