Document 6R5a1w6E7YJOeLaEe8kgZkgXg
Region 6 Compliance Assurance and Enforcement Division
INSPECTION REPORT
Inspection Date(s): Media: Regulatory Program(s) Company Name: Facility Names: Facility Physical Locations:
(city, state, zip code) Mailing address:
(city, state, zip code) County/Parish: Facility Contact:
1/27/2026 Water Clean Water Act City of Donna City of Donna 1800 S. River Rd Donna, TX 78537 307 s. 12th Street Donna, Texas 78537 Hidalgo County David Moreno dmoreno@cityofdonna.org 956-464-3314
Mayor
FRS Number: Identification/Permit Number: Media Number: NAICS: SIC:
TX0132802 (active permit)/TX0024660 (Terminated permit for same site) 4952
Personnel participating in inspection:
Michael Williams
EPA/ 6EN-WMH
Javier Cavazos
City of Donna
Inspector Operator
281-983-2150 956-246-2660
EPA Lead Inspector Signature/Date
Supervisor Signature/Date
MICHAEL WILLIAMS 2026.02.18 16:51:45 -06'00' MICHAEL WILLIAMS
Michael D. Williams
Date
ROBERTO BERNIER Date: 2026.02.19 15:11:49 -06'00' Digitally signed by ROBERTO BERNIER
Roberto Bernier
Date
City of Donna TX0132802/TX0024660
Inspection Date 1/27/2026
Section I - Introduction
PURPOSE OF THE INSPECTION
EPA Region 6 inspector, Michael Williams, arrived at the City of Donna Wastewater Treatment Plant (WWTP) at 10:00 am on January 27, 2026, for an announced National Pollutant Discharge Elimination System (NPDES) inspection. During the opening conference, I met Javier Cavazos, the Chief Wastewater Operator. Mr. Cavazos was informed that this was an EPA lead compliance evaluation inspection to determine compliance with the facility's NPDES permit TX0132802, facility operations and maintenance requirements under the Clean Water Act (CWA). The inspection was conducted under the authority of the NPDES permit program, in accordance with the Federal CWA.
The information presented in this report is based on the materials and information supplied by the City of Donna representatives, observations made during the inspection, and records or reports maintained by the permittee, permittee contract laboratory, the State of Texas and EPA.
FACILITY DESCRIPTIONS
The City of Donna Wastewater Treatment Plant (WWTP) is designed to treat an average design flow of 1.8 million gallons per day (MGD) utilizing the activated sludge process. Treatment begins at the headworks, where incoming raw wastewater passes through both manual and mechanical bar screens. These screens remove large debris such as rags, plastics, sticks, and other coarse materials to protect downstream pumps and mechanical equipment from damage and to maintain efficient plant operation.
Following screening, the influent flows into three aeration basins where biological treatment occurs. Each basin is equipped with surface rotor aerators that provide mixing and introduce oxygen into the wastewater. The aeration process supports the growth of aerobic microorganisms that metabolize dissolved and suspended organic matter.
From the aeration basins, the mixed liquor flows to one of three secondary clarifiers. In these clarifiers, gravity settling separates the biological solids from the treated liquid. The activated sludge settles to the bottom of the clarifier, forming a sludge blanket, while the clarified effluent rises to the surface and is collected for further treatment. A portion of the settled sludge is typically returned to the aeration basins to maintain an adequate concentration of microorganisms, while excess sludge is wasted directly to the belt press or drying beds.
The clarified effluent then undergoes final disinfection through chlorination to inactivate pathogenic organisms. After a minimum contact time of 20 minutes for disinfection, the treated effluent is discharged through Outfall 001.
Solids generated throughout the treatment process are managed onsite. Waste activated sludge is dewatered using a belt press to reduce moisture content and volume. Additionally, sludge drying beds are utilized as a back up to the belt press. These solids handling processes reduce the overall volume and prepare them for final disposal to the Edinburg landfill.
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City of Donna TX0132802/TX0024660
Inspection Date 1/27/2026
Section II- Observations
This inspection revealed the following observations:
On the day of the inspection, only one aeration basin was fully operational. The remaining two basins were operating with reduced capacity, as each basin had one of its two surface rotor aerators out of service.
The City of Donna is currently adjusting the chlorine feed rate for disinfection manually rather than utilizing an automated control system, which may result in inconsistent dosing.
The facility is collecting a single grab sample in the morning to represent its required composite sample, rather than collecting multiple aliquots over the specified time-period and flow to form a true composite sample.
The minimum chlorine and maximum dechlorination values reported on the Discharge Monitoring Reports (DMRs) do not match the corresponding analytical results documented in the laboratory records, indicating discrepancies between recorded data and reported values.
Section III- Areas of Concern
This inspection revealed the following areas of concern:
Chlorine disinfection and dechlorination are required to be applied on a flow-proportional basis to ensure adequate treatment during varying and peak flow conditions. The city currently has a flow-proportional feed system; however, according to Chief Operator Javier Cavazos, the system has been out of service for more than two years. As a result, chemical dosing is not being automatically adjusted in response to changing flow rates. Monitoring data indicates that dechlorination residual levels have exceeded permit limitations, suggesting that the current dosing practice is not consistently maintaining compliance.
The City of Donna has also failed to collect composite samples in accordance with permit requirements. The permit allows either a Sequential Composite Sample or a FlowProportional Composite Sample. A Sequential Composite Sample requires collecting individual aliquots at predetermined intervals and adjusting each aliquot volume based on the corresponding flow rate to ensure the final sample is representative of the discharge over time. A Flow-Proportional Composite Sample consists of collecting a constant sample volume at intervals that vary in proportion to the flow rate (for example, collecting 200 milliliters for every 5,000 gallons of flow). The current practice does not meet either of these approved composite sampling methodologies.
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Section IV - LIST OF APPENDICES
Appendix A - Photos Appendix B - DMRs & Chlorine and Dechlorination Analysis
City of Donna TX0132802/TX0024660
Inspection Date 1/27/2026
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City of Donna TX0132802/TX0024660
Inspection Date 1/27/2026
Appendix A Photograph Log
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Photograph Log
Location: City of Donna
City: Donna
Photo No. 1
County/Parish: Hidalgo
State: Texas
Bar Screen
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Photograph Log
Location: City of Donna
City: Donna
Photo No. 2
County/Parish: Hidalgo
State: Texas
Aeration Basin with Non-Working Rotors
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Photograph Log
Location: City of Donna
City: Donna
Photo No. 3
County/Parish: Hidalgo
State: Texas
Working Aeration Rotors
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Photograph Log
Location: City of Donna
City: Donna
Photo No. 4
County/Parish: Hidalgo
State: Texas
Clarifer #1
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Photograph Log
Location: City of Donna
City: Donna
Photo No. 5
County/Parish: Hidalgo
State: Texas
Clarifier #2
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Photograph Log
Location: City of Donna
City: Donna
Photo No. 6
County/Parish: Hidalgo
State: Texas
Clarifier #3
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Photograph Log
Location: City of Donna
City: Donna
Photo No. 7
County/Parish: Hidalgo
State: Texas
Chlorine Contact Chamber
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Photograph Log
Location: City of Donna
City: Donna
Photo No. 8
County/Parish: Hidalgo
State: Texas
Drying Beds
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Photograph Log
Location: City of Donna
City: Donna
Photo No. 9
County/Parish: Hidalgo
State: Texas
Outfall 001
APPENDIX B Certified Submitted DMRs & Chlorine and Dechlorination Analysis
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