Water Chemistry 2
Sampling
andPresenting Water Analyses
There is much to know and we only scratch the surface here. For
more details see:
USGS document on Collection of Water Samples
http://water.usgs.gov/owq/FieldManual/chapter4/html/Ch4_contents.html

AT THE SAMPLING SITE

Date and time of water sampling

November 8, 2007 11am
Location
Sample #3~ MW33 near clear creek bridge
conditions at the
1 day after a major rain stormWeather
time and, if appropriate,
Well head is rusty
recent weather conditions
8” diam well TD132’ WL32’
Condition, for example,Purged 500 Gal, >3 well volis there any debris? For
Air Temp = 58F
surface water are there
plants in thefish or p
Water Temp = 50Fwater? Is there a lot of
Conductivity= 875 μS/cm
algae? For well samples
document condition of
pH = 9Any other observations that you
think are interesting or
significant (odors, color).

well head and volume
purged from the bore
before taking the sample.

1Sample #3~ MW33 near clear creek bridge EPA Secondary Std
MCL for1 day after a major rain stormTDSis 500 mg/L
Well head is rusty8” diam well TD132’ WL32’
Purged 500 Gal,
Gal >3 well vol
Air Temp = 58F
Water Temp = 50F
Conductivity= 875 μS/cm
pH = 9A quick rough estimate of water quality
TDS? Total
T t l Dissolved
Dil d Solids
S lid
TDS in the lab:weigh a vessel, add water sample, evaporate, note increased weight
In the field we measure Electrical Conductivity … the ability to carry electric
current, which is carried by dissolved ions
Some meters use a function to convert conductivity to TDS

TDS (Total Dissolved Solids)
050

100

Water from distillation
Water frommountain springs
qor aquifers

200300400500

Typical tap water

EPA MCL
Some find this waterfrom the tap or mineralp g unpleasantpsprings

2Types of Solids
TDS Total Dissolved Solids: molecular, ionized or micro-granular(colloidal) solids that will pass through a 2 micron sieve
TSS Total Suspended Solids cannot pass through a 2 micron sieve but
are indefinitely suspended in solution
Settleable Solids will not remain suspended or dissolved in static water
Some dissolved species do not carry charge (e.g. silica), while thosethat are charged may carry different magnitude of charge and havedifferent hydrated sizeThus
conductivity & TDS are approximately relateda factor 0.67 is a widely accepted value but
it depends on the dissolved constituents.
In general:
TDS ~ [0.55 to 0.7] x conductivity
mg/L
μSiemens/cm

Different materials havedifferent relative conductivity due toCharge (higher = more conductive)
Size of the hydrated ion (larger = less conductive)
Cations

Relative
Conductivity
Cd ti itAnionsRelative
Conductivity
Cd ti itH+7.0

OH -4.0

Ca + +2.4

SO4 - -

3.2

Mg + +

2.1

Br -

1.6

Zn + +

2.1

Cl -

1.5

K+

1.5

I-

1.5Na +

1.0

NO3 -

1.4

Li +

0.8

Acetate

0.8

3Note conductivity
is temperaturedependent sorecord T to allow
adjusting conductivity

μS/cm

Different materials
have different
Conducitivity / TDS
ratioshttp://www.eutechinst.com/techtips/tech-tips12.htm

TDS

Some example
Conducitivities and TDS values
Conductivity
µS/cm

TDS

Divide Lake

104.6

Lake Superior

9763

Lake Tahoe

9264

Grindstone Lake

9565

Ice Lake

11079Lake Independence

316213Lake Mead850640

Atlantic Ocean

43,00035,000Great Salt Lake

158,000

230,000

Fresh waters
TDS < 1,000 mg/L

Saline waters
TDS > ~ 35,000 mg/L

Why
is primarily
GSL different
thanresthave
with smallera larger
TDS isNa andClthe
which
value
for
TDS
thanforConductivity?
relative charge.

4

SampleHow
Analysis
do we check correctness of analyses?

