What is required for the earth, upon which impurity has fallen, to become purified?

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The earth is not purified until both the color and the odor of the impurity have disappeared, because their persistence indicates the persistence of the impurity itself. If the color of the impurity cannot be removed except with great difficulty, then its removal is waived, similar to the ruling for clothing. The same principle applies to the odor. If the impurity consists of scattered particles, such as spoiled parts, dung, or dried blood that mixes with the earth, it is not purified by washing, because its essence is not transformed. Purification only occurs by removing the portions of the ground where the impurity particles are certainly gone. If urine is dealt with while wet, and the soil bearing its trace is removed, the remaining ground is pure because the impure substance was wet and has been removed.