El Caracol, Ecatepec

El Caracol Solar Evaporation Pond (Deposito de Evaporación Solar "El Caracol"), also known as El Caracol de Texcoco or "El Caracol de la Ciudad de México, is a large spiral-shaped retention basin located over the former lakebed of Lake Texcoco, northeast of Mexico City, in the municipio of Ecatepec de Morelos, Mexico. Built in 1944 by the SOSA Texcoco corporation, the basin is called el caracol (the snail) due to the short, spiral-shaped concrete levee that circles it. Approximately 3,200 m in diameter, the levee was part of the original plan to create a solar evaporation pond to extract sodium carbonate (soda ash) and calcium chloride (rock salt) from the mineral-rich underground waters of the former Lake Texcoco. Water from the lake entered the structure from a pumphouse situated on an island in the middle of the basin, and was channeled outwards and clockwise (with the channel increasing in width and decreasing in depth) until it became too shallow to flow further. The water would then evaporate in the opposite (counterclockwise) direction, maximizing efficiency and allowing for a predictable collection of 100 tons of salts per day. Half of the soda ash collected was to be processed into calcium hydroxide (lye) at a series of plants nearby. Unfortunately, poor understanding of the principles of alkaline brines made the process (particularly the refining) more expensive than SOSA Texcoco expected, and the venture was not profitable. In the late 1950s, the company was absorbed into the government-administered Fomento Industrial SOMEX conglomerate, which began exploring more profitable uses for the facility. In 1967, it was discovered that the blue-green algae natural to Lake Texcoco's alkaline waters (which had previously been filtered and discarded) could instead be deliberately cultivated in the El Caracol basin, collected with screens and processed into Spirulina, a dry nutritional supplement powder, for commercial sale.