SoluteMeasuredConc (mg/L)

Ca22+

92 0
92.0

Mg2+

34.0

Na +

8.2

K+

1.4

Fe(III)

325.0

2-

84.0

HCO3SO4

0.1-

Cl -

9.6

NO3 -

13.01. Compare
Measured TDS and Calculated TDS
NOTE:When calculating TDS we group the mass ofsome items and call it Alkalinity
Alkalinity = [HCO3-] + 2[CO32-] + [OH-] - [H+]We will talk more about Alkalinity in the next
lecture2. Calculate Charge Balance

Check Correctness of Analysis: Calculate TDS
Calculated TDS =0.6Alkalinity + Na + K + Ca + Mg +Cl + SO4 + SiO2 + NO3-N + F

SoluteMeasuredConc (mg/L)

Ca2+92 0
92.0

Alkalinity= 325 yWhatis they Alkalinity?

Mg2+34.0

Calculated
What is theTDSCalculated= 567.2TDS?
mg/L

Na +

8.2

K+

1.4Fe(III)

0.1-

325.0

SO4 2-

84.0

Cl -

9.6

NO3 -

13.0

HCO3

Measured TDS > Calculated TDS becausesome species are not included in thecalculation (e.g. Fe(III))

acceptable range :1.0 <measuredd TDS< 1.2
calcuated TDS

If the ratio is out of the range,
constituents should be reanalyzed
Measured value in this case 603.5 mg/L
ratio = 1.06 is acceptable
What is the ratio? Is it acceptable?

5Check Correctness of Analysis: Calculate Charge Balance
2. Check Anion-Cation Balance
The solution must be electrically balanced.
Solutes Measured Conc
Conc. Atomic
Molarity(mg/L)
weight(g) (mmol/L)
Ca2+

92.0

Mg2+

34.0

Na +

8.2

K+

1.4

Fe(III)

325.0

2-

84.0

HCO3
SO401
0.1

-

Cl NO3

Valence(charge)

meq/L∑ cations = ∑ anions% difference = 100 ×∑ cations − ∑ anions
ti+ ∑ anionsi∑ cations

Less than 5% ~ reasonable

9.6-

13.0

Let’s check the cation/anion balance
Solutes

MeasuredConc. (mg/L)

Ca2+

92.0

Mg2+

34.0

Na +

8.2

K+

1.4

Fe(III)0.1

HCO3 -

325.0

SO4 2-

84.0

Cl -

9.6

NO3-

AtomicMolarity Valence
weight(g) (mmol/L) (charge)

meq/L

13.0

6

Check the cation/anion balance for this analysis:
Solutes

MeasuredConc. (mg/L)

AtomicMolarity Valence
weight(g) (mmol/L) (charge)

meq/L

Ca2+

92.0

40.08

2.30

2

4.60

Mg2+

34.0

24.31

1.40

2

2.80

Na +

8.2

23.0

0.36

1

0.36

K+

1.4

39.1

0.036

10.036

Fe(III)

0.1

55.8

0.002

30.006

HCO3 -

325.0

61.0

5.33

15.33

SO4 2-

84.0

96.00.882

1.75Cl -96
9.6

35 5
35.5

0 27
0.27

10 27
0.27

NO3 -

13.0

62.0

0.21

10.21

7.79

7.56

− ∑isanions
7.79 − 7.56
∑ cationsWhat
the charge= balance? = 0.0145
it acceptable?
7.79 + 7.56
∑ cations + ∑Isanions

7

Summary checking correctness of analysis
1. Check Calculated vs Measured TDS

measured TDS 603.5== 1.06
1 06
calcuated TDS 567.2
Between 1 and 1.2, so it’s OK!
2. Check Anion-Cation (Charge) Balance∑ cations − ∑ anions = 7.79 − 7.56 = 0.0145∑ cations + ∑ anions 7.79 + 7.56
The cation/anion imbalance for the data is 1.5%
< 5% so it’s OK!

What if there is an electrical imbalance?
Possible reasons:oThe sampling program neglected to analyze for amajor dissolved species. This may indicate ahigh concentration of an unusual anion or cation.

oLaboratory error - some serious systematic error
occurredoIn certain cases the dissolved species of theelement of a compound may not correspond to
the typical species used in making the ion
balance calculation.

