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Evaporation and percolation from the pond are estimated in the table below ('fable 4). In some circumstances, the pond may not be adequate to handle 25 gpm. For this reason a contingency will be prepared to handle excess water by piping to the existing treatment plant, used for wash water. 'llie maximum amount of excess water predicted is 9.9 gpm in winter. Tlie capacity of the treatment plant is 40 gpm. l'be treatment plant is not used in winter. In addition the quality Of groundwater is much higher than the wash water for which the plant was designed. Excess water will pass through the air strippers and be tested according to an operations plan being prepared for submission to the Regional Board. If effluent chloroform levels are below WI)lk the water will be released to the stormwater pond adjacent to the treatment plant. If not, groundwater will cycle back through the plant or will be sent to a monitored spray field where additional volatilization will occur. /application to the spray field in summer will be coordinated with wash treatment water releases so as not to over apply. Lysimeters installed near the surface in the spray field will be used to detect chloroform, which in the event of migration, could escape to the subsurface. 'llie spray field will be located upgradient of the extraction well. Table 4. Water Balance to Aeration Pond For Winter and Summer Operation Item with assumptions November(iVlean) July(mean) (inches) (inches) Influx from 25 g�»n pumping onto 50x 100 ft pond 11.6 11.6 Evaporation from spray is25% of spray volume in -1.8 -4.6 summer and 10% of spray volume in winter assumes 40 gpin spray volume Evaporation from surface -0.06 -0.42 Estimate of infiltration (based on pumping test, assuming -5.1 -5.1 Kh — 4.32 11/d and anisotropy of Kh/Kv =10) Daily excess water in pond 4.6 1.4 Excess water to be extracted from pond per day 9.9 gpm 3.0 gpm L, 14 CONDOR