Saskatchewan Avenue Crossing Replacement at Sturgeon Creek Environmental Assessment Report

APPENDIX C HYDROGEOLOGICAL ASSESSMENT/AQUIFER CHARACTERIZATION STUDY

734-1600070700-REP-V0001-00

Friesen Drillers Ltd. 307 PTH 12 N Steinbach, MB. R5G 1T8 Phone 204-326-2485 Fax 204-326-2483 Toll Free-1-888-794-9355

w a t e r … t h e l i f e b l o o d o f t h e l a n d

April 26, 2017

Isaac Dennett, EIT Geotechnical Engineer in Training Amec Foster Wheeler Environment & Infrastructure 440 Dovercourt Drive Winnipeg, Manitoba R3Y 1N4

Dear Mr. Dennett,

Subject Hydrogeological Assessment / Aquifer Characterization

Sturgeon Creek Bridge - River Lots 101-105 Parish of St. Charles & River Lots 1-4 Parish of St. James

Saskatchewan Avenue, Winnipeg, Manitoba

Friesen Drillers Ltd. is pleased to present this report detailing the results of our hydrogeological investigation. Working in conjunction with Amec Foster Wheeler, the investigation included aquifer testing to determine the potential for aquifer depressurization to allow the construction of a bridge foundation and to evaluate the groundwater/surface water interactions from a potential dewatering program at the above noted site in northwest Winnipeg. The investigation involved test well drilling, aquifer pump testing and technical analysis. The recommendations of this investigation are largely based on the results of a Geotechnical Report produced by Amec Foster Wheeler in 2016. The following is the agreed upon scope of work for the project:

• Obtain a Groundwater Exploration Permit (GEP) from Manitoba Sustainable Development. This is required by the Water Rights Act prior to commencing the work. A copy of the GEP is attached.

• Install two 5 inch (12.7 cm) PVC cased test wells into the carbonate aquifer to a maximum depth of 200 feet (60.96 m) below grade. It should be noted that the upper fractured zone of the carbonate aquifer will be the target.

• Complete a short term pumping test on each of the test wells, including monitoring for recovery.

• Provide engineering services, which include test supervision, aquifer parameter analysis, local well inventory preparation and analytical sampling and monitoring. Provide dewatering estimates to ensure a stable creek bed throughout the construction process.

• Prepare a report which details the results, discussions of groundwater conditions, and options for dewatering, proposed well design, and monitoring.

• The test wells will be maintained and kept functional once this hydrogeological investigation stage is completed. Project Background Amec Foster Wheeler has been retained to replace the Sturgeon Creek Culvert on Saskatchewan Avenue in west Winnipeg, MB. As part of the design process, a Preliminary Design Geotechnical Report has been prepared by Amec Foster Wheeler (2016). The Geotechnical Report details the results of a geotechnical assessment conducted at the Sturgeon Creek Bridge site by Amec Foster Wheeler. It is our understanding from the Amec report that the water level in Sturgeon Creek will be lowered during the constructing of the Saskatchewan Ave, Sturgeon Creek Bridge. The Geotechnical Report (Amec Foster Wheeler, 2016) further identified artesian groundwater pressures in the underlying till at the Sturgeon Creek site that present a risk for basal heave and creek bed instability at lowered creek water levels. Amec Foster Wheeler has retained Friesen Drillers to conduct a hydrogeological investigation at the Saskatchewan Ave Sturgeon Creek Bridge site to assess the local aquifer conditions to aid in the design of a potential aquifer depressurization system. Much of the hydrogeological investigation is based on the findings of the Geotechnical Report (Amec Foster Wheeler, 2016) which indicates that aquifer depressurization will be required as part of the construction process. The dewatering system is anticipated to be in operation between the winter months of November 2017 to February 2018 (Pers. Comm. Amec Foster Wheeler, 2017).

– 2 – April 26, 2017

Site Setting Physical Setting The Saskatchewan Avenue Sturgeon Creek Bridge site, located in northwest Winnipeg, lies at the edge of a major residential development and is bordered by land under agricultural uses. The study site is surrounded by land developed for the following purposes:

• North – Agricultural.

