40 CFR 310.16: What kind of cost documentation is necessary?

Cost documentation must be adequate for an audit. At a minimum, you must:

(a) Include a description of the temporary emergency measures for which you request reimbursement;

(b) Specify the local agency that incurred the cost, (such as, the Town Fire Department, the County Health Department, or the City Department of Public Works);

(c) Include invoices, sales receipts, rental or leasing agreements, or other proof of costs you incurred; and

(d) Certify that all costs are accurate and that you incurred them specifically for the response for which you are requesting reimbursement.