8How do we present the analysis?
The options have advantages and disadvantages
Presentation formats:
Abundance or Relative Abundance• Pie Diagram• Collins Diagram• Schoeller Diagram• Stiff Diagram• Piper Diagram
Spatial Patterns• Contours of individual constituents (often noisy)• Abundance diagrams on a map

PIE CHARTS
Display of concentration ratios forindividual samples
Na+KCaMg

Clp
concentration
Easier to compare
ratios for several different samples
compared with a table of numbers

SO4
HCO3

Na+KCaMg

ClSO4HCO39

COLLINS DIAGRAM

Display of concentrations (not ratios) for individual samples
but as it is a cumulative chart the values are not readily apparent
Total height ~ reflects TDS
Easier to compare samples than pie charts

Conccentration (meq/L)

120

Na++K+Mg2+
Ca2+
ClSO42-

100

80

HCO3- +CO32-

60

40

200

Sample 1

Sample 3

Sample 2

SCHOELLER DIAGRAM• Logarithmic
diagrams of major
ion analyses inmeq/l demonstratedifferent
ffwatertypes on the same
diagramConc (meq/L)
1000
10010• Sample
concentrations notratios are displayedand compared• Similar waters
exhibit similar“fingerprints”

10.1
0.01
KMg CaNa

Cl SO4 HCO3 NO310

STIFF DIAGRAM

Displays concentration ratios for individual samples
Shape makes it easier to compare samples
Especially if displayed on maps
Concentrations in meq/L are plotted on the horizontal axis
Cations on the left Anions on the right
Points are connected to form a polygon

Na++K+

Cl-Ca2+

HCO3-Mg2+

SO42-

Sometimes afourth row isadded for Feand NO380

7060

50

40 30
Cations

20

Stiff Diagram
Example10010meq/L

20

Cations
1510meq/l
5Na+K

1015ClAD002

HCO3+CO3Mg

SO4Na+K

ClAD004HCO3+CO3
HCO3 CO3CCaMg

SO4Na+KMg
Na+K

Ca and Mg are the mostimportant cations

ClAD005 HCO3+CO3Ca

Most samples have a long tailat the sulfate vertex, sulfate
is the dominant anion

Anions

5CaNa, K and Cl rarely extend
horizontallyy beyond
ythevertical axis, so relatively
unimportant in this area

30
4050
AnionsSO4Cl

Ca AD007

HCO3+CO3Mg
Na+K

SO4Cl

S9 3
S97-3

CaHCO3+CO3Mg

SO4Na+KCl

CaSP002

HCO3+CO3Mg

SO4Na+KCl

SPNEWCaHCO3+CO3Mg

SO411

PIPER DIAGRAMSADVANTAGES• Manyy water analyses
ycan be pplotted on the samediagram• Can be used to classify waters• Can be used to identify mixing of waters
DISADVANTAGE• Concentrations are renormalized• Cannot easily accommodate waters where othercations or anions may be significant

PIPER DIAGRAM• Two triangles (cations & anions) &Central diamond-shape (combined)• Cations plotted as percents on
Ca-Mg-(Na + K) triangle• Anions plotted as percents on
HCO3--SO42--Cl- triangle• Percent of Concentration in meq/L• Points on the triangles areprojected up to where theyintersect on the diamond

Mg

Groundwater
FaciesCations
Ca

SO4Anions
Na + K

HCO3 + CO3Cl

12

Plotting on a Piper Diagram
Ca40 ppm
Mg
15 ppm
Na120 ppm
K20 ppm
HCO32.8 meg/L
SO4234 ppm
Cl45 ppm

Mg

Ca80

60

SO 440

Calcium (Ca)

20Na+K

HCO3 +CO3 20%meq/l

CATIONS

40

Plotting on a Piper Diagram
Ca40 ppm
Mg
15 ppm
Na120 ppm
K20 ppm
HCO32.8 meg/L
SO4234 ppm
Cl45 ppm

60

80

Chloride (Cl)ClANIONS

When plotting
many samplessometimes wemake the symbol
size proportional
to TDS

Convert to Equivalents / L
Divide by formula weight
Multiply by charge

Ca 1.996×10-3 HCO3- 2.8×10-3
Mg 1.234×10-3 SO4 4.88×10-3
Na 5.22×10-3 Cl
1.27×10-3
K 0.51×10-3
Sum Na+K
Normalize Ca Mg Na+K to 100%
Normalize HCO3- SO4 Cl to 100%