• East – Residential.

• South – Residential.

• West - Residential. The location of the Sturgeon Creek Bridge site and the two test wells is shown on the following page as Figure 1. The topography of the area is of relatively low relief and surface drainage is directed towards the Sturgeon Creek, which runs north-south

through the project area. Water supplies for the area are provided by the City of Winnipeg municipal water supply system, although many

private will still exist in the area.

Figure 1 – Well Locations – Sturgeon Creek Bridge – Winnipeg, MB. (Source – Google Earth, 2017)

Geological and Hydrogeological Setting The surficial geology underlying the Sturgeon Creek site consists of silty grey clay, approximately 20 feet (6.1 m) thick, overlying 10-15 feet

(3.04-4.5 m) thick unit of calcareous white till with minor layers of sand and gravel. A fractured carbonate rubble zone underlies the till

unit. The thickness of the rubble zone is known to be variable across the area. Some karstic features have also been noted in the area.

The rubble zone gradually changes into more competent, fractured carbonate rock of the Fort Garry Member of the Red River

Formation. The Red River Formation typically consists of alternating layers of limestone and dolostone with basal shale layers. The Red

River Formation is in turn underlain by the Winnipeg Formation clastic (sandstone and shale) unit, and Precambrian basal granites

(Render, 1970)

With the exception of the carbonate rock surface, which is typically quite irregular due to erosion, fracturing, and karstic features, the

– 3 – April 26, 2017

Geological and Hydrogeological Setting (Cont’d) geology within the study area is fairly uniform and consistent. A geological cross section is shown on the following page as Figure 2.

The general hydrogeological conditions of the area were determined from a review of the applicable hydrogeological reports and

information available through Manitoba Sustainable Development (MSD). Groundwater aquifers in the Winnipeg area can be found in the

overburden till (in specific places), the Red River Formation carbonate, and the Winnipeg Formation (Betcher et. al, 1995). The inter-till

sand and gravel aquifers are generally of limited extent in areas of more granular till deposits and are typically hydraulically connected to

the underlying carbonate bedrock. Consequently, to adequately drain the till and inter till material, the underlying and generally higher

yielding carbonate bedrock must be hydraulically depressurized.

Groundwater flow in the carbonate bedrock of the Red River Formation generally occurs in the fracture and joint sets in the rock. The

size, extent, and interconnectivity of the fracture system governs horizontal and vertical groundwater movement through the bedrock.

Due to this geologic condition, aquifer transmissivity and storativity can vary significantly over a relatively short distance, resulting in

substantial variations in well yield (Render, 1970).

The carbonate aquifer system generally comprises two distinct zones (Render, 1980). The upper zone, which is typically higher producing,

locally, and the lower zone. The thickness of the upper zone is highly variable and changes significantly over short distances. We have

noted fracture zones in the upper bedrock to exceed 100 feet.

Figure 2 - Geological cross section through Southern Manitoba; the approximate location of the test wells are plotted in red. (source

Manitoba Geological Survey, 2013) The transmissive conditions in the carbonate aquifer in the Winnipeg region have been mapped by Baracos et. al. (1983). A portion of

this map is shown on the following page as Figure 3. From the map, the transmissivity of the carbonate aquifer in the area around the

Sturgeon Creek Bridge site is anticipated to be greater than 100,000 U.S.G.P.D./ft. (1.44 x 10-2 m2/s) It should be noted in the mapping

that Baracos et al. (1983) did not differentiate between the upper and lower aquifer. Recent testing of nearby wells has indicated

transmissivity conditions well above 100,000 U.S.G.P.D./ft. (1.44 x 10-2 m2/s). The high variability of the transmissive conditions

highlights the importance of aquifer testing, even across relatively small areas. The design and discharge requirements of a dewatering

system would be very different for transmissivity values across this range.

