06-28-1999 Council Packet - Laserfiche WebLink

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?RCM MCE?*:vli •w* • • • • A A A • • • • •r iC:-5 ?T. 1E:-5 NC. : Clustered Collector Systems If on*sitc options arc used with clustered development the cost pictiire changes. In this situation the individual residents share in the costs of collectmg and delivering the raw sewage or septic tank effluent to a central area for final treatment and dispersal. In the current LCNIR Alternative Sewage Treatment Systems Project two cluster systems were built, one using sewage treatment trenches and the other using a constructed wetland system. The per household cost for the installation of the collector sewer, individual septic tanks and controls to deliver the effluent to the final treatment system were $4,100 for the Lake Washington site and $6,300 for Grand Lake. In both cases the actual costs exceeded initial estimates of $3,000 to S3,500 for this part of the project. When retrofitting it should be assumed that there will be problems of tlie types encountered at these locations. A reasonable range in estimated costs for this type oi clustering activity would be 53.000 to 57,000 per household. In terms of the cost of on-site alterratives for the final treatment systems there arc some economies of scale to be gained in terms of treatment unit sizing and operation, maintenance and monitoring costs. The total cost per household at the Lake Washington and Grand Lake were 58.235 and SI I, 377 respectively. For clustered systems that serve JO-20 residences and estimated flows up to 15.000 gpd a reasonable estimate of per household costs would be to add the collector sewer coste to tlie low end to middle of the alternative treatment unit costs (lablc 2). Total costs w'cre determined by adding the average collector sewer cost to the midpoint of the installation cost to the midpoint of tlie annual operation cost multiplied by 20 years. Tabic 2. Clustered on-site sewage Treatment costs per residence Collector Sewer with on-site Treatment option Annual Operation/ Total Costs 1 Design and Installation Ma in tena nce/Repa ir Soil 7 rcatmcni Trenches $7,000 to S8,000 5200 to $400 $18,500 Soil Treatment Mounds Alternative On-Site $10,000 to $14,000 5300 to S500 525,000 Constructed Wetland (subsurface discharge)S8.000 to $16,000 $300 to 5500 $25,000 Constructed W'ctland (surface discharge)$7,000 to $16,000 51,000 to $1500 $41,500 Sand or Peat filter (subsurface discharge)$10,000 to 516,000 5500 to 51,000 $33,000 Drip Irrigation 511,000 to $16,000 $500 to $1,000 $33,500 Spray Irrigation Si 1,000 to 518,000 51,000 to SI,500 $44,500 Aerobic Tank (package plant)58,000 to $14,000 51250 to 53000 $58,500 Above nows of 15,000 to 20,000 Ballons per day sand filters and spray itiigation bejin to have sipiCcant cost advantages over the other on-silc alternatives and eontpete well with costs associated with waste stab.hzation ponds.