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Low-Flow Sampling Study • 3 • 6 January 1995 <br /> DDRW, Tracy <br /> described in Section 3.2.0.2 of the Work Plan. However, as further described in Section <br /> 3.2.0.2, the selection of the depths for the pump intake devices (sampling depths) will be <br /> guided by information presented in existing boring logs and well construction diagrams. The <br /> third guideline presented in Section 2.4 should be modified to clarify that pump intakes <br /> should be positioned based on formation lithologies of the screened interval of the well to be <br /> sampled. <br /> 2. Sampling Depths, Section 3.2.0.2. The third sentence in Section 3.2.0.2 indicates that the <br /> sampling intake will be positioned adjacent to the materials which appear to have the highest <br /> permeability in wells screened in very heterogeneous materials. The use of the term "very" <br /> in this sentence is unclear and seems inappropriate. The approach described in this sentence <br /> should be used in cases where the materials within the screened interval are considered to be <br /> heterogeneous as compared, or relative, to materials which are reasonably deemed to be <br /> homogeneous. The word "very" should be deleted from this section. Accordingly, the <br /> selected depths for the sample devices, as summarized in Table 3-4, should be reviewed and <br /> modified, as necessary, for wells screened in heterogeneous materials. <br /> 3. Purging Procedures, Sections 4.1.2.2 and 4.3.2.4. Sections 4.1.2.2 and 4.3.2.4 state that <br /> "Whenever possible, turbidity of any samples analyzed for metals will be reduced to 5 NTU <br /> or below." However, these sections also state that "the well will be considered sufficiently <br /> purged when turbidity is reduced to 10 NTU or less." It is unclear how long the wells to be <br /> sampled for metals will be purged and if a consistent approach will be used. The term <br /> "whenever possible" in these sections should be clarified. <br /> 4. Analysis of Ground Water Samples, Section 4.4. Section 4.4 summarizes the analytical <br /> procedures for the low-flow-sampling study. It is unclear why two seperate subsections are <br /> necessary. Section 4.4 should be modified to clarify that the same analytical procedures will <br /> be conducted on the samples collected for both low-flow methods and conventional purging <br /> and sampling methods (all samples collected for the study) to analyze for the same <br /> compounds. <br /> If you have any questions, please call me at (916) 255-3065. <br /> �.sn �C � <br /> KAREN A. BESSETTE <br /> Project Engineer <br /> KAB:kb <br />