The nearest MSD hydrograph station is G05MJ008, located a few miles northwest from the Sturgeon Creek Bridge site. The hydrograph record is shown on the following page as Figure 4.

– 4 – April 26, 2017

Geological and Hydrogeological Setting (Cont’d)

Figure 3 – Transmissivity of the upper carbonate aquifer in western Winnipeg; transmissivity given as U.S.G.P.D/ft.

(source - Baracos et. al.,1983)

Figure 4 - G05MJ008 (source MSD, 2015)

From the G05MJ008 hydrograph, it is apparent that groundwater levels in the local carbonate aquifer fluctuate seasonally by as much as 2.5 meters (8.2 ft.). The typical static water level is approximately 234 meters geodetic, and regularly rises sharply to around 236 m geodetic. The hydrograph station contains groundwater elevation records from the mid 1960s to 2010. Over the period of observation, the groundwater elevation has remained relatively constant. The overall magnitude of seasonal fluctuations is very likely correlated to annual precipitation amounts. Given the recent period of above average precipitation, the most up to date hydrographs will likely reflect a somewhat higher potentiometric surface.

– 5 – April 26, 2017

Geological and Hydrogeological Setting (Cont’d)

A major groundwater quality boundary in the regional carbonate aquifer system extends through the city of Winnipeg, with relatively fresh groundwater towards the east and north, and increasingly saline groundwater towards the west. In the area around Sturgeon Creek Bridge, groundwater quality is expected to be slightly brackish, with typical Total Dissolved Solids (TDS) values ranging from 1,000 to 2,000 mg/L. Groundwater in the underlying Winnipeg Formation is generally of poor quality (brackish to saline) in the area around the City of Winnipeg and, as a result, has not been extensively developed. The groundwater quality in the Winnipeg Formation at the Sturgeon Creek Bridge site is saline. Investigations Test Well Drilling To complete an assessment of the aquifer parameters at the Sturgeon Creek Bridge site, two test wells were installed. Both of the wells were constructed using five inch PVC casing installed from grade down to the upper surface of the competent carbonate bedrock. Both test well locations were selected by staff from Amec. Underground services were also cleared and marked by Amec prior to completing the drilling. The total depth of TH-01 and TH-02 was 138 feet (42.1 m) and 136 feet (41.5 m) below grade, respectively. The wells were constructed using 5 inch diameter, PVC casing through the overburden and were drilled open hole in the carbonate bedrock to final depth. The 5 inch Φ PVC casing was set into a three tier, step down socket and was grouted in place with bentonite. A summary of well construction details is given below in Table 1. A copy of the driller’s logs is also attached. Upon completion, the well locations were marked with a hand held, portable GPD unit that is accurate to +/- 5 m. The approximate well locations are also shown on Figure 1.

Table 1 Well Construction Details

Sturgeon Creek Bridge Site, Winnipeg, Manitoba

Well ID Casing/ Screen Depth Casing

Zone of Completion

Total Grout Grout Placement

Latitude Longitude

Well TH-01 5 inch PVC 55 ft. (16.8 m)

82-197 ft. (25-60 m)

197 ft. (60 m)

Bentonite 0-82 ft. (0-25 m)

N 49.95590° W 96.11696°

Well TH-02 5 inch PVC 75 ft. (23 m)

74-99 ft.

(23-30.2 m)

99 ft. (30.2 m)

Bentonite 0-75 ft. (0-23 m)

N 49.95197° W 97.10654°

Table 1 - Construction details of the two test wells – Sturgeon Creek Bridge site.

Pumping/Recovery Testing To assess the local aquifer conditions and to determine how the aquifer responds to pumping, a short term pumping test was completed for each well. The pumping tests were conducted using a 5 HP submersible pump, with groundwater levels were recorded at regular intervals using a pressure transducers in nearby monitoring wells and also manually with a depth sounder. The discharge rate was checked by timing known volumes of discharge at various times throughout the test. Power was provided for the pumping test by means of a portable gasoline powered generator. Table 2, shown below, provides the specific parameters recorded during the pumping tests. The pumping test drawdown data from TH-01 and TH-02 is also attached.

