ML18153D284

Submits Follow Up to 930305 Telcon Rept Re Sewage Treatment Plant Upset at Plant on 930304 Due to Unusually Heavy Rate of Rainfall.No Deficiencies Found in Collection Sys Which May Allow Inflow/Infiltration of Stormwater

ML18153D284
Person / Time
Site:	Surry
Issue date:	03/29/1993
From:	Marshall B VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Christopher Cook VIRGINIA, COMMONWEALTH OF
References
NUDOCS 9304020104
Download: ML18153D284 (2)

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Innsbrook Technical Center

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.! e 5000 Dominion Boulevard Glen Allen, Virginia 23060 CERTIFIED MAIL RETURN RECEIPT REQUESTED March 29v 1993

• VIRGINIA POWER Ms. Camille Cook Piedmont Regional Office Virginia Water Control Board P. o. Box 11143 Richmond, VA 23230 RE: SURRY POWER STATION - VA 0004090 - STP UPSET

Dear Ms. Cook:

This is in follow up to our March 5, 1993, telephone report to Mr.

Ray Jenkins of a sewage treatment plant (STP) -upset at Surry Power Station on March 4, 1993. The plant upset was caused by hydraulic overload to the STP following unusually heavy rainfall, 2. 43 inches, the evening of March 3 through the morning of March 4.

At th~ time of our telephone notification, Mr. Jenkins stated that a *u5;,..day letter" was not necessary in this case and that our follqwup could be* included with the Discharge* Monitoring Report (DMR) for March. Since our DMR submittals are generated at the power station and because of our in-house correspondence processing and review procedures, this followup letter is being submitted separate from the DMR package.

During the morning of March 4, as the flow rate to the STP increased, the principal plant operator was able to manage the increased* influent enough to keep a.11 flow going through the treatment facilities. No bypasses nor overflows occurred.

However, the flow rate through the STP was high enough to wash out some- of the plant contents and by the afternoon of March 4 ,

increased turbidity of the effluent was noticed. Samples analyzed from the peak period of the upset (1500 hrs., March 4) had a Total Suspended Solids of 558 mg/1 and a 5-Day Biochemical Oxygen Demand of 509 mg/1. Despite the high influent flow and the resultant plant upset, the operator succeeded in maintaining disinfection of the effluent throughout this event by placing spare chlorination tubes into service and adding chlorine tablets as needed.

The cause of this upset event was the unusually heavy rate of rainfall,* particularly during the morning of March 4, whic~ created

~ore surface ponding than experienced station personnel recall from any : p:rlor storm during the

• past ten years. Station staff.

investigation* found that two manholes in the collection system, although elevated approximately 18 inches above ground level, were completely submersed. In addition to stormwater entering the 9304020104 930329 PDR ADOCK 05000280 .

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• Ms. Camille Cook March 29, 1993 Page 2 inundated manholes, the gravel parking lot and area surrounding the STP were flooded to an extent that stormwater flowed into the surge tank and the clarifiers. No extraneous stormwater conveyances are connected to the sewer system and no deficiencies in the collection system which may allow inflow/ infiltration of stormwater were found.

As noted above, this plant upset was caused by an unusual storm event which created conditions not previously experienced, nor expected to be frequently experienced, at this facility. Despite the adverse conditions, exemplary actions by the STP operation staff maintained control to. the best achievable extent. Due to the level of treatment, including disinfection, which was attained, and the dilution afforded by the stormwater, it would not be expected that this event would have had an adverse impact on the receiving waters. Also, due to the nature of the causative event and the lack of deficiences in our sewage handling facilities, no further corrective actions are warranted.

Should you need additional information or have any questions about this matter, please contact Daniel James at 273-2996.

~BL B. M. Marshall, P.E.

Manager Water Quality cc: (w/ attachments)

U.S. Nuclear Regulatory Commission Region II 101 Marietta St., NW Suite 2900 Atlanta, GA 30323 Re: Surry Units 1 & 2 Docket Nos. 50-280/50-281 License Nos. DPR-32/DPR-37 U.S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 Re: Surry Units 1 & 2 Docket Nos. 50-280/50-281 License Nos. DPR-32/DPR-37 Mr. M. w. Branch NRC Senior Resident Inspector Surry Power Station