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Low-Flow Sampling Study 2 6 January 1995 <br /> DDRW, Tracy <br /> If dedicated bladder pumps are not proposed for all wells in the WMP, it is unclear how data <br /> from the WMP wells would be compared in the future. Different sampling procedures for <br /> different wells may result in inconsistencies in concentration data which present difficulties in <br /> adequately defining the OU1 ground water plume. Therefore, the Work Plan should discuss <br /> the viability of using dedicated bladder pump systems in the wells which are used to evaluate <br /> the nature and extent of this plume. The Work Plan should also discuss how future data <br /> from wells without the dedicated equipment would be compared to data from wells with the <br /> dedicated equipment. <br /> 2. Limiting Variability. Section 2.2.3.3 states that "the Tracy study will include three types of <br /> samples: one each from the discharge of bladder pump under both low-flow and conventional <br /> purge methods as well as a third sample using conventional purging followed by sampling <br /> with a bailer. However, Section 4.0 which describes the purging and sampling methods that <br /> will be used during the Low-Flow Sampling Study includes conventional purging and <br /> sampling procedures using a submersible electric pump and only low-flow purging and <br /> sampling procedures using the dedicated bladder pump equipment. <br /> Variability in equipment and procedures used in the study should be limited, to the extent <br /> feasible, to adequately evaluate the low-flow sampling method with respect to its <br /> comparability to conventional sampling methods. As discussed in Section 2.2.3.3 of the <br /> Work Plan, use of the dedicated bladder pump equipment to perform both conventional and <br /> low-flow purging and sampling procedures would provide better capability to distinguish if <br /> variability in data results from the sampling method versus the purge method used. <br /> Therefore, it appears that the study would be optimized by using the dedicated equipment to <br /> collect both low-flow and conventional samples. <br /> Furthermore, as indicated in Section 3.3 of the Work Plan, one of the major criteria for <br /> dedicated pump selection was the ability to operate the low flow rates used for low-flow <br /> sampling methods as well as the high flow rates used for conventional purging and sampling. <br /> This capability provides for long-term use of these pumps in future monitoring rounds based <br /> on the results of the study. The study should therefore include data from conventional <br /> sampling using the dedicated equipment. <br /> It is our understanding that the two main data sets to be compared to evaluate the low-flow <br /> sampling method will consist of results from analyzing ground water samples collected from <br /> the discharge of the dedicated bladder pumps under both low-flow and conventional methods. <br /> Section 4.0 should be modified to describe how conventional purging and sampling <br /> procedures will be conducted using the dedicated bladder pumps. The Work Plan should <br /> also discuss any potential benefits to conducting the low-flow sampling prior to the <br /> conventional purging and sampling procedures. <br /> SPECIFIC COMMENTS <br /> 1. Recommended Low-Flow Sampling Guidelines, Section 2.4. The third guideline included <br /> in Section 2.4 specifies that pump intakes should be positioned in the center of the screened <br /> interval of the well to be sampled, unless specific sample depths are required. This approach <br /> is appropriate in wells which appear to be screened in relatively homogeneous materials, as <br />