C onductivity P rotocol
C onductivity P rotocol
features include digital readout, autom atic
B ack ground
tem perature com pensation, and accuracy of ± 0.5% .
C onductivity (or specific conductance) is a m easure Standard salt solutions for testing instrum ent of w ater’s ability to conduct an electrical current accuracy are also available from scientific (Saw yer and M cC arty 1967). T he conductivity of a suppliers. T he recom m ended standard solution for w ater sam ple depends on the w ater tem perature and fresh surface w ater m easurem ents is potassium on the concentration of dissolved salts or other chloride (K C l) w ith a conductivity of 147 substances that can carry an electrical charge.
m m hos/cm . 9
T here is no w ater quality standard for conductivity, but conductivity can be a useful diagnostic tool for
Field Protocol
interpreting other w ater quality inform ation. For
C alibrating E quipm ent
exam ple, dom estic and industrial w astew ater, storm w ater, and irrigation return w ater often have
M ost conductivity m eters are calibrated at the higher conductivities than the receiving stream s.
factory, but it is necessary to check the accuracy
G roundw ater inflow s also typically have higher against a standard solution. For surface w ater conductivities than surface runoff. M easuring
m onitoring the D E Q uses a standard solution of conductivity is also inform ative in estuaries and
potassium chloride w hich has a conductivity of coastal rivers that m ay be influenced by salt w ater
147 m hos/cm .
as a result of ocean tides.
1. T urn on the m eter and rinse the probe in
C onductivity is m easured w ith a m eter and is distilled or deionized w ater. reported in units called m icrom hos/centim eter
2. R inse the probe w ith the C onductivity Standard (m hos/cm ) or m icrosiem ens.cm (s/cm ).
Solution.
C onductivity m eters are usually factory calibrated,
3. Pour about 200 m l of Standard Solution into a but need to be periodically tested for accuracy in a
clean beaker and im m erse the probe. M ake standard salt solution. C onductivity m eters in
sure the tem perature and conductivity sensors general require m uch less m aintenance than pH
are fully subm erged.
m eters or dissolved oxygen m eters. Problem s associated w ith a conductivity m eter are usually
4. Set the m eter to display tem perature. due to dead batteries, a cracked or dam aged cable,
5. A gitate the probe in the solution, but do not or a dam aged or defective electrode.
allow probe to contact the w alls of the Fresh surface w aters in O regon range in
container.
conductivity from about 20 to 500 m hos/cm . In the
6. R ecord the solution tem perature w hen the W illam ette V alley and C oast R ange conductivities
reading is stable.
are typically 150 m hos/cm or less. D istilled or de-
7. Set the m eter to display conductivity in ionized w ater that has been in contact w ith the air m hos/cm w ith the tem perature com pensation. usually has a conductivity of about 1 m ho/cm .
O rdering E quipm ent
9 Note: some meters display an equivalent unit to µmhos/cm called variety of scientific supply com panies. Im portant
C onductivity m eters can be purchased from a
micro-siemens/cm (µS/cm). 1 µmhos/cm = 1 µS/cm Other meters display in milli-siemens/m (mS/m). Be careful not to confuse units! 10 µmhos/cm = 1 mS/m
8. A gitate the probe as in step 5 and record the
7. Set the m eter to display conductivity in conductivity to the nearest w hole num ber.
m hos/cm . M ake sure the m eter is also set for
9. C alculate the R elative Percent D ifference autom atic tem perature com pensation to 25oC . (R PD ) betw een the instrum ent reading and the
8. A gitate the probe as in step 5 and record the Standard Solution’s value.
conductivity to the nearest w hole num ber.
10. T he R elative Percent D ifference should be w ithin 7% for D ata Q uality L evel “ A ” or
A nalyzing D ata
w ithin 10% for D ata Q uality L evel “ B ” (refer
V erify that the data are m eeting the data quality to C hapter 4, D ata Q uality ). If the R PD is
objectives of the Q uality A ssurance Project Plan. greater than the expected value, repeat the
A ccuracy is verified by checking the m eter accuracy test w ith fresh solutions. If that
calibration records. Precision is verified by doesn’t fix the problem , the m eter or probe
com paring the results of duplicate m easurem ents on needs service.
the sam e sam ple.
Sam ple H andling and Preservation
M entors
A s w ith any m onitoring project, questions w ill the probe directly into the w ater. T he D E Q
C ollect a w ater sam ple in a clean container or low er
com e up that are not answ ered or covered routinely m easures conductivity in the field, but
sufficiently in this protocol. T herefore, a group of w hen this is not possible sam ples are analyzed at
m entors that are agency experts in m onitoring have the lab. If conductivity can’t be m easured in the
been identified . T hese m entors m ay be contacted field, sam ples are collected in clean, tightly sealed
w ith specific questions about a particular 500 m l (1 pint) plastic containers.
m onitoring effort.
S a m p le p re se rv a tio n — sam ples are kept cool at 4º C on ice or in a refrigerator. Storage tim e for
Statew ide D E Q V olunteer M onitoring C oordinator sam ples is up to 28 days after collection.
K aren W illiam s: (503) 229-5983 E-mail: w illiam s.karen@ deq.state.or.us
M easuring C onductivity of a W ater Sam ple
N orth C oast L arry C aton (503)229-5983;
1. T urn on the m eter and rinse the probe in
E -m ail: caton.larry@ deq.state.or.us distilled or deionized w ater.
South C oast & W illam ette
2. R inse the probe w ith the w ater sam ple.
D ennis A des (503)-229-5983;
3. Put the probe directly in the w aterbody or pour
E -m ail: [email protected] about 200 m l of sam ple into a clean beaker and
E astern O regon
im m erse the probe. M ake sure the tem perature L arry M arxer (503) 229-5983; and conductivity sensors are fully subm erged.
E -m ail: m arxer.larry@ deq.state.or.us
4. Set the m eter to display tem perature.
5. A gitate the probe in the sam ple, but do not