Table 2

Water Level Drawdowns Observed During Testing – Sturgeon Creek Bridge Site, Winnipeg, Manitoba

Pumping Well Static Water

Level

Pumping Water

Level

Pumping Rate Monitoring Well Distance to

Monitoring Well

Well TH-01 12.5 ft. (3.8 m) 26.5 ft. (8.1 m) 88 U.S.G.P.M.

(5.56 x 10-3 m3/s)

- -

Well TH-02 11.4 ft. (3.5 m) 19.2 feet (5.9 m) 65 U.S.G.P.M. (4.10 x 10-3 m3/s)

TH-01 390 ft. (118.9 m)

Table 2 - Pumping test parameters for each pumping well.

– 6 – April 26, 2017

Well Inventory

To fulfill the conditions set out in the GEP, a desktop inventory of all private and commercial wells within a one mile radius of the Sturgeon Creek Bridge site was conducted. The inventory was conducted using the MSD GWDRILL database (2015). The results of the inventory are shown in Table 3, attached. In total, 17 private and commercial wells were identified within a one mile radius. It should be noted that the current status of the identified wells is not known and the locations of the wells were not verified. Additionally, in some cases, numerous wells were documented as having the same UTM coordinates. The wells range in depth from less than 84 ft. (26.5 m) to over 225 ft. (68.6 m), with an average depth of approximately 150 feet (45.7 m) below grade. The database contains records of wells dating back to the 1960s, with a few logs indicating an unknown time of installation. As a result, some of these wells may no longer be in use and may have been abandoned. Data Analysis Aquifer Testing Analysis The Theis method (1935) is the most common method for analyzing the results from aquifer pumping tests. Some crucial assumptions of

the method were noted during the development. They are detailed as follows:

• Darcy's law is valid

• The aquifer is horizontal and constant thickness

• The aquifer is infinite in areal extent

• The aquifer is bounded by impermeable strata above and below

• Uniform hydraulic conductivity

• Isotropic hydraulic conductivity

• Head always remains above the top of the pumped aquifer

• There are no water level changes that are not due to the pumping.

• Infinitesimal diameter of well

• Fully penetrating the aquifer formation

• Perfectly efficient well

• Single pumping well

• Constant pumping rate

• Constant storage properties through time

• The head is known everywhere prior to pumping.

Through a review of the assumptions, it can be seen that some of the conditions for the analysis of the pumping tests conducted at the

Sturgeon Creek Bridge site are invalid for the Theis (1935) approach. The Theis (1935) approach is highly idealized to the assessment of

the aquifer and represents the state of the art for the determination of aquifer parameters. The conditions are also not being violated

severely, so this approach will be used for the analysis.

The pumping test results were entered into Waterloo Hydrogeologic’s Aquifer Test Professional v2016.1 for analysis of the aquifer

parameters. The data was analyzed using the Cooper-Jacob (1946) and Theis (1935) methods. The hydraulic parameters determined from

the pump tests are shown below and on the following page in Table 4 and 5.

During the pumping tests, the Tcritical was considered to be 15 minutes for casing storage; consequently, only measurements taken after 15 minutes were used for the analysis of aquifer parameters. In reviewing the pumping test results, the Cooper-Jacob (1946) method was used primarily, since emphasis is not placed on early time measurements. By this method, transmissivity values around TH-02 are estimated to be approximately 45,000 U.S.G.P.D./ft. and the value for storativity is estimated to be approximately 3.0 x 10-4. The transmissivity values around TH-01 are estimated from the data to be approximately 35,000 U.S.G.P.D./ft. (5.08 x 10-3 m2/s), and the value for storativity is estimated to be approximately 3.8 x 10-4. These results are within the the range of values expected for fractured, karstic limestone/dolomite formations (Freeze and Cherry, 1979). The variability of transmissive conditions across short distances is also typical of the results from Render (1970) and Baracose et al. (1983). Figures 7, 8, 9 and 10, shown on subsequent pages, contain drawdown vs time and Cooper-Jacob (1946) analysis plots from both pump tests.

