Groundwater and Temperature

　　Groundwater and Its Thermal Variations

　　Have you noticed that water from wells tends to have a consistent temperature? It’s commonly observed that in wells between 30 and 60 feet deep, the water is roughly 2° to 3°F above the local yearly average temperature. The temperature decreases by about 1°F for every additional 64 feet of depth. Typically, deep wells穿透不透水层 to reach an underground water source, while shallow wells are excavated in more permeable layers, just beneath the water table. Deep wells are considered those exceeding 25 feet in depth, with shallow wells being those that do not reach this depth. The depth of deep wells can range from 100 to 3,000 feet, with the majority falling between 100 and 1,000 feet. The composition of water from deep wells changes minimally over time, as demonstrated by a 24-year study of Florida wells, where hardness levels shifted between 342 and 304 parts per million and alkalinity between 168 and 148.

　　Springs are another form of groundwater source, often viewed as clear, colorless, and pure. While many springs fit this description, some are quite murky, especially after heavy rains. Additionally, spring water can have considerable amounts of dissolved minerals and is usually hard. For consumption, spring water should not be deemed safe without regular bacterial testing.

　　Other types of groundwater include mine waters and connate waters. Mines often hold significant water volumes that require pumping. These mine waters can resemble other groundwater sources but frequently contain high levels of sulfuric acid and iron, making them highly corrosive. Connate water, also known as oil field brines, are remnants of ancient seas where sedimentary rock was once laid down, and they are usually very saline. In oil field activities, they are more of a nuisance and present disposal challenges when brought to the surface.

　　Despite the advantages of groundwater sources, they also present challenges. Notable drawbacks include:

• A higher concentration of hardness minerals compared to surface water.
• The presence of iron and manganese in many seemingly good supplies.
• Occasional detection of hydrogen sulfide.
• Higher costs for pumping water from wells than from surface sources.
• Variable mineral content even among wells that are close to each other.
• Potential unpredictability in the availability of the water supply.
• Possible contamination with nitrates or detergents, which may suggest sewage pollution.