Water Chemistry 2

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

1
 Sample #3
~ MW33 near clear creek bridge EPA Secondary Std
1 day after a major rain storm MCL for
Well head is rusty TDS is 500 mg/L
8” diam well TD132’ WL32’
Purged 500 Gal,
Gal >3 well vol
Air Temp = 58F
Water Temp = 50F
Conductivity= 875 μS/cm
pH = 9
A quick rough estimate of water quality
TDS? Total
T t l Dissolved
Di l 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)

0 50 100 200 300 400 500

Water from distillation
Typical tap water
EPA MCL
Water from Some find this water
mountain springs from the tap or mineral
q
or aquifers p g unpleasant
springs p

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 those
that are charged may carry different magnitude of charge and have
different hydrated size

Thus
conductivity & TDS are approximately related
a 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 have

different relative conductivity due to
Charge (higher = more conductive)
Size of the hydrated ion (larger = less conductive)
Cations Relative Anions Relative
Conductivity
C d ti it Conductivity
C d ti it
H+ 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- 1.5

Na + 1.0 NO3 - 1.4

Li + 0.8 Acetate 0.8

3
 Different materials
have different
Conducitivity / TDS
ratios

Note conductivity

μS/cm
is temperature
dependent so
record T to allow
adjusting conductivity

http://www.eutechinst.com/techtips/tech-tips12.htm TDS

Some example
Conducitivities and TDS values

Conductivity TDS
µS/cm
Divide Lake 10 4.6
Lake Superior 97 63
Lake Tahoe 92 64
Fresh waters
Grindstone Lake 95 65
TDS < 1,000 mg/L
Ice Lake 110 79
Lake Independence 316 213
Lake Mead 850 640
Atlantic Ocean 43,000 35,000 Saline waters
Great Salt Lake 158,000 230,000 TDS > ~ 35,000 mg/L

Why
TDS isis primarily
GSL different than
Na and Clthe resthave
which with smaller
a larger
value for TDS
relative charge.than for Conductivity?

4
SampleHow do we check correctness of analyses?
Analysis

Solute Measured
Conc (mg/L)
1. Compare
Ca22+ 92 0
92.0
Measured TDS and Calculated TDS
Mg2+ 34.0
Na + 8.2 NOTE:
When calculating TDS we group the mass of
K+ 1.4 some items and call it Alkalinity
Fe(III) 0.1 Alkalinity = [HCO3-] + 2[CO32-] + [OH-] - [H+]
-
We will talk more about Alkalinity in the next
HCO3 325.0 lecture
SO4 2- 84.0
Cl - 9.6
2. Calculate Charge Balance
NO3 - 13.0

Check Correctness of Analysis: Calculate TDS

Calculated TDS =
0.6Alkalinity + Na + K + Ca + Mg +
Solute Measured Cl + SO4 + SiO2 + NO3-N + F
Conc (mg/L)
Ca2+ 92 0
92.0 Alkalinity
What is they Alkalinity?
= 325 y

Mg2+ 34.0 Calculated

What is theTDS
Calculated
= 567.2TDS?
mg/L

Na + 8.2 Measured TDS > Calculated TDS because

some species are not included in the
K+ 1.4
calculation (e.g. Fe(III))
Fe(III) 0.1
acceptable range :
HCO3 - 325.0
measuredd TDS
SO4 2- 84.0 1.0 < < 1.2
Cl - 9.6
calcuated TDS
NO3 - 13.0 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 Valence meq/L
(mg/L) weight(g) (mmol/L) (charge)
Ca2+ 92.0
Mg2+
Na +
34.0
8.2
∑ cations = ∑ anions
K+ 1.4
% difference = 100 ×
∑ cations − ∑ anions
Fe(III)
-
01
0.1
∑ cations
ti + ∑ anions
i
HCO3 325.0
SO4 2- 84.0 Less than 5% ~ reasonable
Cl - 9.6
NO3 - 13.0

Let’s check the cation/anion balance

Solutes Measured Atomic Molarity Valence meq/L
Conc. (mg/L) weight(g) (mmol/L) (charge)
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 - 13.0

6
 Check the cation/anion balance for this analysis:
Solutes Measured Atomic Molarity Valence meq/L
Conc. (mg/L) weight(g) (mmol/L) (charge)
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 7.79
K + 1.4 39.1 0.036 1 0.036
Fe(III) 0.1 55.8 0.002 3 0.006
HCO3 - 325.0 61.0 5.33 1 5.33
SO4 2- 84.0 96.0 0.88 2 1.75
7.56
Cl - 96
9.6 35 5
35.5 0 27
0.27 1 0 27
0.27
NO3 - 13.0 62.0 0.21 1 0.21

∑ cationsWhat
− ∑isanions
the charge7.79 − 7.56
= balance? = 0.0145
∑ cations + ∑Isanions
it acceptable?
7.79 + 7.56

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:

o The sampling program neglected to analyze for a

major dissolved species. This may indicate a
high concentration of an unusual anion or cation.

o Laboratory error - some serious systematic error

occurred

o In certain cases the dissolved species of the

element 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 for
individual samples
Na+K Ca
p
Easier to compare concentration
Mg
ratios for several different samples
Cl compared with a table of numbers
SO4

HCO3

Na+K Ca

Mg
Cl SO4

HCO3

9
 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
120

Na++K+
centration (meq/L)

