Loading...
HomeMy WebLinkAboutCONIFER HEIGHTS Geology & Soil Conditions' Otll r' 5, ions applied e=r h sc snces Engineering Geology. Mining · Geophysics · Groundwater · Pe~'oleum June 16, 1971 Hewitt V. Lounsbury & Associates 723 West Sixth. Avenue Anchorage, Alaska 99501 ATTENTION: Ma:. Bud Herschbach Re: Geology and Soil Conditions of Conifer Heights Subdivision Gentlemen: Submitted herewith is our report presenting the findings of a geological and soil investigation of Conifer Heights Subdivision. We have enjoyed conducting this study for you. Please call if you have any questions or comments regarding the report. Very truly yours, HJM:js Attachment ALASKA GEOLOGICAL CONSULTANTS · H. J. Moening 2227 SPENARD ROAD ., ANCHORAGE, ALASKA 99503 Telephone: 277-7601 277-7602 GEOLOGY AND SOIL CONDITIONS OF CONIFER HEIGHTS SUBDIVISION REPORT TO HEWITT V. LOUNSBURY & ASSOCIATES ANCHORAGE, ALASKA PRE PARED BY ALASKA GEOLOGICAL CONSULTANTS ANCHORAGE, ALASKA JUN~ 1971 INTRODUCTION Conifer Heights Subdivision is a new residential area being planned without the benefits of public sewer and water utilities. Each lot owner will therefore provide for on-site sewage disposal facilities as well as a potable water supply. The source of water will be from drilled, cased individual wells. Sewage disposal facilities will con- sist of conventional septic tanks draining into either seepage pits or drain fields or a combination of the systems. This report describes the geology, soil conditions and topography of the area as these factors govern the layout and design for on-site sewage disposal facilities. IIqVESTIGATION The investigation reported here consisted of a review of available geologic data pertaining to the site followed by a field reconnaissance and subsurface exploration. Subsurface stratigraphy and geologic soil conditions were defined by six test borings located to provide maximum data. The borings, located as shown on the enclosed drawing (Figure 1), were drilled with a Mobile B-40 rig mounted on a tracked carrier. The borings, which ranged in depth from 15 to 23. 5 feet were advanced with solid flight auger. Soil types and insitu conditions were carefully observed by the supervising engineering geologist. ENGINEERING GEOLOGY Conifer Heights, consisting of slightly more than sixty acres, is situated in the lower slopes of the Chugach Mountains east of Abbott Road. Lot sizes are generous ranging generally from 3/4 acres to 1½ acres in size. Geologically the site is located upon a lateral moraine deposited along the margin of glacial ice of the Pre-Wisconsin, Knik glaciation. The topography is typical'of a lateral moraine with linear ridges -1- paralleling the direction of movement of the former glacier. Water flowin, g along the ' ice edges has formed ice-margin channels which generally parallel the trend of the moraine. Knob and kettle topography is another dominant feature of the moraine. The kettles, consisting of small closed depressions, do not contain water in this subdiviSiom In the nearby vicinity, however, they contain lakes such as Lake Hideaway and other. small ponds. Occasionally the kettles may contain swampy debris, but more often they are unfilled, which indicates moderate to good subsurface drainage in the bulk of the morainal soils. Surface drainage, except for the closed kettle depressions on the south and east border of the subdivision, is excellent. The water table was not encountered in any of the test borings and the soils were generally only slightly damp which furth er substantiates .the good surface and sub- surface drainage. SUBSURFACE SOILS AND CONDITIONS Specific types and depths of subsurface~soils encountered in the test borings at the site are shown on the enclosed boring logs. The soils consist of glacial till of & lateral moraine origin. As is typical of glacial till, the material is heterogeneous, varying from the classical