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. 3-20-1997 8:43PNI FROM �' 3 Page 2 Mr. Meleyco March 19, 1997 ' i nitrate loading impact on groundwater quality to be significantly underestimated. Additionally, the Kleinfelder report does not clarify whether the reference nitrate values and calculations are for nitrate rine:surcd"as ND,„or"as N"; there is a significant difference which appears to be overlooked in the report. My specific points of disagreement are as follows: • Nitrate "as N*' vs Nitrate 64as X03'!- The Klein-felder report does not identify the nitrate measurement units and appears to use values for nitrate "as N"and "as NO3"interchangeably. The values are not interchangeable. The drinking water standard for nitrate is 10 mg/I(as N)and 45 mgfl (as NO,). The Kleinfelder nitrate loading calculations use values for unite as N,but conclude their analysis by comparing the results to the drinking water standard of 45 moll,which is the standard expressed "as NO3". The results should, instead, be compared to the 10 mg/I standard. This is the convention used in the original EIR and in the Cb,ico study that Kleinfelder makes reference to and utilizes data from. i Septic System Nitrogen Content. Kleinfelder assumes a.concentration of 30 rng/i for the nitrate content of septic tank effluent discharged to the leachfieIds. This is an extremely liberal assumption,the this is intended to be nitrate "as NO3"; it would correspond to a value nitrate- nitrogen value of about 6.8 mg/l. Even if the 30 mgll is intended to be nitrate as N, the assumption is still much too low and is not supported by any literature that I am aware of,They cite the fact that they sampled septic systems for nitrate, finding the concentrations to be <1.0 mg/1. The problem with this is that the septic tank effluent rarely contains nitrogen in the nitrate form; it is nearly all in the form of ammonia or organic nitrogsn coming out or the septic tank (an anaerobic environment). It is only after the effluent passes through the aerates soil zone below the leaching trenches that the nitrogen is transformed to nitrate (i.e., by"nitrification'% and this is generally recognized to be a total, 100170 conversion. The discussion and assumptions in the Kleinfelder report appear to completely miss this critic.31 point. Literature data show septic rank effluent to have total nitrogen corcentrations generally in the range or 40 to 60 mg/l; and this-should be used in the nitrate loading calculations in place of the 30 mpyl used by Kleinfe'.der. • Denitrification. The Kleinfelder study assumes a value of 40% for denitrification of the percolating septic effluent. Denitrification is the biological process in the soil whereby certain bacteria utilize the oxvgen in the nitrate (IVO,) and release aitrogen gas (N2 to the: atmusphere. Denitrification is expressed as a percentage, and the normally accepted range is I0 to 25%. It is not something that can be measured, but must be estimated. Qenitrification is generally highest where the soils are wet,fine-textured (i.e_, clayey) and have nigh amounts o;organic matter; well-drained,permeable and sandy soils with a deep water table generally do not provide favorable conditions for high rates of denitrification. In rry opinion, the 40% rate used in the Kleinfelder study significantly overestimates the likely deritrification potential at :he site. The main rationale for a 40% rate cited is the soil texture. This ignores the other factors that are critical to denitrification,namely wet,poorly drained and aigh organic conditions, 'Their analysis f j