WORK PLANS - Laserfiche WebLink

Home Browse Search

l � GES GENESIS ENGINEERING&REDEVELOPMENT The nitrate contour map uses data from the Second Quarter 2013 Groundwater Monitoring event(data included on Table 1). The contour lines are used to divide the Site into areas of equal concentration, and then the water volume and nitrate mass are calculated for each area. For example, the area between the 500 mg/L and 1,000 mg/L contours is assumed to have a concentration of 500 mg/L throughout the entire thickness of shallow groundwater. The area between these two contour lines throughout the Site was determined and multiplied by the aquifer thickness (35 feet) and an estimate of porosity(0.3) to obtain the total volume of groundwater between the two contour lines. The nitrate mass is then calculated by multiplying the water volume by the nitrate concentration. After calculations were made for each set of contour lines, the nitrate mass and water volume were totaled for each area. These totaled values are shown on the table below. Total Nitrate Mass Total Water Volume 64,000 pounds (29,200 kilograms) 12,400,000 gallons There is considerable uncertainty with respect to the nitrate mass calculations. A large part of the uncertainty comes from the assumption that the concentration throughout each area and the entire saturated thickness is a single value. In addition,nitrate concentrations in individual wells vary significantly through time(Table 1), and this estimate was calculated for a single snapshot in time. The uncertainty related to the volume calculation is the porosity assumption. However,the uncertainty is small (i.e. <10%) compared to the nitrate concentration uncertainty. Using the estimated volume of 12,400,00 gallons and a pumping rate of 80 gallons per minute, it will take approximately 3.5 months to extraction water equivalent to the impacted volume. However,because of geologic heterogeneity and preferential flow, more than one volume of water will need to be extracted to remove the nitrate currently residing in the shallow groundwater zone. 1.5 Remediation Goal Elevated nitrate concentrations in groundwater is a recognized problem throughout the Central Valley of California. In the Ripon area,background concentrations in shallow groundwater are approximately 200 mg/L nitrate as NO3. Remediation of the Site will be considered complete when: R.F.Land Inc. 3 of 11 Groundwater Extraction Work Plan October 2014