Laserfiche WebLink
• _ava <br /> CLEARWATER <br /> G R O U P, I N C <br /> Env:ronmentui 5eraces <br /> Volatilization of dissolved contdmindnts may play a significant role in the natural attenuation of <br /> volatile organic constituents such as benzene Volatilization can be estimated using a formula <br /> which takes into account the observed mass loss (contaminant decay rate), however, <br /> volatilization has been demonstrated to account of only 5% of benzene mass loss at a site with <br /> relatively favorable conditions for this process2 <br /> Advection is responsible for the off-site migration of contaminants in concentrations below the <br /> detection limit To evaluate the extent of a plume attenuated through advection, the dissolved <br /> constituents are assumed to move at the same velocity as the groundwater (i a no retardation) <br /> Using the hydraulic conductivity of the water bearing zone, average hydraulic gradient, and <br /> average effective porosity, an approximate volume of hydrocarbons moving off site at <br /> concentrations at or below the detection limit can be estimated using Darcy's Law However, <br /> this process typically accounts for a relatively small percentage of apparent contaminant mass <br /> wloss at most sites <br /> SUMMARY AND CONCLUSIONS <br /> Results from this quarterly monitoring event appear consistent with those from previous <br /> groundwater monitoring activities, and indicate that the contaminant plume is gradually decaying <br /> and is migrating Known contaminant concentrations are highest at monitoring well MW-513 <br /> The contaminant concentrations detected in MW-5B in the current quarter (i e , 21,000 ug/L <br /> TPHg) are consistent with those of previous quarters Contaminant concentrations at MW-6 <br /> were below detectable levels, the contamination detected in MW-6 is not consistent with <br /> previous sampling data Future sampling will need to be performed before the validity of this <br /> quarter's MW-6 data can be evaluated <br /> Proceedings of the Conference on Petroleum Hydrocarbons and Organic Chemicals in Ground Water NGWAIAPI <br /> . 2Chiang,C Y et al (1989) Aerobic Biodegradation of Benzene,Toluene,and Xylene in a Sandy Aquifer-Data <br /> Analysis and Computer Modeling Groundwater Vol 27,No 6,p 823-834 <br /> ZB178C/2ndQtr2004 Monitoring Rpt 8 August 9,2004 <br />