We consider the problem of sharing the cost of cleaning the non-point source pollution of industrial sites among the firms that own these sites. The bilateral liabilities between firms are depicted by an undirected graph. We introduce and characterize axiomatically two allocation rules inspired by the celebrated Polluter pays and Beneficiary pays principles in environmental law. The first one shares evenly the cost of cleaning up a site among the firms that can have caused the corresponding environmental damage. The second one charges to each firm the entire cost of cleaning up its own production site. We also establish connections with cooperative game theory.