National Geographic Today
In the crowded, garbage-strewn alleys and market streets of Mataraya, one of Cairo's poorest and busiest neighborhoods, lies one of Egypt's most sacred sitesAncient Heliopolis. The city and other archaeological treasures in Northern Egypt are under serious threat from forces above the ground, but perhaps even more from below.
A leaking sewage system, exacerbated by a rising population, has caused the water tablethe upper level of groundwaterto rise and threaten to turn the ancient tombs and temples to dust, said Zahi Hawass, National Geographic Explorer-in-Residence and Secretary General of Egypt's Supreme Council of Antiquities.
"The water table brings salt, and this salt damages the limestoneit turns the limestone to a powder," Hawass said.
Heliopolis dates back 6,000 years. It was the first great priestly city of Egypt. It is where the sun god Ra had his temple, where great scholars first invented the obelisk and the solar calendar, and where the legendary phoenix set itself on fire and rose from its own ashes.
But Heliopolis is destined to join the desert sands if the salty waters are not stopped. Hawass has proposed building a new sewage system just for this area.
In addition to faulty sewers, Richard Stephenson, a professor of civil engineering at University of Missouri-Rolla, hypothesizes that the Aswan Dam also contributes to the rising water table. It enables farmers to irrigate year-round and may also cause a buildup of salt.
The Nile Plateau was originally a seabed, and the sands and soil are naturally salty. Before the dam was built in the 1960s, the annual Nile floods would wash the salt into the Mediterranean. Now it prevents flooding, allowing natural and fertilizer salts to accumulate, says Stephenson, who is collaborating with Egypt's National Research Institute of Astronomy and Geophysics to investigate Luxor's disintegrating monuments.
The pore structure of the soil encourages "strong capillary action," Stephenson said, which draws the salty water to the surface and into the porous sandstone foundations of the monuments. The dry desert heat then causes the water in the stones to evaporate, leaving behind "salt crystals that cause the sandstone to split, flake and crack," Stephenson said.
Last July, while in Luxor, Stephenson found white salt deposits on the foundation stone of temples in Luxor.
Possible solutions include installing wells to lower the water table, replacing foundation stones with less porous material, and injecting chemical sealant between structures and the soil to create water barriersall of which are tremendously expensive and risk damaging the monuments.
When archaeologists discovered a 2,500-year-old tomb of a palace worker in Mataraya, it was soaking in sewage. The water was seeping through the exterior limestone and causing the precious hieroglyphs to disintegrate. Hawass says that for a tomb its size, it is one of the most beautifully decorated in all of Egypt.
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