SITE INFORMATION AND CORRESPONDENCE

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Mr. Nathan Esformes IV"J,.w - 2 - 1&August 1998 i mound. The level of reduction necessary and the statistical method for making the comparison must be specified before approval to conduct the test can be given. 3. The work plan does not provide any method for verifying the groundwater gradient beneath the aeration pond or measuring the height of the groundwater mound. The current monitoring program does not include collecting water level or water quality data from beneath the aeration pond. Well MW-1 is approximately 50 feet upgradient from the pond and well MW-4A is approximately 250 feet downgradient. This well spacing does not allow for the mound height or groundwater gradient away from the aeration pond area to be measured. A monitoring well is needed adjacent to the aeration pond to determine the height of any mound and quality of the infiltrating groundwater. 4. The work plan proposes only to investigate the aeration pond as the source of the chloroform. Other points of wastewater discharge exist upgradient of well MW-1, including the stormwater pond and the apricot orchard spray field. According to a flow diagram showing how extracted groundwater and treatment plant effluent are handled, which was submitted by Triple E with its 16 February 1996 comments on the tentative Waste Discharge Requirements (WDRs) of Order No. 96-118, treatment plant effluent that does not meet the WDR effluent limitations is placed in the stormwater pond. Triple E has not reported the concentration of chloroform in this wastewater or the nature and condition of the stormwater pond liner. The 16 February 1996 comments also note that well MW-1 is a downgradient monitoring point for the apricot orchard spray field. Thus, an increase in chloroform in well MW-1 could be from these two other sources. The work plan must address investigation of the impacts from these other potential sources on groundwater quality. The work plan proposes to update the computer simulation of the groundwater extraction system to incorporate recent data, evaluate higher pumping rates and include domestic well pumping in the Fairoaks Road area. An update of the groundwater model is needed because the groundwater extraction system is not capturing the downgradient portion of the chloroform plume as planned. The 15 May 1997 report on the groundwater extraction system effectiveness stated that computer simulations showed the existing extraction system would reverse the groundwater gradient in the Fairoaks Road area in approximately one year. The 5 November 1997 report stated that a reversal of the groundwater gradient at well MW-7 would not occur until after the year 2000, although an approximate date is not presented. Using an analytical model, I have simulated the size of the capture zone created by the existing extraction system and estimated the duration of time needed to capture contamination in the area of well MW-7 to be approximately 20 years. Given that the initial estimate of the pumping time needed to capture the contamination in the Fairoaks Road area was one year, the current estimate of sometime after four years is unacceptable and the groundwater extraction system need to be modified. The proposed work plan for updating of the computer model for the groundwater extraction system is approved provided that: 1) computer simulation results shall show the capture zone for each simulation and the duration of time needed to develop the capture zone; 2) the existing groundwater extraction system shall be simulated to determine the duration of pumping needed to capture groundwater in the Fairoaks Road area; 3) a modified groundwater extraction system shall be designed and simulated which captures contaminated groundwater in the Fairoaks Road area within one year of the beginning of