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HomeMy WebLinkAboutFETROW S-11752Fetrow 5-11752 November 15, 2009 Municipality of Anchorage Building Safety Division On Site Water and Wastewater Program 4700 Elmore Street Anchorage, AK 99507 Attention: Debbie Wockenfuss Su~e~: Fetmw Subdivision Replat, S-11752 Water Availability Study Dear Debbie: We have collected information on several wells in the area of the proposed Fetrow Subdivision to estimate the possible depths and production rates of wells to be constructed in the future on Lots 2 and 3. Field investigations indicate the presence of bedrock at shallow depths on both lots. Typically wells constructed in bedrock have Iow production rates and may be very deep. Very little information is available on the existing well on proposed Lot 2. A flow test was completed in 1985 which indicated a production rate of .4 gallons per minute. This computes to a daily production rate of 576 gallons per day which exceeds the requirements for a three bedroom home, but falls short for a four bedroom home. The well was completed to a depth of 252' and cased to bedrock at a depth of 36'. The static water level was found at 22' below the surface. The well on Lot 1, Fetrow Subdivision is 100' deep with casing to bedrock at 20'. The well log indicates a production rate of 1 gallon per minute. A flow test completed in 1984 indicates a production rate in excess of .5 gallons per minute. The static water level in this well was measured at 40' below the surface. The area surrounding Fetrow Subdivision is mostly undeveloped with large lots. Wyatt Subdivision to the south is virtually vacant with the exception of Lot 2. A well is located on Lot 1, but no information could be found concerning the well. Fetrow Subdivision November 15, 2009 Page 2 It is obvious from our study that any wells to be constructed on Lots 2 and 3 in the future will be placed in bedrock. The depth of the wells will probably exceed 200' and require casing to 20' to 40'. The production rates will be Iow and probably less than 1 gallon per minute. Water storage may be required to provide sufficient water to meet minimum requirements for a four bedroom home. Sincerely, Michael E. Anderson, P.E. Attachments November 15, 2009 Municipality of Anchorage Building Safety Division On Site Water and Wastewater Program 4700 Elmore Street Anchorage, AK 99507 Attention: Debbie Wockenfuss Su~e~: Fetrow Subdivision Replat, S-11752 Septic System Feasibility Study Dear Debbie: The owners of Tract A, Fetrow Subdivision intend to subdivide the tract into two lots. Lot 2 will be served by an existing well and septic system until such time that a new home is constructed or the existing septic system fails. Lot 3 will be served by a new well and septic system. A new driveway will be constructed off of the Old Glenn Highway to serve Lot 3. The driveway along with the proposed and existing septic system absorption areas are shown on the attached site plan. The proposed and existing wells are also shown. The subdivision is located immediately adjacent to the Old Glenn Highway near Birchwood. The surface of the lots slopes steeply from the highway up toward Lot 2. This slope exceeds 25% preventing the placement of absorption systems within 50' of the top of the slope. The ground surface then slopes gently at a 2% to 3% grade across Lot 2 toward Lot 3 then steepens upward at the southern boundary of Lot 2. The steep upward slope does not impact the location of the absorption beds on Lot 3. Test holes were placed on the proposed lots in June of 2009. 