ML20100P631

NPDES Noncompliance Notification:On 951108,discharge 001 Net TSS in Excess of Maximum Daily Limit.Caused by Flaw in Methodology to Calculate Net TSS concentration.Follow-up Composite Samples Taken

ML20100P631
Person / Time
Site:	Limerick
Issue date:	02/28/1996
From:	Boyce R PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Bauer R PENNSYLVANIA, COMMONWEALTH OF
References
NUDOCS 9603110278
Download: ML20100P631 (4)

Text

s Robert C. Boyc3 6

Plant Manaaer Limsnck Generanna Su:.an 4

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PE G PECO Energy Cvraany Lamenca Generating Sunar PO Box 2300 Sanatoga. PA 19464-0920 215 3271200 Ext 2003 February 28, 1996 Robert Bauer, Jr.

Department of Environmental Resources 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

Dear Mr. Bauer:

DESCRIPTION OF THE EVENT l On November 8, 1995, a non-compliance of the National Pollutant Discharge Elimination System (NPDES) permit for the Limerick 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 70.1 mg/l which exceeded the maximum daily limit of 60 mg/1.

During the time frame that the composite samples were taken, and 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 to calculate the net TSS concentration contained in the NPDES permit.

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 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 1

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' Robert Bauer, Jr. February 28, 1996 Dept. of Environmental Resources Bureau of Water Quality Management Page 2 of 3 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 which concentrates TSS in the cooling tower basin per design.  ;

On November 7, 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. After averaging with the fourth makeup

• grab sample collected on November 8, 1995, the TSS concentration of I the composite makeup sample was artificially low. As a result, :

the net TSS value obtained, after subtracting out this artificially  ;

low background value, was inappropriately high.

The flaw in this methodology which led to the non-compliance is ,

thst 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, j based on a mass balance approximation, is 7% from day 1, 15% from

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day 2, 27% from day 3, and 51% from day 4. On November 8, 1995, 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 Follow-up 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> composite samples for the cooling tower makeup and blowdown were started on November 8, 1995. These samples were analyzed on November 9, 1995, and yielded a net TSS result of 1.9 mg/1. This indicates that the expected cooling tower basin TSS 1 concentration is highly dependent on the TSS concentration of the '

makeup water over the past 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and that there were no harmful effects from the permit non-compliance.

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Robert Bauer, Jr. February 28, 1996 l Dept. of Environmental Resources ,

Bureau of Water Quality Management l Page 3 of 3 i

i ACTIONS TO PREVENT RECURRENCE j This event was not caused by the operation of the plant or any other activity controllable by.the plant operators. To prevent t future permit violations, we plan to review our approach to-  !

determining net TSS. Based on this event, a more appropriate-approach will be proposed to the Department of Environmental ,

Protection (DEP) which will take into account appropriate grab i sample volume ratios . These sample ratios will better represent ,

the cycling effects of the cooing towers.

i We apologize for the delay in submitting this report but per our i latest discussion with Mr. Garg of the DEP on February 20, 1996, we l wanted to ensure that the appropriate cause had been identified.  ?

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

Sincerely, l

Robert W. Boyce Plant Manager i DBN:dbn i

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cc: U. S. Nuclear Regulatory Commission Document Control Desk Docket Nos. 50-352/353 washington, D.C. 20555 T. T. Martin Administrator, Region 7, 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 Environmental Protection Agency Water Management Division Environmental Protection Agency Water Permits Section Region III 841 Chestnut Building Philadelphia, PA 19107 f

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