<p>We address the issue of allocating the costs of cleaning non-point source pollution originating from industrial sites among the firms liable for these sites. The bilateral liabilities between firms are depicted by an undirected graph. We introduce and axiomatically characterize two cost allocation rules, which are inspired by the Polluter-Pays and Beneficiary-Pays principles commonly referenced in environmental law. The first rule allocates the cleanup costs of a site equally among the firms contributing to the environmental damage. In contrast, the second rule assigns each firm the full cost of cleaning its own production site. Furthermore, we establish links with cooperative game theory to demonstrate the stability of these allocation rules.</p>