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d' 1 Standard Operating Procedures GROUNDWATER MONITOR / EXTRACTION WELL INSTALLATION AND DEVELOPMENT WELL INSTALL,XTION Tice boreholes for monitor/extraction wells are drilled using a truck-mounted hollow-stem auger drill rig:. The diameter of the borehole is a minimum of four inches larger than the outside diameter of the casing when installing the well screen(DWR Publication 74-91). The hollow-stem auger provides minimal interuption of drilling while permitting soil sampling at the desired intervals. All wells are installed by state-licensed drillers. The monitor/extraction wells are cased with threaded,factory-slotted,blank schedule 40 polyvinyl chhloride(PVC). The perforated interval consists of slotted casing,generally 0.020-i.ncti wide by 1.5-inch long slot size,with 42 slots per foot. A threaded PVC cap is fastened to the bottom of the casing. Centering devices may be fastened to the casing to assure even distribution of filter material and grout within the borehole annulus. The well casing is thoroughly washed and steam-cleaned prior to installation. After setting the casing inside the hollow stem,sand or gravel filter material is poured into the annular space to fill from the bottom of the boring to I foot above the slotted interval. A 1 to 2 foot thick bentonite plug is placed above the filter material to prevent the grout from infiltrating down into the filter material. Neat cement,containing about 5%bentonite,is then tremied into the annular space from the top of the bentonite plug to the surface. A lockable PVC cap is placed on each wellhead. Traffic-rated flush-mounted steel covers are instilled around wellheads for were in parking lots and driveways,while steel stove pipes are usually set over wellheads in lanc,scaped areas. WELL DEVELOPMENT After installation,the wells are thoroughly developed to remove residual drilling materials from the wellbore,and to improve well performance by removing any fine material in the filterpack that can pass from the formation into the well. Well development is performed ir. accordance with Califomia Regional Water Quality Control Board(RWQCB)procedures described in the Leaking Undergrourd Fuel Tank(LUFT)Field Manaul,the Tri-Regional Board Staff Recommendations for Preliminary Evahiation and Investigation of Underground Tank Sites,and local regulatory guidelines.Well development techniques include pumping, bailing,surging,swabbing,jetting,flushing,and airlifting. During well development from three to ten well volumes are evacuated from the well,allowing pH,specific conductivity, temperature and sediment content of the water to stabilize. All development water and rinseate is collected for temporary storage in labeled 55-gallon containers or proper storage tanks,and is then disposed of properly depending on analytical results. To assure that cross-contamination does not occur between wells during drilling and development,all development equipment is either steam cleaned or cleaned using Alconox and rinsed twice with dionized water. Parker Environmental Services, 4185 Rialto Court, Pittsburg, CA 94565-6116 Phone (415) 439-1024 Fax (415) 439-2566