Mg

SO 4

SO4 54.5%

Ca
22.3% HCO3- 31.3%
Mg 13.7% SO4 54.5%
Na+K 64.0% Cl
14.2%

Mg 13.7%
Ca80

6040

Calcium (Ca)CATIONS

20Na+K

HCO3 +CO3 204060

Chloride (Cl)Ca 22.3%%meq/l Cl 14.2%80

ClANIONS

13

Classification of Water
Ca-SO4 waters - typical of gypsum
ground waters and mine drainage
Ca-HCOCa
HCO3 waters - typical ofshallow, fresh ground waters
Na-Cl waters - typical ofmarine and deep ancientground waters
Na-HCO3 waters –typicali l off deeperdground waters
influenced by ionexchange

Mg

SO 4Ca TypeCaSO4 TypeMg
g Typeyp80

Na K Type

6040Calcium (Ca)20

HCO3 Type Cl TypeHCO3 +CO3 20

Na+K%meq/l

CATIONS

406080Chloride (Cl)ClANIONS

Plot on a Piper Diagram distributed in class
Ca131 ppm
Mg
44 ppmNa43 ppm
K7 ppm
HCO3- 200 ppm
SO4431 ppm
Cl19 ppm

If you want to download data in a spreadsheet, go to

http:/inside.mines.edu/~epoeter/_GW/18WaterChem2/WaterChem2.htm/Wildrose-Piper.xls

Mg

Ca80

60

SO 440

Calcium (Ca)CATIONS

20Na+K

HCO3 +CO3 20%meq/l

4060

Chloride (Cl)80

ClANIONS

14

Plot on a Piper Diagram distributed in classCa
131 ppmMg
44 ppmNa43 ppm
K7 ppm
HCO3- 200 ppm
SO4431 ppm
Cl19 ppm
25.6

4.2

70.2

Bicarb+Carb

ChlorideSulfate

53.6
Ca

16.8
K + Na29.7
Mg

Plotted point is approximate
given ppt drawing lmitations

Mg

80

Ca60

SO 440

Calcium (Ca)CATIONS

20Na+K

HCO3 +CO3 20%meq/l

40

60

Chloride (Cl)80

ClANIONS

Rockworks: software for visualizing, interpretingand presenting surface and subsurface data
http://www.rockware.com

Class data sets available for download on today’s class page

http://inside.mines.edu/~epoeter/_GW/18WaterChem2/WaterChem2.htm

Maps
WaterChem2-data.zip

Download those files now
Unzip the zip file to a folder of your choice
You can choose to look at one of 2 data sets
Death Valley (source water identification) orOhio (water quality in a mining district)xls files which you know how to create &atd files from Rockworks which are simply the xls with symbols added inrockworks and saved as an atd – I did this to save you the tedium

15

RockWorks2006• Launch RockWorks2006 (in the Geology applications)• Under “Network User ID”, type your username &continue• If you get a message about UPDATING CANCEL IT• If it opens to a help page Xit IT

Click Utilities

16

To import an xls File|Import|XLS, import data.xls yes, process header line
Afterward you will need to do a lot of set up, column titles, define symbols,
enter project range. I have done that for you in the atd files
SO for this exercise OPEN the rockware file I provided (*.atd)
Choose Death Valley or Ohio according to your interest

Put the path to your verison of the xls file

Now go to Hydrochemistry
Experiment with ion balance, TDS calculation, Piper plot, Stiffdiagram and (for Ohio where we have x,y,z) Stiff MapsWatch the options*** Notice you will need to scan project dimensions if you are to
make a mapp*** Notice when you select an analysis under hydrochemistry abar appears on the left. Be sure to select the correct column
headers on that bar. If there are no data for an item, choose
and empty column. ALSO notice sometimes you need toselect a column for the output of the analysis ... Be sure tochoose an empty column (it is useful to label that column,
right click on the column header for options).
*** Note you may need to wait a bit for a plot or map to appear
appear.
Generally you know it is working because it reports progresson tasks on the lower bar.
Consider whether your outputs make sense(make sure you could do these analyses without Rockware)
Note items to consider on the following slide

17

The sample data that you just plotted on the paper Piper diagram in class is one of
the Death Valley samples, Wildrose Spring. Compare your plotted point to the onethat Rockware plots.
Consider the Data with respect to the maps on the next two slides. (note: we will
discuss these again in an upcoming class)

HOMEWORK:
Make an interesting observation using Rockworks on one of these data sets
sets.
You must attach the associatedRockworks diagram and explain how it supports your observation

Death Valley18

FOhioAC
BE
D

G

0,0

Areas occupied by strip mine
spoils (red)19