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Home My WebLink AboutMOSSFLOWER WOODS S12476Onsite File m wo Am� Ad� fl 4,ss ow r J Prepared for: 1�1►17If1C�7 Prepared By: Grant Mathews, P.E. 49TH •. • • • GRANT W. MATHEWS • • . ' �� •• CE 135444 ,•cv�® ®®�PROFESSIONP .� October 2020 Introduction The following report details the feasibility of the Mossflower Woods Subdivision to support on-site water and wastewater systems for residential single-family homes. The preliminary plat is attached with this report. The site is located in the Lower Hillside area of Anchorage Alaska, south of O'Malley Road and east of Elmore road. See below for a location map. Location Map The parcel is approximately 5 acres in size, zoned R6. Based on the zoning and current code, the parcel could be subdivided into a maximum of four lots. The site is bordered by Wild Iris Subdivision to the west, BLM lots to the north, Karella Subdivision to the east, and Homestead Hills Subdivision to the south. All of the surrounding lots are fully developed with residential single-family homes equipped with on-site water and wastewater systems. 1 Water Availability Data from the MOA On-site department indicates the production of existing wells in the area range from 5 to 15 GPM with an average rate of 9 GPM. The depth of wells ranges from 221 to 282 feet with an average static water level of 216 feet below ground surface. See below for a table of the well depths and production rates for the wells surrounding the subject parcel. Subdivision Lot Well Depth (ft) Static Water Level (BGS) Production (GPM) Wild Iris 4 226 195 10 Wild Iris 3 239 193 9 T12N R3W SEC 22 14 282 230 15 Karelia 20A I Unknown Unknown Unknown Karelia 20B 221 207 6 Karelia 20C 249 232 10 Karelia 20D 262 240 5 The Homestead Hills Subdivision is served by a community well which was not included with this analysis. Future wells for Mossflower Woods Subdivision are anticipated to have similar performance with an average anticipated depth of 225 feet and a production ranging from 5-10 GPM. Individual wells are anticipated to be adequate for the subject property if it is developed under the current zoning designation. The development of this subdivision is not anticipated to have any negative affect on the water availability of the surrounding subdivision or properties. Soils and Septic System Information Test holes were excavated on each of the proposed lots. Native sands and gravels with varying silt content were found throughout the site. Soils logs are attached with this report. Percolation testing was performed for each lot. See below for a table showing the percolation results. Lot Perc Rate Testing Depth (BGS) 1 3 min/inch 4-5 ft 2 <1 min/inch 4-5 ft 3 <1 min/inch 4-5 ft 4 2 min/inch 4-5 ft All lots are suitable for conventional on-site wastewater disposal systems. Development of the individual lots will require an engineered plan for