– 7 – April 26, 2017

Aquifer Testing Analysis (Cont’d)

Table 4 Confined Aquifer Parameters – Well TH-01

Sturgeon Creek Bridge – Saskatchewan Avenue, Winnipeg, Manitoba

Pump Well TH-01

Static Water Level 12.5 feet (3.8 meters)

Pumping Water Level 26.9 feet (8.1 meters)

Drawdown/Pumping Rate 14.4 feet @ 88 U.S.G.P.M. – 180 minutes

Specific Capacity 6.1 U.S.G.P.M./ft.

Method Transmissivity Storativity

Theis Method1 38,000 U.S.G./day/ft. (5.08 x 10-3 m2/s) 3.0 x 10-4

Cooper – Jacob Method2 35,000 U.S.G./day/ft. (5.02 x 10-3 m2/s) 3.0 x 10-4

Notes 1 Theis (1935) method using Waterloo Hydrogeologic Limited – AquiferTest Pro v2016.1 2 Cooper-Jacob (1946) method using Waterloo Hydrogeologic Limited – AquiferTest Pro v2016.

Table 4 - Aquifer parameters from the pumping test of Well TH-01.

Table 5 Confined Aquifer Parameters – Well TH-02

Sturgeon Creek Bridge – Saskatchewan Avenue, Winnipeg, Manitoba

Pump Well TH-02 Monitoring Well TH-01

Static Water Level 11.4 feet (3.5 m) 11.0 feet (3.4 m)

Pumping Water Level 19.2 feet (5.9 m) 11.8 feet (3.6 m)

Drawdown/Pumping Rate 7.8 ft. @ 65 U.S.GPM – 240 minutes

(2.4 m @ 4.10 x 10-3 m3/s)

0.8 feet (0.6 m)

Specific Capacity 8.7 U.S.G.P.M./ft. -

Method Transmissivity Storativity

Theis Method1 45,000 U.S.G./day/ft. (6.35 x 10-3 m2/s) 3.8 x 10-4

Cooper – Jacob Method2 45,000 U.S.G./day/ft. (6.35 x 10-3 m2/s) 3.8 x 10-4

Notes 1 Theis (1935) method using Waterloo Hydrogeologic Limited – AquiferTest Pro v2016.1 2 Cooper-Jacob (1946) method using Waterloo Hydrogeologic Limited – AquiferTest Pro v2016.1

Table 5 - Aquifer parameters from the pumping test of Well TH-02.

Figure 7 - Drawdown vs. time from the pump test of well TH-01; Pumping rate is 88 U.S.GPM. (5.6 x 10-3 m3/s).

– 8 – April 26, 2017

Aquifer Testing Analysis (Cont’d)

Figure 8 – Cooper Jacob method (1946) analysis of pump test data from well TH-01; Pumping rate is 88 U.S.GPM. (5.6 x 10-3 m3/s).

Figure 9 - Drawdown vs. time from the pump test of well TH-02; Pumping rate is 65 U.S.GPM (4.10 x 10-3 m3/s).

Figure 10 – Cooper Jacob method (1946) analysis of pump test data from well TH-02; Pumping rate is 65 U.S.GPM. (4.10 x 10-3 m3/s).

– 9 – April 26, 2017

Aquifer Testing Analysis (Cont’d) The transmissive conditions indicated in this investigation are lower than the transmissivity values indicated by regional mapping of the area. It is important to note that, although the current test wells indicate transmissive conditions between 35,000-45,000 U.S.G.P.D./ft., Baracos et al. (1983) indicated transmissive conditions which exceeded 200,000 U.S.G.P.D./ft. not far from the Sturgeon Creek Bridge site. In addition, Friesen Drillers has conducted testing in the nearby area with transmissive conditions as high as 105,000 U.S.G.P.D./ft. Consequently, the drawdown calculations in this report will be undertaken based the two extremes of the analysis results and our experience in the carbonate aquifer in Winnipeg. These values should provide a reasonable estimation of the upper ranges of discharge rates that would be required to depressurize the aquifer to the necessary elevation under the range of conditions.

