A recent study discovered that many Tel Aviv wells are polluted beyond suitability as drinking water sources. Data collected by the Health Ministry and Water Authority showed that 96 of a total 166 wells in the Tel Aviv area were closed due to contamination. Nearly two-thirds of the wells have been shuttered since 1980, when all 166 were in full operation. The pollution has been caused by two types of activities. First, contaminants from armament manufacturing, agricultural runoff and sewage systems seep into the groundwater table.