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Since results of particle size sieve analysis may not be available, filter pack selection may be performed on the basis of stratigraphy, using the finest grain size unit to be encountered in the screened interval as the defining particle size. Commonly selected grades of filter sand are 1/20 (or equivalent) for use with 0.010-inch slots and 2/12 or 2/16 (or equivalent)for use with 0.020 inch slotted screens. The filter pack should be added slowly to fill the annular space between the well screen and the sides of the boring. The filter pack sand can be emplaced either through the hollow stem of the auger as the auger is removed or in the open hole surrounding the well casing if soil conditions permit. Uniform placement of the filter pack must be monitored during placement to ensure that bridging, or formation of an air gap, does not occur. The placement of the filter pack is monitored using a weighted tape measure to gauge the rate of filter sand placement and break any bridges. A bridged filter pack will eventually collapse and possibly result in failure of the bentonite well seal and impair the well surface seal. A minimum two-foot seal of bentonite is placed above the sand filter pack. The bentonite seal is hydrated by either formation or potable water. Neat cement or a cement/bentonite mixture seals the remaining annular space to the surface. If bentonite is used in the grout mixture, it must not exceed 5% of the mixture, by weight. The grout may be placed using a tremie pipe, if the grout column will be longer than 20 feet or if water is present in the annular space above the bentonite seal. A watertight locking cap and protective traffic-rated vault is installed on top of each well. The traffic- rated vault will be set in concrete and be raised slightly above the surrounding grade to ensure that rainwater or other drainage water does not pool over the wells. Well construction details are presented on the soil boring log sheet for each well. Waterproof tags are attached to each well casing to provide data on well identification, installation date and as-built construction details. GHD completes and submits or determines that adequate information has been provided to the Driller for him to complete and submit the required Well Completion Report to the Department of Water Resources. The last page of this SOP illustrates a Typical Monitoring Well Construction Detail. To make well data suitable for inclusion in the State of California GeoTracker GIS network, well location data must be surveyed horizontally to within than one-meter accuracy using latitude/longitude coordinates and surveyed vertically to within 0.01 foot relative to mean sea level. SECTION II. MONITORING WELL DEVELOPMENT 1. OBJECTIVE To establish accepted procedures for conducting well development prior to purging and sampling activities in accordance with standard practices by engineering professionals. 2. BACKGROUND Following the installation of a monitoring well, it is necessary to develop the well in order to adequately remove the silt and clay (fines) from the filter pack material and in the immediate proximity of the well, in order to minimize the infiltration of fines throughout the life of the monitoring well. GHD SOP MW Install&Dev 4 of 6 Rev 2/14