Cal. Streets and Highways Code § 705

In any case in which the department is required under the provisions of this article to pay the cost of removal or relocation of any utility facility, it shall be entitled to credits as follows: (1) In the amount of any betterment to the utility facility resulting from such removal or relocation, not in excess of the cost of the increased capacity of the facility. (2) The salvage value of any materials or parts salvaged and retained by the utility. (3) If a new facility or portion thereof is constructed to accomplish such removal or relocation, an allowance of an amount bearing the same proportion to the original cost of the displaced facility or portion thereof as the age thereof bears to the normal expected life thereof. A credit shall not be allowed against any portion of the cost which is otherwise chargeable to the utility. A credit allowance for age shall not be applied to publicly owned sewers.