anaerobic septic tank, the transformation of N begins with the breakdown of organically bound N

by microbial enzymes such as proteases, ureases, and deaminases. The resulting N products in the

septic tank are predominantly ammonium and organic N; Otis et al. (1975) gave proportions of 75%

and 25%, respectively, for these forms in STE. Harkin et al. (1979) reported that the effluent N in

33 monitored mound systems was primarily NH4-N (64%), and organically bound (35%). Only 1%

of the N in STE was N03-N. This indicated an anaerobic situation in the pump chamber, and that

the nitrate found in the soil absorption field was the result of nitrification of the N in the effluent in

the absorption field under aerobic conditions. In our study, an average of 79.4% NH4-N, 13.4%

organically-bound N, and 7.2% N03-N were found in the STE from ten septic systems monitored.

Since all the systems from which STE was successfully sampled except that at Site 13 employed a

dosing chamber, the relatively high NH4-N and low organically-bound N level proportions might

indicate a higher efficiency of anaerobic decomposition of organic-N in the septic tank/pump

chamber combination, while the higher N03-N might be a result of aeration during spill over into

or residence in the dosing chamber. The manhole covers on the systems serving Sites 1, 3, 9, 10, 14,

and WHHS were either not tightly fitting on the manhole or damaged/cracked to various extents.

Replacement of the cover with a locking device might reduce air access to the dosing chamber, but

may not be necessarily beneficial. Nitrification-denitrification during septic tank/pumping chamber

transfers may reduce N loadings to the absorption field.

    Results of the N03-N, NH4-N, and TKN contents in the STE or groundwater sampled from each

monitored site are tabulated in Appendix I. Figures 11, 13, 15, and 17 show the mean concentrations

of various nitrogen species in the STE and the groundwater from the four monitoring wells; Figures

12, 14, 16, and 18 exclude the STE data and show the means for the groundwater samples only to

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