Del. Code Ann. tit. 9, § 3402
Any new subdivision or land development in any unincorporated area in New Castle County that is approved after January 13, 2022, shall establish a stormwater maintenance district, as required by the ordinance adopted under subsection (a) of this section, as a condition of plan approval. Fees for the district must not be incurred until the subdivision or land development is complete and the stormwater infrastructure is approved by the appropriate regulating agency.
Any subdivision or land development established before January 13, 2022, in any unincorporated area in New Castle County contained within ascertainable boundaries, may petition county government under the ordinance adopted under subsection (a) of this section to declare the area a stormwater maintenance district.