Laserfiche WebLink
Jim Pinasco <br /> June 21, 1994 <br /> Page 4 <br /> and sampling. In addition, in some cases, it took longer to <br /> stabilize field parameters using low-flow-rate purging compared <br /> to standard purging methods. It is recommended that a comparison <br /> of low flow purging and sampling to standard purging and sampling <br /> be conducted at DDRW-Tracy prior to making a decision to <br /> exclusively use low flow purging with dedicated sampling <br /> equipment. The comparison will provide information on <br /> comparability of data from the two sampling and purging methods. <br /> In addition, field parameters to be monitored and stabilized <br /> prior to collecting water samples should include dissolved <br /> oxygen, redox, and turbidity in addition to specific <br /> conductance, temperature, and pH. A work plan presenting the <br /> wells to be sampled using both methods and the rationale for <br /> selecting the wells should be submitted for review and approval <br /> to the regulatory agencies. The work plan should also include <br /> the details of the low-flow-rate purging method, e.g. , purge <br /> rates, sample rates, criteria for selecting sampling depth, and <br /> number and depth of sampling points for wells with screens <br /> greater than 10 to 12 feet in length. Low-flow-rate purging <br /> should not be implemented until the work plan is approved by the <br /> regulatory agencies. <br /> 4 . Reporting Limits for EPA Method 8260 Analyses <br /> Table 4-2 in Section 4 and Table B-5 in Appendix B lists the <br /> EPA analytical methods, compounds analyzed by each method, and <br /> method detection limits for the respective compounds. However, <br /> it appears that the term "method detection limit" is actually <br /> referencing the reporting limit for each compound rather than the <br /> method detection limit. In addition, the "method detection <br /> limit" presented on the tables is the same concentration as the <br /> State maximum contaminant level (MCL) for several volatile <br /> organic compounds, including benzene, vinyl chloride, <br /> 1, 2-dichloroethane, and 1, 3-dichloropropene. Volatile organic <br /> compounds with the reporting limit equal to the MCL does not <br /> indicate if the compound is at the MCL because the concentration <br /> is reported as not detected. <br /> Recommendations <br /> The reporting limit for any compound analyzed should be at <br /> least half of the MCL. Reporting limits for any compound that is <br /> equal to or greater than the MCL should be revised to be at least <br /> half of the MCL. In addition, Tables 4-2 and B-5 and any <br /> appropriate text should be revised to reflect the correct <br /> MS.k] <br /> MS63.064/10B <br />