ARCHIVED REPORTS_XR0011478 - Laserfiche WebLink

Home Browse Search

A gravel pack of No. 2/16 Lonestar sand was placed in the annular space around the well screen to approximately three feet above the top of the screen. A surge block was used to tighten the sand pack before a 1 1/2- to 2-foot Bentonite plug was placed on top of the sand and hydrated with deionized water. A tremie pipe was used to fill remaining annular space with neat cement grout in order to reduce the risk of damage to the Bentonite seal from free-falling grout. 3.4 WELL DEVELOPMENT The wells wete developed, following the EA protocol (see Appendix C), on 13 August 1990. Records were maintained of the purging methods and volumes of water purged (Appendix F). All purge-water was contained on the site in 55-gallon drums in a fenced enclosure. 3.5 WELL DESTRUCTION Three monitoring wells(MWl-MW3) were destroyed,in accordance with San Joaquin County Health Department regulations, The wells were found dry in February 1989 and have not been sampled since, and they could serve as a potential means of introducing contaminants to the subsurface. All three wells were overdrilled with a 6-inch hollow-stem auger, and as much of the 2-inch diameter PVC and well completion materials were recovered as possible. The result- ing hole was filled with neat cement grout from the bottom of the boring to within 10 feet of the surface using a tremie pipe, a►td the remaining 10 feet was filled using the free-fall method. After the cement settled a few feet,the boreholes were filled to the surface with soil. 3.6 WELL SURVEY The elevations of the tops of the well casings were surveyed relative to two existing monitoring wells and referenced to mean sea level, using a transit and stadia rod, shooting off a known elevation point. Yellow paint was used on the top of the well casing to mark the survey point, to provide an established reference point for all future water level measurements. The results of weff surveying and gauging are presented in Table 6. 3.7 GROUNDWATER SAMPLING The wells were sampled on 17 August 1990,following standard EA protocol (Appendix Q. The presample purge records are included in Appendix F The two groundwater well samples, a trip blank, and a decontamination blank were analyzed by the laboratory for TPH as gasolin. with BTXE distinction by DHS-modified EPA Method 8015/8020. c67/97780/tx 5 - 1