SOP - 20. Top of Casing Survey

An accurate Top of Casing (TOC) survey is an essential to determine groundwater flow direction. Time for the TOC survey is included in the well installation (Section 6 of the Scheduled Pay Items). It is generally not necessary to perform this survey more than once for any site, other than to “tie in” new wells as they are installed (although the survey for TOC is best left until the first sampling event to allow time for the casing to settle). The TOC survey should be standardized to measure the elevation of the top of the well on the NORTH side of each well casing. It may be appropriate to put a mark or small notch in the casing to indicate where the casing elevation was measured, thereby ensuring that depth-to-water measurements (measured to a hundredth of a foot) are consistent and accurate.

In addition, it may sometimes be appropriate to re-survey the TOCs if it has been an extended time since the last elevation survey. This re-survey may be appropriate because casing may shift over time and groundwater elevations are typically measured to the hundredth of a foot over distance of 20 to 30 feet or more (this is a slope of less than three feet in a mile).

Although there are situations in which a new TOC survey is warranted, the scope and frequency of such a survey does not lend itself readily to the SPI unit rates in the ATC Contract. Therefore, when you do need to do a new TOC survey, the level of effort for existing wells should be built up using the appropriate number of labor hours.

Return to: PRP Site Manager Standard Operating Procedures (SOP) webpage.