Final answer:
The long-term test should be conducted when the initial short-term test results for radon levels are above 4 pCi/L. Radon is a known carcinogen and can increase the risk of lung cancer. It is important to monitor radon levels in water and take necessary measures to mitigate the risk.
Step-by-step explanation:
The long-term test should be conducted when the initial short-term test results for radon levels are above 4 pCi/L. Radon is a radioactive gas that can be found in soil, air, and drinking water. It is a known carcinogen and can increase the risk of lung cancer.
Long-term exposure to radon can occur through contaminated drinking water or indoor air. The recommended levels for radon in water are less than 10-50 µg/L. It is important to conduct a long-term test to monitor radon levels and take necessary measures to mitigate the risk if the initial short-term test results are high.