Cal. Code of Civil Procedure § 1250.420

The parties may by agreement refer a dispute that is the subject of an eminent domain proceeding for resolution by any of the following means: (a) Mediation by a neutral mediator. (b) Binding arbitration by a neutral arbitrator. The arbitration is subject to Chapter 12 (commencing with Section 1273.010). (c) Nonbinding arbitration by a neutral arbitrator. The arbitrator’s decision in a nonbinding arbitration is final unless within 30 days after service of the arbitrator’s decision a party moves the court for a trial of the eminent domain proceeding. If the judgment in the eminent domain proceeding is not more favorable to the moving party, the court shall order that party to pay to the other parties the following nonrefundable costs and fees, unless the court finds in writing and on motion that the imposition of costs and fees would create such a substantial economic hardship as not to be in the interest of justice: (1) All costs specified in Section 1033.5, limited to those incurred from the time of election of the trial de novo. Nothing in this subdivision affects the right of a defendant to recover costs otherwise allowable pursuant to Section 1268.710, incurred before election of a trial de novo, except that a defendant may recover the costs of determining the apportionment of the award made pursuant to subdivision (b) of Section 1260.220 whenever incurred. (2) The reasonable costs of the services of expert witnesses who are not regular employees of any party, actually incurred and reasonably necessary in the preparation or trial of the case, limited to those incurred from the time of election of the trial de novo. (3) The compensation paid by the parties to the arbitrator.