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 15.5' where possible and to bedrock refusal in other areas. The locations of the test holes were determined in the field and placed in areas which would be most beneficial for septic system construction in the future. Percolation benches were constructed at various depths in the holes, but primarily 2' to 3' below the original ground surface. A percolation cavity was prepared to determine the absorptive Fetrow Subdivision November 15, 2009 Page 2 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 poorly graded gravel (GP) with sand was encountered above the bedrock layer. The majority of the material will pass the Number 4 sieve indicating no sand liner is required. The percolation rate in this material ranged from 1.2 to 4.6 minutes per inch. All work was completed under the direction of technicians and engineers at Anderson Engineering. The results of the pemolation tests and test hole logs are included as well as the water monitoring results. ^ monitor tube remains in place in each hole to determine the groundwater elevation over a period of time. Readings of the groundwater levels were completed on October 15, 2009. No water was found in any of the holes with only a minor presence in Test Hole No. 6. The presence of water in this hole may be attributable to heavy surface runoff as readings were taken al[er a period of very heavy rain. The presence of bedrock, will not allow the use of conventional gravity flow septic systems on Lot 3. We therefore required the use of the Category 3 Nitrate Reducing septic systems like the Advantex Treatment System. in addition, any home to be constructed on Lot 3 will be limited to four (4) bedrooms through a plat note. An application rate of 4 gallons per day per bedroom was utilized to design the absorption beds. ^ total of 150 square feet is required for a four bedroom home. We have doubled the size to 300 square feet for each absorption bed. The beds will be constructed a minimum of 6' above the bedrock level or approximately 1' above the existing ground level. Coarse sand will be required to elevate the beds to meet Municipal design criteria. Bedrock was found 6.5' to 15.5' below the surface on Lot 2. Three new absorption trenches were designed around Test Hole No. 6 which has bedrock at 13.5' below the surface. The existing absorption trench on the lot was designed for a three bedroom home and is currently operating in accordance with the original design requirements. The new absorption trenches were designed for a four (4) bedroom home with an application rate of 1.2 gallons per day per square foot. They are 50' long by 3' wide with an effective depth of 6'. The total depth of the trenches is 7.5' which places the bottom of the trenches 4' above the water table recorded on October 15, 2009 and bedrock at 13.5'. They are located more than 50' from any break in grade greater than 25%. Based on our field study and water monitoring completed to date it appears Lots 2 and 3 of the proposed Fetrow Subdivision are capable of supporting an onsite septic system and well. The size of the homes to be constructed on the lots must be limited to four (4) bedrooms. Copies of the test hole logs, percolation tests, test hole location map and the contour