The Importance of Including Fracture Data

It had been noted by Murray Journeay, Shannon Denny, Diana Allen and several others in the “Integrated Groundwater Resource Assessment of Fractured Bedrock Aquifers in the Gulf Islands, BC” that there is the presence of controlled fractured bedrock aquifers surrounding the perimeter of Hornby Island. It is intuitive that the presence of fractures in the subsurface will lead to pathways for water contaminants to travel along and therefore increase the potential for aquifer contamination as well as influencing the time frame it takes for aquifer contamination. Due to the increased potential of contamination where fractures are present, we understand that it is important to include fracture data in the Aquifer Vulnerability DRASTIC model assessment of Hornby Island in order to obtain a more accurate result than if it were not present. Unfortunately, because of time constraints we were unable to incorporate this data into our analysis. On the other hand, with this project as a start, we do hope that future mapping projects will incorporate the fracture data to increase the accuracy of the aquifer vulnerability assessment of Hornby Island.

The Importance having Complete Digitized Well Log data

As mentioned previously, the digitized Well Log data was only approximately 50% complete and of that 50% there were approximately only 8% of the wells that had the depth at which water was first reached during the drilling process. Due to this data set being so important for the Aquifer Vulnerability DRASTIC model we realize that there is inaccuracy present in out assessment of Hornby Island. It is in the interest of the residences of Hornby Island for this data set to be completed in order to obtain a more accurate result in Aquifer Vulnerability for the Island. We hope that this project will inspire and encourage such a completion of this data set as the groundwater supply of fresh water is so important to its residences and therefore needs to be cherished.

The Importance Validating the DRASTIC model with Geochemical Data

One method by which the DRASTIC aquifer vulnerability model could be validated for accuracy would be to examine the spatial distribution of elevated groundwater chemicals with respect to areas identified as vulnerable by the model. Dr. Diana Allen of SFU and Gregory Matsuo have already completed well testing to establish levels of ions in Hornby Island groundwater, which we have digitized.

The original file given to us by Diana Allen was in an excel spread sheet format therefore it had to be transformed into raster format. To do this we first opened the Excel file and removed rows 1 and 3, which were the title and units of the chemicals. The chemicals were all listed in mg/L. We then proceeded to format the cells so that they would all display numbers to the correct decimal value. For the UTM locations we appended X and Y respectively to each of the UTM labels and inserted 0s in the cell directly below the UTM label. We then saved the excel file as a .dbf document and accepting the defaults that appeared. We then opened arcCatalogue and right clicked on the in the .dbf to selected “create feature class”, “from XY Table”. We selected the appropriated field for the X and the Y, left the z blank and then selected the appropriate projection (UTM) under Spatial Reference of Input Coordinates. We accepted the defaults and created a shape file of all the well positions and their associated attribute data. We then repeated this process and then before finalizing the process selected Advanced Geometry Options. Here, we chose a different spatial reference; this was accomplished by selecting edit and then browsing to an existing shape file that is already presented in BC Albers. The end result was two shapefiles of chemical data. Presented below is an image of the well locations of the geochemistry work completed by Dr. Allen.

Once the geochemical data was digitized we realized that we were lacking background geochemical data in order to determine what ionic concentrations exist naturally within the island geology. In turn we think that determining the background geochemical data of Hornby Island would be extremely helpful in confirming the accuracy of the Aquifer Vulnerability assessment.