well and septic locations that will be reviewed and approved by MOA On-site to ensure that the septic tanks and absorption fields are placed outside of the existing and proposed well radii. Nitrate Analysis No existing wells within 250 feet of the proposed subdivision have known nitrate levels exceeding 10 mg/I. V There are wells in the surrounding area with known nitrate levels exceeding 5 mg/I, however the wells with higher levels of contamination were drilled 40 -50 years ago and may have grout failure or may not have been properly installed with bentonite at the time of drilling, which can result in surface water contamination. Wild Iris Subdivision, immediately west of the subject property is most representative of the proposed development and has minimal nitrate contamination with less than 2 mg/l. Drainage The soils within the area are well-suited to infiltrate runoff and the large lot -sizes stipulated by the R6 zoning helps to ensure that the ratio of impervious area to vegetated area remains low. An engineered grading and drainage plan has been approved by MOA Private Development as part of the Subdivision Agreement process. Drainage generated by this development is handled on-site and is not anticipated to have any negative affects to neighboring properties Conclusion The subject property and the associated preliminary plat is well-suited for on-site water and wastewater systems. Well and septic information from the immediate vicinity of the parcel indicate that aquifer production is adequate for single family homes; the soils are well -draining and will support septic systems. A final soils report including test holes, percolation testing, and detailed recommendations will be provided prior to final plat approval. 3 DATA FROM SURROUNDING PROPERTIES TAKEN FROM MOA ON SITE DOCUMENTS AND HAS NOT BEEN VERIFIED FOR ACCURACY MOSSFLOWER WOODS SUBDIVISION LOT # DEPTH TO GW PERC RATE LOT 1 NGWE 3 MIN/INCH LOT 2 NGWE <1 MIN/INCH LOT 3 NGWE <1 MIN/INCH LOT 4 NGWE 2 MIN/INCH GRAPHIC SCALE 40 0 20 40 80 160 ( IN FEET j 1 inch = 40 ft. LAND LLC I \ IIRIS WILDIVI111 SUBDSION , 1 135'2 TO EX KU ---4— H - 239 ELLH=239 FT TER LEVEL (BGS) = 193 FT j N=9GPM .r. .ED 2004 / \ :VELS = UNKNOWN ) 3 111 1 1 I 1 I - PC EX 18" CMP CULVERT 'I 111 ' 1 i _ IU I ill i . • .'� 1 WELL DEPTH = 226 STATIC WATER LEVEL WELL DEPTH = UNKOWN PRODUCTIONDRIED 10 G i31 WE 1 NITRATE LEVELS = C 1 I C71. 604 TO PRODUCTION = 6 GPM a t I11; I WELL DRILLED 1964 I 300'+ TO EX WELL ON LOT 14 EX WELL RADIUS (7YP) \ V 418.59 \\ ----- — 1\ -------r WELL DEPTH = UNKOWN a - STATIC WATER LEVEL (BGS) = 215 FT I C71. 604 TO PRODUCTION = 6 GPM EXWELL ! / WELL DRILLED 1964 I fx = — / NITRATE LEVELS = 5.3 MG/L W «a As RECORD DRAWING 1. DATA PROVIDED 20A \ j BY: This _ ` ` ------- '� �- �-'� �, I will serve to erlify a 11,11 these Beco d Ora«Inq area true and accurate - ' -_---- - �- - — represenlotion of Na project 1a constructed. 