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The tanks that will be used to store the groundwater during and after the aquifer-pump <br />test are closed tanks. The steel interior of the tanks will be rust resistant due to the nature of steel <br />itself and the low oxygen content of the groundwater. Even if the formation of rust, which is <br />oxidized iron, were to occur on the interior of the tank, it would not degrade the water quality of <br />the water stored in the tank. Variation in temperature of the groundwater upon injection will not <br />have a negative effect on water quality within the A2 aquifer, so there are no requirements in the <br />Final Permit related to the temperature of the water. Powertech must keep the water in the tanks <br />from freezing for practical considerations that are beyond the scope of this permit. It is rare for <br />algal growth to occur without sunlight. The stored groundwater will be not be exposed to <br />sunlight from the time it is pumped to the surface until it is reinjected. Algae that would grow <br />under these conditions are not a water quality or human health concern under the Class V permit. <br />B. Concerns related to bacterial contamination of the stored groundwater. The <br />second concern related to potential changes in water quality is that the groundwater may be <br />exposed to sources of bacteria or may contain anaerobic bacterial populations that would <br />increase during storage before reinjection occurs. Some commenters thought sodium <br />hypochlorite bleach should be added to the tank to prevent bacterial growth. <br />EPA Response: <br />In response to the concerns expressed about bacterial contamination in comments <br />received on the Draft Permit, the Final Permit requires the permittee to collect a composite <br />sample of stored groundwater from the storage tanks and analyze the sample for Total Coliforms, <br />just before the water is reinjected back into the A2 sandstone. The results will be submitted to <br />the EPA for review, before the EPA issues authorization to reinject the stored water. <br />The reason Total Coliforms was selected as the analyte is because this analysis is used at <br />drinking water treatment plants as an indicator for exposure to other sources of bacterial <br />contaminants. It is important to distinguish between harmful, pathogenic bacteria, which cause <br />diseases in humans, and nonpathogenic bacteria that do not cause diseases in humans. The <br />microbiological constituents regulated under the Safe Drinking Water Act are pathogenic <br />bacteria. The anaerobic bacteria referred to in the comment may be present within an aquifer <br />under natural conditions and are not pathogenic. Coliforms are not usually pathogenic, but their <br />presence in drinking water indicates the possible presence of pathogen. <br />The types of microbiological tests required for drinking water under the Safe Drinking <br />Water Act include tests for Cryptosporidium, Giardia lamblia, Legionella, Heterotrophic Plate <br />Count, Mycobacteria, Total Coliforms, Turbidity, and Viruses. These contaminants originate <br />from sources that the groundwater will not be exposed to while being pumped from the aquifer- <br />pump test well to the storage tanks, before being returned to the aquifer. The groundwater will <br />not be exposed to dirty equipment and human hands, because it will be isolated within clean <br />hoses and storage tanks from the time it leaves the aquifer-pump test well until it is reinjected <br />into the aquifer. <br />If Total Coliforms are found to be present, then Powertech will be required to either <br />perform more detailed bacteriologic analyses to determine if any regulated bacteria are present, <br />or to disinfect the stored water. If regulated bacteria are present, the stored water will be <br />Page 5 of 24