Two monitoring stations were installed in March, 2003. The drainage area of PC1 was about 2.4 acres of which 1 acre was the wooded riparian buffer. The area draining to PC2 was about 6.4 acres; however, 4.2 acres of this was from the homes along Hanna Street leaving only 2.2 acres from the site (Figure 1). The PC1 station consisted of an automated sampler and a rectangular weir. Because the drainage channel was not well defined, an extended plywood diversion (figure 2) was installed to channel runoff to the weir. The PC2 station was located along a roadside ditch and consisted of an automated sampler and a 3-ft rectangular weir.
Figure 1. Drainage areas to monitoring stations.
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A 2 ft rectangular was installed at PC1 and a 3 ft rectangular weir at PC2 during the pre-development period. An automated sampler with an integrated flowmeter was installed at each weir to continuously measure water depth over the weir. The flowmeter was programmed to continuously convert the depth to discharge using the standard equation for each weir. Flow-proportional samples were collected by each sampler and stored in individual bottles within the machine. Paired samples were collected with one of the samples being placed in a pre-acidified bottle and the other in a nonacidified bottle. The acidified (pH<2) samples were used for nitrogen and phosphorus analysis, while the nonacidified sample was used for sediment and turbidity analysis. The PC2 station was removed after only 9 months due to equipment problems and to prepare for the start of construction. The automated sampling equipment was moved to the outlet of a sediment basin constructed on-site. This station, referred to as PC3, had a 120 deg v-notch weir installed downslope of the overflow and skimmer outlets of a sediment basin (Figure 3).
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Once every 2 weeks (more frequent if >1.5 in of rainfall occurred) the sampler was visited and the individual flow proportional samples were combined into one sample per period for laboratory analysis. Samples were analyzed for turbidity using a turbidimeter measuring in Nephelometric turbidity units (NTUs). For high turbidities (> 1000NTU) the sample was diluted and a linear extrapolation of the measured value and dilution ratio was used to estimate the turbidity of the runoff sample. Also, samples were analyzed for total suspended solids (TSS) using standard method 2540D. For sample with TSS concentrations greater than 5,000 mg/L, method 2540D was not used due to the overwhelming amount of sediment on the filter. For these samples method 2540B was used to compute total solids (TS), which was then assumed to be equal to TSS. Past experience has shown that at very high sediment levels, TSS and TS are nearly equal in most cases.
Rainfall amounts were continuously recorded via an 8-inch diameter tipping bucket-recording rain gage installed near the PC2 site. The gage measured rainfall amounts to 0.01 inch and stored the amounts in 15-minute increments.