map showing the surface topography of the property are included for your use. The Fetrow Subdivision November t5, 2009 Page 2 most recent water monitoring results completed on October 15, 2009 have been added to the test hole logs. In addition, the design of the proposed absorption systems for each lot is included with this submittal. Please let me know if you have further questions. Sincerely, Michael E. Anderson, P.E. Attachments MUNICIPALITY OF ANCHORAGE DEVELOPMENT SERVICES DEPARTMENT l+700 ELMORE ROAD ANCHORAGE, AK 99519-6(>50 SOILS LOG - PERCOLATION TEST LEGAL DESCRIPTION: PERFORMED FOR: DATE: 6/20/09 PARCEL ID#: DEPTH (feet) OG/OL I 2 3 4 5 TRACT A, FETROW SUBDIVISION MARGARET AND LESLIE FETROW 6 TEST HOLE # 8 9 POORLY GRADED GRAVEL w/BOULDERS GP 20 BEDROCK @ 6' PROJECT No.: TECHNICIAN: A. HARALA SLOPE Z SITE PLAN SEE SITE PLAN WAS GROUND WATER ENCOUNTERED? NO IF YES ~ WHAT DEPTH?.__ ~ DEPTHOFWATERAFTERMONiTORING: NONE l SEE SITE PLAN DATE OF MONITORING:. 10/15/09 DEPTH TO WATER NET DROP DATE READING 3ROSS TIME NET TIME (MINUTES) (MINUTES) (INCHES) (INCHES) 6/20 TEST HOLE PRESOAKED PRIOR TO TESTING: 1 12:02/12:12 10 2.13/10.2: 8.12 2 12:13/12:23 10 .625/9.5 8.25 3 12:24/12:34 10 .75/9.5 8.12 4 12:35/12:45 10 .75/9.5 8.0 5 12:46/12:56 10 .75/9.5 8.06 6 12:57/1:07 10 .75/9.5 8.0 PERCOLATION RATE: 1.2 (MIN/INCH) PERC. HOLE DIA. 6 (INCHES) TEST RUN BETWEEN: 2 FT. and 3 FT. COMIVlENTS: TEST HOLE PRE SOAKED PRIOR TO TEST. TEST PERFORMED BY VETECH ENGINEERING TECHNICAL SERVICE. I, MICHAEL E. ANDERSON CERTIFY THAT THIS WAS PERFORMED IN ACCORDANCE WITH ALL STATE AND MUNICIPLE GUIDELINES 1N EFFECT ON THIS DATE: MUNICIPALITY OF ANCHORAGE DEVELOPMENT SERVICES DEPARTMENT /-*700 ELMORE ROAD ANCHORAGE, AK 99519-6650 SOILS LOG- PERCOLATION TEST ] LEGAL DESCRIPTION: TRACT A, FETROW SUBDIVISION PERFORMED FOR: MARGARET AND LESLIE FETROW DATE: 6/20/09 PROJECT No.: TECHNICIAN: DEPTH (foot) 1 2 3 4 5 6 7-- 8-- 9-- PARCEL ID/*: OG/OL TEST HOLE# 2 [ POORLY GRADED GRAVEL w/BOULDERS GP BEDROCK @ 5' A. HARALA SLOPE WAS OROLr/qD WATER ENCOUNTERED? NO DATE 6/2l 0 SITE PLAN SEE SITE PLAN SEE SITE PLAN I DEPTH TO GROSS TIMEINET TIME NET DROF READING (MINUTES) [ (MINUTES)(INCHEs)WATER (INCHES) TEST HOLE PRESOAKED PRIOR TO TESTING: 1 8:53/9:03 10 .75/7.88 7.13 2 9:04/9:14 10 1.00/8.06 7.06 3 9:15/9:25 10 .88/7.94 7.06 4 9:26/9:36 10 1.00/8.00 7.00 5 9:37/9:47 10 .75/7.75 7.00 6 9:48/9:58 10 1.13/8.07 6.94 PERCOLATION RATE: 1.4 (MrN/rNcu) PERC. HOLE DIA, 9 TEST RUN BETWEEN: 2 FT. and 3 FT. __.(INCHES): COMMENTS: TEST HOLE PRE SOAKED PRIOR TO TEST. TEST PERFORMED BY VETECH ENGINEERING TECHNICAL SERVICE. I, MICHAEL E. ANDERSON CERTIFY THAT THIS WAS PERFORMED IN ACCORDANCE WITH ALL STATE AND MUNICIPLE GUIDELINES IN EFFECT ON TH/S DATE MUNICIPALITY OF ANCHORAGE DEVELOPMENT SERVICES DEPARTMENT Z~700 ELMORE ROAD ANCHORAGE, AK 99519-6650 SOILS LOG - PERCOLATION TEST LEGAL DESCRIPTION: TRACT A, FETR0W SUBDIVISION PEI~ORMED FOR: MARGARET AND LESLIE FETROW DATE: 6/20/09 PARCEL 1Y)#: DEPTH 3 (feet) 1 2 3 4 5 6 7 8 9 PROJECT No.: TECHNICIAN: A. HARALA I TEST HOLE # 0G/0L POORLY GRADED GRAVEL w/BOULDERS GP BEDROCK @ 5.5' SLOPE SITE PLAN SEE SITE PLAN WAS GROUND WATER ENCOUNTERED? NO IF YES ~ WHAT DEPTH? ~ DEPTHOFWATERAFTERMONiTORING: NONE I SEE SITF PLAN DATE OF MONiTOPSNG:. 