﻿ Sample Module > Calculate Water Type

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# Calculate Water Type

The Calculate Water Type sub-menu that is accessible through the Samples item in the Main menu (and related functions in toolbar of the Sample List) allow you to calculate the Water Type of a sample.

## Theory

The Water Type, also known as the water facies, of a sample describes its major ionic constituents.  The Water Type of a given sample will be influenced by the interaction of the water with the minerals that it has been in contact with. These types of interactions include precipitation, dissolution, ion exchange, geological structure, and the mineralogy of watershed/aquifer.

The Water Type is determined by calculating the percent contribution of each cation and anion to the total concentration of ions in solution on a equivalents per liter basis. In Hydro GeoAnalyst, you can calculate a "short'" water type or a "long" water type.  The "short" water type is calculated by concatenating the cation and anion with the highest equivalent concentrations. The "long" water type is calculated by concatenating cations and anions with concentrations above a specified percent contribution threshold.

The threshold for determining if an ion is major is normally 10%; however in some countries 12.5% is more common. the higher the threshold, the smaller number of parameters that may exceed this threshold is. Usually, only major ions (Na, Ca, Mg, HCO3, Cl, SO4) will have a concentration that allows them to exceed the defined threshold. If you want to make sure, that other important elements such as potassium or nitrate appears in the water type expression, then you can achieve this by lowering the threshold value.  Examples of short and long water calculations are shown in Table 1 below.

Table 1. Major Ions and Water Type for Example Samples

SAMPLE

MW-1-04

MW-2-07

OW-3-04

OW-4-05

Cations

Na+

3.74 (15%)

1.96 (5%)

10.66 (28%)

0.22 (1%)

K+

0.06 (0.2%)

0.06 (0.2%)

0.05 (0.1%)

0.05 (0.1%)

Ca2+

6.74 (26%)

14.72 (40%)

6.29 (17%)

13.65 (34%)

Mg2+

1.93 (8%)

1.50 (4%)

1.70 (4%)

10.81 (27%)

Anions

Cl-

3.61 (14%)

0.90 (2%)

9.90 (26%)

0.23 (1%)

HCO3-

2.13 (8%)

9.51 (26%)

2.46 (6%)

2.48 (6%)

CO32-

0.46 (2%)

0.53 (1%)

0.41 (1%)

0.55 (1%)

SO42-

6.77 (27%)

7.31(20%)

6.42 (17%)

12.28 (30%)

Water Type

Short

Ca-SO4

Ca-HCO3

Na-Cl

Ca-SO4

Long (20%)

Ca-SO4

Ca-HCO3-SO4

Na-Cl

Ca-SO4

Long (10%)

Ca-Na-SO4-Cl

Ca-HCO3-SO4

Na-Ca-Cl-SO4

Ca-SO4

### Menu Commands

The options in the menu include:

Calculate the water type:

For the active sample set: calculates the water type for the active sample set, that is the sample set shown in the sample list

For all samples: calculates the water type for all samples in the project database

Settings...: opens the Water Type tab in the project settings window and allows you to configure how the water type will be calculated.

### Water Type Toolbar Commands in the Sample List

The Sample List view also contains buttons to help you calculate the water type for samples in the active sample set:

Calculates the water type for the selected record(s).

Calculates the water type for all records in the sample list (i.e. the active sample set).