NCS000598_2021 DMR_20220119

Augas
an Air Uquide company
January 13, 2022
DEQ Winston-Salem Regional Office
Attention: DEMLR Stormwater Program
450 West Hanes Mill Road
Suite 300
Winston-Salem, NC 27105
Subject: Stormwater Permit Data Monitoring Report (DMR) for Period 2 in 2021
NPDES Stormwater Permit No. NCS000598
Airgas USA, LLC — Mebane Facility
Mebane, Alamance County, North Carolina
To Whom It May Concern:
Airgas USA, LLC — Mebane Facility is submitting the enclosed Stormwater Discharge Outfall (SDO)
Monitoring Report as required in the National Pollutant Discharge Elimination System (NPDES) Permit
No. NCS000598. In accordance with the monitoring schedule in the NPDES Permit, the stormwater
discharge monitoring at Outfall 001 is required twice a year: Period 1 from January through June and
Period 2 from July through December. This report is for Period 2 in 2021.
In accordance with the facility design, industrial stormwater runoff from the facility is first collected in
the onsite wet pond and then discharged through the wet pond outlet/effluent pipe (Outfall 001). The
stormwater discharge sampling location is Outfall 001 and the sampling occurs when there is a discharge
flow at Outfall 001 during the monitoring period. Due to the design of the wet pond, the stormwater
discharge occurs at Outfall 001 when the water level in the wet pond reaches the drawdown orifice of the
riser structure. This drawdown orifice is approximatelyl0 feet above the bottom of the wet pond. Thus,
the stormwater discharge at Outfall 001 occurs if and when there is a significant rainfall and does not
occur automatically nor immediately when it rains.
As shown in the enclosed SDO Monitoring Report, the required stormwater discharge monitoring could
not be conducted. The water level in the wet pond has not reached the drawdown orifice of the riser
structure during the monitoring period and there was no measurable flow at Outfall 001. When there is a
significant rainfall, there can be a discharge flow from the wet pond as designed and the required
stormwater discharge monitoring can occur. It is noted that in accordance with a visual inspection of the
wet pond conducted in December 12, 2021, the riser structure reportedly leaks and Airgas plans to further
investigate the leaking riser structure and correct the leakage issue.
If you have any questions, please contact me at [phone] or at rodne .st.'ohn air as.com.
cc: File
Enclosures: As Noted

STORMWATER DISCHARGE OUTFALL (SDO) MONITORING REPORT FOR PERIOD 2 IN 2021

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