ARCHIVED REPORTS_REMEDIAL INVESTIGATION REPORT 2000

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i Project Status Update Report,Subsurface Investigation �--`-� Banner Island, Stockton, CA Septcmber 17, 1992 W060':.1 C The groundwater gradient beneath the two sites on August 7, 1992 was 0.017 ft/ft in a northwesterly direction. A groundwater gradient map is included as Figure 2. Groundwater samples were collected on August 7, 1992 from wells MW-1 through MW-9, after purging and stabilization of pH, electrical conductivity (EC), and temperature. Depth to water measurements ranged from 19.54 to 29.25 feet below the top of the well casings. Electrical conductivity measurements ranged from 802 to 1,577 µmhos/cm. The three samples with the highest electrical conductivity readings were submitted for analysis of total dissolved solids. All field work was performed in accordance with RESNA's Quality Assurance/Quality Control Plan (Attachment 1). Well purge logs are included in Attachment 2. Laboratory Analvsis Groundwater samples collected from wells MW-1 through MW-9 were analyzed for California Title 22 Metals; the samples collected from wells MW-7, MW-8, and MW-9 were also analyzed for Total Dissolved Solids (TDS) concentrations and the samples collected from wells MW-1 and MW-4 were submitted for Volatile. Organics utilizing EPA method 8240. Laboratory analysis indicated concentrations of priority pollutant metals above method detection limits in the groundwater samples collected from wells MW-1 through MW-9. Although none of the levels detected exceeded the maximum Soluble Threshold Limit Concentration (STLC) values as listed in Title 22 of the California Code of Regulations, several of the samples contained concentrations of arsenic (BI-MW-4), barium (BI-MW-3), selenium (BI-MW-1), and zinc (BI-MW-9) above the State Maximum Contaminant Level (MCL). TDS analytical results indicated that the samples collected from wells MW-7 (790 mg/f), MW-8 (1,100 mg/f), and MW-9 (690 mg/P) exceeds the recommended Secondary State Drinking Water Standard. No volatile organic analytes were detected in either sample MW-1 or MW-4 above the laboratory method detection limit. The laboratory results for the water samples are presented in Table 2. Laboratory reports, chain of custody documentation, and laboratory QA/QC data, are included in Attachment 3. Sampling of Adjacent Site One groundwater monitoring well located at the nearby Weber Point site (MW-5) was sampled on August 7, 1992. The Weber Point site is currently undergoing investigation and remediation of previous releases of petroleum hydrocarbons. This well was selected for sampling because it had no prior history of hydrocarbon impaction and is considered to be "clean". The Weber Point site is located approximately 1/4-mile east of the Banner Island Property (Figure 3). R EroRrsweo9o9sz.trn, 2