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r Manna Pro Stockton • Quarterly Groundwater Monitoring Report July 1992 3 labeled and placed in an tce-chilled cooler for transport to GTEL Environmental Laboratories, Inc in Concord, California, and were accompanied at all times by a chain-of-custody record Samples from the April 23, 1992 sampling event were analyzed for the following parameters ■ pH using Standard Method 4500 H ■ Specific Conductance using Standard Method 2510 ■ Aromatic Volatile Organics and Total Petroleum Hydrocarbons as Gasoline using EPA Methods 5030, 8020 and Modified 8015 ■ Total Petroleum Hydrocarbons as Diesel Fuel using Modified EPA Methods 3510/8015 ■ Total Lead using EPA Method 7421 The results of laboratory analyses are presented in Table 3 The laboratory analytical reports are also included as an attachment to this letter As shown in Table 3, pH ranged from 71 to 7 7 . Specific conductance ranged from 1,000 to 2,600 micro-mhos per centimeter (µmho/cm) at 25 degrees Centigrade Because the results of pH and specific conductance in the samples collected were generally similar, this suggests that the water is from the same hydrologic zone Aromatic volatile organics analyzed for and detected included benzene, toluene, ethylbenzene and xylenes (BTEX) Total BTEX ranged from 2 micrograms per liter (µg/L), or parts per billion (ppb) in the sample from well MW-4 to 110,000 µg/L in the sample from well MW-1 Total petroleum hydrocarbons (TPH) as gasoline similarly ranged from 74 µg/L in MW-4 to 140,000 µg/L in MW-1 In general, the analytical data for TPH as gasoline and total BTEX has fluctuated between quarterly sampling events, however, no specific trends are observed A modest increase in TPH as gasoline and BTEC has been noted in well MW-3, however, this data correlates better with the data from well MW-5 Even though MW-3 is closer to the tank pit than MW-5, the data still show lower TPH as gasoline and BTEX concentrations than at well MW-5 Total petroleum hydrocarbons as diesel fuel were not observed above the detection limit of 10 µg/L in any of the samples Because diesel fuel has not been detected for three consecutive quarters of groundwater monitoring and sampling, we recommend no further TPH-as-diesel fuel analyses be performed Lead was not detected in any of the samples collected this quarter Previous analytical results (10/91 and 1/92) indicated total lead in selected wells ranging from 11 to 33 µg/I However, those samples were unfiltered and the detected lead may have been related to sediment in the samples ETGROUNDWATER TECHNOLOGY, INC