EPA REGION 1 LIBRARY
JFK FEDERAL BLDG.
BOSTON MA 02203-2211
DRAFT CALIBRATION OF
(temperature, pH, dissolved oxygen,
oxidation/reduction potential
I. SCOPE & APPLICATION
The purpose of this standard operating procedure
field instruments used to measure water
Water quality parameters include
conductance, oxidation/reduction
does not replace, EPA analytical
dissolved oxygen,
This SOP is written forrn
oxygen,
probe
SOP #
Region I Calibration of
Field Instruments
Revision Number: DRAFT
Date June 3, 1998
Page 1 of 10
(temperature, pH, dissolved
on/reduction potential [ ORP]) and the
conductance are automatically corrected
(programming and displaying the
a display/logger or a computer. Information sent to the
the display/logger or computer. It is desirable that
storage capabilities. If the instrument does not have a
for entering infonnation into the instrument.
instrument must be equipped with a flow-through-cell, and the
screen needs to be large enough to simultaneously contain the
the instrument. Turbidity is measured using a separate instrument
be measured in a flow-through-cell. This procedure is applicable for
ion 1 Low Stress (low flow) Purging and Sampling Procedure for the
Water Samples from Monitoring Wells.
All monitoring instruments must be calibrated before they are used to measure environmental
samples. Part of the calibration is performed prior to the field event. For instrument probes that
rely on the temperature sensor (pH, dissolved oxygen, conductivity/specific conductance, and
U S. ENVIRONMENTAL PROTECTION AGENCY
REGION1 ‘
/ -
e -afimework for calibrating
i ater and surface water.
ñductivity/specific
SOP supplements, but
40 CFR 141 for temperature,
II. GENERAL

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SOP #
Region I Calibration of
Field Instruments.
Revision ,Number DRAFT
Date J jne’3, j998 -
Page 2 of 10
oxidation/reduction potential [ ORP]), each temperature sensor needs to be checked for accuracy
against a thermometer that is traceable to the National Instituie of Standards and Technology
(NIST). Before any instrument is calibrated or used to perform enviränmental measurements,
the instrument must stabilize (warm-up) according to ma fhcturer’s instr tions -
Most instruments will require at least two standards to bracket tb xpected niea ui ment ‘range,
that is, one standard less than the expected value and oii higher; ‘Calibration mu t.bè perfonned
at the beginning of each sampling day prior to sample co l1óefioii i.p determine if the instruments
have remained in calibration during transport to each sai fin k o$icm., use one of the
previously used standards as a check standard at the sa p1ing’ +’ I Oi check measurement
does not agree with the initial calibration or to of .ihe instrument, then
the instrument must be re-calibrated. When an tirement falls outside
the calibration range, the instrument must b 4 range before
continuing measurements.
instrument
must be cleaned according to the manufacturer’s
maintenance) can lead to erratic measurements.
measuring, make sure there are no air bubbles lodged between the probe and
Most instrument manuals state there is no calibration of the temperature sensor, but the
temperature sensor must be checked to determine its accuracy This accuracy check is performed
This SOP requires that the
specifications) accompany the
IL’.
that the following parameters to be measured will be
dissolved oxygen, mgfl dissolved oxygen, conductivity,
solutions must be sufficient to cover both the probe and
manufacturer’s instructions for additional information).
TEMPERATURE

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