The city shall cause to be issued an invoice for the costs incurred in mitigating or causing the mitigation of the effects of a release. Such bill shall be due and payable within fifteen (15) days after the billing date. Failure to pay after sixty (60) days from the billing date shall result in an additional ten percent late charge. Unpaid bills may be referred to a collection process after ninety (90) day delinquency or be assessed against the parcel of land pursuant to Section 38773.5 of the Government Code as amended and shall thereafter be transmitted to the tax collector for collection. Per the discretion of the finance director or his designee, collectible costs can be billed on a periodic basis. (Prior code § 4520)