Table 1. Methods for digitizing sewersheds.
| Method | Method description | Count | Percent | Median flow (mgd) | Mean flow (mgd) |
|---|---|---|---|---|---|
| Digitized from address list | Digital shapefile boundary for the sewershed was provided by a third party (i.e., the treatment plant operator or owning municipality). | 1 | 0.2 | 0.09 | 0.09 |
| Digitized from manhole/sewer main shapefile | NY State Tax Parcel database was used to estimate parcels served by this sewer system. Parcels that are cross listed on the address list provided were assigned to the sewershed to draw the boundary. | 35 | 5.8 | 0.40 | 1.93 |
| Digitized from physical map (JPEG/PDF) | Manhole and or sewer main data were sent by the treatment plant operator and the boundary for the service area was created using these data and NY State Parcel data that intersected with the manhole/sewer main data. | 126 | 21.0 | 0.52 | 3.77 |
| Parcel digitized from DANC records | A document containing a map of the region served by the treatment plant was used to draw the boundary using ArcGIS software. | 55 | 9.2 | 0.10 | 1.26 |
| Parcel digitized from description | Development Authority of the North County (DANC) provided a shapefile of sewersheds that were created starting in 2010 and updated annually. The version this project used was obtained in 2021. Boundary matches current estimates and therefore DANC boundary was used for this treatment plant’s sewershed. | 19 | 3.2 | 0.99 | 3.30 |
| Parcel digitized no description | Treatment plant operator provided a text description of the service area including roads, natural boundaries, number of influent points, and towns/villages/cities served. The boundary was drawn using ArcGIS software and Census data for major roads, municipal boundaries, and NY State Tax Parcel database. Tax parcels that are recorded as paying a sewer tax and fall within the described service area were assigned to this sewershed. | 304 | 50.8 | 0.35 | 1.34 |
| Provided by treatment plant/municipality/county | New York State Tax Parcel database was used to estimate the parcels served by this sewer system. Parcels that are recorded as paying a sewer tax and proximate to the wastewater treatment plant’s geolocation were assigned to the sewershed. | 58 | 9.7 | 11.00 | 47.14 |
| Adjacent sewer systems were subdivided using sewer district data when available. | |||||
| Village boundary | No adjacent parcels were indicated to be on sewer. Municipal village boundary was used as a placeholder. | 1 | 0.2 | 0.05 | 0.05 |
| Total number of sewersehds | 5991 (596 WWTPs) |
Note: Of the original 638 treatment plants identified in DEC’s database, sewersheds were drawn for 592 of them with 4 additional identified that were not in the database. There were 46 that we did not draw sewersheds for because they either do not exist anymore or are included in another system.