NC State Stormwater Research Update: Jordan Lake Nutrient Study

Transcription

1 2019 Jordan Lake Nutrient Management Study Research Symposium NC State Stormwater Research Update: Jordan Lake Nutrient Study Bill Hunt, Jeffrey Johnson, & Sarah Waickowski Department of Biological & Agricultural Engineering NC State University

2 NCSU Research Bioretention Water quality performance of a very old BRC Media study Sand Filters Column study on media depth Floating Treatment Wetlands Research synthesis Land Conservation as a SCM Research synthesis

3 NCSU Research Bioretention Water quality performance of a very old BRC Media study Sand Filters Column study on media depth Floating Treatment Wetlands Research synthesis Land Conservation as a SCM Research synthesis

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5 Site Characteristics Characteristic Chapel Hill BRC Year constructed 2001 Monitoring Periods Initial: ; Return: Watershed area (ac) Initial: 0.15; Return: 0.28 Imperviousness 100% BRC surface area (sf) 970 Bowl storage (in) 4 Media depth (ft) 4 Ksat (in/hr) Original media P-index 4-12 Vegetative cover Perennial grasses, trees, shrubs 5

6 Results 6

7 Annual Load Comparisons POLLUTANT LOAD (LB/AC/YR) Jordan Lake TN Load Jordan Lake TP Load TN TP In Out In Out 7

8 Effluent TN Comparisons Compared to Piedmont NC WQ thresholds from McNett et al.,

9 What s Different? Post-construction After 17 years Mature vegetation Roots and Carbon Average carbon content is now similar to a cultivated field 9

10 Effluent TP Comparisons Compared to Piedmont NC WQ thresholds from McNett et al.,

11 Take Home Points monitoring period observed significant reductions in TAN, NO 3 -N, TN, and TP Comparing monitoring periods: TN removal sustained after 17 years Increase in nitrate removal Carbon source builds over time TP removal improved High phosphorus concentrations building in the soil media Elevated concentrations observed in the top 8 inches of media similar to Komlos and Traver (2012) Media depth of 4 ft should allow continued sorption capacity for future P removal (~100 years) 12

12 Take Home Points Median effluent concentrations are now below assigned values for TN and TP for nutrient reduction calculations from NC DEQ Period TN (mg/l) TP (mg/l) NC DEQ Credit Not only does bioretention work, it can get even better with time and may even be undervalued 13

13 Open Access Journal Article Just published

14 NCSU Research Bioretention Water quality performance of a very old BRC Media study Sand Filters Column study on media depth Floating Treatment Wetlands Research synthesis Land Conservation as a SCM Research synthesis

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16 Apex Greensboro McLeansville Burlington

17 Bioretention Media Study Soil samples from ~30 BRCs in Jordan Lake watershed BRC ages range from 2 to 18 years Examine N, P, and C content of the filter media Textural analysis (% sand, silt, clay) Statistics to detect trends Accumulation rates Design factors Watershed factors

18 Bioretention Media Study Additional takeaway: BRCs can be multi-functional!

19 NCSU Research Bioretention Water quality performance of a very old BRC Media study Sand Filters Column study on media depth Floating Treatment Wetlands Research synthesis Land Conservation as a SCM Research synthesis

20 Sand Column Study Lack of data from NC sand filters Reflected in updated NC DEQ SCM removal credits Conducting laboratory sand filter study Complementary data from constructed sand filters will be analyzed Using stormwater runoff from parking lot Replicates (x3) of two different ponding depths (1, 2 ft)

21 Sand Column Study Preliminary Results Column Average Concentration (mg/l) TKN NH 3 N NO 3 N TN TP Influent Effluent- Ponding Depth 1 ft Effluent- Ponding Depth 2 ft Currently sampled 7 storm events Will collect data for 15 storm events

22 NCSU Research Bioretention Water quality performance of a very old BRC Media study Sand Filters Column study on media depth Floating Treatment Wetlands (FTWs) Research synthesis Land Conservation as a SCM Research synthesis

23 FTWs Used as retrofits to (hopefully) improve wet pond nutrient removal Can be homemade or proprietary Pollutant removal mechanisms Plant uptake, filtration by roots, sedimentation, and other biogeochemical processes Varied performance TSS & particulates, metals, nutrients, some temperature Best removal of particulate bound pollutants Unanswered questions Optimal placement, coverage area, sizing

24 NCSU Research Bioretention Water quality performance of a very old BRC Media study Sand Filters Column study on media depth Floating Treatment Wetlands (FTWs) Research synthesis Land Conservation as a SCM Research synthesis

25 Land Conservation = SCM? Authoring a white paper for policy makers people in this room Summarize existing empirical data to (attempt to) address: WQ and nutrient removal associated with land conservation in urban areas Value compared to traditional SCMs Constraints Future research opportunities

26 Questions Bill Hunt Bioretention, FTWs, & Land Conservation Jeffrey Johnson Sand Filters Sarah Waickowski