Aquifer Drawdown Estimation From the geotechnical assessment, the elevation of the dewatered creek channel is 231.2 m geodetic (Amec Foster Wheeler, 2016). In addition, the total head (static water level) at the till surface was calculated in the geotechnical report to be 234.5 m geodetic (Amec Foster Wheeler, 2016). The nearby hydrograph station record (G05MJ008) further indicates typical static water levels to be approximately 234.0 m geodetic elevation. The static water level in the test wells at the time of testing was noted to be approximately 232 m geodetic. Based on the results of the geotechnical investigation conducted, the underlying upper carbonate aquifer should be depressurized to 231.2 m geodetic in order to achieve a minimum safety factor of 1.4 and ensure a stable creek bed during the construction process. Consequently, assuming the provided static water level of 234.5 m geodetic, lowering the potentiometric surface to below the creek bed elevation will require 3.3 m (10.8 ft.) of drawdown under the creek. It is important to note that the following calculations were undertaken assuming the conditions provided by the Geotechnical Report (Amec Foster Wheeler, 2016). Due to the dynamic nature of groundwater systems, the conditions at the time of construction may be different from those assumed here. This assessment seeks to estimate the upper limits of discharge rates that may be required under various hydrogeological conditions. Both test wells (TH-01 and TH-02) are located within 150 ft. (45.7 m) of the opposing bank of Sturgeon Creek. To ensure the drawdown cone extends beyond the creek bed towards the east, a pumping rate that generates 3.8 m (12.5 ft.) of drawdown at a radial distance of 250 ft. (76.2 m) will be calculated. Applying a local transmissivity value of 35,000 U.S.G.P.D./ft., a pumping rate of 220 U.S.G.P.M. from both wells for a total of 440 U.S.G.P.M. would be required to achieve the necessary drawdown. Applying a transmissivity value of 45,000 U.S.G.P.D./ft., a pumping rate of 280 U.S.G.P.M. from both wells for a total of 560 U.S.G.P.M. would be required to achieve the necessary drawdown. The drawdown cones resulting from the two pumping scenarios are shown below as Figure 11.

Figure 11 - Left: drawdown cone generated by pumping two wells at 220 U.S.G.P.M. with a transmissivity of 35,000 U.S.G.P.D./ft.; Right:

drawdown cone generated by pumping two wells at 280 U.S.G.P.M. with a transmissivity of 45,000 U.S.G.P.D./ft.

– 10 – April 26, 2017

Aquifer Drawdown Estimation (Cont’d) To provide some indication of the required pumping rates necessary under the higher transmissive conditions identified around the Sturgeon Creek site, the drawdown was also calculated assuming a transmissivity of 130,000 U.S.G.P.D./ft. With these higher transmissive conditions, pumping rates on the order of 700 U.S.G.P.M. per well for a total discharge rate of 1,400 U.S.G.P.M. would be required to generate the necessary drawdown. In order to determine the drawdown cone created by using depressurization wells, the drawdown after 120 days of operation for the site was calculated at distance using the Theis equation at an average pumping rate of 280 U.S.G.P.M. per well (combined 560 U.S.G.P.M.) with a transmissivity of 45,000 U.S.G.P.D./ft. The drawdown at a radial distance of one mile after 120 days of continuous pumping was calculated to be 8.4 feet. The results of the drawdown calculations under different transmissive conditions are shown below in Tables 5, 6 and 7. A range of transmissivity values are used to provide some indication of the extreme variability of the carbonate aquifer in the Winnipeg area. With higher transmissive conditions, higher pumping rates are required to generate the same amount of drawdown. The drawdown cone generated during aquifer depressurization is estimated to be relatively large and would certainly extend off site. As a result, a detailed well inventory should be completed by a qualified hydrogeologist prior to major pumping operations.

