HSC §25299.93: (a) A joint claim may be submitted for reimbursement of corrective action costs for a commingled plume if all of the following conditions are met: (1) Each person named in the joint claim is an owner,

(a) A joint claim may be submitted for reimbursement of corrective action costs for a commingled plume if all of the following conditions are met: (1) Each person named in the joint claim is an owner, operator, or other responsible party ordered to perform corrective action or remedial action pursuant to this chapter, Chapter 6.7 (commencing with Section 25280), or Division 7 (commencing with Section 13000) of the Water Code. (2) After performing a soil and water investigation in accordance with Article 11 (commencing with Section 2720) of Chapter 16 of Division 3 of Title 23 of the California Code of Regulations, the joint claimants demonstrate to the satisfaction of the local or regulatory agency and the board that a commingled plume exists and that every identified unauthorized release or discharge has contributed substantially to the commingled plume. (3) At least 85 percent of the commingled plume is comprised of petroleum contamination resulting from an unauthorized release from a tank whose owner or operator is eligible for payment of a claim pursuant to Section 25299.54. (4) At least two contributing sites involve an unauthorized release. (5) The joint claimants have coordinated corrective action as soon as practicable. (6) The joint claimants agree to seek preapproval of corrective action costs in accordance with subdivision (c) of Section 25299.57. (7) The joint claimants have entered into a written agreement that provides for a coordinated corrective action plan. The written agreement shall require the joint claimants to do the following: (A) Appoint one of the joint claimants to represent the joint claimants for purposes of interacting with the local or regulatory agency and the board. (B) Permit the joint claimants reasonable access to contributing sites as necessary to perform corrective action. (C) Identify any corrective action costs incurred at contributing sites and assess if any of those costs may be eligible for reimbursement under this chapter. (D) Estimate responsibility among the joint claimants and provide a formula or method for apportioning costs that are not eligible for reimbursement under this chapter or which exceed the limitations prescribed in Section 25299.94. (E) Identify all money or other compensation received by any joint claimant which is related to contamination at any contributing site or the commingled groundwater plume. (b) A joint claim may be submitted for reimbursement of third parties as provided in Section 25299.58 subject to both of the following conditions: (1) The conditions set forth in subdivision (a) are satisfied. (2) An owner or operator named in the joint claim is liable for a third-party compensation claim.