2011-12-15_AgendaPacket - Laserfiche WebLink

Home

i- i ni o 2olr Monitoring Results Although the amount of data collected was limited by below average precipitation, the monitoring data gathered during the 2011 season will be very useful in evaluating the calibration of the existing P8 model (which will determine whether or not re- calibration of the model is necessary). At all 3 monitoring sites continuous flow data was collected during the 3 -month period and water quality sampling occurred for two storms. Flow 15- minute continuous flow data for 3 months was collected during the period 8/4/2011 — 11/16/2011 using automated samplers. Daily precipitation depths were obtained from the Climatology Work Group for the nearest location at station 217381 which is located approximately 2.1 miles southwest of Roseville Area High School at the University of Minnesota Farm in St Paul (see Figures 24). These graphs show very few significant rainfall events: the most prominent being a 1.82" rainfall event on 8/16/2011 (see Figures 5 -7). This large event produced peak flows of —30 cfs at each site which will prove useful for evaluation of the existing calibration (and possibly re- calibration) of larger storm hydrology. Additionally, smaller storms of 0.76" and 0.82" occurred during the monitoring period and generated peak flow rates of 1 to 9 cfs at the monitoring locations. This data will be critical to evaluating the complex hydrology associated with smaller storm events. Water Quality Samples The two water quality samples collected in 2011 correspond with the two largest rainfall events encountered during the monitoring period: the 1.82" and 0.76" rainfall events. The samples were analyzed for TP and TSS (Table 1). The sampler at RHE was not functioning properly for the 10/13 event so no data is reported for that site. This issue related to the sampler had to do with a loose nut on the distributor arm which has since been corrected. All recorded TP and TSS measurements were within reasonable levels given the landuse of the drainage areas. The most interesting result of this monitoring effort is the striking increase in TP and TSS between the two sampled events. Two things contribute to this increase. The first is the presence of some leaves beginning to fall and contribute to the TSS and TP load in the 10/13 sample, this is a minor contributor to the increase because most trees were still holding all leaves at this point in the season. The second is the buildup of particulate matter over dry periods. Prior to the 8/17 sampled event, only 4 days had passed since the last washoff event (0.82" on 8/1.3) so the drainage area was somewhat clean prior to this event. For the 10/13 event, there had been no appreciable rainfall for 23 days, allowing for a much greater level of buildup of particulates on impervious surfaces. Having local data to describe how the build -up occurs in this watershed will be very useful in evaluating the existing calibration of the P8 model as this information will allow P8 to mimic this phenomenon using the buildup /washoff routine to calculate pollutant concentrations from impervious surfaces based on real time since the last precipitation event. Table 1. Water quality monitoring summary Site Date TP m /L TSS m /L] Galtier 8117/2011 0.23 20 RHE 8/17/2011 0.26 6 RHW 8117/2011 0.21 8 Galtier 10/13/2011 1.30 46 RHW 10/13/2011 0.74 39 Emmons & Olivier Resources, Inc. 651 Hale Ave N, Oakdale, MN 55128 p: 651.770.8448 f: 651.770.2552 www.eorinc.com