Monitoring Results
Hydrology
The DISs performed well during their respective study periods. The Site L and M DISs combined for a total capture rating of 97%, well above typical BMPs. Meanwhile, the less conservatively designed, and more challenged DIS at Site K still acquired a high capture rating at 80%. The table below summarizes this monitoring.
Table: DIS Hydraulic Performance
| Site | Rainfall (in) |
Total Stormwater Flow (cf) | Total Overflow (cf) | Total Captured Flow (cf) | Capture Rating (%) | Monitoring Duration (yr) |
|---|---|---|---|---|---|---|
| K | 47.3 | 934,212 | 185,756 | 748,456 | 80 | 1.0 |
| L | 108 | 132,654 | 0 | 132,654 | 100 | 2.6 |
| M | 397,849 | 15,457 | 382,392 | 96 |
Water Quality
The DISs and associated dunes have performed well, with respect to water quality, as well. The stormwater enterococcus concentrations have most been above the state maximum for Tier I Beaches, while the groundwater levels have remained much lower. The following table and figures summarize the bacteria monitoring results. The control was not monitored for stormwater as there was no direct input into the dunes, such as with the DIS sites.
The state Maximum for Tier I Beaches is 104 MPN/100 mL. Tier I beaches include all ocean front beaches and those located near resorts, hotels, and camps.
Click on the images for a larger view.
Table: Stormwater Enterococcus Monitoring Summary
| Site | Maximum Stormwater Enteroccocus Concentration (MPN/100 mL) | Median Stormwater Enteroccocus Concentration (MPN/100 mL) | Number of Samples Exceeding the State Maximum | Total Number of Samples Collected | Exceedance Rate (%) |
|---|---|---|---|---|---|
| K | 24,196 | 1,540 | 33 | 35 | 94 |
| L | 89,680 | 185 | 17 | 24 | 71 |
| M | 3,076 | 435 | 19 | 24 | 79 |
Table: Groundwater Enterococcus Monitoring Summary
| Site | Maximum Groundwater Enteroccocus Concentration (MPN/100 mL) |
Median Groundwater Enteroccocus Concentration (MPN/100 mL) | Number of Samples Exceeding the State Maximum | Total Number of Samples Collected | Exceedance Rate (%) | Reduction from Stormwater Concentrations (%) |
|---|---|---|---|---|---|---|
| K | 4,839 | 16 | 21 | 132 | 16 | 99 |
| L | 945 | 4 | 12 | 285 | 4 | 98 |
| M | 3,063 | 5 | 22 | 206 | 11 | 99 |
| Control | 429 | 5 | 7 | 122 | 6 | N/A |
| Figures: Enterococcus Monitoring Boxplots for Sites L, M, and Control | Figures: Enterococcus Monitoring Boxplots for Sites K and Control |
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