SITE INFORMATION AND CORRESPONDENCE

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Mr. Harry Galles -2- 26 December 1990 5. Finding 6 has been changed to show a design flow from the ground water treatment system (GWTS) of 200 gallons per minute (gpm) (288,000 gallons per day (gpd)) . Although this figure was listed on Form 2D of the NPDES permit application as "average flow" , your 19 December 1990 letter states the average flow actually will be 60 gpm (86,400 gpd) . This average flow also has been listed in Finding 6. The finding also has been clarified to state that LLNL expects to achieve nondetectable levels of volatile organic compounds (VOCs) in the effluent as stated in the 19 December 1990 letter. Effluent Limitations 6. The effluent limits have been changed to monthly median and da, l,, maximum values. Although the monitoring program requires only monthly sampling after three months, LLNL is free to take more samples. If only one sample is taken per month, the monthly median will have to be met in that sample. 7. We know of many analytical laboratories that routinely achieve a detection limit of 0.5 ug/1 using EPA Methods 601 and 602. Therefore, we have retained 0.5 ug/1 as a 30-day median, but have added a daily maximum of 5 ug/l for any one VOC with the provision that the total VOCs in any one sample not exceed 5 ug/l . As noted above, if LLNL samples the effluent only once a month, that sample may contain no more than 0.5 ug/1 . These limits are consistent with other GWTS permits in our region for VOCs and are based on the physical ability of air strippers to remove VOCs effectively. 8. Item A.2 has been clarified to state the concentration of any VOC in the discharge other than those listed in Item A.1 may not be more than 0.5 u9/1 . 9. In Item A.3, I have retained the pH range of 6.5 to 8.5 to meet the water quality objectives for inland surface waters in the Board' s Water Quality Control Plan. An occasional excursion above 8.5 in the effluent will not be cause for enforcement action. If you still want a higher pH limit, you will have to provide sufficient data to shoe: the higher limit is needed and will not cause a water quality problem. y 10. In Item A.4, the average daily dry weather flow limit has been changed to 86,400 gpd to reflect the new proposed average flow rate of 60 gpm. 11. Item A.7, which contained effluent toxicity limits, has been deleted. Receiving Water Limitations 12. Turbidity has been added to the monitoring program to measure compliance with Item B.7. Provisions 13. Provision C.2 which contained the compliance time schedule for various investigations has been deleted since an FFA is being negotiated.