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Page 2 Ms. Margaret Lagorio February 17, 1994 SJEHD's correspondence raised concerns that 30 feet of screen above the top of groundwater is longer than typical monitoring wells. SJEHD stated that most wells have 5 to 10 feet of screen above the groundwater table. However, the depth to historical groundwater has been as high as 35 feet, so a longer screen length will allow monitoring if future groundwater levels rise. To facilitate the SJEHD's concern, Burlington will shorten the screen length above the current groundwater table to 20 feet (from a depth of 35 to 55 feet). SJEHD's correspondence also stated that typical monitoring wells are screened 10 to 15 feet below the groundwater table, and that groundwater samples collected from wells with 20 -foot screens may be diluted and not accurately representative of subsurface conditions. Burlington's experience monitoring light petroleum hydrocarbon compounds (such as gasoline), in longer screened intervals beneath the water table, do not result in diluted samples if proper well purging and sampling procedures are utilized. Well purging will be performed at a rate that minimizes turbulent groundwater flow into the well that could cause sample dilution. After the well has recovered from the purging, and groundwater temperature, conductance, and pH parameters have stabilized, representative samples will be collected from the well by slowly lowering a bailer into the top two feet of groundwater. Soil Sampling and Laboratory Analysis Burlington's original workplan stated that soil samples will be collected from the well boreholes at 5 -foot intervals, logged by a site geologist, screened for hydrocarbons with a photoionization detector, sealed, and stored on ice for subsequent analytical testing. Tested samples will be selected based on observations of hydrocarbon impact by the geologist, and detection by the photoionization detector. As requested by the SJEHD, analyzed samples will include those collected from depths of 35 to 55 feet meeting the above criteria. Samples will be tested for hydrocarbon compounds by the state -certified Curtis & Tompkins, Ltd. analytical laboratories in Berkeley, California. Health and Safety Plan As requested by the SJEHD, a site-specific Safety Evaluation is included in this addendum (Attachment B) for your review and approval.