A 'normal' fault is a possible cause of warm groundwater being expelled from the deep subsurface. With such a fault, the hanging wall tends to move vertically down thereby compressing the Earth crust and forcing water out of the formation. If the well intersects fault-lines, it would be worthwhile to investigate the type of faulting and possibly the mineral composition of the fractured region. Some minerals can form vein-like structures that transfer fluids from the subsurface.

Hello Muhammad,

First, 30-37 °C might not be so anomalous at a depth of 300m. If the local geothermal gradient is weak, then one reason could come from exothermic reactions between your "hard material" and percolating fluid. Lukewarm water ( or evidence of) can be found when buried granitic bodies undergo meteoric alteration. A number of chemical reactions (e.g. biotite -> chlorite) occuring during alteration are largely exothermic. This is one possible reason, among many others.

This is a very interesting problem. There are very few sources of heat for groundwater, so maybe just working through the possibilities will let you eliminate what it is not, and whatever is left will be the most likely reason? Generally, possible sources of thermal energy include physical, chemical and biological processes.

Under physical sources, there’s the sun, geothermal, and technological. It sounds like you have ruled out geothermal as a possibility so the only other possible physical sources of heat would be the sun or a man-made source. Although as Laurent mentioned, weak geothermal gradients can still exist even if there are no obvious active features, so revisiting this to be sure might be worthwhile. Obtaining some soil and groundwater temps, including vertical profiling, might help you determine where the heat is coming from; ie: if soil temperatures above the wetted zone are greater than that of the ground water with increasing temperatures to the surface, this may be related to thermal storage of solar energy and therefore a function of thermal conductivity of the soils. Or if groundwater temperatures increase with depth then a geothermal source is likely. Another thought, is it possible that the water comes very near to the surface or daylights anywhere nearby? Direct or near-direct solar exposure could allow temperatures to rise to this point, a look at the areas for groundwater recharge and surface water infiltration might help you determine if this is a potential cause. Also, are there any power plants or steam generation/transmission facilities in the area? Re-injected groundwater used for power generation could certainly reach the temperatures you’re describing. Also, I’ve seen temperatures in groundwater like this before, but from underground steam transmission piping in New York City; the localized transmission of steam, in piping located 10 feet above the apparent water table interface, resulted in ground water temperatures between 30 and 40 degrees C.

Under chemical sources some geochemical analysis of the groundwater may be revealing; a simple example would be a reaction with the infiltrating water or groundwater as it moves through the subsurface; for instance, if the water is acidic, and soils are highly basic, it is possible that a exothermic reaction might take place. A comparative study of pH of soils, ground water, and rainwater might be revealing. Additional geochemical markers such as carbonate and sulfates may help to understand if there are any significant geochemical changes taking place that might be generating a thermal reaction in the subsurface.

Under biological, a look at dissolved oxygen and oxidation-reduction potential (ORP) values in ground water in your study area and organic carbon in soils may be revealing. If dissolved oxygen levels are very low then it may be an indication of ongoing biological processes. I’ve seen several sites where high rates of biological activity can produce significant changes in thermal gradients in subsurface aquifers. Usually this is only in areas of groundwater contamination though, where significant mass of organic compounds are present, but it is something to consider.

Dear amer and Laurent, Pump well depths range from 500 to 700 ft

Dear jude Musuuza, As I have mentioned depth to hard rock is more 1000 ft, so wells interception by fault lines may not be possible.

I agree with Laurent about the possibility of exothermic reactions.

Thanks a lot for the response.

Any experience with similar conditions anywhere else in the world?

A regional flow discharge. Is there high mountains not far from the wells?

I don't know the distance between the wells and basement outcrops, but an input of warm water laterally from the basement to the alluvional deposits is possible. Here, near Pisa - Italy, we have geothermal springs on the mountains (Mesozoic fold and thrust units), that feed the alluvional deposits in the adjacent plain. Groundwater from sands and gravel some 10 km from the basement and 100 m below surface maybe up to 27°, and geochemistry reveals its provenance from mixing with the geothermal aquifer.

Dear Muhammad, I have to add one comment: the source of temperature may be far away from the drilled well, therefore, first you have to check the regional groundwater flow. this may indicate the source of temperature. good luck

Dear Mohamed, first of all did you observe any seasonal variation in the temperature? If so it is very simple, a matter of heat transfers. Otherwise you can study the options from Brian Shedd which need more investigations to be taken.

Best of Luck

In general the ground water temp.is increasing by depth and as you told there is hard rock at bottom may be the reason.The movement of ground water also contributing the temp.

Are you sure that is a natural phenomena? Aren't there any antropic heat source nearby, such as industries that pump down in the borehole hot reject water?

