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Overall, the subsurface soil conditions, as identified in the test pit logs (see Appendix B), are generally <br /> homogeneous, comprised of medium sand with traces of finer grained materials and gravels at the elevation <br /> of the bottom of the basin. The predominance of the sand suggests suitable conditions for infiltration of <br /> treated wastewater. <br /> 3.2 Constant Head Test Results <br /> The first set of testing at each basin was constant head testing. As described above, the constant head <br /> testing entailed adding water to the basins at the same rate that water drained out of the basin. <br /> During the testing period, flow was measured with a 5-gallon bucket and a stopwatch. The valve used for <br /> flow control was adjusted as necessary to increase or decrease the flow. As a result, conversion from <br /> gallons per minute to gpd/sf showed some variation as a result of the:adjustments to the flow control valves <br /> in order to maintain a flow rate equivalent to the infiltration rate. This being considered, the infiltration rates <br /> from constant head tests remained generally consistent The raw data from, the constant head tests is <br /> presented in Table 2 and summarized in Table 3. The basins generally accepted a flow of 39 to 98 gpm. <br /> Using the lowest rate observed, 39 gpm as a conservative estimate of the loading rate, this equates to <br /> 56,160 gallons per day(gpd). The discharge of 56,160 gpd in a 107footdiameter basin(surface area 78.5 sq. <br /> ft.) equates to approximately 715 gpd/sf. <br /> USEPA protocols for conducting loading tests suggest that, although loading tests are probably the most <br /> accurate means of estimating loading rate, loading tests have a greater,horizontal flow component than full- <br /> scale installations; therefore, loading tests overestimate full-scale capacity, Therefore, USEPA recommends <br /> design rates that are only 10 to 15 1percent of observed rates in loading tests. The loading tests suggest an <br /> infiltration rate of approximately 715 gpd/sf, hence a design loading rate of up to 72 gpd/sf can be considered <br /> reasonable. MassDEP suggests a maximum design loading rate of 5 gpd/sf, but allows proponents to make <br /> a demonstration for a greater, loading rate through ,hydraulic loading tests and through longer-term <br /> operations. <br /> Therefore, based on the results of the constant head testing, a design loading rate of up to 72 gpd/sf would <br /> be considered, which is significantly higher than the MassDEP-recommended rate of 5 gpd/sf for rapid <br /> infiltration beds, which would appear to be very conservative for this site. <br /> 3.3 Falling Head Tests Results <br /> As an alternate methodology to the constant head test results, falling head tests were performed in each of <br /> the basins after the constant head tests were completed. Between the test runs, water was continuously <br /> added to the basins to retain'the saturated soil conditions. <br /> To complete the falling head tests, basins were filled to a specific measured mark. The water supply was <br /> then turned off and the rate at which the water level in the basin dropped was recorded. The falling head <br /> tests were repeated as many times as possible within an 8-hour day at each basin, with the basin being <br /> refilled at the beginning of each test run. The results of the falling head tests are presented in Tables 4 and <br /> 5. <br /> Infiltration rate is presented in three different units on the tables: minutes per inch, inches per hour, and <br /> gallons per day per square foot (gpd/sf). Infiltration rates in gpd/sf for all of the tests are summarized on <br /> 5 <br />