100 Mg2+
Ca2+
80
Cl-
SO42-
HCO3- +CO32-
60
Conc

40

20

0
Sample 1 Sample 2 Sample 3

SCHOELLER DIAGRAM
• Logarithmic
diagrams of major Conc (meq/L)
ion analyses in 1000
meq/l demonstrate
different
ff water 100
types on the same
diagram
10
• Sample
concentrations not
ratios are displayed 1
and compared
0.1
• Similar waters
exhibit similar
“fingerprints” 0.01
K Mg Ca Na Cl SO4 HCO3 NO3

10
 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 a
fourth row is
added for Fe
and NO3

80 70 60 50 40 30 20 10 0 10 20 30 40 50
Cations meq/L Anions

Stiff Diagram 15
Cations
10 5
meq/l
5
Anions
10 15

Example Na+K Cl

Ca AD002 HCO3+CO3

Na, K and Cl rarely extend Mg

Na+K Cl
SO4

horizontallyy beyond
y the C
Ca AD004HCO3+CO3
HCO3 CO3
vertical axis, so relatively Mg SO4
unimportant in this area Na+K Cl

Ca AD005 HCO3+CO3

Mg SO4
Ca and Mg are the most Na+K Cl

Ca AD007 HCO3+CO3
important cations
Mg SO4
Na+K Cl

Ca S9 3
S97-3 HCO3+CO3
Most samples have a long tail
Mg SO4
at the sulfate vertex, sulfate Na+K Cl

is the dominant anion CaSP002 HCO3+CO3

Mg SO4
Na+K Cl

SPNEW
Ca HCO3+CO3

Mg SO4

11
 PIPER DIAGRAMS

ADVANTAGES
• Manyy water analyses
y can be pplotted on the same
diagram
• Can be used to classify waters
• Can be used to identify mixing of waters

DISADVANTAGE
• Concentrations are renormalized
• Cannot easily accommodate waters where other
cations 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

Mg Groundwater SO4
• Points on the triangles are
projected up to where they Facies
intersect on the diamond

Cations Anions

Ca Na + K HCO3 + CO3 Cl

12
 Plotting on a Piper Diagram
Ca 40 ppm
Mg 15 ppm
Na 120 ppm
K 20 ppm
HCO3- 2.8 meg/L
SO4 234 ppm
Cl 45 ppm

Mg SO 4

Ca 80 60 40 20 Na+K HCO3 +CO3 20 40 60 80 Cl

Calcium (Ca) Chloride (Cl)
%meq/l
CATIONS ANIONS

Plotting on a Piper Diagram

Ca 40 ppm Convert to Equivalents / L When plotting
Mg 15 ppm Divide by formula weight many samples
Na 120 ppm Multiply by charge sometimes we
K 20 ppm make the symbol
HCO3- 2.8 meg/L
SO4 234 ppm size proportional
Cl 45 ppm to TDS
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% Mg SO 4

Normalize HCO3- SO4 Cl to 100%

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

Mg 13.7%

Ca 80 60 40 20 Na+K HCO3 +CO3 20 40 60 80 Cl

Calcium (Ca)
Ca 22.3%
%meq/l Cl 14.2%
Chloride (Cl)
CATIONS ANIONS

13
Classification of Water
Ca-SO4 waters - typical of gypsum
ground waters and mine drainage

Ca-HCO
Ca HCO3 waters - typical of
shallow, fresh ground waters

Na-Cl waters - typical of

marine and deep ancient Mg SO 4
ground waters

Na-HCO3 waters – SO4 Type

Mg
g Type
yp
typical
i l off deeper
d
ground waters
influenced by ion
exchange Ca Type Na K Type HCO3 Type Cl Type
Ca 80 60 40 20 Na+K HCO3 +CO3 20 40 60 80 Cl
Calcium (Ca) Chloride (Cl)
%meq/l
CATIONS ANIONS

Plot on a Piper Diagram distributed in class

Ca 131 ppm If you want to download data in a spreadsheet, go to
Mg 44 ppm http:/inside.mines.edu/~epoeter/_GW/18WaterChem2/WaterChem2.htm/Wildrose-Piper.xls
Na 43 ppm
K 7 ppm
HCO3- 200 ppm
SO4 431 ppm
Cl 19 ppm

Mg SO 4

Ca 80 60 40 20 Na+K HCO3 +CO3 20 40 60 80 Cl

Calcium (Ca) Chloride (Cl)
%meq/l
CATIONS ANIONS

14
 Plot on a Piper Diagram distributed in class
Ca 131 ppm
Mg 44 ppm
Na 43 ppm
K 7 ppm
HCO3- 200 ppm
SO4 431 ppm
Cl 19 ppm

25.6 4.2 70.2 53.6 16.8 29.7

Bicarb+Carb Chloride Sulfate Ca K + Na Mg

Plotted point is approximate

given ppt drawing lmitations Mg SO 4

Ca 80 60 40 20 Na+K HCO3 +CO3 20 40 60 80 Cl

Calcium (Ca) Chloride (Cl)
%meq/l
CATIONS ANIONS

Rockworks: software for visualizing, interpreting

and 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) or
Ohio (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 in
rockworks 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, Stiff
diagram and (for Ohio where we have x,y,z) Stiff Maps
Watch the options
*** Notice you will need to scan project dimensions if you are to
make a map p
*** Notice when you select an analysis under hydrochemistry a
bar 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 to
select a column for the output of the analysis ... Be sure to
choose 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 progress
on 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 one
that 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 associated
Rockworks diagram and explain how it supports your observation

Death Valley

18
Ohio F

A
C
B
E
G
D

0,0

Areas occupied by strip mine

spoils (red)

19