Stormwater Evaluation Phase II Stormwater Sampling

Transcription

1 Rehoboth Beach Commissioners Meeting Stormwater Evaluation Phase II Stormwater Sampling Leita Bennett Associate Jeff Sturdevant Principal March 2018

2 Rehoboth Beach Stormwater Evaluation Update Agenda Stormwater Evaluation Purpose Phase I Goals Phase I Results Phase II Goals Sampling Overview Sampling Results Next Steps 2

3 Stormwater Evaluation - Purpose DNREC issues TMDL for Delaware Eliminates Rehoboth Beach WWTP discharge to Lewes-Rehoboth Canal Selects WWTP ocean discharge Requires stormwater investigation to meet goal to assure: All practical means to avoid and minimize environmental harm from implementation of the selected alternative. 3

4 Phase I Stormwater PER - Goals Estimate stormwater characteristics on 5 outfall locations Identify potential stormwater management practices Evaluate Best Management Practices Evaluate outfall extensions Provide further evaluation alternatives Keep Rehoboth Beach s Best in beach water quality ranking 4

5 Phase I Stormwater Hydraulic Model Inputs Existing SW Management devices Inlets & manholes Sand filters (annual clean) Perforated pipe Stormceptors (annual clean) Lake Gerar Waterway Restoration & Mgmt Plan Land use Outfalls Rainfall Impervious Areas Bacterial Indicator (Enterococcus, FENT) data 5

6 Outfalls SWM Phase Fac I Stormwater Investigation Inlets Filters Tmt Area Model Inputs 6

7 Phase I Stormwater Hydrodynamic Model Results 10 year storm Outfall Average 8,132 cfu/100 ml (DNREC) 0 6 hours: 24 hours: 48 hours: 2,001 5,000 fu/100 ml cfu/100 ml 0 35 cfu/100 ml Beach Action Value (BAV) 60 cfu/100 ml 7

8 Phase I Stormwater management options BMP Type Public Education & Outreach Recommended Locations City-Wide Non-Structural Structural Storm Drain Marking Storm Drain System Cleaning/ Flushing Infiltration and Bioretention Delaware Sand Filters Engineered Biofiltration Perforated Pipe Infiltration Permeable Pavement Outfall Extensions (1,300 ft) 300 inlets 36,000 linear feet of pipe Rebate provided per household 16 sand filters As needed Replacement of aging or failing pipe 175,000 sq ft on Rehoboth Avenue 4 combined outfalls 8

9 Phase II Stormwater Evaluation Goals Gather real-time data to: Calibrate models Rerun models Correlate storm events with FENT Identify high FENT locations Confirm SW source of FENT 9

10 Phase II Sampling Locations 5 outfalls (5,7,3,2) SWM devices, - upstream (14) - downstream (10, 9) Land use - residential (14) - commercial (3, 10) - mixed (2) Grenoble Maryland Rehoboth Delaware Laurel 10

11 Phase II Sampling Protocols/Frequency 6 major storms Parameters based on MS4 requirements Enterococci (FENT) Total Suspended Solids Total Phosphorus Oil and Grease ph Temperature Ammonia Autosamplers based on water depth 11

12 Phase II FENT Sampling Results Comparisons Outfall/ Sampler Location PER Average FENT (cfu/100 ml) Flow-Weighted Average FENT (cfu/100 ml) Type of area discharge 2, Delaware 8,370 9,606 Mixed Use & Residential 3, Rehoboth 8,480 17,025 Mixed Use 5, Grenoble 7,080 2,017 Lake 7, Maryland 8,490 18,506 Mixed Use Laurel* 8,240 9,606 Mixed Use & Residential 9 7,080 11,511 Residential Treated 10 NA 33,220 Mixed Use Treated 14 7,080 13,521 Residential Average 7,831 14,377 12

13 Phase II Sampling Results Observations Mixed Use FENT results considerably higher than Residential Downstream of treatment FENT higher, large storms Site 9 (residential, trap system) higher FENT than 14 (residential, no trap) Site 5 (Lake Gerar discharge) lowest FENT Site 2 (Delaware Ave) low FENT with most number of SW manholes 13

14 Phase II Other Data Results - Averages Site # TSS (mg/l) NH3 (mg/l) TP (mg/l) O&G mg/l Type of area discharge 2, D Mixed Use & Residential 3, R Mixed Use 5, G Lake 7, M Mixed Use Residential Treated Mixed Use Treated Const Mixed Use Residential Ave Mixed Use Typical SW* Mixed Use 14

15 Phase II Modeling Outcomes and Comparisons

16 Modeling Results: 0 6 hours Phase I, PER Phase II, Actual Data fcu/100ml 16

17 Modeling Results: 24 hours Phase I, PER Phase II, Actual Data fcu/100ml 0 fcu/100ml Phase II, Actual Data 17

18 Modeling Results: Extend Rehoboth Ave Only, 0-6 hours Phase I, PER Phase II, Actual Data 61 2,000 fcu/100ml 61-1,000 fcu/100ml 18

19 Modeling Results: 80% FENT Reduction, 0 6 hours Phase I, PER, no Reduction Phase II, 80% FENT Red fcu/100ml fcu/100ml 19

20 Modeling Results: Extend All, 0-6 hours Phase I, PER Phase II, Extend all 0-75 fcu/100ml 0-60 fcu/100ml

21 Phase II Modeling Results: Extend All - 12 hours 0-30 fcu/100ml 21

22 Phase II Stormwater Evaluation Recommendations Need severe reduction at Rehoboth and Maryland Avenue s discharges Determine source of high FENT levels from Rehoboth and Maryland Avenues Clean filters more frequently, particularly during summer months (monthly) Determine human from non-human FENT Finalize BMP SWM recommendations based on above results No need for extension of Grenoble 22

23 Phase II Stormwater Evaluation Relative Costs BMP Type Recommended Locations Estimated Cost Public Education & Outreach City-Wide Minimal Non-Structural Storm Drain Marking 300 inlets $2,800 Storm Drain System Cleaning/ Flushing 36,000 linear feet of pipe $144,000 Infiltration and Bioretention Rebate provided per household $2,500 per household Engineered Filters 16 sand filters $736,000 Structural Engineered Biofiltration As needed Varies Perforated Pipe Infiltration Permeable Pavement Replacement of aging or failing pipe 175,000 sq ft on Rehoboth Avenue ($10/sf) With new projects $1.9 million Outfall Extensions (1,300 ft) 4 combined outfalls $15 million 23

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