Table 5 Drawdown Estimation at Distance after 120 days of Pumping

Transmissivity of 35,000 US.G.P.D./ft. Two Wells at 220 U.S.G.P.M. (440 U.S.G.P.M. Total)

Distance Pump Well 100 feet 150 feet 200 feet 250 feet 500 feet 1,500 feet 2,500 feet 5,280 feet

Drawdown (ft.) 24.79 17.29 16.95 16.57 16.18 14.66 11.66 10.21 8.06

Table 5 – Estimated Drawdown resulting from 440 U.S.G.P.M. after 120 days of continuous pumping – Sturgeon Creek Bridge site.

Table 6 Drawdown Estimation at Distance after 120 days of Pumping

Transmissivity of 45,000 US.G.P.D./ft. Two Wells at 280 U.S.G.P.M. (560 U.S.G.P.M. Total)

Distance Pump Well 100 feet 150 feet 200 feet 250 feet 500 feet 1,500 feet 2,500 feet 5,280 feet

Drawdown (ft.) 23.00 17.50 17.18 16.79 16.45 14.91 11.94 10.50 8.37

Table 6 – Estimated Drawdown resulting from 560 U.S.G.P.M. after 120 days of continuous pumping – Sturgeon Creek Bridge site.

Table 7 Drawdown Estimation at Distance after 120 days of Pumping

Transmissivity of 130,000 US.G.P.D./ft. Two Wells at 700 U.S.G.P.M. (1,400 U.S.G.P.M. Total)

Distance Pump Well 100 feet 150 feet 200 feet 250 feet 500 feet 1,500 feet 2,500 feet 5,280 feet

Drawdown (ft.) 22.86 16.45 16.13 15.80 15.49 14.18 11.62 10.36 8.52

Table 7 – Estimated Drawdown resulting from 1,400 U.S.G.P.M. after 120 days of continuous pumping – Sturgeon Creek Bridge site. Groundwater Geochemistry Sampling Groundwater samples were collected from the test wells as part of the hydrogeological investigation. The analytical results were provided by ALS Laboratories of Winnipeg, which conducted an analysis of the routine and stable environmental isotope parameters. In general, the results were very consistent with other sampling that has been conducted in the area. The water quality is considered to be brackish, with Total Dissolved Solids (TDS) concentrations of 1,820-2,400 mg/L. It should be noted that, although water quality is typically expected to become worse with pumping, the samples indicate fresher groundwater results in the post test analysis. The freshening of the groundwater with pumping is likely a result of an interconnection between the carbonate aquifer and the overlying clay and till deposits. This interpretation is further evidenced by the results of the stable isotope analysis, discussed below. Table 5, shown on the following page, details the results from the analytical sampling of the pump well (TH-02) during the aquifer testing. The complete results from ALS laboratories are also attached (L1900256). A tri-linear Piper plot of the pre and post test analysis results is shown on the following page as Figure 12. The groundwater chemistry results generally compare well with the regional water quality in the area. The groundwater is a Sodium/Potassium/Chloride type, which is

– 11 – April 26, 2017

Groundwater Geochemistry Sampling (Cont’d) expected for the area. The groundwater chemistry results from station G05MJ067 have been included on Figure 12 for comparison.

Table 8 Groundwater Analytical Results

Sturgeon Creek Bridge – Saskatchewan Avenue City of Winnipeg, Manitoba

Parameter Pre-Test Post-Test

Total Dissolved Solids 2,400 mg/L 1,820 mg/L

Chloride Ion (Soluble) 767 mg/L 636 mg/L

Conductivity 3,610 umhos/cm 2,950 umhos/cm

Hardness (as CaCO3) 995 mg/L 566 mg/L

pH 7.50 7.45

Calcium 197 mg/L 117 mg/L

Sodium 507 mg/L 425 mg/L

Table 8 –Groundwater analytical chemistry – Sturgeon Creek Bridge Site (source – ALS Laboratories, 2017)

Figure 12 – Piper Plot – Sturgeon Creek Bridge Site (data source: ALS Laboratories, 2017; MSD, 2016)

In addition to the routine geochemistry, water samples were also collected for the analysis of stable environmental isotopes. The purpose

of this analysis is to determine the origin and provenance of groundwater at the site, and to determine relative ages and possible

interactions that could modify groundwater on the site. With the proximity of the pumping wells to the Sturgeon Creek, it is important to

identify the potential for interconnection between the bedrock aquifer and the surface water bodies at the site.

