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Home My WebLink AboutJEM Lots 1-4 S-5412 DATE: ]V~unicipality o~ Anchorage MEMORANDUM ' October 9~ ~980 TO: Jerry Weaver F~OM: IIealth and Environmental Protection SUBJECT: Jem Subdivision - S-5412 This department finds soils in Lots 1 and 2 will support an on-site' septic system by designing~t~he ~system four (4) feet above the water table per bedroom as the soils rat~. Environmental Specialis ~ ~. ' .-~ ~,[i/ l q~ ~ ~ ... / MUNICIPALITY OF ANCHORAGE DEPARTMENT OF HEALTH & ENVIRONMENTAL PROTECTION ENVIRONMENTAL HEALTH CASE REVIEW WORK SHEET CASE NUMBER S-5412 DATE RECEIVED July 1, 1980 COMMENT TO PLANNING BY ~July 25, 1980 FOR MEETING OF PLATTING BOARD [~] PLANNING & ZONING NAME JEM Subdivision, Lots 1-4 CASE OF [] PUBLIC WATER NOT AVAILABLE TO PETITION AREA E~ PUBLIC SEWER NOT AVAILABLE TO PETITION AREA REVIEWER'S COMMENTS: 71 014 (Rev. 2/78) 825 "L" STREET ANCHORAGE, ALASKA 99501 (907) 264-4111 GEORGE M, SULLIVAN, MAYOR · ' DEPARTMENT OF HEALTH AND ENVIRONMENTAL PROTECTION BARNARD ENGINEERING ' 203 West 15th Avenue Anchorage, Alaska 99501 ~ Subject: S-5412: Jem Subdivision gs This department has reviewed the soils information on the above subject and finds there is a water table at the 12, 11, and 9 foot levels.~ -~ ~ reconm~endation for the developer is to test the soils within the area of the proposed sewer system and monitor the water table for approxJ.mately three(3) months. The developer should propose a design of an on-site sewer system that can support Lot 3. If there are any further questions, pl~ease department at 264-4720. Sincerely, /~,~f/~ John W. Lynn~}~ Environmental Specialist BARNARD ~EERING ENERGY /~UblICI PLAN ~ MACHINE ~ ~ -~r. o~ ~,~.~,,~o,,~ ~ MATERIAL ~,AL ;:'iOTECTION E~ DESIGN F-~ CONSTRUCTION [] RESOURCE DEV~P. iMgNi~0 BARNARD ERING [] DESIGN 203 WEST 15TH AVENUE T ENERGY PLAN ~ MACHINE · M^TERi^L PRODUCT CONSTRUCTION [] RESOURCE DEVELOPMENT · ANCHORAGE, ALASKA 99~0! · TE~.~i~_h~-~?~ ENVIRONMENfAL ,:,J TECT~ON GROUND WATER DIVERSION DAM AU6 1 8 1980 FOR HILLSIDE ABSORPTION SYSTEMS RECEIVED Introduction: The area located southeast of Anchorage and commonly known as "hillside" depends totally on on-site sewage dis- posal systems. Most of the area has slopes which vary from near flat to as much as twenty-five percent. The average slopes are in the range of ten to fifteen percent. Soil conditions vary throughout the area. Areas which have ground water conditions present special problems in the operation of an on-site sewage disposal system. The soil profile for areas with ground water conditions typically include a top strata of glacial till (GM) underlain by a strata of sandy gravel (GW) and then a strata of glacial till (GM). The glacial till is basically impervious while the sandy gravel is pervious. Ground water conditions on the hillside develop when water percolates through and along the bottom of the gravel strata. The glacial till underlying the gravel acts as a container or barrier to the water. Actually the water migrates downhill in a thin sheet along, the top surface of the lower strata of glacial till. The amount of water varies seasonally from no flow to relatively high flow. Therefore, the design, construction and operation of hillside absorption systems is something less than a positive procedure. The exceptions or positive situations where ground water is not encountered include the areas with uniform glacial till and gravel strata which are located at a drainage apex. That is, the glacial till has a very low percolation rate and the drainage apex simply circumvents the groundwater around the high point. In either of these cases, ground water is not a problem. Proposed Ground Water Diversion Dam: In warmer climates, curtain drains are utilized to free an absorption trench system of ground water by diverting the water away from the system area. The diverted water of necessity must be piped to the surface at some point. This procedure would be undesirable and unworkable in Alaska because of climatic conditions. The curtain drain concept has suggested the use of. a Ground Water Diversion Dam. Such a dam can easily be con- structed to divert ground water away from the absorption trench system area. First, a trench located somewhat parallel to the absorption trench and at a higher hydraulic elevation would be excavated. The trench depth would extend through the water-bearing gravel strata and into the underlying impervious glacial till. During excavation, the gravel strata would be carefully separated from the glacial till. The trench would then be backfilled