WaterTech 2013 April 10 12, Banff, Alberta

Transcription

1 WaterTech 2013 April 10 12, Banff, Alberta Treatment of Dissolved Sulphides in Woodwaste Landfill Leachate Using Engineered Wetlands: Challenges and Long-Term Sustainable Solution Presented by: Christina Chan, P.Eng. Co-Authors: Francisco Perelló, P.Eng, Michael Geraghty, P.Geo., Kyla Bryant, BIT, Antonia Gunardi, EIT 1

2 Table Of Contents Site Background Remediation Drivers Remediation Challenges Wetlands Design Results Questions 2

3 Site Description Former log sort and logging operations centre in South Vancouver Island Located in the southwest coast of Vancouver Island, along the south shore of the Jordan River and fronting the Strait of Juan de Fuca. 3

4 Wood Waste Landfill Landfill A wood waste landfill is located on the property, adjacent to the Jordan River to the west and a spillway that was associated with a former hydroelectric generating station. Jordan River Former BC Hydro Spillway Strait of Juan de Fuca 4

5 Remediation Drivers On closure: a portion of the property was sold to the Capital Regional District for future park use. Purchase sale agreement: the Seller agreed to complete remediation of the property and deliver a Certificate of Compliance. Investigations found that landfill leachate seeps were discharging to the spillway and to the Jordan River. The leachate contained dissolved sulphides as H2S at concentrations up to 50 times the British Columbia Water Quality Guidelines Regulations for Contaminated Sites (2006) for marine environments. 5

6 Landfill Seep Locations 6

7 Sulphides Concentrations at Landfill Seeps Area 1 Area 2 Area 2 7

8 Seep at Jordan River Area 1 8

9 Seep into Spillway Area 2 9

10 Remediation Challenges The leachate is expected to continue to be released from the landfill for several years following the land sale. Following completion of the sale, the Seller will not have staff operating from the facility. Require a remediation strategy that is low maintenance and sustainable over a long time. 10

11 Remediation Challenges Physical, chemical and biological treatments were considered. Problem 1 = all require ongoing operator attention. Problem 2 = the Site is in a remote location. Solution = Engineered Wetlands. Minimal maintenance. No additional operator duties. No additional utility requirements. 11

12 ENGINEERED WETLANDS DESIGN 12

13 Design Objectives Primary Objective: To reduce dissolved sulphides concentrations to levels below the BCWQG. Secondary Objective: To enhance the existing environment by providing additional habitat for aquatic life. 13

14 Design Consideration 1 Wetland Holding Capacity Calculating the minimum area required at the base of each wetland for adequate tidal holding capacity, and maximizing plant growth zones. 14

15 Design Consideration 2 ph Neutralization Calculating the required holding time to allow for ph neutralization of the seep. Neutralizing the discharge water facilitates the chemical reaction for the transformation of dissolved sulphides to H 2 S gas. 15

16 Design Consideration 3 H2S Off-Gassing Increasing the seep discharge path to increase aeration for off-gassing the H2S from the sulphides in solution. 16

17 Design Consideration 4 Tidal Fluctuations Determining seasonal tidal fluctuations to make sure the wetlands have consistent influx and drainage. 17

18 Design Tidal Fluctuation 18

19 Design Consideration 5 Plants Re-using native vegetation for the replanting of the engineered wetland to take advantage of the root oxygen release rates for further oxidation of the dissolved sulphides as H 2 S. 19

20 Vegetation Transect to Determine Planting Plan Mean % Cover A B C Transects Lyngbye's Sedge Tufted Hairgrass Woody Debris Bare Soil Salal Baldhip Rose Bluejoint Grass Red-osier Dogwood Organic Layer 20

21 Design Calculations 21

22 Engineered Wetlands Area 1 Wetland Area 2 Wetland 22

23 Solution Engineering and Biological Design Area 1 Wetland Intercepted Seep 23

24 Wetland Area 1 During Construction Before Planting 24

25 Wetland Area 1 During Planting 25

26 Wetland Area 1 Installing the Culverts 26

27 Solution Engineering and Biological Design Wetland Area 2 27

28 Wetland Area 2 Planting Plan 28

29 Wetland Area 2 Plant Survival Tufted Hairgrass Lyngbye s Sedge 29

30 Post Construction - Monitoring The seep in Area 1 was intercepted and the flow is now visible into the north end of the wetland Seep 30

31 Post Construction - Monitoring The seeps in Area 2 were intercepted and the flow is not visible at this point in time Areas of former seeps Seep 31

32 Post Construction - Sampling Conducted field titrations for dissolved sulphides at the seep in Area 1, discharge of Area 1 and discharge of Area 2. Calculated H2S using the pka dissociative constant. Dissolved sulphides as H2S reduced from 54.6 ug/l at the seep to 1.9 ug/l at the discharge in Area 1. 32

33 Post Construction Sampling Results 33

34 Engineered Wetlands - Results Concentrations of dissolved sulphides (as H2S) in the wetlands discharge was less than the reported detection limits and the BC Water Quality Guidelines during sampling in both wet and dry seasons. 34

35 Results Successful results were submitted to the MOE in December 2012 A Certificate of Compliance was issued in 2013 and the property was transferred to the CRD Future plans are to create park land for public use 35

36 Results 36

37 Thank You! Questions Christina Chan, P.Eng. Keystone Environmental Ltd. (604)