10/15/09 DEPTH TO DATE READING GROSS TINE!NET TINE WATER NET DROF (MINUTES) (MINUTES) (INCHES) (INCHES) 6/20 TEST HOLE PRESOAKED PRIOR TO TESTING: 1 10:15/10:25 10 1.25/7.50 6.25 2 10:26/10:36 10 1.00/7.13 6.13 3 10:37/I0:47 10 1.13/7.13 6.00 4 10:48/10:58 I0 1.25/7.25 6.00 5 10:59/11:09 10 1.25/7.31 6.06 6 11:10/11:20 10 1.13/7.13 6.00 PERCOLATION RATE: 1.7.(MINANCH) PERC. HOLE DIA. 8 .(INCHES) TEST RUN BETWEEN: 2 FT. and 3 FT. COMMENTS: TEST HOLE PRE SOAKED PRIOR TO TEST. TEST PERFORMED BY VETECH ENGINEERING TECHNICAL SERVICE. I, MICHAEL E. ANDERSON CERTIFY THAT THIS WAS PERFORMED 1N ACCORDANCE WITH ALL STATE AND MUNICIPLE GUIDELINES IN EFFECT ON THIS DATE MUNICIPALITY OF ANCHORAGE DEVELOPMENT SERVICES DEPARTMENT Z~700 ELMORE ROAD ANCHORAGE, AK 99519-6650 SOILS LOG - PERCOLATION'TEST DEPTH (feet) 2 LEGAL DESCRIPTION: PERFORMED FOR: DATE: 6/20/09 PARCEL ID#: 3 4 5 TRACT A, FETROW SUBDIVISION MARGARET AND LESLIE FETROW PROJECT No.: TECHNICIAN: TEST HOLE# 4 ] 0G/0L 20- ML POORLY GRADED GRAVEL w/BOULDERS GP BEDROCK @ 8.5' A. HARALA SLOPE SITE PLAN SEE SITE PLAN WAS GROUND WATER ENCOUNTERED? NO DEPTHOFWATEKAFTERMONrrOR1NG: NONE SEE SITE PLAN DATE OF MONITORING:. [0/[5/09 DATE READ NG GSOSS TIM. E ,NET TIME DwE~,~RTO NET DRO. F t. MINUTES) I(MINUTES) I (INCHES) I (INCHES) 6/20 TEST HOLE PRESOAKED PRIOR TO TESTING: 1 1:34/1:44 lO .38/7.88 7.50 2 1:45/1:55 I0 .50/8.00 7.50 3 1:56/2:06 10 .38/7.75 7.38 4 2:07/2:17 10 .25/7.50 7.25 5 2:18/2:28 10 ·38/7.63 7.25 ~ 6 2:29/2:39 10 .50/7.75 7.25 PERCOLATION RATE: 1.4 .(MIN/INCH) PERC. HOLE DIA. 9 .(INCHES) TEST RUN BETWEEN: 3 FT. and 4 FT. COMMENTS: TEST HOLE PRE SOAKED PRIOR TO TEST. TEST PERFORMED BY VETECH ENGINEERING TECHNICAL SERVICE. I, MICHAEL E. ANDERSON CERTIFY THAT THIS WAS PERFORMED iN ACCORDANCE WITH ALL STATE AND MUNICIPLE GUIDELINES iN EFFECT ON THIS DATE.'. MUNICIPALITY OF ANCHORAGE DEVELOPMENT SERVICES DEPARTMENT l+700 ELMORE ROAD ANCHORAGE, AK 99519-6650 SOILS LOG - PERCOLATION TEST ] TRACT A, FETROW SUBDIVISION MARGARET AND LESLIE FETROW DEPTH (f~) 1 2-- 4 7 8 20 LEGAL DESCRIPTION: PERFORMED FOR: DATE: 6/20/09 PARCEL ID#: PROJECT No.: TECHNICIAN: I TESTHOLE# 5 [ OG/OL POORLY GRADED GRAVEL w/BOULDERS GP BEDROCK @ 15.5' A, HARALA SLOPE SITE PLAN SEE SITE PLAN WAS GROUND WATER ENCO~? NO DEPTHOFWATERAFTERMONITORING: NONE SEE SITE PLAN DATE READING GR, OSS TIH. E ,NET TIME DWE/~R~0 NET DRQP [MINUTES) I[MINUTES) I (INCHES) (INCHES) 6/20 TEST HOLE PRESOAKED PRIOR TO TESTING: 1 3:02/3:12 10 1.13/7.63 6.50 2 3:13/3:23 10 1.00/7.38 6.38 3 3:24/3:34 10 1.06/7.56 6.50 4 3:35/3:45 10 1.25/6.69 6.44 5 3:46/3:56 10 1.13/7.50 6.38 ~ 6 3:57/4:07 10 1.00/7.38 6.38 PERCOLATION RATE: 1.6 (M~CH) PERC. HOLEDIA. 8 (INCHES) TEST RUN BETWEEN: 4 FT. and 5 FT. COMMENTS: TEST HOLE PRE SOAKED PRIOR TO TEST. TEST PERFORMED BY VETECH ENGINEERING TECHNICAL SERVICE. I, MICHAEL E. ANDERSON CERTIFY THAT THIS WAS PERFORMED IN ACCORDANCE WITH ALL STATE AND MLrNICIPLE GUIDELINES 1N EFFECT ON THIS DATE: MUNICIPALITY OF ANCHORAGE DEVELOPHENT SERVICES DEPARTHENT /+700 ELHORE ROAD ANCHORAGE, AK 99519-6650 SOILS LOG - PERCOLATION TEST LEGAL DESCRIPTION: PERFORMED FOR: DATE: 6/20/09 PARCEL ID#: DEPTH (feet) OG/OL 1 2 4 5 7 8 20 TRACT A, FETROW SUBDIVISION iViARGARET AND LESLIE FETROW PROJECT No.: TECHNICIAN: SILTY GRAVEL W/CLEAN GRAVEL LENSES GH BEDROCK @ 15.5' A. HARALA SLOPE SITE PLAN SEE SITE PLAN WAS GROUND WATER ENCOUNTERED? NO DEF~-IOFWATERAFTERMO~TrOIGNG; [I,5' SEE SITE PLAN DEPTH TO DATE READING GROSS TIHE NET TIHE WATER NET DROP (HINUTES) (HINUTES) (INCHES) (INCHES) 6/20 TEST HOLE PRESOAKED PRIOR TO