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Home My WebLink AboutSNOWBIRD S-11932Snowbird 511932 ANDERSON ENGINEERING P.O. BOX 240773 ANCHORAGE, AK 99524 522-7773 677-7766 (FAX) November 6, 2012 Municipality of Anchorage Building Safety Division On Site Water and Wastewater Program 4700 Elmore Street Anchorage, AK 99507 Attention: Debbie Wockenfuss Subject: Snowbird Subdivision - S11932 Septic System Feasibility Study Dear Debbie: The owner of BLM Lot 102 intends to subdivide the tract into two lots. The two lots front Mount McKinley View Avenue in Birchwood. The new subdivision will be known as Snowbird Subdivision. Lot 102A is currently under development and a well and septic system has recently been constructed. The permits were issued on the entire lot, but construction was limited to the confines of Lot 102A. The ground surface of the lots is virtually flat from Mount McKinley View Avenue to approximately 150' south where the surface slopes upward at a grade approximating 35% to 40%. A note will be added to the plat stating "All Septic Systems Placed on Slopes >25% must be Category Ill Nitrate Reducing Systems." The cross slope on the property is slightly to the west at less than 5%. The absorption system on Lot 101A is placed parallel with the contours of the ground at locations where the slope is the shallowest. Test holes were placed on the proposed lots in April of 2012. Water monitoring has been ongoing with readings last taken on May 15, 2012. At that time both test holes were dry. The purpose of the test holes was to assess the underlying soil conditions and to determine whether septic systems could be placed on the lots to serve single- family homes. The test holes were placed to depths of 13' with no bedrock or impermeable lenses of material encountered. The locations of the test holes were determined in the field for use in the future for developing septic systems. Percolation benches were constructed at various depths in the holes~ but primarily 3.5' to 4.5' below the original ground surface. A percolation cavity was prepared to determine the absorptive characteristics of the soils encountered. The cavity was presoaked in accordance with Municipal requirements and a percolation test performed. The results of the tests are included in the attached documentation. In every case silty gravel (GM) with varying degrees of sand was encountered to the bottom of each test hole. The percolation rate in this material ranged from 2 to 3 minutes per inch. Snowbird Subdivision November 6, 2012 Page 2 All work was completed under the directiOn of technicians and engineers at Anderson Engineering. The results of the percolation tests and test hole logs are included as well as the water monitoring results. No groundwater was found in either test hole and none has been detected during the monitoring period. The new absorption trench on Lot 102A was designed and constructed for a three (3) bedroom home with an application rate of 1.2 gallons per day per square foot. The trench is 38' long by 5' wide with an effective depth of 4'. The alternate site for Lot 102A is an Advantex Treatment System with a 15' long by 5' wide by 4' effective depth absorption trench. Both systems are shown on the attached drawing. A 10,000 square foot reserve area has been designated for Lot 102B. As mentioned earlier a portion of the reserve area contains positive slopes with grades of up to 40%. Based on our field study and water monitoring completed to date it appears both lots of the proposed subdivision are capable of supporting an onsite septic system and well. A note will be required on the plat limiting the type of system constructed on the slope in the reserve area on Lot 102B. We hereby request your approval of the subdivision as designed with the septic systems and reserve area at the locations shown. Sincerely, Michael E. Anderson, P.E. Attachments \ / WELL / = \ / -- \ / 38',~nq x 5' Wide I ~OT 102e ~.4 Ef~ct~, O~pth NOTE: 