ARCHIVED REPORTS XR0009475 - Laserfiche WebLink

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Pilot Testing Report and Conceptual Corrective Action Plan July 15, 1994 Manna Pro, 4004 South EI Dorado, Stockton, CA 15 ' and expansion of the confined groundwater when the head pressure is reduced during groundwater extraction The average storativity value of 007 corresponds to typical values expected for a ' confined or semi-confined aquifer ' Hydraulic conductivity (K) is defined as the rate of flow of water in gallons per day through a cross section of 1 square foot of a permeable medium under a unit hydraulic gradient The average hydraulic conductivity value of 74 gallons per day per square foot (gpd/ft) calculated from the pumping test is within the range of values characteristic of sand (approximately 10 to 10,000 gpd/ft2) or silty sand (approximately 1 to 1,000 gpd/ft2), the dominant grain sizes of the water- bearing zone ' Transmissivity M is defined as the rate at which water is transmitted through a unit width of an aquifer under a unit hydraulic gradient Transmissivity is equal to the hydraulic conductivity multiplied by the saturated thickness of the water-bearing zone The aquifer thickness was estimated to be 10 feet based on the thickness of the saturated sand unit in the pumping well The average transmissivity value of the tested wells was calculated to be 738 gallons per day per foot (gpd/ft) The hydraulic conductivity values and transmissivity values for each analyzed monitoring well were ' all nearly within an order of magnitude The differences may be attributed to non-homogenous conditions occurring in the subsurface ' The average rate of groundwater flow beneath the site was calculated using a porosity typical of medium sand, the average conductivity value of 74 gpd/ft2 (9 9 ft/day), and an average hydraulic gradient of 0 004 foot per foot (ft/ft) The effective porosity, which is less than total porosity due to non-interconnected pores, is estimated for an aquifer from measured or generally recognized specific yields of the substrate The specific yield is the quantity of water that will drain from a unit volume of the aquifer due to the gravity influence The effective porosity is used for calculating the velocity of flow within the voids using Darcy's Law An average effective porosity value of 26 percent for a medium sand (Pettyjohn, W A, et al, 1982) was used The groundwater gradient was ' approximated from groundwater elevations measured on February 3, 1993 (Figure 5) The average velocity is calculated at 0 15 feet per day (approximately 55 feet per year) The flow direction is predominantly to the north toward Duck Creek • 2819RO34 070 GROUNDWATER ' TECHNOLOGY, INC