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1 <br /> Southland/Stockton 16 <br /> March 1991 <br />' MONITORING WELL AND DOMESTIC WELL MONITORING AND SAMPLING <br />' A monitoring well and domestic well monitoring and sampling program is proposed as shown on <br /> Figure 6, Site Closure Decision Tree This program consists of the collection of groundwater data for a <br />' specdied period of time, the evaluation of this data and then either a continuation of the existing <br /> program, or a reduction or increase in sampling frequency <br />' Because of the impact of the reported analytical results on future activities, the infrequency of <br /> the sampling and the possibility for false positive indications, Groundwater Technology is recommending <br />' that a confirmation sampling round be performed whenever analytical results report concentrations <br /> significantly greater than recent concentration trends The confirmation round would consist of returning <br />' to the site to collect another water sample from the well in question for repeat analysis Confirmation <br /> would be conducted when the following situations occur <br />' • When recent trends are less than 10 ppb of TPH-as-gasoline, a confirmation sample will <br />'0 <br /> be run when results are greater than 25 ppb of TPH-as-gasoline <br /> • When recent trends are greater than 10 ppb of TPH-as-gasoline, a confirmation sample <br /> will be run when either, (1) results are double or more the trend, or (2) when results <br /> exceed the historic high for that particular well <br /> t <br /> The monitoring wells are currently on a quarterly sampling and monitoring schedule <br />' Groundwater Technology proposes to continue the quarterly frequency to complete one-year of <br /> quarterly sampling April 1991 As shown on the Site Closure Decision Tree (Figure 6), the data <br /> will be evaluated at that time and if it is confirmed that concentrations have not exceeded the <br /> data trends, then the frequency will be reduced to bi-annual (twice per year) The bi-annual sampling <br /> will continue until drinking water standards have not been exceeded for the samples from the site wells <br /> for two consecutive sampling events Upon the completion of one year of biannual sampling, during <br /> which it has been confirmed that the drinking water standards have not been exceeded, compliance with <br />' the clean-up will have been achieved and mondoring well activity will cease Conversely, if it is <br /> confirmed that drinking water standards have been exceeded, then the sampling and monitoring <br />' program will continue If concentrations are apparently increasing (i e, two events with consecutively <br /> increasing concentrations reported) at any time during the program, then the frequency reverts to a <br />' quarterly schedule for evaluating the need for reactivation of the hydraulic control system <br /> k GROUNDWATER <br /> TECHNOLOGY, INC <br />