Underground Waters

Categories / City Topography/Nature and Natural Phenomena
UNDERGROUND WATERS. St. Petersburg is located in the northwestern part of Moskovsky artesian basin. The water content of the crystalline rocks relate to the residuum and zones where they meet. Their practical utilisation ends in the North of the Karelian Isthmus. The sedimentary cover ground waters are diverse. The primordial ones refer to the Gdov sands of the early Proterozoic: the high-pressure sweet waters around Sestroretsk are used for water supply. They flow 40-250 meters beneath the earth's surface and have an output of 3-10 litres/second. Southwards from Sestroretsk at the lowering level they mineralize and are utilized for balneological treatment. Sestroretsk and Petrodvorets health spas have onsite chloride natrium base springs. They sink deep into the earth approximately 180 meters beneath the earth's surface and have an output of 6-10 litres per second. This reservoir supplies St. Petersburg with water for technical purposes. The constant temperature of about 12 degrees Сelsius and commercial sterility makes it indispensable for many technological processes. The long-term utilization of ground waters in St. Petersburg resulted in the formation of a so-called cone of depression. This was caused by a drop in the water level with a diameter of approximately 100 kilometres and depth reaching 60-70 meters in the centre. The northern wing is faulted with local cones which emerge around the bore-hole intakes of Sestroretsk, Solnechny, Repino, Komarovo, Zelenogorsk. A high-pressure aquifer which relates to the sandy aleurite loam rocks of Lomonosovo suite of the early Cambrian period is located in the southern part of St. Petersburg amidst the waterproof clay of the late Proterozoic. Its capacity is 10-15 meters. Sweet water is concentrated along the fringe and it has a low output. Two more ground water reservoirs are located southwards from Baltic-Ladoga Glint (escarpment) - in the sands and sandstone bands of the Cambrio-Ordovician Period and in carsted ordovician carbonate strata. Both contain high-pressure sweet water fit for consuming. The discharge of the water reservoir occurs along the bench foot through numerous springs and exposals which give rise to the Izhora River, Slavyanka River, Dudergofka River, Strelka River and Shingarka River. The drain of several rivers is captured by water conduits, and is used for water supply and for the fountains of Petrodvorets and Strelna. The waters of the Cambrio-Ordovician reservoir are used only for local needs in the outer part of the Izhora Plateau. The fissure-karst waters of the Ordovician limestone are widely utilized for water supply of Petrodvorets, Lomonosov, Kronstadt, and Krasnoe Selo. Large underground water springs in the outer part of Izhora Plateau - Taitskie, Orlovskie, Demidovskie springs - were captured in the early 19th century. The output of the largest tappings reaches 30-50 thousand cubic meters per day. In the vicinity of the settlements of Ropsha and Lopukhinka they are used for filling up circulating ponds and fish-farming. Some of the Izhora Plateau springs have a hydrocarbonate composition and a mineralization rate of 200-300 milligram per litre. The radon springs near the northern bench of the Ordovician Plateau have long standing fame. The sandy intermoraine strata of Pleistocene deposits being the main ground water reservoirs had been extensively utilized by men from the earliest times. The water they contain is mostly sweet with a high iron concentration. They are processed at aerating plants to be ready for consumption. The Okhta River basin contains an upland intermoraine reservoir related to Polyustrovo ferrocarbonate ground water reservoirs discovered back in 1718. It contains an underground lake situated 41 meters beneath the earth level which supplies water and caters for a mineral table water bottling plant. The mineralization of Polyustrovo water reaches 100-115 milligram per litre, the concentration of iron reaches 40-60 milligram per litre. Their durable exploitation resulted in the level drop and formation of depression cones which was due to the decreased pressure of the waters being pumped out. Similar high-pressure waters flow in the surroundings of Zelenogorsk (iron content - 10 milligrams per litre, used by the local health centre) and around Pavlov on Koltushi Hills. The High-pressure waters of intermoraine deposits impede the development of the underground area of St. Petersburg especially the excavation of various tunnels, foundation pits, and construction of deep foundations. Sometimes underground waters may contain organic residues which when they decompose, condition the increase of gas content of nitric methane concentration in the water. This is particularly true of the residue in the upper reservoirs of the intermoraine strata, as they are also exposed to man-made contamination which sometimes renders it unusable. The new residential areas are threatened by the rising of the underground water level, as it often comes out to the surface, causing additional problems in the territory development and water utilization.

References: Гидрогеология СССР. Т. 3: Ленинградская, Псковская и Новгородская области. М., 1967.

Y. P. Seliverstov.