Database Manual

Oak Ridges Moraine Groundwater Program

Section 2.7

Section 2.7 Multi-Screen Installations

Multi-screen installations are a common groundwater monitoring technique used to investigate local hydrogeological conditions. They generally include one or more boreholes with multiple screens (intervals/monitors) in each borehole. These types of boreholes have been dealt with in a variety of ways within the database depending upon the actual borehole/screen characteristics and the source of the data.

As a prelude to this discussion, a note on the MOE well record database is warranted. Historically the MOE well record database primarily held only those wells that were drilled for water supply purposes and that were drilled by water supply well drilling companies. These wells typically held only one screen/interval per borehole. In the odd circumstance where two pipes were put down one borehole (e.g. for municipal monitoring purposes) the Ministry database would only retain information one of the two screened intervals and the information on the second interval would be missing from the digital MOE database.

Starting in 2003 the Ministry started collecting information on boreholes that were drilled under consultant oversight by geotechnical borehole drillers. At this time the Ministry adopted a methodology of ‘clustering’ wells that allowed the geological description of one borehole (presumably the deepest borehole) to effectively represent all other boreholes drilled on that site. In such cases, a ‘representative’ geologic description from one on-site borehole reflects the conditions for the entire site. All boreholes drilled on the site are then linked in the MOE database and only one ‘master’ location would include the geological description. All other on-site boreholes would incorporate all other information typically associated with an MOE borehole (i.e. well depth, construction details, screen details, pumping test details, etc…).

When these cluster wells are incorporated into the database, each borehole is given its own unique LOC_ID in the D_LOCATION table and is linked to its related boreholes through the use of the LOC_MASTER_LOC_ID field (also in D_LOCATION). The LOC_ID of the ‘master location’ is copied into the LOC_MASTER_LOC_ID field for all associated boreholes. Excepting the D_GEOL_LAYER, all linked boreholes would have unique data (particular to that ‘linked’ location) in each of the other database tables.

It is important to note that these MOE clustered wells are not considered to be multi-screen installations in the typical sense. They only share a common geological interpretation of the ‘representative’ well.

Multi-screen installations would include:

Depending upon the person entering the data, these types of multi-screen boreholes could be entered into the database in one of two different ways:

Note that in some instances (generally within the MOE Water Well database) a single well can have multiple screened intervals associated with a single casing pipe (i.e. the well screen has been designed purposefully to leave a solid blank casing - for example, opposite a silty zone in an aquifer - between two screened intervals within an aquifer). Other cases might have a screen adjacent to a coarse aquifer unit high up in a well and a second screen at depth associated with a second deeper aquifer. Since the extracted water samples and any recorded water levels would reflect contribution from both aquifers, only one interval, and one set of temporal data, would be recorded for such wells in the database. However, the multiple screen tops and bottoms for such an interval are retained in the D_INTERVAL_MONITOR table. These situations are fairly uncommon. These wells would not be considered to be multi-screen installations in the typically understood hydrogeological sense.

Although municipal pump houses could be incorporated into the database as multi-screen equivalents, to date they have not been represented in this way. Pump houses have been assigned a LOC_ID in the database and the wells that are linked or contribute to a municipal pump house or reservoir are currently linked through the LOC_MASTER_LOC_ID field in the D_LOCATION table.

There has also been some discussion of having multiple intervals within the database for the climate stations and the surface water stations. In the case of a climate station, for example, one interval could be established to represent a thermometer and house the temperature data whereas a second interval could represent a rain gauge and house the precipitation data. To date this has not been done and each surface water and climate location contains only one interval that houses all temporal data tied to the location.