10' ~., ,. ~-,,, ..:~ SITE PLAN A700 MUNICIPALITY OF ANCHORAGE DEVELOPMENT SERVICES DEPARTMENT BRAGAW STREET ANCHORAGE, AK 99519-6650 LEGAL DESCRIPTION: PERFORMED FOR: DATE: z+/15/201Z PARCEL ID#: DEPTH (feet) 0B/OG 1 2 3 4 5 -- SILTY GRAVEL WITH SAND 6-- GM 7-- 8-- 9-- SOILS LOG - PERCOLATION TEST ELM LOT 102 11 20 BOH @ 15' TROY DAVIS HOMES, INC. PROIECT No.: TECHNICIAN: [TEST HOLE 1 ] MEA SLOPE No DATE OF MONITORING: 5/15/2012 E SITE PLAN · THZ THI 2% DEPTH TO DATE READING GROSS TINE NET TINE WATER NET DROF (MINUTES) (MINUTES) (INCHES) (INCHES) TEST HOLE PRESOAKED PRIOR TO TESTING: 4/5 1 12:14 1.63" 2 12:24 10 5.87" 4.24" ' 3 12:25 1.50" 4 12:35 10 5.50" 4.00" 5 12:36 1.75" 6 12:46 10 5.75" 4.00" PERCOLATION RATE: 2.5 (MIN/INCH) PERC. HOLE DIA. 6" (INCHES) TEST RUN BETWEEN: 3.5 FT. and 4.5 FT. COMMENTS: TeST HOLE PRE SOAKED PRIOR TO TEST. TEST PERFORMED BY ANDERSON ENGINEERING. I, MICHAEL E. ANDERSON CERTLF~ THAT THIS WAS PERFORMED IN ACCORDANCE WITH ALL STATE AND MUNICIPLE GUIDELINES IN EFFECT ON THIS DATE: 10/26/Z012 A700 DEPTH (feet) 1 2 3 4 5 6 7 8 9 11 MUNICIPALITY OF ANCHORAGE DEVELOPMENT SERVICES DEPARTMENT BRAGAW STREET ANCHORAGE, AK 99519-6650 LEGAL DESCRIPTION: PERFORMED FOR: DATE: Z+/15/2012 PARCEL ID#: SOILS LOG - PERCOLATION TEST BLM LOT 102 OB/OG SILTY GRAVEL WITH SAND GM BOH @ 13' TROY DAVIS HOMES. INC. PROJECT No.: TECHNICIAN: SLOPE SITE PLAN · TH2 · THI WAS GROUND WATER ENCOUNTERED? NO IF YES ~ WHAT DEPI~q?.__ ~ DEPTH OF WATER AFTER MONITORING: NONE 20/0 DATE OF MONITORING: 5/15/2012 ~ ~ DEPTH TO DATE READING SROSS TIME NET TIHE WATER NET DROP (MINUTES) (MINUTES) (INCHES) (INCHES) TEST HOLE PRESOAKED PRIOR TO TESTING: 4/5 1 12:18 .75" 2 12:28 10 4.25" 3.50" 3 12:29 .87" 4 12:39 10 4.37" 3.50" 5 12:40 .75" 6 12:50 10 4.25" 3.50" PERCOLATION RATE: 2.8 (MIN/INCH) PERC. HOLE DIA. 6" .(rNCn~S) TEST RUN BETWEEN: 3.5 FT. and 4.5 FT. COMMENTS: TEST HOLE PRE SOAKED PRIOR TO TEST. TEST PERFORMED BY ANDERSON ENGINEERING. I, MICHAEL E. ANDERSON CERTIFY THAT THIS WAS PERFORMED IN ACCORDANCE WITH ALL STATE AND MUNICIPLE GUIDELINES IN EFFECT ON THIS DATE:_ 10/25/2012 ANDERSON ENGINEERING P.O. BOX 240773 ANCHORAGE, AK 99524 522-7773 677-7766 (FAX) November 5, 2012 Municipality of Anchorage Building Safety Division On Site Water and Wastewater Program 4700 EImore Street Anchorage, AK 99507 Attention: Debbie Wockenfuss Subject: Snowbird Subdivision, S-11932 Water Availability Study Dear Debbie: We have collected information on several wells in the area of the proposed Snowbird Subdivision to estimate the possible depths and production rates of wells to be constructed in the future on Lot 102B. The well on Lot 102A has already been constructed and is in production. Our research indicates all wells are constructed in sand and gravel formations without the presence of bedrock. The wells are cased the entire depth and range in depth from 102' to 163'. The most accurate information was obtained from the well only recently constructed on Lot 102A. This well is located 230 east of the proposed well on Lot 102B The well is 124' deep with casing to 122'. Soil formations encountered during drilling include silty sand and gravel and some clay. The static water level was found at 69' and the production rate was determined to be 15 gallons per minute. Snowbird Subdivision November 5, 2012 Page 2 A breakdown of the wells in the area with their respective production rates follows: SNOWBIRD SUBDIVISION WATER AVAILABILITY STUDY WELL LEGAL DESCRIPTION I DEPTH PRODUCTION - LOG PRODUCTION - TEST BLM Lot 102A 124' 15 GPM BLM Lot 107 102' 20 GPM BLM Lot 116 112' 4GPM BLM Lot 76 I 170' 3 GPM 1.03 GPM BLM Lot 101 I Unknown 5.3 GPM It is obvious from our study that any well to be constructed on Lot 101B of Snowbird Subdivision in the future will be placed to a depth of less than 150' and will probably be constructed in silty sand and gravel. The production rates will be between 3 and 5 gallons per minute. Sincerely, Michael E. Anderson, P.E. Attachments