ARCHIVED REPORTS_XR0010354 - Laserfiche WebLink

Home Browse Search

TABLE 1 Third Quarter 1993 Monitor Well Physical Parameter Data Summary San Joaquin County Human Services Building Site Sample Date: August 12 and 13, 1993 Well Well Elevation' Depth to Groundwate? Groundwater Temperature' pH' Electrical Conductivity' ID (feet) (feet) Elevation' (feet) (°F) (umhos) ' MW-4 1346 4991 -3645 699 70 1,200 MW-5 1283 48 13 -3530 727 70 652 MW-6 13 17 4912 -3595 732 70 1 347 IMW-7 13 14 5095 -3781 756 70 1,146 MW-8 1376 5148 -3772 717 70 1,153 1 Elevations are given in feet relative to Mean Sea Level (MSL) and are based upon measurements from top of PVC casing (TOC) 2 Measured from TOC 3 Measured at end of purge I4 MW-2 and MW-3 were dry 2.2 Chemical Analysis Summary IConcurrent with the measurement of the physical parameters, groundwater samples were collected and analyzed for the following parameters by the methods referenced �? + Benzene, toluene, ethylbenzene and xylene (BTEX), EPA Method 602 • Total petroleum hydrocarbons as gasoline (TPH-G), Method 8015M fThe chemical analytical results for the third quarter 1993 monitoring event are summarized In Table 2 while the complete analytical report is presented in Appendix B. INo BTEX compounds were detected in any samples this quarter TPH-G was detected in only two wells, MW-4 at a concentration of 37 µg/L(which is an estimated value below the analytical method detection limit) and in MW-8 at a concentration of 1,700µg/L. These results are lower than those observed in the previous two quarters With regard to the quality control samples, analysis of the primary well sample MW-8 and the blind duplicate (labeled MW-10) had analytical results for TPH-G of 1,700µg/L and 2,900µg/L respectively Due to this difference in the primary and duplicate analytical results, WESTON requested that the laboratory review the analytical procedures used for these two samples. The Ilaboratory Quality Assurance/Quality Control (QA/QC) department advised WESTON that the initial analytical run, conducted on August 18, 1993, yielded results of 2,600 µg/L and 2,900 ,ug/L for samples MW-8 and MW-10, respectively. However, due to low surrogate recovery Iin the initial run of MW-8, a second vial of that sample was run on August 24, 1993, with a good surrogate recovery and a TPH-G concentration result of 1,700µg/L Sample MW-10 was not analyzed a second time Although the first analytical run of sample MW-8 yielded a value closer to that of MW-10, the laboratory advised WESTON that the relative difference between the reported concentrations is not significant for field duplicates and the variation may be due to several factors. The reported values for MW-8 and MW-10 were taken from analytical runs which were six days apart, but still within the specified holding time. This may have resulted SnCrRP'rS\S1C 3RD WP 4 10115/93