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t' <br /> k" KLEINFELDER <br /> File No. 20-2983-03 <br /> October 26, 1990 <br /> not likely to increase the nitrate concentration in the upper <br /> aquifer beyond the State limit of 45 mg/1. <br /> We note that our conclusion is based on both measured and assumed <br /> values. In our review of references 1 through 4 it is clear that <br /> the techniques used to evaluate the affect of septic tanks on the <br /> rt nitrate level in groundwater is very much an art rather than a <br /> science. In addition, the "Hantzche" mass balance equation used <br /> a by the CRWQCB does not take into account all of the factors <br /> connected with the impact of septic systems on groundwater quality <br /> which include (see reference 2) : <br /> Internal Factors <br /> 1. Depth to the water table <br /> 2 . Hydraulic conductivity of the aquifer <br /> 3 . Groundwater gradient and direction of flow <br /> 4 . Aquifer thickness and effective mixing <br /> thickness <br /> 5. Background nitrate-nitrogen concentration of <br /> E groundwater <br /> 6. Aquifer geology (e.g. unconsolidated sands, <br /> fractured bedrock, etc. ) <br /> 7 . Potential for denitrification <br /> External Factors <br /> 1. Density of septic systems <br /> tt <br /> 2 . Present and potential use of aquifer <br /> 3 . Impact on down-gradient users <br /> 4 . Leakage to (i.e. contamination of) other <br /> aquifers <br /> } <br /> 4 ' <br /> Copyright 1990 KLeinfelder, Inc. 7 <br /> t .. <br />