with the impervious glacial till to form a barrier to ground water which would normally flow into the absorption system area. The attached diagram shows the details of the plan. After the diversion dam is completed, the ground water will percolate along the uphill side of the dam and around the ends of the absorption field to a point where the sheet of water will then flow down hill. Conclusion: A ground water diversion dam when properly constructed will protect an absorption trench system from the intrusion of ground water which percolates along a sloping strata of impervious soil. The dam will be simple to construct from the glacial till excavated from the diversion dam trench and the surplus till from the absorption trench after wash rock has been added. The gravel from the diversion trench can be utilized elsewhere on the site. Otherwise, the absorption system can be designed and constructed according to the same criteria as used in GW soils which are free of ground water. DATE: TO: FROM: SUBJECT: /Vtun c pahty Ancho£Zge MEMORANDUM September 4, 1980 Planning Department Health and Environmental Protection S-5412: Jem Subdivision This department has the following comments regarding the above case: (1) No objection to the diversion dam. (2) Sewer system must be installed four(4) ~.eet a~ov__ e the water table. ~ (3) Water table must be defined after diversion dam is in place and water level monitored for thirty(30) days. (4) Replacement sites must be shown. Robert C. Pratt, R.S. Acting Senior Environmental Specialist Rolf R. Strickland, R.S. Division Manager RCP/RRS/ljw 91-010 (5/78; ALASKA EFIUIROnMI FITAL conTi OL SERUICE $, IriC. I~n~ineerinq & I~nuironmcntal Studies / Dear Rr. Neredith: ~ On February 12, 1981 we made a soils test on your proposed i lot 3, JEM Subdivision. The hole is located about 30 Ft up ~ hill From test hole 2. A soils log is attached which shows soils to 9 Feet below ground level. As the material was a silty sandy gravel we attempted a percolation test. It was unsuccess- Ful as the water drained out before data could be taken. This verified that the silt content of the hale is lower than it appeared. The level From 4 to 9 ft below ground level should be acceptable For on-site sewer systems. At -9 Ft the maLeriaI chamges.to a. silt. IF possible this should be avoided. Because of the high permeability of the over laying soil compared to the silt below the on-site system should be placed well back From any roads to preclude out break of waters. If you have any questions please let me know. Sincerely, d President 1220 LUest 25th ,~uenue · ,~nchorage, Alaska 99503 · (907) ~7e:1351 MUNICIPALITY OF ANCHORAGE DEPARTMENT OF HEALTH AND ENVIRONMENTAL PROTECTION 825 L. Street, Anchorage, Alaska 99501 264-4720 SOILS LOG- PERCOLATION TEST PERCOLATION TEST PERFORMED FOR: LEGAL DESCRIPTION: DEPTH 2 3 4 5 6 7 8 9 10 11 12 13 14 15- 16- 17- 18- 19- 2O COMMENTS ~'-/J~ PERFORMED BY: WAS GROUND WATER ENCOUNTERED? IF YES, AT WHAT DEPTH? DATE PERFORMED= SLOPE SITE PLAN S L 0 Gross Net Depth to Net Reading Date Time Time Water Drop 1~ J-b-' ,~' ~ " PERCOLATION RATE minutes/inch) TEST RUN BETWEEN 2,,~,--FT AND ~' / FT ?,,,~ /,~,.,.,,~ ,~.4 ~d/ c/~,.~, ~'/-~'" /~K~,/ CERTIFIED BY: DATE: 72-008 (6/79) OG OF SOIL TYPE ~OHtNO:-- ~~o~ ~ 3 3 SOIL DESCRIPTION ~ SURFACE: ELEV. /~ ~llJli- Og ~/~ -I0- -I~- . ~5- SO- BARNARD-MARTH 8~ ASSOCIATES 15TH AVE.--ANCHORAGE ~i~E:d~z,Y ~.~/~,,~,~ LOG OF' SOIL TEST--': TYPE BoRiNG: ~-~ ~ ~~ LOCATION: ~ SOIL DEOCRIPTION ~ SURFACE: ELEV. /~ ~ -20- .25- .35, BARNARD--MARTH & ASSOCIATES--Z0:5 WEST I TH AVE.--ANC~'~-RAGE ~ ~ SOIL DESCRIPTION ~ SURFACE: ELEV. /~ ~ ~ 25- '30' 35- BARNARD--MARTH & ASSOCIA'I 15 AVE.--AN ~r"'.~ LOG OF sOtL'TES~:;"'~'/:'~'~ ~,,/ ' TYPE BORING~-~-~ ~ ~z~- LOCATION:-~ ~~- ' ' ~ 3 SOIL DESCRIPTION ~ SURFACE: ELEV. /~ ~ ~/. ~- BARNARD--MARTH & ASSOCIATES--203 WE5 15TH CHORAGE DATE:~_~ LOG OF SOIL TEST TYPE BORt~ ~;~ '-~: ~~ LOCATION: ~ SOIL DESCRIPTION SURFACE: ELEV. 5 I0- /..~ ~ - - ~0- ) ~5- ......................... BARNARD--MARTH 84 ASSOCIATES--';)C 5 WEST AVE.--ANCHORAGE DATE; ",~/")Z.,'Y''~ '~"~'.,/~'~'°LOG OF SOIL TEST ~Z'-oW,.~ - W'ZZ.~:,,vA .~,,~;_ _ .. TYPE BORING: ,,~"~.,.~'"~ ~gx'V/k'/~Z:~.'"~Z" LOCATION: ~ SOIL DESCRIPTION SURFACE: ELEV. /01~ 5- ~,~ I0 ~ /-' -20- - 25- ~0- ~5- BARNARD-MARTH 8~ ASSOCIATES--203 WE~T 15TN A~TE.--ZANCHORAGE ~ . ....................... : 'eAT E:-' ' L/Z~-~ ~'~:: --~.-.~,~ l~ :::::::::::::::::::::::::::::::::::::::::::::::::: TYPE BORING::~~'' :' '' .... ~ ~ SOIL DESCRIPTION ~ SURFACE: ELE~ ~.. // , ,35- BARNARD-MARTH 8~ ASSOCIATES--20:5 WEST I ? . (81-57)F0 ~//