ML20115G115

NPDES Noncompliance Notification:On 960619,resulting Net TSS Value 82.8 mg/1,exceeded Max Daily Limit of 60 Mg/L.Caused by Excessive Storm Water Runoff.Net TSS Revised

ML20115G115
Person / Time
Site:	Limerick
Issue date:	07/12/1996
From:	Boyce R PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Oneil S PENNSYLVANIA, COMMONWEALTH OF
References
NUDOCS 9607180255
Download: ML20115G115 (4)

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-4 Robert W.Boysa

• Plant Manager ,

Lunenck Generattig Staton  !

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- _=iigm l V PECO NUCLEAR escOene,gvcemnan, Lunenck Generating Staten A Unit of PECO Energy PO Box 2300 Sanatoga. PA 19464 0920 610 718 2000 July 12, 1996 4

Steven J. O'Neil, l Chief, Operations Section l Department of Environmental Resources l Bureau of Water Quality Management Suite 6010, Lee Park 555 North Lane Conshohocken, PA 19428

SUBJECT:

Limerick Generating Station, Units 1 and 2 Non-Compliance with NPDES Permit No. PA 0051926 Discharge 001 Net Total Suspended Solids in Excess of the Maximum Daily Limit l

Dear Mr. O'Neil:

DESCRIPTION OF THE EVENT ,

l On June 19, 1996, a non-compliance of the National Pollutant i

. Discharge Elimination System (NPDES) permit for the Limerick l Generating Station occurred. Composite samples for both the Discharge 001 (i.e., cooling tower blowdown) and river water input (cooling tower makeup) were analyzed for Total Suspended Solids (TSS) and compared. The resulting net TSS value was 82.8 mg/l which exceeded the maximum daily limit of 60 mg/1. i During the time frame that the composite samples were taken, and l for the preceding week, both units were operating at a nominal 100%

! power and the cooling towers were operating at normal cycles of concentration.

CAUSE OF THE NON-COMPLIANCE The cause of this non-compliance is a flaw in the methodology for calculating the net TSS concentration contained in the NPDES permit as previously described in our letter of non-compliance dated February 28, 1996. This method does not take into account the effects of rapid and significant changes in river water TSS associated with storm related high run-off conditions. The method subtracts the TSS concentrations of a composite of four (4) daily river water grab samples from that of a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> continuous 9607100255 960712 D PDR ADOCK 05000352 -

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Steven J. O'Neil Dept. of Environmental Resources Bureau of Water Quality Management July 12, 1996 Page 2 of 3 composite sample collected from the 001 plant discharge. One of the four (4) daily grab samples is collected during the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> composite sample period.

The other three (3) samples are collected on the three (3) consecutive previous days. These grab samples are also analyzed for silica concentration and compared with the 001 plant discharge silica concentration to determine a concentration factor associated with cooling tower operation. This methodology was developed with the intent to subtract out natural river water TSS concentrations and the effect of the cooling tower operation i which concentrates TSS in the cooling tower basin per design.

On June 18, 1996, excessive storm water runoff caused a large increase in river water suspended solids. This caused the cooling tower makeup and blowdown TSS concentrations to also rapidly increase. The three (3) cooling tower makeup grab samples collected prior to the storm were low in TSS. Af ter averaging with the fourth makeup grab sample collected on June 19, 1996, the TSS concentration of the composite makeup sample was artificially low.

As a result, the net TSS value obtained, af ter subtracting out this artificially low background value, was inappropriately high.

The flaw in this methodology which led to the non-compliance is that the makeup water composite is comprised of four (4) equal volumes of grab samples collected over a four (4) day period. The actual ratio of water in the cooling tower basin on the fourth day, based on a mass balance approximation, is 7% from day 1, 15% from day 2, 27% f rom day 3, and 51% from day 4. On June 19, 1996, using the NPDES permit calculation method, 75% of the makeup water composite sample was comprised of water with low TSS concentrations from the three (3) days prior to the storm. A more representative composite grab sample would contain just 49% of the pre-storm makeup water.

CORRECTIVE ACTIONS TAKEN No corrective actions were taken due to previous experience and the submittal of the change to the net TSS calculation methodology.

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Steven J. O'Neil l Dept. of Environmental Resources l

Bureau of Water Quality Management July 12, 1996  ;

Page 3.of 3 ACTIONS TO PREVENT RECURRENCE This event was not caused by the operation of the plant - or any other activity controllable by the plant operators. To prevent l- future permit violations, we submitted for review a revised net TSS calculation methodology based on this and previous events. This methodology was approved on July 5, 1996, by the Department of Environmental Protection (DEP) which will take into account l appropriate grab sample volume ratios. These sample ratios will ,

i better represent the cycling effects of the cooing towers.

If you have any questions, please contact Jim Kantner at l (610) 718-3400.

Sincerely, V

l DJP/DBN:vhc l l

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cc: U. S. Nuclear Regulatory Commission Document Control Desk Docket Nos. 50-352/353 Washington, D.C. 20555 l T. T. Martin l Administrator, Region I, USNRC Docket Nos. 50-352/353-

N. S. Perry USNRC Senior Resident Inspector, LGS

' Docket Nos. 50-352/353

! Program Management Section-(3WM52)

Permits Enforcement Branch l Environmental Protection Agency l Water Management Division Environmental Protection Agency i Water Permits Section l Region III 841 Chestnut Building Philadelphia, PA 19107 i

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