The ratios of the main isotopes that compose the water molecule (18O/16O) and 2H/1H are important for hydrogeological investigations (Freeze and Cherry, 1979). The units are presented in delta (δ) units as parts per thousand or ‰ (Freeze and Cherry, 1979) relative to standard mean oceanic water (SMOW). The two isotopes of water have different freezing and vapour points, which leads to different concentrations as a result of freezing, condensation, melting, and evaporation (Freeze and Cherry, 1979). As water is evaporated from the ocean, there is a decline in the 18O concentration by a specific amount. As the vapor condenses, the precipitation has a higher 18O concentration. This process continues as the vapor moves inland, and undergoes many cycles of condensation and evaporation. This fact

makes deuterium and 18oxygen very useful for hydrogeological investigations, as the origin and mixing of different waters can be

determined. In order to determine the changes from local precipitation, deuterium and 18oxygen results are plotted to determine the local

meteoric water line, which would be expected to be the typical concentrations in recent precipitation events in the area.

– 12 – April 26, 2017

Groundwater Geochemistry Sampling (Cont’d) Within Manitoba, glacial water (~10,000 years ago), typically shows 18oxygen concentrations of -23 to -19 ‰. Groundwater that contains a mixture of more recent groundwater with older glacial waters typically has an isotopic composition between -19 and -17 ‰, and recent meteoric groundwater has a composition between -17 to -14 ‰ (Freeze and Cherry, 1979).

At the Sturgeon Creek Bridge site, the isotope results indicate that the groundwater contains a mixture of glaciogenic and recent meteoric

groundwater. A plot of the results against the local meteoric water line (IAEA, 2012) is shown below as Figure 13. It is apparent from

Figure 13 that the isotopic composition of the groundwater changed with pumping. The groundwater sample collected at the end of the

test appears to be more recent than the groundwater from the pretest sample.

The change in isotopic composition of the groundwater during the pumping test is characteristic of the bedrock aquifer conditions in the

Winnipeg area. Drawdown induced in the carbonate bedrock allows for localized vertical drainage of the overlying clay and till deposits

(Day, 1977). Groundwater in the overburden is expected be enriched in 18Oxygen relative to the older bedrock groundwater. The shift to

more recent groundwater with pumping suggests an interconnection between the bedrock aquifer and the overlying till and clay material. It

should be noted that the geochemical changes noted in this investigation occurred over a relatively short pumping duration. Longer term

pumping to depressurize the aquifer would likely cause more significant shifts in the groundwater geochemistry. This result highlights the

importance for regular monitoring of groundwater quality for the duration of the project, should dewatering be required.

Figure 13 – Stable environmental isotope analysis; Sturgeon Creek Bridge Site. (source – ALS Laboratories, 2017; IAEA, 2012)

Discussion and Recommendations

The Sturgeon Creek Bridge site represents the typical variability of the carbonate aquifer in Winnipeg. This type of variability has always

made numerical simulations of groundwater very difficult to assess. Lowering the potentiometric surface by 12.5 feet (3.8 m) across the

site will require at least two pumping wells. Even assuming the high transmissive conditions, drawdown will still be present at distance. In

addition, the groundwater quality is shown to change with pumping, and will require regular monitoring during the dewatering operation.

Should geotechnical engineering dictate that dewatering is required, we recommend the following activities:

• The site will require a GEP from MSD.

• To generate the necessary drawdown, a dewatering system will likely need to sustain a total discharge rate of 440-600 U.S.G.P.M. It should be noted that under conditions identified near Sturgeon Creek Bridge, pumping rates could be as high as 1,400 U.S.G.P.M.