Water Resources--Office of Water Quality

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Multiply   By   To obtain
micrometer (µm)   0.00003937   inch
millimeter (mm)  
centimeter (cm)  
microliter (µm)  
  ounce, fluid
milliliter (mL)  
  ounce, fluid
liter (L)  
  gallon (gal)
nanogram (ng)  
3.53 x 10-11
microgram (µg)  
3.53 x 10-8
milligram (mg)  
gram (g)  
  ounce, avoirdupois
  pound per squar inch
picocurie (pCi)  
  Becquerle (Bq)


Temperature: Water and air temperature are given in degrees Celsius (°C), which can be converted to degrees Fahrenheit (°F) by use of the following equation: °F = 1.8 (°C) + 32


Selected Terms

Editors and authors of the National Field Manual have attempted to use terms common in the water-quality community. Some of the terms used have restricted meanings within the context of this report. The following terms either are used in a context familiar primarily to USGS personnel, or in a format that is more succinct, or that is considered to be more specific than a common usage:

Accuracy: The degree of agreement of a measured value with the true or expected value (from Taylor, 1987).

Analyte (target analyte): "Substances being determined in an analysis" (from Bennett, 1986). The term target analyte is used in this report to refer to any chemical or biological substance for which concentrations in a sample will be determined. The definition for target analyte does not include field-measured parameters such as temperature, specific electrical conductance, pH, dissolved oxygen, Eh, alkalinity, color, or turbidity.

Bias: Systematic error inherent in a method or caused by some artifact or idiosyncrasy of the sample measurement, collection, or processing system. The error can be positive (indicating contamination) or negative (indicating loss of analyte concentration) (from Taylor, 1987).

Contaminant: Biological or chemical substances added to the medium of concern, commonly through human activity.

Contamination (of water): Change of ambient water composition by the addition of biological or chemical substances as a result of human activity or natural processes. Addition of such substances can be detrimental to the quality of the water resource.

Data-quality requirements: The subset of data-quality objectives pertaining specifically to the analytical detection level for concentrations of target analytes and the variability allowable to fulfill the scientific objectives of the study.

Quality Assurance (QA): The systematic management of data-collection systems by using prescribed guidelines and criteria for implementing technically approved methods and policies. Quality assurance incorporates a comprehensive plan that outlines the overall process for providing a product or service that will satisfy the given requirements for quality.

Quality Control (QC): The specific operational techniques and activities used to obtain the required quality of data. Quality control consists of the application of technical procedures to achieve prescribed standards of performance and to document the quality of collected data. Quality-control data are used to identify and evaluate any corrective actions necessary to improve performance or data interpretation to acceptable levels.

Trace element(s): For the purpose of this report and to maintain consistency with common usage, the term trace element(s) is used to refer to metal and nonmetal inorganic elements such as arsenic, antimony, selenium, and tellurium that usually are present in natural surface-water and ground-water systems in concentrations less than 1 mg/L (modified from Hem, 1985). Common usage of this term, as defined above, is inexact and not rigorous with respect to aqueous chemistry.


cc cubic centimeter
lb/in2 pounds per square inch
min minute
mg/L milligram per liter
µg/L microgram per liter (equivalent to parts per billion (ppb))
mL/min milliliters per minute
ng/L nanogram per liter
ng/µL nanogram per microliter
pCi picocuries
ppb parts per billion (see µg/L)
ANC acid neutralizing capacity
ASR Analytical Services Request
BNA base-neutral acids
CFC chlorofluorocarbon
CH Clean Hands
DH Dirty Hands
DIC dissolved inorganic carbon
DIW distilled/deionized water
DOC dissolved organic carbon
FA filtered, acidified sample
FAR filtered, acidified sample for analyses of selected radiochemicals
FCA filtered, chilled, acidified sample
FCC filtered, chilled sample
FEP fluorinated ethylene-propylene
FU filtered, untreated sample
GCC glass, chilled sample for analysis of nonvolatile organic compounds
GC/MS gas chromatograph/mass spectrophotometer
IBW inorganic-grade blank water (water with certified analysis of trace elements and other inorganic constituents and used for blank QC samples for analysis of inorganic constituents)
MBAS methylene blue active substances
NAWQA National Water-Quality Assessment Program
NFM National Field Manual for the Collection of Water-Quality Data
NPDES National Pollutant Discharge Elimination System
NWQL National Water Quality Laboratory of the USGS
OWQ Office of Water Quality of the USGS
PBW pesticide-grade blank water (water certified free of pesticide compounds)
PCB polychlorinated biphenyl
QA quality assurance
QC quality control
QW quality of water, or water quality
QWSU Quality of Water Service Unit, USGS, Ocala, Florida
RA raw, acidified sample
RAH raw, acidified sample for analysis of antimony, arsenic, and (or) selenium
RAM raw, acidified sample for analysis of mercury
RCB raw, chilled sample
RU raw, untreated sample
RUR raw, untreated sample for analysis of selected radiochemicals
RUS raw, untreated sample for analysis of stable isotopes
SOC suspended organic carbon
SPE solid-phase extraction
TOC total organic carbon
URL Uniform Resource Locator
USEPA U.S. Environmental Protection Agency
USGS U.S. Geological Survey
VBW volatile-organic-compounds-grade blank water (water certified free of VOCs)
VOC volatile organic compounds
WCA raw, chilled, acidified nutrient sample


Chemical Formulas

Ag2S silver sulfide
AgNO3 silver nitrate
BaSO4 barium sulfate
13 C/12C carbon-13/carbon-12 isotope ratio
14 C carbon-14
CuSO4 copper sulfate
2 H/1H deuterium/protium isotope ratio
3 H/3He tritium/helium-3 isotope ratio
HCl hydrochloric acid
H2O water
H2S hydrogen sulfide
H2SO4 sulfuric acid
H3PO4 phosphoric acid
HNO3 nitric acid
HNO3K2Cr2O7 nitric acid/potassium dichromate
NaCl sodium chloride
NaOH sodium hydroxide
15 N/14N nitrogen-15/nitrogen-14 isotope ratio
18 O/16O oxygen-18/oxygen-16 isotope ratio
34 S/32S sulfur-34/sulfur-32 isotope ratio
SrCl2 strontium chloride


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