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Land Management Assistance Program

Ontario Farm Groundwater Quality Survey
Summer 1992

View/ Download "Ontario Farm Groundwater Quality Survey" [795 KB pdf].


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  1. Executive Summary

    This section summarizes the main results, observations, and conclusions from the Ontario Farm Groundwater Quality Survey: Summer, 1992. This program investigated the same set of drinking water wells and multilevel monitoring wells that were sampled during the initial survey conducted in the winter of 1991-1992. Some reference to results from the winter survey are presented for the purposes of comparison. A complete summary of the winter survey is contained in the report of the Ontario Farm Groundwater Quality Survey Winter 1991/92, available from Agriculture Canada.

    Section 1: Water Well Survey

    • Approximately 1300 domestic farm wells were re-sampled between June 1992 and August 1992 and the groundwater analyzed for nitrate-N, total and faecal coliform bacteria, and several common herbicides, which are referred to as pesticides.

    • The majority of the wells (900) were located in areas of intense agriculture on the most common soil types and on farms involved with the most common agricultural land-use practices. The remainder of the wells were located in less agriculturally intense areas including Northern Ontario.

    • The maximum acceptable concentration (MAC) of total coliform bacteria in private drinking water supplies was revised by the Ontario Ministry of Health, in October 1992, from 10 to 5 colonies per 100 mL. The results were analyzed relative to both the old and new objectives.

    • 40% of all wells tested contained one or more of the target contaminants at concentrations above the previous Provincial drinking water objectives (43% with the updated objectives).

    • 32% of wells exceeded the previous maximum acceptable concentration for at least one of the coliform bacteria selected for analysis (36% with the updated MAC).

    • 25% had faecal coliform bacteria.

    • 15% exceeded the Ontario maximum acceptable concentration for nitrate (7% exceeded the maximum acceptable concentration for both coliform bacteria and nitrate (previous objectives) and 8% exceeded the acceptable concentration for nitrate alone).

    • 121 of the wells had de wells showed pesticide concentration in exceedence of Ontario interim maximum acceptable concentration (IMAC) values.

    • Several trends between the occurrence of groundwater contamination and various physical factors were found in the summer survey:

      1. Dug or bored wells and driven sandpoints were the most frequently contaminated of all well types regardless of depth;

      2. The frequency of contamination of any well type appeared to decrease with depth and increase with age;

      3. No direct correlation was observed between specific land-use practices and the frequency of water wells found in exceedence of the objectives for any of the target contaminants. The incidence of groundwater contamination did not differ significantly between any of the common types of cropping practice;

      4. At sites where manure was spread regularly, levels of coliform bacteria, especially faecal coliforms, tended to be somewhat higher than on farms not using manure. This trend was not observed for nitrate;

      5. Coliform bacteria tended to be less abundant in groundwater under permeable soils than under less permeable soils;

      6. Nitrate-N concentrations tended to be higher in groundwater under the higher permeability soils;

      7. The spatial distribution of wells contaminated with nitrate tended to fall within areas of the Province previously classified by the MOEE as high susceptibility risk to groundwater contamination. Bacteria distribution was somewhat more evenly spread throughout the Province; and,

      8. Coliform bacteria levels tended to increase with decreasing separation distance between the water well and feedlot. No other specific correlations were observed between potential point sources of contamination and groundwater quality in the water wells.

    • When the data from the winter and summer surveys are compared, several additional observations can be made.

      1. The frequencies of contamination in the water I wells were quite similar in both surveys, which provides further confidence that the levels of groundwater contamination found in these surveys are representative of actual groundwater quality in the Province;

      2. Both seasonal variation and inherent variabilities in bacteria concentration in groundwater likely contributed to the observation that different sets of wells were found to be contaminated in the surveys. Although different sets were contaminated, the overall frequency of bacterial contamination was similar in the two surveys; and,

      3. The set of wells contaminated with nitrate was similar in both summer and winter samplings and no specific seasonal variability was observed. The mean concentration of nitrate, however, increased by almost 7% between the two samplings.



    Section 2: Multilevel Monitoring Well Survey

    Resampling of 141 multilevel wells occurred during the summer of 1992. The wells had been installed during the winter survey at 160 farms in Southwestern Ontario. At each of these farms, a multilevel well was located in a cropped field adjacent to the drinking water well. At 16 farms a multilevel well was also installed in a woodlot adjacent to the cropped field. After the winter sampling, the field multilevels were buried below plow depth so they would not interfere with normal field practices but could be located for resampling during the summer survey. Each multilevel provided groundwater samples from various discrete depths. Results were therefore analyzed in terms of either average or maximum contaminant concentration in samples from a multilevel. Results from the summer sampling of the field multilevels were as follows:

    • 21% of the multilevels gave an average nitrate-N concentration that exceeded the Ontario drinking water objective.

    • 44% of the multilevels gave a maximum nitrate-N concentration that exceeded the drinking water objective.

    • 32% of the multilevels indicated groundwater 81 contamination with total coliform bacteria and 10% with faecal coliforms, considering averaged bacterial concentrations.

