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SENT BY: 6-27-96 ;10:37AM ; CLAYTON PLEASANTON- 411 F l)NVfR NMENTAL ♦� (QNSU(IAN I? The well seal in newly developed wells must set up for 48 to 72 hours prior to development. Since development of the well can volatilize contaminants present, the well must also settle for at least 48 to 72 hours between development and the first purging/sampling incident. All monitoring wells are initially developed to clean the well and stabilize sand, gravel, and disturbed aquifer materials around the screened internal perforations. Wells are developed by pumping (or bailing) and surging until water turbidity and specific conductance stabilize. In some cases, where wells arc installed in low permeability formations and the wells purge dry, the well is allowed to recover and is purged dry three times. Clean tap water is introduced into the well if it does not recover rapidly enough. Pending results by laboratory analysis, purge water from well development and sampling is placed into DOT-approved drums, labeled with the name of the site, address, well number, and left at the site. Uncontaminated water may be disposed of by the client. Water found to contain levels of contaminants above local or state action levels requires that the client dispose of it in accordance with hazardous waste requirements. At the client's request, we can assist with the disposal of contaminated purge water. GROUNDWATER SAMPLING To collect a representative sample of the groundwater, stagnant water within the well casing and filter material must be purged and fresh aquifer water allowed to replace it. The water is purged from the well by pumping or bailing at least three well volumes. Well volumes are calculated by measuring depth to groundwater to the nearest 0.01 foot upon arrival at the well before any purging has begun. Groundwater samples are collected only after purging has been of sufficient duration for pH, temperature, and electrical conductivity to stabilize. When purging low-yield wells, the wells are purged to dryness. When the well recovers to 80% of the depth measured upon arrival, samples are collected. Field sampling logs maintained for each well include: • Monitoring well identification 0 Static water level, before and after pumping • Well depth e Condition of water prior to purging(e.g., amount of free product) • Purge rate and volume • pH, temperature, and conductivity during purging • Time purged • Time of sample collection • Sampling method • Name of sampler e Climatic conditions Water samples are collected using clean TeflonTm bailers. All equipment that contacts samples is thoroughly cleaned before arrival at the site and between sampling events.