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i URS Ms. Devra Lewis Regional Water Quality Control Board July 3, 2002 Page 2 of 3 Comment 2: The Report states there was "noise in data" for well W-2. Phillips needs to provide a discussion describing what "noise in the data" is, how it affected the results, and how this lead to the decision not to use the data. Response 2: The drawdown data for observation point W-2 was described as having "noise" because the recorded data was sporadic for the initial 10 minutes of the constant-rate test. Typically, response data for observation wells exhibit a smooth, continuous response except during one of the following scenarios: • change in pumping rate; • boundary conditions (i.e., recharge supply, dramatic change in lithology, rock formation); • disconnection of the screened interval to the aquifer/formation; • instrument error. A change in pumping rate did not occur during the initial 10 minutes of the constant-rate test as it was monitored by field personnel, and other observation wells did not exhibit a similar response to observation point W-2. A recharge supply, such as a lake or river, does not occur in the immediate vicinity of observation point W-2 or any other observation wells, and its effects would not be noticed until further into the pump test. The soil borings for observation points N-1, N-2, W-1, and W-2 all had a similar lithology with no dramatic changes in soil types or rock formations. Therefore, it was deduced that either a disconnection exists between the well screen and the aquifer/formation (like smearing of the screen interval from well installation), or the transducer in observation point W-2 produced some variations in the data during the initial 10 minutes (instrument error). Either case would not produce valid data that could be used in the calculations of aquifer characteristics. After the initial 10 minutes, the groundwater response in observation point W-2 became smooth and continuous, but exhibited less drawdown than observation points N-1, N-2, and W-1, which had very similar responses to each other. The lower drawdown exhibited by observation point W-2 represents a lower hydraulic conductivity, but the lithology appeared to be similar for observation points N-1, N-2,W-1, and W-2. This indicates that either a disconnection exists between the screened interval of the well and the aquifer/formation exists, or the transducer did not collect and provide accurate data. The Hantush solution for observation point W-2, alone, resulted in a hydraulic conductivity that was 20% less than the hydraulic conductivity calculated for observation points N-1, N-2, and W-1. The initial "noise"raised uncertainty as to the accuracy of the transducer for observation point X:\x_env\_wuste\PHILLIPS\PROJEC'rS\Sttwktun\RWQCB\pump text responseF.duc