What Is OnSemi Allowed to Release Into Gildersleeve Brook?

A renewed industrial wastewater permit has reopened for one narrow change: a proposed Total Dissolved Solids limit of 510 milligrams per liter instead of 500. Here is what changed, what did not, and how residents can comment before July 31.

The public notice for the OnSemi facility in East Fishkill sounds enormous at first glance. It describes an existing discharge of up to six million gallons per day of treated sanitary and industrial wastewater into Gildersleeve Brook, along with stormwater from multiple outfalls across the Hudson Valley Research Park.

But that is not the new proposal currently open for comment.

The New York State Department of Environmental Conservation has already reviewed a broader five-year permit renewal. The reopened comment period is limited to one revision: changing the proposed Total Dissolved Solids, or TDS, effluent limit from 500 milligrams per liter to 510 milligrams per liter.

That distinction matters. Residents are not being asked to comment on a brand-new six-million-gallon discharge. They are being asked to comment on whether the TDS limit should be 510 instead of 500.

What are Total Dissolved Solids?

Total Dissolved Solids is a broad measurement of dissolved material in water. It can include minerals, salts, metals and other substances small enough to pass through a filter. TDS does not identify one particular pollutant. It provides a combined measurement that can help regulators track changes in water chemistry.

A ten-milligram-per-liter increase may sound small. Whether it is environmentally meaningful depends on how the limit is measured, the facility’s actual discharge data, the stream’s existing condition and the technical basis DEC used to select 510.

Hudson Valley Happenings asked DEC, OnSemi and Riverkeeper to explain why the number changed, what recent monitoring shows and what the difference could mean for Gildersleeve Brook. DEC acknowledged the questions but did not provide substantive technical answers before publication. OnSemi and Riverkeeper did not respond.

What is already part of the draft permit?

According to DEC’s public notice, the draft permit covers the existing treatment system serving the OnSemi East Fishkill facility and other parcels in the former IBM East Fishkill complex.

The permit addresses treated wastewater released through Outfall 001 into Gildersleeve Brook, a Class C(t) waterbody, as well as stormwater from additional outfalls.

The broader draft includes numerous added, revised and removed limits, a toxicity-reduction evaluation compliance schedule, a mercury-minimization plan and notification requirements for new discharges or facility expansion. Those changes were part of the earlier review process.

For this reopened comment period, DEC says only the TDS revision from 500 to 510 milligrams per liter is open to comment.

What should a useful public comment address?

A comment does not become more persuasive because it is angry or long. It becomes useful when it addresses the specific decision before the agency.

• What monitoring data supports a 510-milligram-per-liter limit?

• Is the proposed number a daily maximum, monthly average or another type of limit?

• How frequently will the discharge be tested?

• What are the facility’s recent TDS readings?

• How was the condition of Gildersleeve Brook considered?

• What would happen if monitoring shows repeated exceedances?

• Why was 500 changed to 510 after the earlier draft was noticed?

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Comments about unrelated parts of the permit may fall outside this reopened review because DEC has explicitly limited the current comment period to the TDS change.

How to comment

Written comments must be received by Friday, July 31, 2026. Requests for a legislative public statement hearing must also be submitted in writing by that deadline.

Reference: Application ID 3-1328-00025/00002 SPDES Number NY0005096 OnSemi East Fishkill Facility

Send comments to: Rebecca Crist NYSDEC Region 3 Headquarters 21 South Putt Corners Road New Paltz, NY 12561 Phone: 845-256-3014

Email: dep.r3@dec.ny.gov

The bottom line

The permit is large. The question currently open to the public is small and specific.

DEC is considering whether to finalize a Total Dissolved Solids limit of 510 milligrams per liter instead of 500 for an existing permitted wastewater discharge.

Residents who want their concerns entered into the official record have until July 31 to submit written comments focused on that change.

Source: NYSDEC Notice of Completed Application, published July 1, 2026.