1

I. Water Supply Networks and Facilities

Topic I.3. Sources for Water Supply - Surface Waters and Groundwater : Quality and Peculiarities

Water Quality

General classification of water quality parameters: Physical - temperature, transparency, turbidity, colour, smell, taste,

conductivity, suspended solids

Chemical - dry residuals (total, soluble), hardness, alkalinity, pH, oxidability, gas saturation

bacteriological and biological - pathogens, coli-index, coli-test, etc. and hydrobionts, algae, fitoplancton, zooplancton, etc.

2

Water Quality

A. Physical Water Quality Parameters

Temperature

Rivers - 0o - 26o C

Lakes - relatively constant (equal to the mean air temperature)

Bulgarian State Standards (BSS) - 6o - 12o C (degree santigrade)

Transparency/Turbidity

Snelen’s type (symbol) - for transparency (30 cm according to the BSS)

Suspended solids concentration, SS (SS < 2 mg/l according to the BSS)

Colour

Platinum-cobalt scale (solution of K2PtCl6 and CoCl2 in H2SO4)

Roubliov’s scale (solution of K2CrO2 and CoSO4), [degree];For natural waters - 10 - 20; For drinking water < 30 degree according to the BSS

3

Water Quality

Taste

Salty, sweet, bitter, sour (no any taste is permissible in drinking water)

Smell

Aromatic (pleasant), hydrosulfuric (H2S), phenolic, marsh, chloric (Cl2);

5-grade scale (based on probe dilution) is applicable for smell detection; smell < 2 degree is permissible for drinking water according to the BSS

B. Chemical Water Quality Parameters

Dry residuals (DR)

DR < 1000 mg/l is the standard limit for drinking water accord. to the BSS

Non-organic residuals (NOR)

4

Water Quality

Hardness

It is due to presence of Ca2+ and Mg+ salts of carbonic acid (temporal hardness) and/or Ca2+ and Mg+ salts of strong acids (permanent hardness)

Measures - mg-equiv./l, degree (German, French and English); 1o Germ. = 10 mg/l CaO

According to the BSS, hardness > 25o Germ. is not permissible for drinking water

Alkalinity

It is due to presence of HCO3-, CO3

2-, K2SO4, Na2SO4,KCl, NaCl

pH (active reaction)

H2O H+ + OH-

[H+] = 10-7 mol/l - neutral

pH = -log[H+] = -log(10-7) = 7 - neutral active reaction

5

Water Quality

Oxidability

Measure - the mass of KMnO4, necessary for oxidation of the organic substances in a unit water volume, [mg/l]

Standard limit - 2,6 [mg/l]

Content of Fe2+ and Mn+

In groundwater Fe2+ and Mn+ are usually in the form of Fe(HCO3)2 and Fe(HCO3)2 , respectively

On the surface: 4Fe(HCO3)2 +O2 + 2H2O = 4Fe(OH)3 + 8CO2

4MnHCO3 + O2 + 2H2O = 4MnOH + 4HCO32-

The Fe(OH)3 and MnOH create a bitter taste and a black colour of water

Standard limits:0,2 mg/l for Fe(OH)3 and 0,1 mg/l for MnOH, respectively

Carbonic acid balance

4HCO32- CO3

2- + CO2 + H2O

The above balance depends strongly on pH value

6

Water Quality

Dissolved gases

CO2 presents in natural water at pH < 8,3

O2 concentration depends on water temperature and atmospheric

pressure

H2S (and/or its ions HS- and S2- in ratio, depending on pH and

temperature) present in some groundwater

7

Water Quality

C. Bacteriological and biological water quality parameters

Bacterial content

Bacteria general division: pathogens (creating illness); saprophytes (non-

harmful)

Esherihia Coli - a saprophyte, accommodating at the human stomach and

faeces is an indicator for faecal pollution of water

Measures: coli index - number of the coli-bacteria in 1 l water volume;

Standard limit: coli index < 10

Biological content

General division: Fauna - zooplancton (suspended), bentos (sediment),

hydrobionts (attached); Flora - phytoplancton (suspended), algae

(suspended, rooted)

Saprobility (symbioses): polysaprobe, mezosaprobe ( and ) and

oligosaprobe

8

Water Supply Sources Peculiarities

A. Surface Waters: Rivers

Source of feeding - atmospheric water and groundwater

Runoff regime - great variety of flowrates and water levels

Water intake Water level security, %

category min max

I 1 97

II 3 95

III 5 90

Water quality - depends on geological, climatic and anthropogenic factors

Erosion and silt regime

9

Water Supply Sources Peculiarities

B. Surface Waters: Lakes and Reservoirs

Stratification in depth

I zone (0 - 4 m) - higher temperature and pollution, low O2 concentration, plankton development

II zone (under 4 m) - lower temperature (1o C decrease in every 1 m depth), highest O2 concentration

III zone (above the bottom) - lowest temperature and O2 concentration, high H2S, Fe2+ and Mn+ concentrations

Water quality

It depends on: geological features of the catchment and the lake bottom; anthropogenic impact; evaporation (increasing water salinity), euthrophication (phytoplankton “blooming”).

Silting

(The “dead” volume filling)

10

Water Supply Sources Peculiarities

C. Groundwater

General classification:

I. According to the salinity (mineral salts content) Fresh (sweet) water - up to 1 g/l dry residuals Slightly mineral water - 1 - 3 g/l dry residuals Average mineral water - 3 - 10 g/l dry residuals Mineral water - 10 - 50 g/l dry residuals Strong mineral water - above 50 g/l dry residuals

II. According to the temperature Very cold water - about 4o C Cold water - 4o - 20o C Hot water - 20o -37o C Warm water - 37o - 42o C Very warm water - 42o - 100o C

11

Water Supply Sources Peculiarities

III. According to the hydrogeological conditions Shallow aquifer (water-bearing stratum) -less than 10 m Deep (10 - 30 m) non-pressurised aquifer - over impervious

layer (clay) Deep (10 - 30 m) pressurised aquifer - between two

impervious layers

IV. According to water location At the river terrace (send, gravel) At the rock cracks Springs - water coming out of pressurised or non-

pressurised aquifers Artesian water - coming out of pressurised aquifer and

with

piesometric head above the ground level