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NOMA September 14, 1992 Working To Restore Nature Fire Engine Company No 2, Stockton, California PRESENT GROUND-WATER SAMPLING On July 16, 1992, a technician from RESNA measured the water-levels in wells MW-1 through MW-4 and collected ground-water samples from the wells for subjective and laboratory analyses The field methods and procedures used are presented as an attachment to this report Water samples from wells MW-1 through MW-4 exhibited no subjective evidence of hydrocarbons during this site visit (Table 1) Purge water from the wells was stored temporarily in 55-gallon steel drums pending the results of laboratory analyses The City of Stockton is responsible for the disposal of the purge water The top of the four monitoring wells were surveyed relative to mean sea level and the ground-water flow direction and gradient were evaluated as described in the attached Field Procedures The ground-water gradient on July 16, 1992, was approximately 0 0032 with _ a flow direction to the north, as shown on Plate 3. The direction of ground-water flow previously ranged from southeast to north-east with gradients of 0 0028 to 0 033 The elevations of the ground-water surface in each well are shown in Table 1 Ground-water samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg) . and as diesel (TPHd) using Environmental Protection Agency (EPA) Method 8015 (modified for gasoline and diesel) and for benzene, toluene, ethylbenzene, and total xylene isomers (BTEX) using EPA Method 602 These samples were analyzed at RESNA Environmental Laboratories in Fremont, California (Hazardous Waste Testing Laboratory Certificate No 1211) Results of laboratory analyses indicated that dissolved TPHd was not detected in water sampled from the four wells Dissolved TPHg was detected in ground water samples collected from wells MW-1 through MW-4 TPHg concentrations ranged from 93 ppb (MW- 3) to 1600 ppb (MW-1) BTEX concentrations of 31 ppb, 13 ppb, 2 3 ppb and 11 ppb, respectively were detected in the water sample collected from MW-1 Results of laboratory analyses are summarized in Table 2 Copies of the laboratory analysis reports are attached WORK IN PROGRESS RESNA has constructed three vapor-extraction wells and one ground-water pumping test well during August and the beginning of September 1992 The vapor-extraction wells will be used to evaluate vapor extraction as an alternative for remediating residual hydrocarbons in soil A ground-water pumping test is scheduled for the week of September 21, 1992, to obtain hydrogeological data of the water table aquifer, and to evaluate the feasibility of removing dissolved hydrocarbons from ground water beneath the site N09-c 3 33009-4 2