Generally speaking, geothermal field in a basin is disturbed mainly by geological structures, thereby causing geothermal anomalies. What you have observed in a deep groundwater aquifer in Lahore is not a high temperature geothermal anomaly that requires an extrodinary heat source. There are many other hot water aquifers or hot springs found in your country.

I am thankful to Brian Shed for the detail of possibilities of such a temprate groundwater. The answer by Zhonghe Pang is also very reasonable. As a conclusion to my question on high temprature groundwater, I fully agree with Pang.

the highest concentrations of radio elements Potassium , Uranium and Thorium or other chemical elements in this case would be the main reason for the elevation of the temperature gradient especially in the abcence of thermal activity.

Mohammad,

Your question is very interesting and scientific and so are scholarly suggestion for plausible causes of high groundwater temperature. But, I have another point of view. Generally in under sprawling cities with significant high heat island, there develop an underground heat island due to impervious surface. There is available significant literature available on this phenomenon which is attributed with heat islands and increasing Earth temperature. I consider it as an opportunity as "every cloud has a silver lining". It is expected that intensity of this phenomenon will be higher in the subtropical countries than temperate region even though experiment in Canadian cities have proved it. Most relevant and technical literature may be obtained from the Digital Library of AGU. This opportunities may be used for cooling in summer and heating buildings in winter by installing heat-pumps.

I am contemplating to submit a project in my own country to study potential of this energy in cities of different sizes and substrate to an appropriate research funding agency.

Interesting to read from M Firoz Khan, yes, it is well reported in literature about asphalt and concrete surfaces acting as heat trap in big cities. But, the observations took by myself reveal that groundwater tempratures increase instead of decreasing towards the periphery of the city. In my opinion, it is a phenomenon linked to some activities to deeper depths.

Thank a lot for sharing.

A source of thermal anomalies I have not seen mentioned yet is the transport of heat by groundwater to discharge areas. If the area has topography that creates gravitational basin flows from high to low elevation, and if there is high geothermal heat flow (~100 mW/sq. m), for a specific range of permeability cold recharging groundwater at high elevation can pick up heat from the geothermal gradient, lowering heat flow in recharge areas, and transports it to the discharge area producing elevated heat flow and groundwater temperatures. Groundwater flow from a wide radius toward a convergent discharge can divert a significant amount of heat toward a local area of discharge.

Georgy

You are very right. Heat transfer in a porous media due to geothermal gradient is possible. There are several hot springs in nearby Himalayas, but the temperature is not of the required level. Most important is possibility of of nearby presence of some radioactive material. In my Punjab (Indian Punjab) recently prevalence of cancer higher than national rate and sometime back presence of uranium in human body and hair in our Punjab is a complementary evidence to this speculated possibility, if there are other reasons of prevalence of cancer and finding of uranium in the bodies of people of our Punjab.

Gregory and Firoz Khan

Heat transfer itself can have two modes of transfer: i) due to temprature gradient itself; and ii) owing to fluid transport i.e. groundwater flow itself. In contrast to mentioned by Gregory, there is no issue of topography in and around Lahore. Also my own groundwater modeling experience and travel time caluclations for plain area like Punjab (on both sides of the border) groundwater travels a distance of about 0.5 to 2 km in 100 years time span (with normal gradients). Creation of cone like shape of contours i.e. pointing groundwater levels to very lower elevations in areas with heavy groundwater pumping (like in Lahore city) also supports slow movement of groundwater in the aquifers. Thus, heat transfer from some far away distance can be naggated. In my opinion it can be some geothermal activity/source deep enough, which may show its evidence in future times.

Two possibilities:

1, As being said already, you do have geothermal activity. Either by groundwater percolating deep into the earth crust or by groundwater being in contact with geothermal sources closer to the surface. I do remember that Pakistan has still active mud-vulcanoes, thus has actual geothermal activity (but maybe not in your area).

2, Rapid groundwater recharge happens in summer where temperatures are high (in the order of what you find in groundwater). At rapid groundwater flow those temperatures could be preserved till discharge.

Looking at the hydrochemistry should help you to check for geothermal activity. You may also want to date the groundwater. If it's young groundwater (a couple of years old) you may have high recharge temperatures. More elaborate analysis could include noble gas analysis, where high helium content is found in geothermal waters.

Take a look at Applied hydrogeology in page that explains some kinds o springs. it is possible to have hot springs without a heat source. groundwater can be heated by geothemal grade and, depending on geological structures, it may flow up without losing the heat acquired.

