This map shows the locations of identified leaking underground storage tanks (LUSTs) in the valley (pink dots). In the southern valley, a survey of all underground fuel storage tanks (USTs) is also shown (similar information for the northern valley is not available). Based on the rate of occurrence of LUSTs in the southern valley, fully 30% of UST sites have problems. Note that because steel tanks corrode with time, it is not a question of whether USTs will leak, but when and how badly. Although many of these LUST sites were commercial fuel stations and did not affect local ground water when they leaked, some were major releases from large storage facilities which have directly affected ground water (e.g. Union Pacific rail yard diesel tank releases).