MRD283-Ambient Groundwater Geochemistry
Product Information and GIS Download
Published 2011
Ambient Groundwater Geochemistry Data for Southwestern Ontario
The Ambient Groundwater Geochemistry Program seeks to characterize the natural geochemistry of groundwater across Ontario. This release contains the data from the first 4 years of sampling, which covers all of southwestern Ontario and encompasses over 40 000 km's. The data include detailed inorganic chemistry for more than 900 water samples. Parameters tested include dissolved gases, major ions, trace elements and field measurement of temperature, pH, redox potential and electrical conductivity. Isotopes of water were also tested and will be released at a later date. This data release includes a brief explanation of the data and quality control methods (.doc); precision and accuracy plots for all parameters (.jpg); single-parameter maps for bedrock wells plotted over bedrock geology (.tif); single-parameter maps for overburden wells plotted over Quaternary geology (.tif); and a single flat-file containing analytical data plus station data including well depth, type, deepest formation penetrated (.xls), etc.
Hamilton, S.M. 2011. Ambient Groundwater Geochemistry Data for Southwestern Ontario; Ontario Geological Survey, Miscellaneous Release Data 283.
The data are available on 1 CD-ROM. $20.00 or can be downloaded free of charge.
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Area of Breathing Wells
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The author would like to thank Ron Hopper of W.D. Hopper and Sons Ltd. for sharing his considerable knowledge of the groundwater conditions in southwestern Ontario.
R. Hopper, personal communication. 2010
Watch the video below to see examples of Breathing Wells in southern Ontario.
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Data

Well Depth
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This layer contains information such as Well Depth and other characteristics of the well itself which may include Subcropping unit, Terrain type, Year drilled, Static water level and descriptions.

Overburden Well Depth

Bedrock Well Depth

Groundwater Temperature
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Temperature was determined using the most representative parts of the logged trends collected with the multiparameter instruments. The database includes 3 temperature parameters: T_final_°C, T_trend and T_representivity. Based on an experiment using down-hole temperature loggers, it was determined that heat gained from the plumbing and pump on a typical site results in an average 0.82 °C temperature increase (Hamilton and Freckleton, 2009). In addition, the differences between the accuracy of the muliparameter instrument and the more correct down-hole testing instrument results in a further average gain of 0.23 and 0.31 degrees for the YSI and Hanna instruments respectively. The temperatures in the T_final_°C field therefore result from subtraction of 1.05 and 1.13 °C from the raw values for the 2007/2008 and 2009/2010 datasets respectively. By comparing the individual instruments against each other in a water bath, it was clear that the precision of all 6 instruments was considerably better than 0.1 °C (Hamilton and Freckelton 2009).

Overburden Wells

Interface Wells

Bedrock Wells

Dissolved Oxygen
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Early in field program, the measurement of D.O. was hampered by frequently encountered H2S in some waters and its tendency to render the D.O. probe non-functional until the next calibration. The YSI probe, which has a standard Clark-Cell design, is particularly susceptible because the membrane is difficult to replace and impossible to individually cover in the event of high H2S. The dissolved oxygen probe on the Hanna is also a Clark-Cell but has a membrane system that is easy to replace and to cover with a (homemade) cap when H2S is present. From 2009 onward both multiparameter instruments have been used while sampling; the YSI to collect pH, conductivity, redox and temperature, and the Hanna to collect dissolved oxygen and temperature. The 2 instruments have similar levels of precision and accuracy for all the parameters. If significant H2S (>0.1 ppm, or as indicated by smell) occurs in water the Hanna is not used or the probe is capped and D.O. is recorded as zero for that site. D.O. and H2S are incompatible in solution for any more than a few minutes and, therefore, groundwaters naturally containing H2S have no D.O. Whenever a D.O. probe failed or the reading was suspect for any reason, a sample was collected and analyzed by Winkler Titration and the resulting ppm value converted to % saturation. The final database reports D.O. using the most reliable method available for each site, whether by the instrumental or Winkler technique.

Drilled Wells

Subcrop Wells

Deeper Wells

Electrical Conductivity

Bored or Dug Wells

Field pH

Oxidation/Reduction Potential
Oxidation-reduction potential was determined instrumentally using ORP probes referenced against the Ag-AgCl half-cell after continuously logging for a period that generally exceeded 10 minutes.

