Groundwater Supply Well Surveys




Water Supply Well Survey, Hollister, CA


Former Ordnance Manufacturer


The former ordnance facility began operation in 1957 and continues in a limited fashion under new ownership to the present.  Past operations at the facility released perchlorate, trichloroethene (TCE) and hexavalent chromium to the subsurface, impacting soil and groundwater.  Groundwater impacts of TCE and perchlorate affected on and off-site agricultural and domestic water wells.  Selected agricultural and domestic water wells have been shut down and destroyed, well head treatment systems have been installed, and city water has been provided to nearby residences.  To identify all the water supply wells in the vicinity of the site including wells that could have been installed since the last well survey, the Central Coast Regional Water Quality Control Board (CCRWQCB) requested that an updated well survey be performed.  There was also a need to expand the well survey area to support efforts to find replacement agricultural water supply for a 600 gallon per minute, 350-foot deep well that was destroyed due to perchlorate and TCE impacts.


Perform an updated and expanded well survey to include an area 1.5 miles wide and 2.2 miles long around the former ordnance facility.


To accomplish the well survey, Trinity sent a private well survey questionnaire to each land owner in the survey area, reviewed past well survey documents in the project record, conducted door-to-door surveys as needed to complete all questionnaires, reviewed local and state records pertaining to well permits, installation, construction details and use, and documented findings in a detailed report.


  • The results of the well survey showed that new agricultural and domestic water supply wells were installed inside the well survey area since the last survey was completed.  Older supply wells that were missed or incorrectly located were identified and records and location maps were updated and corrected.  Selected supply wells in close proximity to the site and associated dissolved plumes for TCE and perchlorate were sampled for the presence of perchlorate per Board directive.  Per the site’s Clean-up and Abatement Order, an updated well survey is due in 2011 and every three years thereafter to maintain an accurate and up to date record of existing, new and abandoned water supply wells in the study area.