Any activity, with a few specific exceptions, which will alter (1) a wetland area, (2) land within 100-feet of a wetland area, and/or (3) land within 200-feet of a perennial stream or river, known as the riverfront area (RFA) must obtain a permit from the Leominster Conservation Commission.
A great place to start is by typing in your address to the Leominster Web GIS. This shows many of the existing wetlands in Leominster. BE WARNED; if there are no wetlands indicated on the map, this does not necessarily mean there are no wetlands on site or that you do not require a permit from the conservation commission. Wetlands are dynamic and may expand or contract over time.
Depending on the project, you may need to submit a Request for Determination of Applicability (RDA) to formally determine the extent of nearby wetlands or hire a wetlands specialist to properly delineate a wetland boundary.
In any case, if you are unsure whether or not proposed work requires wetland permitting, please contact the Leominster Conservation Agent for an informal evaluation.