1.0 introduction and background - british …...completed with, for example, a fixed ring...

File: 00305-01

Core6 Environmental Ltd. 777 Hornby Street, Suite 1410

Vancouver, BC V6Z 1S4 Canada

www.core6.ca

September 22, 2017

British Columbia Ministry of Environment and Climate Change Strategy Land Remediation Section 525 Superior Street Victoria, BC V8V 1T7 Re: Estimation of Regional Infiltration Rates in British Columbia Protocol 2 Groundwater Protection Model 1.0 INTRODUCTION AND BACKGROUND The following recommendations were prepared by Core6 Environmental (Core6) for the British Columbia Ministry of Environment and Climate Change Strategy (BCMOE) with funding provided by BCMOE and the Society of Contaminated Sites Approved Professionals of British Columbia (CSAP). It is recognized that any BCMOE protocols or guidance informed by these recommendations, may differ from those provided herein. The BC Contaminated Sites Regulation (CSR) Schedule 5 matrix soil standards were originally derived in 1996 using the Contaminated Sites Standards Taskgroup (CSST) model. The model was specifically developed to simulate the transport of various organic and inorganic contaminants of concern (COCs) in groundwater towards various receiving environments, for the purpose of protecting four water uses (i.e., drinking water, aquatic life, irrigation water, livestock water). Recently, the standards have been updated using a refined version of the CSST model, now renamed the Omnibus model. In November 2017, it will be possible to calculate site-specific soil standards using the Omnibus model under Protocol 2 (P2) of the CSR. Core6 completed a detailed sensitivity analysis of the Omnibus model in April 2017 and found that it is sensitive to the infiltration rates used while determining the transport of COCs from soil to groundwater. Based on these findings, Core6 worked with BCMOE to develop a regional map that defines the infiltration rate for any location within the province. The intention of the regional infiltration map was to facilitate the use of the P2 model when determining a local infiltration rate. 1.1 Objectives The primary objective of the work was to develop infiltration rates for BC and present them in simple and easy to use format such that they can be utilized directly in the P2 model, thereby facilitating use of the model.

1.2 Scope of Work The following tasks were completed to meet the project objectives:

Compile representative data for the total annual precipitation and evapotranspiration at urban centres in BC using the Environment Canada and Farmwest databases;

Define regionally representative precipitation rates, evapotranspiration rates and runoff rates;

Estimation of Regional Infiltration Rates in British Columbia, Protocol 2 Groundwater Protection Model

Core6 Environmental Ltd

Define an appropriate method for calculating infiltration rates using the above information;

Develop a regional reference map of annual infiltration rates for BC; and

Provide instructions for how to use the defined infiltration rates when carrying out site- specific studies under P2.

2.0 METHODOLOGY To be consistent with how infiltration rates are calculated using the CSST and Omnibus models, a water balance approach was used to define the regional infiltration rates (IR). This method uses the common hydrogeological water balance where the amount of infiltration into the ground is defined as the difference between the precipitation (P) in the form of rainfall and snowfall, and the sum of the evapotranspiration (ET) and surface water runoff (RO). The following expression summarizes the water budget equation: IR = P – (ET + RO) [1] This approach is a deviation from a site-specific determination of infiltration rate which may be completed with, for example, a fixed ring infiltrometer to estimate the unsaturated hydraulic conductivity and unsaturated groundwater velocity. Instead, the water budget method represents more of an annual average infiltration rate that may occur into the ground cover according to the water budget, rather than considering the permeability of the soils. Because the objective of this work was to derive regional estimates of infiltration rate, more site-specific infiltration rate estimates based on soil type was not feasible or practical. The water budget method was instead selected as it is consistent with the original methods used in the CSST model and current method used in the Omnibus model. In addition, P and ET data is readily available for the province through Environmental Canada and Farmwest online databases. Surface water runoff (RO) is a direct function of precipitation, and has been calculated as a percentage of the total annual precipitation. Precipitation data was accessed through the Environmental Canada Historical Climate Data webpage (http://climate.weather.gc.ca/index_e.html) for locations at or near to the Farmwest stations with available ET data. Most stations had easily accessible climate normal data for the period from 1981-2010, where the total annual precipitation values were accessed. In some remote locations, the climate station record did not include climate normal records due to lack of sufficient data over that time period. In these cases, the entire climate station record was accessed and average annual precipitation rates were calculated from monthly averages going back as far as 1981 where data was available.

