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Ronald Rowe &Margaret Lagorio <br /> October 8, 1999 <br /> Page 2 <br /> { <br /> • Estimates of dispersivity. Dispersivity is a measure of how a plume spreads out and is the <br /> most elusive of all solute transport parameters (Freeze and Cherry, 1979) and is extremely <br /> difficult to measure. Given the history of groundwater flow direction changes, and the <br /> stratified nature of the aquifer at the Disco site, any predicted dispersivity value for the <br /> aquifer beneath this site would be highly suspect.- Monitoring wells installed around the <br /> perimeter of a plume are a more practical, and defensible method to assess the extent of a <br /> groundwater plume. <br /> • Validated contaminant degradation rates. Estimates of degradation rates can be performed <br /> using geochemical models, such as BIOSCREEN, or with monitoring well time-series <br /> plots of concentrations. However, "validated" contaminant degradation rates would <br /> require a long-term bench-scale test, using actual contaminated aquifer material and <br /> laboratory simulation of aquifer conditions. While the scope and cost for such a test was <br /> not explored, our consultant, CH2Mhill, feels that this level of effort for the BTEX plume <br /> at this site is unnecessary. <br /> A copy if this work plan is being submitted concurrently to the State Water Resources Control <br /> Board Underground Storage Tank Cleanup Fund (UST Fund) for Pre-Approval. A copy is <br /> also being submitted to the Central Valley Regional Water Quality Control Board <br /> (CVRWQCB). We are requesting a meeting with representatives from PHS, CVRWQCB, and <br /> the UST Fund, at the UST Fund office, to review this work plan, obtain pre-approval, and <br /> ( discuss the overall project direction. We will contact you to schedule a convenient meeting <br /> time. <br /> Due to the significant cost increase between the August 17, 1999 submitted work plan, and <br /> the enclosed work plan brought about by your September 13, 1999 letter, we are seeking <br /> approval from the UST Fund prior to implementing this Work Plan. <br /> If you have any questions or comments,please feel free to call me at(415) 247-3520. <br /> Regards, <br /> P.W <br /> 1Xp <br /> �/lt.� <br /> Steven P. Ronzone w/ <br /> cc: Mark List, CVRWQCB. <br /> Jim Munch, CVRWQCB <br /> Wennilyn Fua, SWRCB / USTCF <br /> Richard Fish, Del Monte Foods <br /> Bill Sawyers, Del Monte Foods <br /> Liz Dodge, CH2M HILL <br /> Keith Sheets, CH2M HILL <br /> David Irey, SJC District Attorneys Office <br /> Nancy Bice, Geosyntex Consultants <br /> Sara Flanagan, Pillsbury Madison & Sutro <br /> W. L. Simmons, c/o Sidney Rudy, Esq. <br /> RE1Stockton#331PHS Rowe Amended Work Plan 3 <br />