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25 <br /> MMO& michael m. hughes, p.e. <br /> Civil Engineers <br /> In conclusion,the single large field for the entire community negates these challenges and is most <br /> appropriate because of how it fulfils, and is in harmony with,the overall site design and <br /> community goals. <br /> 2) What are the risks of failure? <br /> The risk of failure for any of the alternatives is measureable without appropriate monitoring and <br /> maintenance. The advantage to the single larger system for the entire community is that not only <br /> will it be required by State permit to be monitored monthly by a certified operator,but also the <br /> liquid dosing of the array of fields is sequenced by an automated control system minimizing the <br /> risk of failure, and evenly distributing the septic tank filtered waste water over the entire disposal <br /> area. This is not the case with individual systems. The larger system for the entire community will <br /> by design have an overall lower risk of failure for these reasons. <br /> 3) How would repair areas be managed? <br /> Drawing on the challenges discussed in the first question for individual or clustered systems,the <br /> repair areas are much more difficult to arrange and access for these systems. The footprint of the <br /> community out of necessity would have to be larger with either individual or clustered systems <br /> with the primary and repair septic areas much more proximal to the homes. <br /> In contrast the repair area of the large community based system is much easier to access with <br /> piping and effluent distribution systems and, as a result, less costly. With individual or clustered <br /> systems,the maintenance (pumping) is not overseen by a licensed operator and they are more <br /> likely to need repair sooner than the community system. When they fail the process of repairing <br /> the individual systems is much more invasive and problematic for the community. The centralized <br /> solution in this instance negates these challenges. <br /> 4) Which is less expensive? <br /> The capital cost of the community system is expensive inasmuch as it all needs to be constructed <br /> upfront, and because of the State regulatory requirement to be monitored monthly by a certified <br /> operator, it is more expensive to operate. However, because of economies of scale,the cost per <br /> individual household is less for the larger community system taking into account of the aggregate <br /> costs of individual tanks and fields, and the additional piping and land area required because of the <br /> need to expand the footprint of the community for the individual or community systems. <br /> We hope that this clarifies the considerations in the design of the waste water system for Harts Mill, <br /> please feel free to call or e-mail if additional information or clarification is required <br /> Ver/yy truly yours, <br /> l U � <br /> Michael M. Hughes,PE <br /> 8112 Orange Grove Road Chapel Hill,NC 27516 (919)270-6462 <br />