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Manna Pro Stockton 2 Quarterly Groundwater Monitoring Report January 1992 ramundwWer Monitoring D On October 2, 1991,the sax existing groundwater monitoring wells were monrtored for depth-to-water(DTW) The DTW measurements were taken from surveyed points on the top of each well casing, which are referenced to a common datum (designated as 100 feet above mean sea level) During this monitoring event the DTW in the six wells ranged from 4125 to 43 4 feet This corresponds to static water level elevations ranging from 57 77 to 59 68 feet above mean sea level (MSL) The results of groundwater monitoring are presented In Table 1 A potentiometric surface map as interpreted from the data in Table 1 Is presented as Figure 1 As shown in Figure 1, the average groundwater gradient is approximately 0 03 ft/ft towards the west-southwest in the site vicinity The groundwater flow pattern suggests hydraulic mounding near, and potentiallyll�vlated to, the tank excavation eGroundwater QualityData The sbt monitoring wells were sampled on October 2, 1991 following groundwater level monitoring Prior to sampling, the wells were purged by bailing to enable collection of samples representative of aquifer conditions The standard protocol for sampling is to purge 3 to 5 well casing volumes prior to collecting samples However, when a well is balled dry before 3 to 5 casing volumes are removed, the water level in the well is allowed to recharge to approximately 80 percent of static water level prior to collecting samples All six wells bailed dry after bailing between 10 and 15 gallons of water from each well as shown in Table 2 Samples were collected using a TeflonTm bailer and placed into sample containers supplied by the laboratory performing the analyses Sampling equipment was cleaned between wells using an AlconoxTm and water wash and deionized water rinse Samples were labeled and placed in an ice-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 October 2, 1991 sampling event were analyzed for the following parameters • pH using Standard Method 4500 H • Specific Conductance using Standard Method 2510 a 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 7 1 to 7 9 Specific conductance ranged from 980 to 2,400 micro-mhos per centimeter at 25 degrees Centigrade(umho/cm,25) 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 �J GROUNDWATER TECHNOLOGY, INC