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There was no improvement in the TPH-g concentration between the fourth and fifth batches,but it must be kept in mind that the volume removed in the fifth batch was only slightly over 3,000 gallons. The Total BTEX concentration continued to decline, reaching a value of 10,970 µg/1. This represents a decline of 37% from the peak concentration on June 8. However, the combined TCE/PCE concentration in the final batch was 304µg/1 as compared to 170µg/1 in the May 13 sample that was collected at the end of the step test. The final concentration was 179%of the initial sample. 4.0 CONCLUSIONS Overall, the results of this test were mixed. On the positive side, pumping does appear to have resulted in some reduction in gasoline concentrations. The TPH-g concentration declined by 8%from the baseline sample (27,700 µg/1 to 25,500 µg/1)but the Total BTEX concentration declined 37%percent from its peak after the first 6,800 gallons had been removed. As we noted in our groundwater monitoring report for the third quarter of 2009, gasoline concentrations in VM-2 and VM-4 were slightly lower in September than they were in March,which might indicate that VM-2 had a radius of influence extending out as far as VM-4. The data were not conclusive, and in any event the slight decline in VM-4 was partially offset by an increase in VM-6. Therefore,we are unable to make a confident assessment of the radius of influence. On the negative side, the test showed that pumping is sporadic and unreliable, at least from a 2-inch diameter well. Frequent trips were required to restart the pump, raising the operating cost and reducing the rate at which groundwater can be extracted. A low pumping rate of only about 1 gpm was used,but even this low rate could not be sustained without sucking air. One or more larger diameter wells would be needed to establish an acceptable extraction rate, but whether this would improve the reliability of the pump equipment is not known. A second and more difficult negative aspect of the pump-and-treat method that was revealed by the test is caused by the presence of chlorinated hydrocarbons in the groundwater. This precludes continuous groundwater discharge to the sanitary sewer and requires that batch discharge procedures be used, which will increase operation and maintenance costs such as the frequency of site visits to collect samples and empty storage tanks, as well as the number and costs of required analyses. Further, it requires the mobilization and use of larger storage tanks and carbon filter canisters and will cause delays while the stored water is filtered and sampled and the samples are analyzed at the laboratory. As a result,batch pump and discharge cycles will average about 2 weeks at the 1 gpm pumping rate and 10,000-gallon/batch storage rate. At these rates, only about 250,000 gallons of water could be processed in a year. With an additional storage tank and a larger and more efficient extraction well, each batch could be larger and collected at a faster rate,but the standard 5-day laboratory turnaround time would still create a 2- week cycle time. 5