Evapotranspiration data was obtained from Farmwest (farmwest.com/climate/et), which is sponsored by Environment Canada. For the purposes of defining the annual ET rate, the most recent five years of consecutive ET data was obtained for each available station located within the Province. In total, 44 stations were available for obtaining ET data. According to Farmwest, ET is calculated using an analytical model following the FAO Penman-Monteih equation. At Golden and Telegraph Creek, there was not five years worth of available data, thus only one year of complete data was used to estimate ET rates at these locations. Similarly, Skookumchuck had only two years of available ET data that was used to estimate the annual ET rate. In addition, a total of eight stations (44, 27, 07, 10, 09, 08, 16, and 02) had anomalous records for the year 2013, which were excluded from the averages to prevent bias associated with anomalous measurements. To obtain a representative annual ET rate for each station, the data collected was averaged. Given that Farmwest is largely used to support the agricultural industry, the ET rates represent more of a rural region that is highly vegetated rather than urban region that is less vegetated. As a result, through discussions with BCMOE it was decided that the ET rates were likely skewed to higher ET as they pertain more to crop growth. At the request of BCMOE, seven months of



evapotranspiration were used at a given station to represent the annual ET. Specifically, the period between January 1 to April 30 and October 1 to December 31 were used as these were considered to be the portions of the year when less crop irrigation and growth (i.e., transpiration) would be taking place. The seven months of ET values were summed for these time periods, and then prorated to a 12 month period by multiplying by a factor of 12/7 to represent annual evapotranspiration rate.

Surface runoff (RO) was calculated from the total annual precipitation rate at each station according to a predetermined percentage. The percentage of precipitation which constitutes RO was derived using a combination of the P and ET data defined for the EC and Farmwest stations located in Vancouver, and the default infiltration rate used in the CSST/Omnibus models’ (i.e., 550 mm/year). Keeping the P and ET data fixed, a RO value was derived by multiplying the P by a percentage such that when P – (ET + RO) = 550 mm/year, or equivalent to the model defaults. Following this approach, a RO equivalent to 24% of P was derived to represent the ET. This percentage was then applied to all other locations across BC for the purpose of defining the RO rate at a given station. Finally, annual infiltration rates were calculated using the above precipitation, evapotranspiration and runoff datasets according to the mass balance relationship presented in Equation 1. In regions where infiltration rates were <80 mm/year, due to very low precipitation and/or high evapotranspiration rates, a minimum value 80 mm/year was assigned. The data as points was then plotted on a map of BC and interpolated in GIS using a statistical interpolation method (Kriging). 3.0 RESULTS The annual P, ET, and RO and IR are presented in Table 1 for the 44 station locations that represent BC. The location names are shown in Figure 1, and a map of calculated infiltration rates and interpolated is presented in Figure 2. Overall the infiltration rates follow patterns similar to the precipitation patterns across BC, with higher infiltration rates in coastal regions where precipitation rates are higher. The interior of BC has low relative precipitation rates, and higher evapotranspiration rates, resulting in very low – negative calculated infiltration rates that were set to a minimum value of 80 mm/year. 3.1 Recommended Method for Use of the Data in the P2 Model When using the P2 model, the IR is a variable that is calculated upon input of the P and (ET+RO). As such, instances where the site to be modeled is situated within the same town/city of the climate station, the P and (ET+RO) values can be obtained directly from Table 1 and inputed into the P2 model input interface. The following instructions are provided in situations where the site is not located in one of the urban centres listed in Table 1:

If the site is located within a 20 km radius of a listed urban centre in Table 1, it is recommended to take the value listed at that location. For example if a site is located within 18 km from Vancouver, the listed infiltration rate of 550 mm/year defined for Vancouver should be used.

If the site is located outside a 20 km radius and in between two urban centre listed in Table 1, and does not cross an infiltration contour on Figure, it is recommended that the infiltration rates provided in Table 1 for the urban centre that is closest to the site be used. An average of the two infiltration rates can be calculated in situations where the site is located equidistant from the two stations.

