The coastal city of Shenzhen is likely to be threatened by major seawater intrusion unless urgent measures are taken to curb excessive groundwater use, a survey shows.

Sources with the Shenzhen Municipal Bureau of Water Resource said yesterday that the city in south China is suffering lowering levels of groundwater, which means it faces becoming contaminated with seawater coming in to replace it.

"The excessive use of groundwater since the 1980s has lowered the underground water level," Zhao Bingbing, an official with the bureau told China Daily yesterday.

He is calling for urgent measures to be taken to prevent the problem.

Experts said too much groundwater has been exploited in Shenzhen as tap water was not widely used until the 1980s when the city witnessed urban expansion.

According to Zhao, the city's water authority conducted a survey early last year and found that seawater has already intruded into some coastal areas in the city.

Groundwater in Xiangmi Lake, Huaqiao Town and Zhuzilin, along the Shennan Dadao, a major highway along the coastal line in the city, has been found to contain too much seawater, according to the survey.

"Seawater has intruded northward beneath the highway, and it is expected to come over to the city's centre," Zhao said.

The area currently affected totals nearly 56 square kilometers, Zhao said.

Shenzhen has a coastal line of more than 230 kilometers, which is likely to be further intruded by water from the sea if no prompt measures are taken to curb excessive groundwater consumption, according to Zhao.

It could lead to the salinization of land and making fresh water salted, which deteriorates its quality.

"Residents are being suggested not to use groundwater in the southern part of the Shennan Dadao since it has been invaded too much by seawater," Zhao said.

Groundwater there is found to contain chloroquine of 4,000 milligrams per liter, much higher than the average standard of drinking water.

It is reported that more than 20 people suffered with diarrhoea and stomach complaints earlier this year after drinking water there.

The problem of seawater intrusion could also destroy geological structures by lowering ground surface levels, Zhao said.

At present, the city still has more than 1,000 private wells in operation.

"These wells must be soon prohibited," Zhao said.

Zhao added that groundwater exploitation should also be banned in areas along the city's coastal line.

He has called for a monitoring system along the coastal line to detect problems, Zhao said.

(China Daily December 8, 2005)