TESTING: 1 6:45 3.50 2 7:15 30 10.12 6.62 3 7:17 3.38 4 7:47 30 9.94 6.56 5 7:50 3.25 6 8:20 30 9.75 6.50 PERCOLATION RATE: 4.6 (MIN/rNCH) PERC. HOLE DIA. 9 TEST RUN BETWEEN: 3 FT. and 4 FT. (INCHES) COMMENTS: TEST HOLE PRE SOAKED PRIOR TO TEST. TEST PERFORMED BY VETECH ENGINEERING TECHNICAL SERVICE. I, MICHAEL E. ANDERSON CERTIFY THAT THIS WAS PERFORMED IN ACCORDANCE WITH ALL STATE AND MUNICIPLE GUIDELINES 1N EFFECT ON THIS DATE: LOT 2, FETROW SUBDIVISION DESIGN FACTORS: SYSTEM REQUIREMENTS: Four Bedroom Home DeepTrench System Perc. Rate: .1-5 Min./Inch Existing '1,000 Gallon Septic Tank Application Rate: 1.2 GPD/SF 9' Drainfield Rock 4 Bedrooms X 150 GPD/'1.2 GPD/SF (Application Rate) = 500 SF Absorption Area 500 SF/'10 SF/LF = 50 LF Trench Length THEREFORE: Construct a 50' Long x 3' Wide x 6' Effective Depth Absorption Trenches at the Location Shown. Flow Line Elevation in Trench to be '1.5' Below Original Ground Surface. Total Depth to be 7.5' Below Existing Ground. Provide 4' Cover Over Septic Tank and 3' Cover Over Absorption Trench. Maintain '100' Separation from Wells in the Area. Natural Backfill \© Gectextile Fabric 4" Perforated PVC (Holes Down) Drainfield Rock r TYPICAL DEEP TRENCH SECTION -- -- NOTE: Grade Area Over Trench to Drain Away. Minimum 6' Separation From Bed~k. ~,,,,,J......4~......~.2~...~...~ Minimum 4' Separation From Groundwater. ~,~~ Minimum 100' Separation From Wells in the Area. ~'"~;;~'~'~'~?~ Minimum 100' Separation From Su~ce Water or Streams' ~ LOT 3, FETROW SUBDIVISION DESIGN FACTORS: SYSTEM REQUIREMENTS: 4 Bedroom Home Raised Bed System Perc. Rate: 1-5 Min./Inch 4 Bedroom Advantex Treatment System Application Rate: 4 GPD/SF 500 Gallon Add On Lift Station Raised Bed Absorption System 4 Bedrooms X 150 GPD/4 GPD/SF = 150 SF Absorption Area 150 SF/15 SF (Width) = 10 LF Bed Length THEREFORE: Construct an Oversized Raised Bed 20' Long x 15' Wide as Shown Below. Place Bottom of Bed 1 Above Original Ground Surface. Remove Organics and Fill and Place Coarse Sand to Provide 6' Separation From,Bedrock., Place Insulation and 2' of Cover Over Bed or Mound Over Bed Minimum of 3. Place 4 of Fill Over Tank. Existing Ground 1' or As Require( Top 6" of Mound Must Be Topsoiled and Vegetated to Prevent Erosion. Natural Bacldill 2" Insulation & 2' Cover ('Min.) / / / / / / / / /~ 4 O O O ~ Drainfleld Rock ~ 1,j",~P~ ,C -- 3/16" Holes ..... ~ 10 Each Lateral Coarse Sand (See Specification) As Required for Levelling Existing Ground And Replacement of Fill and Organics. In Situ SWSoil 2.5' 5.0' 5.0' 2.5 NOTE: TYPICAL BED SECTION (NO SCALE) Grade Area Surrounding Bed to Drain Away. Minimum 6' Separation From Bedrock. Minimum 4' Separation From Groundwater. Minimum 100' Separation From Wells in the Area. Minimum 100' Separation From Surface Water or Streams. Minimum 10' Separation From Water Service Line. OLD GLENN HIGHWAY PLAT NO. 85-33 FETROW SUBDIVISION TRACT A LOT 3 65,919 S.F. 1.51 ACRES ® LOT 2 2 2. 02,983 S.F. .~ oPM 2.36 ACRES NOTE: Three Septic Sites on Lots 2 end 3. House Size Limited to Four (4) Bedrooms on Both Lots. Septic Sites on Lot .3 ere 15' x 20' Roised Beds with Categor~ 3 Nitrate Reducing Septic Sytems Due to Shallow Bedrock. No Driveways or Permanent Sructares May be Placed Over Septic Sites. 535.50' WELL & SEPTIC SYSTEM FEASIBILITY FETROW SUBDIVISION LOTS 2 & 3 ANDERSON ENGINEERING 800 E, DIMOND BLVD,. SUITE 3-540 ANCHORAGE', ALASKA 99515 907-522-7773