If the site is located at a horizontal distance greater than the 20 km radius from an uban centre listed in Table 1 and one or more infiltration rate contours are crossed, it is recommended that the infiltration rate be defined by the value indicated by the closest infiltration rate contour to the site.

If the site is located between two contour inervals, the infiltration rate can be estiamted to the nearest 100 mm/year, for example the town of Sechelt is located midway between the 800



mm/year and 600 mm/year contours, and the best approximation would be to take a value of 700 mm/year to represent the annual infiltration rate for this city.

4.0 CLOSURE We trust this information is sufficient for your needs and requirements, please do not hesitate to contact the undersigned should you have any questions or concerns. Kind regards, Core6 Environmental Ltd ORIGINAL SIGNED Kalina Malowany, MSc, GIT Hydrogeologist ORIGINAL SIGNED Stephen Munzar, MSc, PGeo. Senior Hydrogeologist / Partner



5.0 REFERENCES Environment Canada. Historical Climate Data, Canadian Climate Normals. Accessed April 2017. http://climate.weather.gc.ca/climate_normals/index_e.html. Environment Canada. Historical Climate Data, Historical Data. Accessed April 2017. http://climate.weather.gc.ca/historical_data/search_historic_data_e.html Farmwest, Pacific Field Corn Association. Evapotranspiration Data. Accessed April 2017. http://farmwest.com/climate/et



Tables

Table 1: Results from the infiltration rate determinations at 44 locations across British ColumbiaLocation No. Station Name Latitude Longitude Precipitation

(mm)ET + RO

(mm)Infiltration Rate (mm)

01 Abbotsford 49.03 -122.3807 1538 764 77402 Ashcroft 50.71 -121.28 209 559 80*03 Burns Lake 54.38 -125.7667 437 434 80*04 Comox 49.72 -124.9032 1154 616 53805 Cranbrook 49.62 -115.7859 385 548 80*06 Creston 49.08 -116.5113 662 544 11807 Dawson Creek 55.73 -120.4528 453 439 80*08 Dease Lake 58.43 -130.01 445 334 11109 Fort Nelson 58.83 -122.5893 452 385 80*10 Fort St John 56.23 -120.7394 445 328 11711 Golden 51.4357 -117.0571 467 484 80*12 Hope 49.37 -121.5 2342 957 138513 Kamloops 50.7 -120.4418 387 563 80*14 Kelowna 49.97 -119.38 387 586 80*15 Lillooet 50.68 -121.93 349 567 80*16 Lytton 50.23 -121.5767 431 591 80*17 Nakusp 50.27 -117.8011 840 563 27718 Nelson 49.65 -117.2937 924 612 31219 North Cowichan 48.82 -123.72 1153 708 44520 Ootsa Lake Skins Lake Spillway 53.77 -126 417 533 80*21 Osoyoos 49.03 -119.46523 323 600 80*22 Pemberton 50.3 -122.739 933 658 27523 Penticton 49.47 -119.6052 346 574 80*24 Pitt Meadows 49.22 -122.6904 2155 915 124025 Port Alberni 49.32 -124.8069 2199 933 126626 Port Hardy 50.68 -127.37 1908 787 112127 Prince George 53.88 -122.6739 595 514 8128 Prince Rupert 54.29 -130.44 2619 888 173129 Quesnel 53.03 -122.4932 536 547 80*30 Revelstoke 50.96 -118.18 950 640 31131 Salmon Arm 50.7 -119.28 653 614 80*32 Saturna Island 48.78 -123.04 812 498 31433 Skookumchuck 49.9943 -115.7611 455 599 80*34 Smithers 54.82 -127.1835 509 415 9435 Squamish 49.78 -123.16 2437 1258 117936 Tatlayoko Lake 51.67 -124.4 436 505 80*37 Telegraph Creek 57.9141 -131.1712 345 342 80*38 Terrace 54.47 -128.58 1341 575 76639 Vancouver 49.18 -123.1811 1189 639 55040 Vernon 50.23 -119.2921 500 577 80*41 Victoria 48.65 -123.4291 883 671 21242 Warfield 49.11 -117.74 779 656 12343 White Rock 49.02 -122.8036 1108 640 46844 Williams Lake 52.18 -122.1387 451 497 80*

* Annual infiltration rate assigned a minimum rate of 80 mm/year


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