    • 6% of multilevels had detectable concentrations of pesticide residues, and one multilevel showed a pesticide concentration in exceedence of its IMAC value.

    • Several additional observations can be made with respect to the summer multilevel data:

      1. At the majority of sites, the concentrations of the target contaminants in the multilevel wells were similar to those observed in the water wells, indicating a clear correlation between the levels of groundwater contamination found in farm wells and those found in adjacent farm fields;

      2. The frequency of groundwater samples found to exceed the Ontario drinking water objectives for any of the target contaminants was fairly consistent under all agricultural land-use practices. A slightly higher frequency of nitrate contamination was seen under "corn systems" (rotations in which corn and/or soybeans occupy more than 30% but less than 90% of the land area);

      3. The application of manure to a given field did not appear to correlate with higher bacteria concentrations in the monitoring wells;

      4. When concentrations of coliform bacteria and nitrate-N from a field multilevel and a corresponding multilevel in a woodlot were compared, levels of bacteria were very similar but nitrate-N tended to be considerably less under the woodlot; and,

      5. Nitrate-N tended to decrease nearly linearly with depth below the water table, whereas coliform bacteria appeared to persist to greater depths before significant decreases in concentration were observed.

    • In comparing the multilevel data from the summer and winter surveys, several observations can be made.

      1. Very little seasonal variation in nitrate-N concentration was observed;

      2. The frequency of contamination by coliform bacteria was significantly less during the summer sampling, although the overall trends in the data were very similar; and,

      3. Significant seasonal variations in bacterial concentrations in the shallow groundwater systems appear to occur.

  1. Introduction

    In response to growing concerns related to land-use and development, and the subsequent impacts on groundwater quality, Agriculture Canada initiated a major effort to evaluate the condition of the groundwater resources used by the rural community for drinking water supplies. One of the main motivations for the study was the international awareness of the potential impacts that agricultural activity may have on shallow groundwater quality. Some research work has been completed and more is currently underway in many parts of Canada, the United States, and Europe, to gauge the current and potential impacts of intensive agricultural development on surface and groundwater resources.

    An initial survey of approximately 1300 domestic farm wells and about 150 multilevel monitoring wells located in active farm fields was conducted during the winter months of 1991-1992 as the first part of Agriculture Canada's study. The main objectives of this initial survey were to:

    • determine the quality and safety of drinking water for farm families, and

    • determine the effect of agricultural management on the quality of groundwater.

    Groundwater samples taken from these wells were analyzed for nitrate-N, total and faecal coliforms, and several common herbicides. The results indicated that approximately 37% of all drinking water wells sampled contained concentrations of at least one of the target contaminants at levels above the drinking water objectives specified by the Ontario Ministry of the Environment and Energy (MOEE) and the Ontario Ministry of Health (MOM). Evaluation of data from the multilevel monitoring wells suggested that the quality of the shallow groundwater beneath the active agricultural fields adjacent to the drinking water wells correlated fairly closely with that observed in the water wells themselves. This indicated that the agricultural land-use practice may be directly influencing groundwater quality in the water wells. A detailed report on the results of this survey is contained in the Ontario Farm Groundwater Quality Survey (OFGQS), Winter 1991/92 prepared for Agriculture Canada (September, 1992).

    A second complete survey of the same network of water wells and monitoring wells was carried out during the summer months of 1992. The main objectives of the second survey were to:

    • verify the conditions and trends observed in the first sampling program and enhance the statistical validity of the data set; and,

    • examine the influence of seasonal change, both climatic and related to specific agricultural activity, on the quality of groundwater resources on Ontario farm lands.

    As was the case in the first survey, the project involved the collaboration of eight different groups including Agriculture Canada. The overall program was coordinated through the Ontario Soil and Crop Improvement Association (OSCIA) and involved the Waterloo Centre for Groundwater Research (now- Dept of Earth & Environmental Sci.) at the University of Waterloo, the Centre for Land and Water Stewardship (CLWS) at the University of Guelph, the Resources Management Branch (RMB) and the Pesticide Residue Laboratory (PRL) of the Ontario Ministry of Agriculture and Food (OMAF), the Ministry of the Environment and Energy (MOEE) and the Ministry of Health (MOH).

    In this report, the results from the summer sampling are presented and evaluated with respect to spatial distribution, land-use practices, soil characteristics, and several additional factors. Recent surveys published or made available recently and not reviewed in the winter survey report, are included here for background information.

    The results from the summer survey are reviewed with respect to the winter survey data and an evaluation and discussion of the combined data sets is presented. Information on sampling protocol, soil and land-use classification systems and statistical analysis procedures are included in the appendices.

    The information in this report is not intended to represent an exhaustive study of groundwater quality throughout rural Ontario but is designed to indicate general trends in drinking water quality for farm families in relation to common agricultural land-use practices.



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Created: October 24, 1997 09:40:52 AM
Last Revised:  Tuesday, May 10, 2011 07:21:42 PM