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s ,Lk Quarterly Groundwater Monitoring Report, June -August, 1992 October 15, 1992 Manna Pro, 4004 South EI Dorado, Stockton, CA 2 groundwater was outlined Sod treatment will likely involve in situ soil venting, whereas groundwater remediation will Involve groundwater extraction and treatment to maintain hydraulic control of the plume Groundwater Monitoring Data On July 31, 1992, the sic existing groundwater monitoring wells were monitored 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) During this monitoring event the DTW in the six wells ranged from 41 06 to 43 16 feet This corresponds to static water level elevations ranging from 58 01 to 59 87 feet The results of groundwater monitoring are included in Table 1, Historical Groundwater Monitoring Data 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 0 016 ft/ft toward the west-southwest in the site vicinity The interpreted groundwater potentiometric surface suggests hydraulic mounding near, and potentially related to, the tank excavation Groundwater (duality Data The sic monitoring wells were sampled on July 31, 1992, following groundwater level monitoring The wells were purged to enable collection of samples representative of aquifer conditions Approximately four well volumes were bailed from each well The wells were allowed to recharge to approximately 80 percent of static water level before samples were collected Samples were collected using a Teflon® bailer and placed into sample containers supplied by the laboratory performing the analyses Sampling equipment was cleaned between wells using an Alconme and water solution and rinsed with de-lonized water A field blank and rinsate sample were collected In the field for Quality Assurance/Quality Control (QA/QC) measures 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 July 31, 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 (TPH)-as-gasoline using Environmental Protection Agency (EPA) Methods 5030, 8020 and modified EPA Method 8015, GROUNDWATER EEETECHNOLOGY, INC