G.25 Correction of Water Levels and Associated Data
- TO BE UPDATED
Estimated Recurrance Time: As necessary
As part of the process for creation of regional water level surfaces (whether shallow or deep), checks and corrections - as necessary - should be made with regard to the water level data as contained within D_INTERVAL_TEMPORAL_2. In most cases, invalid water levels arise out of calculated elevations based upon an invalid or old reference elevation (as found in D_INTERVAL_REF_ELEV). These water levels can be corrected through a modification of the existing reference elevations (either or both of REF_ELEV and REF_ELEV_OUOM; note that REF_POINT should be updated to include the value of the stick-up), removal of the calculated values populating RD_VALUE (in D_INTERVAL_TEMPORAL_2) and re-running the data-calculation scheme within SiteFX.
However, other errors can be found.
Water Levels as Metres-Above-Sea-Level (masl)
When existing RD_VALUE_OUOMs are in units of ‘masl’, the REF_ELEV is not used. In this case, the existing REF_ELEV should be used to change these values to depths (as appropriate; note that in some cases, the ELEV_ORIGINAL in D_LOCATION_ELEV may need to be used, instead). The SiteFX routine should then be run to re-calculate the correct RD_VALUEs.
In some cases, no original value or reference elevation seems to apply to these water levels (i.e. the application of the above correction cannot be performed; the original elevation to which these water levels were referenced has been lost). Where these values are ‘very-incorrect’ such that they impact the water level surface calculation being performed, a mid-point depth (based upon the borehole depth and the variation in the water levels) is assigned instead. The original values are recorded in RD_COMMENT with an explanation.
Invalid or Incorrect BH_BOTTOM_DEPTH
In these cases, the BH_BOTTOM_DEPTH indicates that the well depth is above that of the recorded water levels. (The case of a ‘deep’ well with shallow water levels is not usually considered as invalid and must be examined/corrected using an alternative scheme.) Here, the view V_YPDT_ELEVS_AND_DEPTHS is used to check whether the calculated BH_BOTTOM_DEPTH is valid in comparison with construction detail depths (D_BOREHOLE_CONSTRUCTION), interval monitor depths (D_INTERVAL_MONITOR), geologic layer depths (D_GEOLOGY_LAYER) and, finally, water level depths (D_INTERVAL_TEMPORAL_2). Preferably, the deepest (largest depth) recorded amongst the first three parameters is used to correct the BH_BOTTOM_DEPTH (and related information; e.g. BH_BOTTOM_ELEV). In cases where no other depth is present, a depth is assigned based upon the water level depth - usually a ‘0.3’ metre value is added dependent upon the number of water levels recorded. If more than a single value is found, this value should be added to the largest (in all cases thus far, only a single water level has been found).
The view CHK_YPDT_ELEVS_AND_DEPTHS can be used, generally, to find those boreholes whose currently assigned BH_BOTTOM_DEPTH is not within ‘+/- 1’ metre of the deepest (i.e. the maximum) of the various depths being examined (the ‘1’ metre value is arbitrary and may be adjusted).