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a. Nitrite/Nitrate Nitrogen (NOx) Results Table 2 and Figure 2 show the average NOx concentrations at the various sample locations along the canal length. TABLE 2 -8th Street Canal NOx-Nitrogen_ (mg/1) 2 - AVERAGE NOx NITROGEN ALONG CANALm 1 ( g�) SAMPLE DATE A B C D E F 9/13/2016 0.03 0.03 0.03 0.09 0.27 0.06 - 0.a5 9/20/2016 0.03 0.03 0.06 0.14 0.45 0.09 o.ao i 9/27/2016 0.10 0.04 0.03 0.13 0.31 0.14 0.35 9/30/2016 0.19 0.03 0.03 0.08 0.32 0.12 0.30 10/4/2016 0.08 0.03 0.03 0.08 0.34 1 0.14 0.2S 0.20 10/11/2016 -- 0.03 0.03 0.08 0.17 0.03 10/18/2016 0.03 0.03 0.03 0.11 0.53 0.15 0.15 10/25/2016 0.01 0.01 0.02 0.17 0.60 0.11 0.10 11/1/2016 0.01 0.01 0.02 0.13 0.79 0.14 0.05 A COUNT 1 8 9 9 9 9 9 0.00 AVERAGE 1 0.06 0.02 0.03 0.11 0.42 0.11 _ A g C D E F iNOx-N=Nitrate+Nitrate Nitrogen The canal section between Sample Points A and C covers the northern boundary of the WRWWTF plus a residential subdivision and ranchette parcels. In this canal section, the average NOx concentration is approximately 0.04 mg/I. Note however, that Sample Point A was located at the far western reach of the 8th Street Canal. Although the 8th Street Canal has a pipe connection to the adjacent D-4 Sublateral Canal running north -south along 90th Avenue, the two canals are not hydraulically connected except during extreme rainfall events. This is because the connecting pipe's invert is installed higher than the D-4 Canal's normal water level. As a result, the 8th Street Canal water at Sample Point A is normally stagnant and very shallow. Because of this, we suspect water samples from Sample Point A had a high risk of contamination with detritus, which could cause elevated sample results. If Sample Point A results are dismissed, the average NOx concentration in this canal section is .approximately 0.03 mg/I. As discussed later in the TKN results section, the highest TKN value occurs at Sample Point B opposite the wetland, which might imply some leaching of water into the canal from the wetland cells. If so, one might ask why the canal NOx concentration is not elevated also at Sample Point B. If such seepage is occurring, the low NOx values at this location are most likely due to the reduction of NOx by bacteria in the soil, which through biological denitrification reduces the nitrogen in the NOx molecule to a gaseous form. Average NOx concentrations increase 0.01 mg/I from Sample Point B to Sample Point C. Concentrations begin to increase sharply east of Sample Point C, reaching 0.11 mg/I at Sample Point D and 0.42 mg/I at Sample Point E, which is a little west of the canal's connection to the Lateral C Canal paralleling 74th Avenue. Sample Point F is located east of the Lateral C Canal and is not 5 FAPublic Works\KeithM\Stormwater Projects\IRFWCD 8th Street Canal Water Study\Memo 2 - 8th Street Canal.doc 36