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HomeMy WebLinkAboutMOUNT MCKINLEY VIEW ESTATES Proposed Sewage Disposal DEPT. OF ENVIRONMENTAL CONSERVATION J~ine 28, 1973. WILLIAM A. EGAN, GOV£R~IOI~ / POUCH 0 -- JUNEAU 99801 Mr. Rolf Strickland Chief Sanatarian Dept. of Environmental Quality Greater Anchorage Area Borough 3330 "C" Street A~ichorage, Alaska 99503 SUBJECT: Mt. McKinley View Estates Dear Mr. Strickland: We have reviewed the soils and topographic information which you submitted to this office and have held discussions with Mr. R. Rutherford, Consulting Geologist, who prepared the soils and topographic study. We have the following con~ents: (i) Based on the report covering the proposed sewage disposal facilities in the Mt. McKinley View Sub- division it appears that if the constraints followed in the report are met and careful location is done in the manner proposed by the report, that septic tanks and lea~hing systems could possibly work in this subdivision. (2) Because of the topography and soil conditions which exist in the subdivision no further subdivision should be allowed until the area is served by public sewer or until a method is proposed that does not require the use of leaching sy~%ems for effluent disposal. (3) We are not familiar enough with the water supply situation in this area to comment regarding the possibility of obtaining a sufficient supply for domestic use. This should be very carefully weighed in any consideration of the subdivision. Also it will be most necessary that all wells in the area extend into bedrock and that proper grouting be done at the soil rock interface to insure that water is being drawn from the rock itself and is not receiving ground seepage. In summary I would say that our concerns are basically that the waste disposal and water supply systems be located in accordance with the provisions set out in the report and that it be determined that sufficient water is available for domestic use in the subdivision. Also all wells in the area Mr. Strickland -2- June 28, 1973. should be developed carefully to insure that contamination does nto occurr from the ground water seepage from the soil cover. Also no further sub- division should take place in this particular project until public sewer or another means of waste disposal is available. This review is based on the subdivision as presented to this office and we have no knowledge of the conditions which might exist adjacent to this particular project. These of course should be weighed carefully in the review of th~s sub- division. Yours truly,~ GREATER ANCHORAGE AR~A ~PT, ~ ~Y{~gNMENTAL QUALITy June 4, 1973 Greater Anchorage Area Borough Department of Environmental Quali'by and Planning pepartment Anchorage, Alaska ATTN: A~r. Allen Sheen and 1V[r. I~oi~ Strickland Re: Proposed Sewage Disposal Facili~Ties ~or Lots in the Proposed A~cli[nley View Subdivision Gentlemem The follo~ving is intended to describe approximately rather than design specL-- ~ically a system o~_ se~,~zage disposal that will v;ork ~or sirk%ie family units in Alt. ]?IcKinley View Subdivision as presently proposed. Soil conditions are des- cribed by the accompanying report o~ A{ay 20, 1973. Basica]J.y the system would involve one or more deep (36" or more) and long (up to 100') absorption trenches in serial distr{but{on coupled xvi'~h a two part septic tank and a dos;~g siphon chamber. These components together wi~h care[ul site selection a~nd design ~ill tend to disperse the e~luent quic]dy and in light dosages over a large area. The capacity o~ the system, o~ course, be dependent upon the specific needs o~ the individual and in accordance with Borough regulations. Specifically, trenches should not be placed on hillsides reaching grades gf greater than 50% as recommended by Pubi{c Health Serv5ce publication 326. Suggested locations for absorption ~ieids included in the soils report Jot subdivision never exceed 40% and are more commo~.y 30/0. Vegetation is hearty on all slopes and erosion should not be a problem. Trenches should be level (£ollo~.ving contours) and should be as long as is feasible so that maximum hill- slope area is utilized. Trench bottoms should be kept four £eek above bedrock and should have a minimum of 12 inches of clean gravel (~."--255") below the drain tiles or per~orated drain pipe to discourage root cloggingo. In areas where the soil contains large fractions of material finer than sand, trench and gravel fH! depths shot~ld be increased. The drain tiles or pipes should be at least three feet below the ground surface or, if not, insulation should he added to insure t}?.t seasonal frost does not penetrate ~he gravel fill. When more 'khan one trench is used in a system the trenches sho~d be connected serially. That is. t'n~ dov,,nh]ll trench will not be usedun~'~.u the upniil trench has become satur- Greater Anchorage Area Borough June4~ 1973 Page 2 ated to the top of the gravel fill (usually 2" above drain tile or pipe). A mini- mum of six feet should be allowed between trenches and the distance between top of gravel fill and the sloping ground surface should never be less than two feet. The septic tank (s) should have two compartments for settlement and a to contain a dosing or Miller siphon. Although discharges from single family dwellings should be small enqugb so that a dosing siphon would not normally be needed, the dosing siphon will provide better distribution of the effluent over the entire length(s) of the trench(es). Furthermore, -the interval between dosages oE effluent will allow oxygen to recirculate in the soil, thus encouraging anaerobic bacteria and oxidation reactions to work. The double, septic tank w ill insure that sludge and scum passing into the drainage field w~].l be held to a minimura, thus increasin~ the effective li~e of the field. The septic tanks themselves should have provision for adequate inlets and outlets, baffles and ven~s in accordance with GA_AB regulations and recommendations of the Public Health Service. The depth of soil to bedrock is shown in the accompanying soil report. In gen- eral, the soil is of good quality and should require no more than 125 square feet of wall area per bedroom. The bedrock varies in depth {-rom 3 to.13 feet. In all cases absorbing fields can be located where soils are eight feet or more deep. With a system as described, it is considered by experts in the field that effluent can be successfully absorbed without concentrating along the bedrock/ soil interface. The recommendations of the Public }{ealth Service in their Manual of Septic Tap& Practice have been followed closely in pr6posing this system. Discussions with A'!r. Ky!e Cherry, sanitary engineer for the State of Alaska, and with Mr. Sid Clark of tBomhoff and Associates have also been valuable. In construction~ economics, maintehance, and most important, in successful operation, this system offers the best alternative to disposal of sewage for the propmsed Mt. ?,Ickdnley View Subdivision.