Draft Tracer Test / Water Quality Monitoring Work Plan

Transcription

1 Draft Tracer Test / Water Quality Monitoring Work Plan November 17, 2017 Peer Review Meeting John Koreny, PG, PHG, PEG HDR Engineering, Inc.

2 Presentation Outline Objectives Work Plan Methods Schedule Summary Application of information

3 Big Picture Where are we? Task 1. Assessment of residual chemicals Task 2. Assess Treatment effectiveness Hydrogeological Characterization Tracer Test & Groundwater Quality Characterization Groundwater Model Risk Assessment

4 How This Information will be Used Tracer Test Travel times/distances/flow paths. Where does reclaimed water go when it leaves the basin? Aquifer characteristics for use in groundwater modeling. What rates and concentrations of RW eventually discharge to surface water or groundwater wells? Water Quality Monitoring Assess water quality changes over time in the subsurface How effective is soil aquifer treatment at attenuation of residual chemicals and nutrients?

5 Tracer Test / Water Quality Monitoring Objectives 1) Down gradient flow paths 2) Travel Times 3) Water quality evolution

6 Estimated Travel Times

7 Work Plan Tracer Test Water Quality Monitoring Methods What tracers will be used? How will they be introduced into groundwater? Which parameters will be monitored? Where will sampling occur? Schedule Frequency of sampling? Duration of test?

8 Schedule Summary Q M M Q M Q M M Q Martin Way RW Plant May be Off Nov-Dec. Q= Quarterly WQ Monitoring Event, M = Monthly WQ Monitoring Event

9 Test Setup Basin 4 Split in half Alternate halves for wetting/drying Monitor gw and basin water levels and temps.

10 Test Setup Reclaimed water routing options: Bypass wetlands for entire test Bypass wetlands for ½ of test (summer)

11 Reclaimed Water 0.5 to 1 mgd Flow Rates Into Basin 2014 Water Depth at 0.75 mgd flow rate

12 Tracer Method

13 Tracers Two tracers proposed, for redundancy Both are non-toxic, inert, easily detected at low concentrations Potassium Bromide (KBr) Salt from Dead Sea, refined by ICL. Mix into reclaimed water entering the basin at 50 mg/l Track movement through vadose zone (lysimeters) and groundwater (wells) Sulfur Hexafluoride (SF6) Inert non-reactive gas Diffuse into solution and inject in four wells in/around the basin Track movement through groundwater (wells)

14 Tracer Detection at Monitoring Well Reclaimed Water Recharge Site in Arizona, 2008, WateReuse Foundation Project WRF

15 Tracer Detection at Monitoring Well Reclaimed Water Recharge Site in Arizona, 2008, WateReuse Foundation Project WRF

16 Bromide Tracer Delivery Methods Potassium Bromide mixed to 5,000 mg/l in two 2,000 gallon tanks Delivered into both sides of basin Flow controlled at 2-4 gpm Distribution pipe placed on basin floor in front of reclaimed water inflow pipe. Mixes with ~1 mgd of reclaimed water to achieve 50 mg/l concentration 7 days delivery

17 SF6 Tracer Delivery Methods SF6 mixed into 5-10 gallons of potable water by diffusion (overnight) in flexible bags. SF6 denser than air. SF6 solute delivered to monitoring wells 1, 2, 15, 16 around Basin gallons of potable water plus 5 gallons solute. 1 x per day for 5 days.

18 Groundwater Modeling to Estimate Bromide Tracer Travel Time and Concentration Peak arrival of tracer (~62 days) Bromide Tracer Introduced 7 days, 20 mg/l recharge Initial arrival of tracer (~25 days) Travel time associated with center of mass (~70 days) Tracer Concentration at a Well Located 1,000 ft from Basin 4 Actual results at proposed 50 mg/l delivery into basin are 2.5 x shown results. Note: This is an example for illustrative purposes only.

19 Tracer Sampling Schedule and Frequency Schedule Schedule is (June Nov 2018) Beyond 6 months is optional, depending on findings from Jan to July. Tracers introduced for 2 week period (Jan 2018). Bromide: 7 days SF6: 5 days Sampling frequency ranges from every other day to once per month, based on: Proximity of sampling location to Basin 4 Anticipated travel time

20 Wells Used for Tracer Monitoring Work Plan 4 lysimeters 23 shallow wells 3 deep wells Wells located within ~3,500 feet of Basin 4

21 Work Plan- Tracer Sampling Schedule

22 Wells Used for Tracer Monitoring X X X X X X Streamlining X 4 lysimeters 17 shallow wells 2 deep wells Wells located within ~3,500 feet of Basin 4

23 Streamlining - Tracer Sampling Schedule

24 Water Quality Sampling Locations Reclaimed water (entering the basin) Vadose zone Two sets of three lysimeters each (10, 25, 50 feet) Groundwater 11 shallow wells 1 deep well

25 Wells Used for Water Quality Monitoring Lysimeters 10 ft 25 ft 50 ft 11 shallow wells 1 deep well

26 Water Quality Parameters / Schedule Monthly sampling events (10-12 times; Jan Oct/ Dec) Total and biodegradable organic carbon Nitrogen and phosphorus Chloride Quarterly sampling events (4 times; Jan, Apr, Jul, Oct) Above parameters Residual chemicals Disinfection byproducts Metals Coliform

27 Questions / Discussion

28 Affect of Wetlands on Water Quality End of Pipe (Pre Wetlands) Wetlands Residual Chemicals Variable Variable, but consistent degradation four compounds Nitrate Ave. 6.6 mg/l Ave. 2.8 mg/l (Ave. 3.2 mg/l reduction) Total Chlorine 0.3 to 0.7 mg/l All ND Bacteria Total Organic Carbon Biodegradable Organic Carbon No significant amount of bacteria 5 to 6 mg/l ND to 0.62 Bacteria present 5 to 6 mg/l ND to 2.7

29 Four Residual Chemicals With Consistent Concentration Reduction After Flowing Through Wetlands 1,4 Dioxane Atenolol Fluuxetine Lopressor Event 1 (11/12/2014) Event 4 (10/07/2015)

30 Residual chemicals commonly detected in reclaimed water.