ARCHIVED REPORTS_XR0002987 - Laserfiche WebLink

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�C." it + Cl ALISTO ENGINEERING GROUP , September 18, 1995 AFI, ? z 1995 Mr Scott Hooton -J BP Oil Company fir v'.L ,.0 Environmental Resources Management ENVIRONMENTAL DEPT. 295 S W 41st Street vVEST COAST REGION OFFICE Building 13, Suite N Renton, Washington 98055 10-136-04-001 Subject Revised Analysis of Baildown Test Results BP Cil Company Service Station No 11193 3202 West Hammer Lane Stockton, California Dear Mr Hooton On February 21, 1995, Alisto Engineering submitted the results of the baildown testing at BP Oil Company Service Station No 11193, 3202 West Hammer Lane, Stockton, California After further review of the test data and results of analysis, it was determined that the reported values of hydrogeologic properties for MW-1 needed to be revised The time-displacement plots of the test data revealed a "double straight line effect" This phenomena was described by Herman Bouwer in an article titled The Bouwer and Rice Slug Test_- An Update published in the May/June 1989 issue of Ground Water In accordance with the recommendations presented therein, the second straight line portion of the plot was considered more indicative of flow in the undisturbed aquifer and was used for calculations The interpretation of the test data for MW-1 was previously based on the "first leg" of the plot, which was not consistent with the data analysis for MW-2 and MW-5 or recommendations in the Bouwer article The revised calculation of hydrogeologic parameters for MW-1 is shown in the enclosed graph, and the revised test results are presented in Table 1 During testing of MW-1, the submersible pump was only capable of drawing down 15 feet of groundwater in MW-1 at a maximum pumping rate of 6 gallons per minute The rapid recovery may be due to the sand unit encountered in the lower portion of MW-1 and may not be representative of the material in the saturated zone Based on a review of the boring logs, the predominant soil types of the water-bearing zone are silt and silty sand underlain by fine to medium sand, which generally have K values ranging from approximately 1 to 1 x 10-5 cm/s (Freeze and Cherry, 1979) The values of the aquifer parameters calculated from the baildown tests are within the lower range of expected values and consistent with the types of soils encountered at the site 1575 TREAT BOULEVARD SUITE 201 -WALNUT CREEK CA 94598 • (510) 295-1650 • (5I0) 295-1823 CONTRACTORS LICENSE NO A-652544