Dear Dr M Basharat,

You have not mentioned of the chemical composition of the ground water or have not reported of any bacteriological signatures. In certain cases bacteriological factors too could initiate exothermic events contibuting to temperature rise. On the other hand simple presence of anomalous sulfate too could indicate a possible geothermal source. Sometime even rapidly flowing ground water or ground water seated near some shallow subsurface radioactive pockets / inland saline water pockets contribute towards a temperature increase. I would request you to kindly provide some more detailed information in this regard

Dear Choudhury,

Thanks for the ur comment. Yes the chemical composition is normal except some samples having As values above the UN standard of 10 ppb. The water is used for domestic purpose without any treatment. Also the pumping is from depth of 500 to 700 ft, where bactarial contamination is out of question, However, I am unaware of the sulphate contents, again I would say it is drinking quality groundwater.

On basis of this discussion, I have concluded this to be Geothermal activity at some deepr depths.

Thanks once again.

You do not necessarily have to invoke a geothermal cause, in the sense of having a geothermal heat source at depth and in particular if you do not have a geochemical signature of such a geothermal origin. these warm waters could simply be the effect of a rapid uprise from depth (simply hot for normal geothermal gradient). These waters could upflow along a fault and succesively circulate inside the sediments. These hot waters colud simply indicate the presence of a nearby fault, possibly an active fault buried under the sediments.

I completely agree. One problem still unresolved is to understand how deep hot fluid could simply rise in transient permeable fault zones... Velocities are low, and high permeability zones cannot stay tens of (hundreds of) years highly permeable... I suspect that low thermal diffusivity of rocks plays a role... (Once hot fluids have arisen, their thermal inprints may be stored in the surroundings)...

I uphold the opinion by Laurent as the possible reason for high groundwater temperatures in the area. Another reason for mildly high temperatures is that depth to bed rock is more than 330 m. Therefore any geothermal heat source has less effect on the upper groundwater which is being pumped for domestic and industrial use.

I fully agree with Montanari. Rapid uprise can occur the dramatic thermal anomaly. Threr are some similar hot springs(well type, within 300m depth) in Korea. In addition, all of them are distributed around the faults. And the stable isotopes, such as hydrogen and oxygen, show the quite stable values at each of hot springs. It means that the source water of hot spring is also quite stable, even with the high pumping rate. In our cases, high temperature of groundwater at hot spring are highly denpendent on the heat convection, due to the rapid uprise of groundwater (actually, still debatible).

Dear Mr Basharat.

I fully agree and support the views of Dr.D. Montanari and suggest work on the lines outlined by Mr. Taehee.Our extensive work on Indian hot springs also supports his inferences. Mohan Gupta.

Aside from the alluvium. What is the geology of the place. do you have any limestone and basaltic rocks in the area. One possible explanation would be the exothermic reaction of groundwater with limestone and basalt or probably ophiolite. The chemical reaction can result in elevated temperature in groundwater. There is one example in the Philippines where reaction of groundwater with ophiolitic rocks result in elevated temperature around 35 degrees Celsius. Please review the geology.

I agree with Montanari; several thermal springs are fed by groundwater hot for normal geothermal gradient. Anyway, more details would be necessary before to give an opinion. Is the phenomenon observed in many (or a few) Wells? How much is extended the area in wich Thermal water is pumped? What about the depth reached by the Wells? What is the average value of atmospheric temperature? .....

Dear Mr. Basharat,

Here is a reference that may be of interest to you:

http://onlinelibrary.wiley.com/doi/10.1111/j.1745-6584.1983.tb01943.x/abstract

Kind regards,

Dan

One possible explanation of thermal groundwater of the type you describe, in the absence of magmatic activity, results from deep circulation of meteoric water in a terrane with an elevated geothermal gradient.

A possible explanation that this water is coming from a deep groundwater aquifer ( the depth to upper surface of the aquifer range from few to several hundreds of meters below ground surface). Circulation could be through deep faults or fractures.

Las formaciones estratificadas, con estructura vertical, permiten que el agua

ascienda desde zonas profundas (500-1000 m) sin que apenas tengan

enfriamiento.

Thank you Aria for the links

Good sources of infromation. Thank you!

It would be very useful to see the chemistry of those waters. If you have analyzed major ions you may deduce the "water/rock interaction" history of your waters. For example, you may deduce if those waters have dissolved important amounts of carbonates like calcite or sulphides like pyrite, as both dissolution reactions are highly exothermic. There are mine waters with temperatures as high as 50-60 ºC only because of their interaction with pyrite. The geological knowledge of the area would be also very useful.

Javier, very nice to know your answer, I will check the ionic composition

Please also check if this is related to fluctuations in the basement-bedrock underneath the loose sediments. Uprise of bedrock may cause heat redistribution-accumulation in these localities.

Exothermic reaction from serpentinization, radioactivity, faults

Look at the chemical composition and isotopic composition of groundwater, there are no inflow at the bottom?

Surface temperature from 33-37 degree centigrade is just a warm water.There are various reasons for the occurences of thermal water such as :

(1)Deep water percolation

(2)Frictional movement of the hard rock masses.

(3)exothermic reactions

(4) radio active activities.

(5) high heat flow values.