San Mateo County Seal San Mateo County
Health Department

Rationale For Use of No Purge Alternative


Under certain conditions, the use of a no purge alternative has been shown to be an effective sampling protocol for properly developed groundwater monitoring wells . GPP will evaluate sites for use of a no purge alternative upon request of the RP/consultant with submittal of appropriate documentation. In order to qualify for the no purge alternative, monitoring wells must meet the following criteria.

  • Installed in an unconfined aquifer.
  • The well has been properly developed.
  • Competent wellhead completion.
  • Well log and construction detail must be included in the GPP file.
  • Top of screened interval is above the groundwater level.
  • All constituents of concern are LNAPLs (no DNAPLs).

Wells that do not meet these criteria may petition for use of the no purge alternative by submitting a pre-purge sample and a post-purge sample, along with a written request. Forms relevant to application for the no purge alternative are included in Appendix H.