407. 99 I coNTBACTDR: i WELL DEPTH = 221 FT nnE:_DATL j STATIC WATER LEVEL (BGS) = 207 FT 2. DATA TRANSFERRED 2OB PRODUCTION = 6 GPM BY: WELL DRILLED 2014 COl1PANY: 1 NITRATE LEVELS = 4.47 MG/L DATE I 280'2 TO EX I 1 I ',�- 3. DATA TRANSFER CHECKED Bosea 1n periltlic Dela m- WELL % t L _I er by the Engineer y the i / I i I w^imNd (or d.v under hia/ her direct supervision), the Contractor -provided data LA /t \,K R � oppearoq c�ep—ent the protect lruelad. 1 ^i IQr/ VISION 1\1_..�__3 !// 1 BY: COMPANY: 40246-------- f Ii WELL DRILLED 1979 !Y/p III NITRATE LEVELS = 7. 1 1 I270'2 TO EX WELL -'--- �r I I1 ----- 416.83 \1 — ` 7\ Y ' ` I I I 270'1 TO EX mu 1 1 1 1 _ 1 r WELL DEPTH = 262 F1 1\ I STATIC WATER LEVEL J\ I PRODUCTION = 5 GPM 1 WELL DRILLED 1977 \ r- \` NITRATE LEVELS = 5.4 425.91- --- /—EiDITCH _— HOMESTEAI) HILLS - —t SUBDIVISION Subdivision Agreement Number 19-012 6T: N `n M Z LLJ O Z WiU)J 30 n" wt�'� NC9 Ca CG V] I—Q V) V) N Q �� Cn Z� 0 Municipality of Anchorage Development Services Department On -Site Water and Wastewater Section 4700 Elmore St. P.O. Box 196650 Anchorage, AK 99519-6650 WW.MLini.or /oq nsite F (907)343-7904 Soils Log ® Percolation Fest Performed For: LAND LCC Legal Description: MOSSFLOWER WOODS, LOT 1 1- 2- 3- 4- 5- 6- 7- 8- 9- 10- 11- 12- 13- 14- 15- 16- 17- 18- 19- 20- 5VkzR(.E 09'raANtC5 (,0a16 PooRv� C.fut e,D CiaAV6"L Q Wq.X Ct s GJZAV tL 51VT- (Mt. i• Date Performed: Township, Range, Section: WAS GROUND WATER Date ENCOUNTERED? NO Net Time Depth to Water s IF YES, AT WHAT DEPTH? L Depth to Water After o P Monitoring? NGWE E FA 49TH ••� A W. 61A EWS••• CE 135444 ,•��2` 10-17-20 Site Plan SEE ATTACHED SITE PLAN Date: 10-19-20 1 ohgXZ, o /JonC 'r -o, G/7 Reading Date Gross Time Net Time Depth to Water Net Drop 10-17-20 --- 0 MIN 42" --- 5 MIN 5 MIN 43.75" 1.75" 5 MIN 10 MIN 45.5" 3.5 5 MIN 15 MIN 47.5 5.5" PERCOLATION RATE :i (minutes/inch) PERC HOLE DIAMETER 6" TEST RUN BETWEEN 4 FT AND 5 FT COMMENTS HOLE WAS PRESOAKED PRIG TO TESTING. PER(; RFAnIN(,S ARF IA/ITHIN 1/a" PERFORMED BY: TRIAD ENGINEERING, LLC I GRANT MATHEWS, PE CERTIFY THAT THIS TEST WAS PERFORMED IN ACCORDANCE WITH ALLSTATE AND MUNICIPAL GUIDELINES IN EFFECT ON THIS DATE. DATE: 10-19-20 Municipality of Anchorage Q Development Services Department On -Site Water and Wastewater Section 4700 Elmore St. P.O. Box 196650 Anchorage, AK 99519-6650 www.muni.org/onsite (907) 343-7904 Soils Log - Pelrco8ati®n Fest Performed For: LAND LCC Legal Description: MOSSFLOWER WOODS, LOT 2 1- 2- 3- 4- 5- 6- 7- 8- 9- 10- 11- 12- 13- 14- 15- 16- 17- 18- 19- 20 - WLFPa OIZf&AN%CS �o�) IL" SANG (SM� POow LADED 611p, 1, WI S E Stx� Co%'btES r"a 6 _ E OF A�gs��4� >k 49 TE . ........ GR T S THEW �C E 1 95444 44�tjw�PROFESSIONP�m � Date Performed: 10-17-20 Township, Range, Section: Site Plan SEE ATTACHED SITE PLAN WAS GROUND WATER ENCOUNTERED? NO S IF YES, AT WHAT DEPTH? L Depth to Water Aker P Monitoring? NGWE E Date: 10-19-20 Reading Date Gross Time Net Time Depth to Water Net Drop 10-17-20 0 MIN 42" --- 5 MIN 5 MIN 48" 6" PERCOLATION RATE <1 (minutes/inch) PERC HOLE DIAMETER 6" TEST RUN BETWEEN 4 FT AND 5 FT COMMENTS HOLE WAS PRESOAKED FRIO TO TESTING. PERC READINGS ARE WITHIN 1/4" PERFORMED BY: TRIAD ENGINEERING, LLC I GRANT MATHEWS, PE CERTIFY THAT THIS TEST WAS PERFORMED IN ACCORDANCE WITH ALLSTATE AND MUNICIPAL GUIDELINES IN EFFECT ON THIS DATE. DATE: 10-19-20 Municipality of Anchorage Development Services Department On -Site Water and Wastewater Section 0 4700 Elmore St. P.O. Box 196650 Anchorage, AK 99519-6650 www.muni.org/onsite (907) 343-7904 Soils Log - Percolation Test Performed For: Legal Description 1- 2- 3- 4- 5- 6- 7- 8- 9- 10- 11- 12- 13- 14- 15- 16- 17- 18- 19- 20 - LAND LCC MOSSFLOWER WOODS, LOT 3 5 Lkgr- CE ox-IA0105 (O k ) 5IiIN SRW) (5"� CtF_� VDaLLN amee 5A0 (sp) tv) CoMu:s Date Performed: Township, Range, Section: WAS GROUND WATER ENCOUNTERED? NO s 50%0 IF YES, AT WHAT DEPTH? L Depth to Water After o P Monitoring? NGWE E Date: 10-19-20 101-7 q 12 n A�gs��o 9TH 9! ..:.r T THEWS ... . 'A9Fc CE 113p354444nn @I�de ��Rt)FESSIO�`�.oG"o.� 10-17-20 Site Plan SEE ATTACHED SITE PLAN Reading Date Gross Time Net Time Depth to Water Net Drop 10-17-20 --- 0 MIN 48" --- 5 MIN 5 MIN 60" 12" PERCOLATION RATE <1 (minutes/inch) PERC HOLE DIAMETER 6" TEST RUN BETWEEN 4 FT AND 5 FT COMMENTS HOLE WAS PRESOAKED FRIO TO TESTING PFRc RFAnINGS ARF IAnTHIN 11A" PERFORMED BY: TRIAD ENGINEERING, LLC I GRANT MATHEWS, PE CERTIFY THAT THIS TEST WAS PERFORMED IN ACCORDANCE WITH ALL STATE AND MUNICIPAL GUIDELINES IN EFFECT ON THIS DATE. DATE: 10-19-20 Municipality of Anchorage Development Services Department On -Site Water and Wastewater Section 4U*j700 Elmore St. P.O. Box 196650 Anchorage, AK 99519-6650 www.muni.org/onsite (907)343-7904 Soils Log - Percolation Test Performed For: LAND LCC Legal Description: MOSSFLOWER WOODS, LOT 4 1- 2- 3- 4- 5- 6- 7- 8- 9- 10- 11- 12- 13- 14- 15- 16- 17- 18- 19- 20 - �u .E 09ap'N"C5 (0� S11.N SAO (5M) &AVIF, w1 5A�D 5 Stli CSP- C-tM� C'IkP*L Ftp ;D 3" 50µi CoB>;+O Date Performed: Township, Range, Section: WAS GROUND WATER ENCOUNTERED? NO s 30vk IF YES, AT WHAT DEPTH? L Depth to Water After P Monitoring? NGWE E Date: 10-19-20 I I 1 /0/10 /2-0 AJ,,i, OF A4 -\A4 Z. v NTYl'. ' THEWS • CE 135444 FE 10 10-17-20 Site Plan SEE ATTACHED SITE PLAN Reading Date Gross Time Net Time Depth to Water Net Drop 10-17-20 --- 0 MIN 50" --- 5 MIN 5 MIN 52.25" 2.25" 5 MIN 10 MIN 56.5" 6,5° 5 MIN 15 MIN 59.5" 9.5" PERCOLATION RATE 2 (minutestinch) PERC HOLE DIAMETER 6" TEST RUN BETWEEN 4 FT AND 5 FT COMMENTS HOLE WAS PRESOAKED PRIO TO TESTING. PERC READINGS ARE WITHIN 1/4" PERFORMED BY: TRIAD ENGINEERING, LLC I GRANT MATHEWS, PE CERTIFY THAT THIS TEST WAS PERFORMED IN ACCORDANCE WITH ALLSTATE AND MUNICIPAL GUIDELINES IN EFFECT ON THIS DATE. DATE: 10-19-20