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L Mr.Harlin Knoll Checklist for No Further Action Request and Monitoring Well Destruction Work Plan September 29,2010 Page 4 Based on the information presented in Table 1 and the data previously submitted in the first half 2010 groundwater monitoring report and request for closure on March 26,2010,the threat to human health and the environment has been abated at the WOS site;SHN therefore requests that a No Further Action letter be issued for this site. Monitoring Well Destruction L MW-3 MW-4,MW-5, SHN will supervise the abandonment of monitoring wells MW-1,MW-2, , MW-6,and MW-7 at the WOS site in Acampo,California pending a NFA letter from the San Joaquin County Environmental Health Department(SJCEHD) (Figure 2). Well constructions details are included in Attachment B. According to the San Joaquin County Well Standards dated February 2005,if the well construction is unknown and/or is located in an area of known or suspected pollution or contamination,the well shall be destroyed by removing all material within the original borehole(including the well casing,screen,filter pack,and annular seal);and the created hole,filled completely with appropriate sealing material. In addition to these overdrill procedures,SHN recommends that five on-site wells be permitted to be pressure grouted. These wells have not had detectable levels of petroleum hydrocarbons associated with them. Historical soil analytical data has been presented in the first half 2010 groundwater monitoring report and request for closure on March 26,2010,and is contained in Attachments A and B. A description of the well destruction process is presented below. Scope of Work The following activities will be performed to abandon the wells: • SHN will submit permit applications for well destruction and schedule an inspection with a representative of SJCEHD,prior to conducting the site activities. LSHN will coordinate monitoring well destruction work with a licensed well driller. • Monitoring wells MW-1,MW-3,MW-5,MW-6,and MW-7 will be grouted using a L pressurized"Chem-Grout-Mad-tine"with a rated pressure of 150 pounds per square inch(psi). From the top-of-casing,a Portland cement and a 5% powdered bentonite mixture will be pushed through the monitoring well screen and into the surrounding ` formation(approximately three well volumes). After the monitoring wells are filled Lwith the grout mixture,the well boxes will be removed using an air-compressed jackhammer. First,a hole at least 1 foot larger in diameter than the originally drilled hole shall be excavated around the outside of the well casing to a depth of 5 feet BGS,then the well casing shall then be cut off 6 inches above the bottom of this excavation and removed. The grout used to fill the well shall be allowed to spill over into the excavation,during the sealing operation,and fill it for a thickness of 1 foot and form a"cap" that has a diameter of at least 1 foot greater than the diameter of the originally drilled hole. The hole will be covered using like material to surface grade. The selected licensed driller will follow the California Well Standards, Bulletin 74-90 (Supplement to Bulletin 74-81). \\Eureka\Projects\2007\007152-WOS\PUBS\rpt\20100929-NFA.doc �-iw