2017 AGM Presentations
Continuing Professional Development Session: Groundwater Resources and Management
Development of indices to assess the potential impact and risk of drought to private wells in Nova Scotia
G.W. Kennedy, P.Geo., J. Drage, P.Geo., and G. Check, P.Geo.
In the summer and fall of 2016, southwestern Nova Scotia (NS) experienced moderate to severe drought conditions, with rainfall deficits persisting into the winter months. Available provincial observation wells in southwestern NS, all constructed in bedrock aquifers, showed historical lows or below normal water levels. It is estimated that over 1000 private well users in southwestern NS experienced water shortages as a result of the drought, especially well users relying on dug wells (>90% of dry wells) for domestic water supply. The provision of temporary water sources (bottled water deliveries, fill stations) were among the various interventions by government to assist these well users.
The NS Department of Natural Resources developed an index map to show areas of the province where private well owners are more likely to experience water shortages (especially owners of shallow wells) and was published as a web map application for planning and risk communication purposes. The relative impact of drought to private wells index map was based on the following criteria; severity of existing drought conditions, forecasted and recent precipitation patterns relative to normals, the density of sensitive wells (e.g. dug and shallow drilled wells), and the density of groundwater use.
A groundwater level index was also developed to characterize water levels recorded by the observation well network and published on the map. The index was calculated for the most recent water level (using data from all previous years) and was divided into five categories: above historical high (water level > the maximum level on record for that day); above normal (water level > 75th percentile); normal (water level > 25th and ≤ 75th percentile); below normal (water level is ≤ 25th percentile); and below historical low (water level < minimum level on record for that day).
The development of an arsenic in well water risk map for Nova Scotia based on the relationship between arsenic in well water and bedrock geology
G. W. Kennedy, P.Geo. and J. Drage, P.Geo.
The distribution of arsenic in the province’s well water compared to available bedrock geology mapping was investigated to further advance the understanding of the relationship between arsenic occurrence in well water and various bedrock units, and to develop a new risk map to communicate the risk of arsenic exposure to well owners. Arsenic exposure in well water is associated with an increased incidence of skin and internal cancers and adverse birth outcomes.
Arsenic in well water in Nova Scotia is principally attributed to geogenic sources, including arsenopyrite and arsenian pyrite, which is hosted in various bedrock types. Bedrock geology is therefore the most important provincial-scale control on the distribution of arsenic concentrations in well water, and it is mainly drilled wells that are associated with elevated levels of arsenic. Available arsenic in well water data were compiled for drilled wells and a source aquifer (i.e. bedrock unit) was assigned to each sample location. The frequency of arsenic in well water samples exceeding the Health Canada maximum acceptable concentration (MAC) of 10 µg/L was tabulated for the province’s five major groundwater regions and over 60 bedrock units. Based on the observed exceedance rates of the Health Canada MAC for arsenic in well water for the various bedrock units, an arsenic in well water risk map was produced dividing the province into low- (<5% exceeding), medium- (5 to <15% exceeding) and high- (≥15% exceeding) risk zones.
Both the highest concentrations (i.e. >1000 µg/L) and exceedance rates were found in the metamorphic and plutonic groundwater regions of Nova Scotia, largely due to the presence of arsenic mineralization in these rocks. The study highlighted other potentially important controls on arsenic occurrence and mobility including metamorphic grade, contact metamorphism and the geochemical environment. Well water samples collected from Goldenville Group and South Mountain Batholith bedrock aquifers in southern Nova Scotia were associated with the highest frequency of arsenic exceeding the safe limits for drinking water (>40%), and these aquifers are situated in areas of high-density domestic groundwater use. Demographic analyses indicate that over 80,000 households (37%) are in high-risk areas and the overall frequency of private well water exceeding safe drinking water limits in Nova Scotia may be as high as 20% (~90,000 persons). The risk map will be published in several formats to communicate risk to private well owners in Nova Scotia with the aim encouraging appropriate well water testing and treatment and preventing disease.
Using numerical groundwater models as a land use planning tool – Town of Torbay, NL
John Kozuskanich, P.Geo.
The Town of Torbay, NL has grown quickly over the last two decades as a bedroom community for the neighbouring cities of St. John’s and Mount Pearl. Growth has been primarily focused in three developments around the periphery of the town in the form of half- to one-acre lots with private servicing. Approximately 30% of the residents in the older portions of Torbay rely on municipal servicing for their drinking water which is sourced from one of the many surface water ponds that dominate the landscape. This study is the first of its kind in NL to go beyond the scale of individual unserviced developments and evaluate the cumulative effects of development on the community’s groundwater resources. A steady-state equivalent porous media groundwater flow model was developed as a tool to assist in planning the growth and sustainability of their community. Well log information was utilized in an effort to incorporate some of the attributes of the discretely-fractured bedrock groundwater system into the definition of adverse condition drawdown targets. The model was used to assess water availability under different future commercial and residential development schemes, rank development options, identify areas to be left undeveloped, define sustainable pumping rates, and evaluate the potential for municipal well fields. The results highlight the need for larger-scale hydrogeological assessment as part of the land use planning decision making process for semi-urban greenfield development.
Delineation of Well Head Protection Areas for Small Groundwater Supplies in Newfoundland and Labrador
Colin Walker, P.Geo.
Communities throughout Newfoundland and Labrador rely on groundwater for the supply of fresh drinking water. Water is drawn from 255 wells, grouped into 106 well fields across the province. Well Head Protection Areas (WHPAs) were delineated for each of these wells using an automated 1D analytical solution. The solution provided a 20-year time of travel zone around each well based on the pumping rate and ambient groundwater flow conditions. The shapes of WHPAs varied from circular, near the well head, to more elongated zones that stretched backward toward the recharge zone of the aquifer.
The size and shape of each WHPA depended on the pumping rate of the well and the properties of the aquifer providing water to the well. This information was gathered from the well operators, provincial mapping, the province’s Drilled Well Database, and aquifer tests. In many cases the pumping rate of each well was estimated based on the number of people served by the well, and aquifer properties were estimated based on drilling records for domestic wells in the area. WHPA maps are intended to be used by communities to begin the process of developing a Well Head Protection Plan, and to consider how to manage land uses within the WHPA. As the method to draw the WHPAs was automated using GIS and other tools, each zone can be readily recalculated to incorporate site specific data that becomes available.