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T Page 2 Mr. Meleyco March 19, 1997 nitrate loading impact on groundwater quality to be significantly underestimaced. :gdd:tionally, the Kleittfdder report does not clarifv whether the reference nitrate values and calculations are for nitrate M=ured "as NO,"or"as N"; th' is a si report. My specific points of disagreement are as follows:difference which appcars to be ove:Iooked in the 4 • Nitrate "as N" is iYitrate syp3+ The Kleinfelder report does not identify the nitrate measurement units and ap s to use values " „ _ I� al es for nitrate as N »inte The values are not interchan¢eable. The drinking water standard for. itrate is 10 mgn;changeably. (as N)anl d 45 mgA (as Nr03). The Klcinfelder nitrate loading calculations use values for ait_ate as N,'but conclude their analvsis by comparing the results to the driWking water standard of 45 mg/l, which is the standard expressed "as NO,". The results should, instead, be cOr"Pattd t he In standard. This is the convention used in the original EIR and in the C co steed,that tKleinfelder makes reference to and utilizes data from. • Septic System Nitrogen Content Kleinfelder assumes a concentration of 30 n:g/I for the nitrate content of septic tank effluent.discliarged to the.Ieachfields. 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/1. Even if the 30 mg/1 is intended to be nitrate as lv, the assunagtion is still much too low and is not supported by any literature that I am aware of. They i cite the fact that thev sampled septic systems for nitrate, finding the concentrations to be [l.o mgA. The problem with this is that the septic tank effuent rarely contains nitrogen in the nitrate forth; it is nearly all in t;re fora of ammonia or organic nitrogen conung out eI'the septic tank (an anaerobic cavironment). It is only after the effluent passes through the aerated soil zone below the leaching trenches that the nitrogen is transformed to air-rate (i.e., by"nitrification"), and this is generally recognized to be a total, 16090 conversion_ The discussion and assumptions in the Kleinfelder report appear to completely miss this critical point. Literamm data show septic " tank effluent to have total nitrogen concentrations r-nerally in the range of 40 to 60 mgA; and -,this-should be used in the nitrate loading calculations in place of the 30 mg,'l used by Kleinfelder. • Denitrification. The Kleinfelder study assumes a'value of 40% for denit ' � nfication of the perco?ating septic effluent. Denitrification is the bioiogical-process in the soil whereby ceratin bacteria uEUjzc the oxygen in the nitrate (NOS) and rc;lease nitrogen gas (NI' to the atrnusphere. Denitrification is expressed as a percentage, and the nornnally accepted range is 10 to 25%. It is not something that can be measured, but must be estimated. Denitrification is generally highest where the soils are wet, fine-textured (i.e., clayey;, and have high amounts ox organic matter,'well-drained,permeable and sand soils MCI a deep water table generally do not provide favorable conditions for high rates of denitrification_ in-nv opinion, the 4.0%a rate used in the Kleinfelder s:udv significantly overestimates the likely denitrification potential at the site. The main rationale for a 40% rate cited is the soil texture. This ignores the other factors that are c.iticaI 10 denitrification,namely wet,poorly drained and high orgastic conditions. Their analysis