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Austin Road Landfill Section 2 Contaminant Plume Characterization Report Field Investigation Methods The aquifer testing program began on December 2,1997 and was completed on December 19, 1997. An existing groundwater extraction system,consisting of two pumping wells(EW-1 and EW-2),is in operation at the ARL. Ten monitoring wells existing north of the ARL,and the two extraction wells,were included in the aquifer test. The aquifer test consisted of turning the wells off and then on again,allowing several days between each change in pumping status. The test consisted of five phases: (1)background monitoring with both wells operating, (2)turning off well EW-1, (3)turning off well EW-2, (4) turning on well EW-1, (5)turning on well EW-2(resumption of full extraction system). Eleven days elapsed between test phases 2 and 5 when the remediation system was not in full operation,and 4 days elapsed between phases 3 and 4 when the extraction system was completely shut down. This sequencing had been discussed with and agreed to by the CVRWQCB and City of Stockton staff prior to initiating the aquifer test. i The methods used to perform each phase of the testing and the data analysis and results are presented in Section 3.4 and Appendix D. An evaluation of plume capture provided by extraction wells EW-1 and EW-2 is presented in section 4.0,including methods of analysis and capture zone results. 2.4 Deviation r the Work Plan Several deviations from the field sampling workplan were made during the field investigation at I ARL. These deviations include drilling boreholes ARL-1C and-313 deeper than initially planned and performing additional groundwater sampling. i Initially,the soil borings were designed to be drilled to a depth of about 140 feet bgs. Following review of boring data and groundwater results,borings ARL-1C and-313 were drilled to depths of ' 170 and 180 feet,respectively. These borings were extended to provide detailed geologic data of the previously undefined deeper aquifer materials and to collect groundwater samples from the deeper aquifer zone to characterize groundwater quality of the deeper aquifer layers. As part of this extended groundwater evaluation,the additional water quality parameters, dissolved organic carbon(DOC)and total iron and manganese,were analyzed by the laboratory for hydropunch groundwater samples collected from ARL-1C and-313. In ARL-313 the parameters— specific conductance,pH,redox,alkalinity as CaCO3,dissolved oxygen,sulfate,and ferric iron— were analyzed in the field to characterize aquifer conditions at this location. The purpose of collecting and analyzing the additional groundwater samples was to better understand the geochemical conditions of the aquifer to assist in the evaluation of the fate and transport of contaminants. CDM Camp Dresser&McKee CS 010764A 2-3 M W:\REPORTS\STOCKTOARLPLUM E.98\S EC2.W PD City of Stockton 190855-0006