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' Per San Joaquin County Well Standards, monitoring wells shall be constructed by a C-57 licensed contractor under the direction of a California Registered ' Professional Engineer, California Professional Geologist, or a California Certified Engineering Geologist. Prior to construction, permits will be obtained from the San Joaquin County Environmental Health Department (SJCEHD) and ' Underground Services Alert will visibly mark all subsurface utilities, pipelines, tanks, septic systems or other structures. Inspections will be made as required by the County during all phases of construction and development. Well ' inspections shall be scheduled with the County and all sealing operations performed in the presence of a County inspector, unless directed otherwise by the County. Within 90 days of obtaining approval of a Groundwater Well Project Description ' Addendum, the Discharger shall submit a Well Installation Report. The Well Installation Report shall describe the activities completed and explain any deviations from the approved Groundwater Well Project Description Addendum. ' The Well Installation Report shall be compliant with Attachment F of the WDRs "Requirements for Monitoring Well Installation Workplans and Monitoring Well Installation Reports"(a copy of Attachment F from the WDRs is provided in Appendix B of this report). 2.2 Drillinq Equipment and Techniques The well driller shall employ an approved mechanical means (i.e., auger, rotary, or cable tool methods) to bore the holes and construct the well to a maximum ' depth of about 1 foot below the bottom of the designed well screen depth. The borehole diameter shall be selected so there is a minimum 2-inch radial thickness of sealing material between the well casing and borehole wall. For the ' prevailing subsurface conditions encountered in the Lathrop area (i.e., unconsolidated sediment), a hollow-stem auger has successfully been used to drill monitoring well boreholes. ' 2.3 Decontamination Procedures At this time, no hazardous constituents are expected at the drilling locations. The following steps therefore represent the minimum decontamination procedures to be employed. ' • To the extent possible, drilling activities shall proceed in order from up gradient to down gradient wells. • All equipment used for constructing wells must be free of contamination and cleaned to prevent potential cross contamination. Equipment, tools, ' materials, etc. shall be decontaminated prior to the beginning of the work and prior to each well installation. For example, all screens and casings used for monitoring wells should be in a sterile and contaminant-free condition when ' - 4 -