Cal. Health and Safety Code § 25269.6

The department shall adopt a billing system for oversight costs which meets all of the following criteria: (a) Invoices shall be issued within 60 days to the extent practicable, with appropriate incentives for prompt payment. In no event shall invoices be issued less frequently than on a quarterly basis. (b) Invoices shall be mailed to the correct person for the potentially responsible party. (c) Sufficient detail shall be included with each invoice, so that the potentially responsible party can relate the items on the invoice to the benefits received, and additional details, including daily timesheet personnel data, shall be made readily available. (d) Invoices shall be supplemented with statements of any changes in rates and a detailed justification for any such changes. (e) Invoices shall be reviewed for accuracy and appropriateness by a member of the department staff who has direct knowledge of the remediation action. (f) Invoices shall be reasonably consistent with expectations regarding costs, benefits, and outcomes developed during the meet and confer process specified in subdivision (a) of Section 25269.5, if the department’s knowledge of site conditions or other factors which may substantially impact the department’s costs associated with the site, have not changed significantly since the last conference. (g) A process for the timely review and settlement of any outstanding accounts shall be developed and implemented.