10/24/1996 BOARD OF HEALTH Minutes

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5 , Lot (Figure 1). This area appears to be well defined by the factthat facility to AP 62 TCE as not detected in 93 wells (monitoring and residential) outside ofthis area. � Therefore, it seems unlikely that residences located laterally or downgradient from the estimatedlurne area have been affected TCE contamination in the past, s reported, TCE was only used at the Augat facility in the spring of 1993 and if TC was released from the facility at that bine,the earliest date by which any TCE from the site couldhave reached the closest of the impacted private wells e,g., APLot 2 would be late spring of 1994. This estimate is based on worst case assumptions about the possible movement of TCE from the reported time of the original spill i.e. spring 1993) to the first downgradient residential location. In essence, it is assumed that the TCE was spilled at the seater of the facility,that the TCE immediately readied the groundwater after the spill, that thegroundwater beneath the site travels about 2 feet per day, and that the distance between the Au at site and the closest private well at AP 62 Lot 72 is 630 feet. The goo t groundwater flow velocity for this site was estimated based on the results of a groundwater model used b the Mashpee water District and published reports by the U.S. Geological Survey n contaminant transport in gape hod aquifers (M� 1996,Le Blanc 19 . Applying these assurn tions, the earliest time that contamination could have ppy P reached the well at AP 62 Lot 241 would be the spring of1995 i. ., 1,390 feet from -ugat to AP 62 Lot 2 1 - 2 feet per day= 695 days). Thus, the very earliest that i residents could have been exposed to TCE by drinking and cooking with water from rivate wells inhaling TC in the air inside the houses, and by bathing with contaminated water would have been spring of 1994 for AP 62 Lot 72 or spring of 1995 for AP 62 Lot 24 1. An alternative approach to estimating exposure to TCE to residents of the two affected houses is to locate the leading edge of the TCE plume i.e., approximately in the vicinity f the well at AP 62 Lot 2 1 and back calculate the duration of exposure to residents living at AT 62 Lot 72 i.e., 760 ft from AP 62 Lot 241 to AP 62 Lot 72+ 2 feet per day 380 days). Because it appears from the recent downgradient monitoring well data that the leading .g e din ed a of the TCS plume does not extend appreciably beyond AP 62 Lot 24 1, it is most reasonable to conclude that the TCE contamination at AP 62 Lot 241 began very recently spring tl i.e. s rin of 1996 . In this case the residential well located upgradient at AP 62 Lot 2 would have first been affected by TCE contamination approximately 12 months earlier or spring of 1995, 1t is very possible that the TCE reportedly spilled in the facility in 1993 did not immediately enter the groundwater. Because the actual time of entry o TC into groundwater eater is not known, it is reasonable to assrx- e that the tune o initial opportunity for exposure t AP 62 Lot 2 could be later than spring of 1994. Because of these many uncertainties regarding the spill and environmental fate and transport of TCE, we believe - the current monitoring data coupled with the estimated aquifer characteristics that using g to estimate the slates of exposure i.e., back calculating from the monitoring data) will yield the more accurate estimate of the timing of opportunities for exposure. considerations and assumptions, the family at AP 6 Lot 2 could Thus, based n these earopportunityfor TC exposure beginning in spring of have had approximately one carbon filtrations sterns were installed. The family at P 62 1995and ending when the y 7