Hydrogen Sulphide

Calcium

Magnesium

Potassium

Sodium

Bicarbonate

Sulphate

Chloride

Nitrate

Nitrite

Ammonia

Organic Nitrogen

Bromide

Fluoride

Phosphate

Dissolved Inorganic Carbon

Dissolved Organic Carbon

Boron

Iron

Strontium

Silicon

Dissolved Methane (% Saturation at Depth)
Methane samples are collected in 1 litre glass bottles filled to the 600 mL line and tightly capped. The samples are allowed to temperature-equilibrate overnight and the methane (and O2 and CO2) gas concentrations in the headspace are measured the next day. The equilibration temperature is also recorded and the Henry?s Law constant for methane is used to calculate the dissolved methane concentration at the time of sampling. The Ideal Gas Law is then used to calculate the in situ methane concentrations at depth using the known well depth, known or estimated static water level, and certain assumptions regarding the pump depth. This value was converted to units of percent saturation, using the known groundwater temperatures. Methane in the MRD plots is shown in units of: (1) CH4(g), i.e. measured in the 400 mL headspace of the original sample; (2) CH4(aq) concentration in the original sample, i.e. calculated using Henry?s Law from (1), and (3) In situ % Saturation, i.e. the degree of saturation at the estimated depth of the water source.
Methane gas concentrations were mostly determined using an Eagle multigas meter equipped with two CH4 sensors:
1) a low level catalytic sensor that measures total combustible gases to 50,000 ppm (5%) as CH4, and
2) a high level infrared sensor that measures CH4 to 100%.
The sensors are calibrated and/or checked daily with 2 methane standards (typically 1000 ppm and 50% CH4 respectively) and using fresh air as a zero methane adjustment. The meter also has an infrared CO2 sensor with a range up to 5% and an electrochemical O2 sensor with a range up to 40%. These are also checked and/or calibrated daily. In 2007 a flame ionization detector (FID) was used to measure total combustible gases as CH4. This proved to be problematic, first because it has a maximum range of only 5% (50,000 ppb) but also because it requires a minimum concentration of about 11% oxygen in the sample or the instrument ?flames-out? and needs to be re-calibrated. This happened so often that samples containing free methane were later excluded from direct testing using the FID. Instead, the gas was verified as combustible (by igniting it) and a minimum value of 50,000 ppm was recorded for that sample. These minimum values are indicated in red in the CH4 figures in the MRD. If any of the remaining samples flamed-out, a bifurcated hose was used to draw equal amounts of air and sample gas, which ensures the minimum O2 concentration in the sample. The resulting CH4 concentration was then doubled to yield a CH4 value for the sample. Since the bifurcated hose was used as a second test of the same sample after the initial flame out, the resulting CH4 concentrations are minima and are included in the red offscale values shown on the CH4 figures.

Offscale Values

Dissolved Methane (Concentration In Water)

Silver

Aluminum

Arsenic

Barium

Beryllium

Cadmium

Cobalt

Chromium

Caesium

Copper

Europium

Gallium

Hafnium

Mercury

Holmium

Heavy Rare Earth Elements
Gd + Tb + Dy + Er + Tm + Yb + Lu

Field Iodide
A 60 ml sample is collected for iodide measurement. The iodide bottles contain 2 ml of a saturated solution of nickel acetate to precipitate any dissolved sulphide (S2-) that would otherwise interfere with the iodide analysis. This quantity of nickel is more than a 10 times excess required to precipitate S2- at the upper range of detection of the H2S field testing equipment. The addition of nickel acetate was not carried out in the 2007 field season, which resulted in some of the iodide data being compromised by instrument interference with dissolved H2S. These data have been removed from the database. Iodide is measured in the field within 24 hours of sampling using an Orion 9453BN Iodide Ion Selective Electrode (ISE). In 2007 and 2008 this was connected to a personal computer via an Orion Sensorlink PCMCIA card, which allowed continuous logging and real-time data recording of the iodide reading in mV. From 2009 onward the meter used was an Orion 4-Star portable pH/ISE meter. With both instruments, the probe was calibrated using 10-5 M (1267 ppb) and 10-7 M (12.67 ppb) iodide standards. With the Sensorlink the calibration was done after-the-fact by determining the slope of the concentration / mV line for the two standards measured prior to each batch of samples. The ISE meter is calibrated each day prior to measurement of the samples and the read-out units are ppb.

Lithium

Light Rare Earth Elements
La + Ce + Pr + Nd + Sm

Manganese

Molybdenum

Niobium

Nickel

Lead

Rubidium

Antimony

Selenium

Tin

Thorium

Titanium

Thallium

Uranium

Vanadium

Tungsten

Yttrium

Zinc

Zirconium