nonsorted mixture of boulders, cobbles, gravel, sand, and silt to silty gravel, sandy gravel, and gravelly sand. Boring No. 6 encountered a thick stratum of clean sand which exhibited excellent water sorting by glacial meltwater. These sorted materials were found randomly oriented thrcmghout the subdivision. The soils throughout the subdivision were found to be of dense consistency thus assuring excellent bearing strength for structures in the proposed development. CONCLUSIONS AND RECOMMENDATIONS On the basis of information developed in this investigation,! we conclude that the soil conditions are excellent for the proposed development. W,e further conclude that the topography and percolation qualities of the soil are ideally suited tO on-site sewage' disposal utilizing seepage pits or drainfiel'ds in combination with septi~ tankS, Seepage ~' area requirements for individual systems will var~f from as low as 14t5 square feet per bedroom to as much as(269 ~quare feet per bedroom,' based upon calculations made on, selected sites throughout the subdivision. We recommend that'.care should be taken in laying out the sewage disposal system so that drainage is not in the direction of the water well. We conclude that the lot sizes proposed are more than ample for this type of development. The glacial granular soils are moderately permeable and non-homogeneous because of intermittent water sorting. An overall average ,seepage requirement for the area will be of the order of 208 square feet per bedroom. We recommend that each lot owner should arrange to have the soil tested on his property to define the seepage area requirement fda: that site. Respect/ully submitted, ALASKA. GEOLOGICAL CONSULTANTS H. J. Moem. Neil H. Twelker LOg OF' BORING NO. CONIFER HEIGHTS SUBDIVISION TYPE BORING: Auger LOCATION: See Plat >o :~m:~a' SOIL DESCRIPTION ~ / SUR. ELEV.,: Approximatel~ ~,!2' , ~Organics (topsoil) GM S[i~ sandy ~avels (225 sq. ft. per bedroom) GP Sandy ~avel with minor amounts of s[l~ to (190 sq. ft. per bedroom) -10 - GM S~I~ ~andy ~avel~ (225 sq. fh per bedroom) -15 - _ ......... -20 - Seepage area required based upon a 12' pit wt~ 2' cover [~ ~ ~quare fee~ per bedroom ~MPLETION DEPTH: 15.5' DEPTH T~"WATER:, Nowater DATE: ,lune 10, 1971 DATE: NATIONAL SOIL SERVICES &I. ASKA GEOLO{31CAL CONSULTANTS CONSULTIN~ ENGINEERS CONSUl.TING (~EOL,O~tST8 LOG OF BORING NO. 2 CONIFER HEIGHTS SUBDIVISION. TYPE BORING: Auger LDC, ATION: See Hat SOIL DESCRIPTION SUR. ELEy.: Approximately 757' Silty sand with gravels (250'~Sq. ft. per bedroom) Seepage area required based upon a 12' deep pit is 250 square feet per bedroom COMPLETION DEPTH: 19. 5' DEPTH TO WATER: DATE: une 10, 1971 DATE: .A'nONAL SO~ SE"VInES , CONSULTING ENGINEERS No water ALASKA GEOLOGICAL CONSULTANTS CON~JLTIN~ 8EOLO~IST8 LOG OF BORING NO. CONIFER HEIGHTS SUBDIVISION TYPE BORING: Auger ,, LOCATION: See Plat I-~ -J ~ ~ O _j mr,- o::O co o. SOIL DESCRIPTION \ / SUR. ELEV.: At)vroxtmatelv 776' Organics (t°ps,,o. fl.) ........... ML Sand silts with gravels (275 sq. fro per bedroom) 5- SM Sandy 'slit with i. ncrease in sand and gravela ~ to (265 sq. ft. per bedroom) ML _~ _ SP F~ne sand with pebbles and gravels (150 sq. ft. per bedroom) SM ..xS[lty sand'with gravel.q '(250 ~q. fl:. 'per' bedroom) -20 - ' ......... Seepage area required based upon a 12' deep pit wtth 2' of cover ta 209~square feel: per bedroom © COMPLETION DEPTH: 19.0' DEPTH TO WATER: No water DATE: Junel0i, 1971 , , DATE: NATIONAL SOIL SERVICES ALASKA GEOLOGICALCONSULT$~ITS CONSULTIN~ ENGINEERS CON~tJLTIN~ GEOLO(tlST8 LOG OF BORING NO. CONIFER HEIGHTS SUBDIVISION TYPE E~RING: Auger LOCATION: See Plat I-: _j L~ ~m u-o L~ 0 _J ~ ~ SOIL DESCRIPTION >o u~l \ / SUR. ELEV. '. Approximately Organics (topsoil) GM Sandy gravel to gravelly sand with some stlt I' 5 -to (175 sq. ft. per bedroom) SW . -10 - GM Silty gravelly sand to stlty sandy gravol - 15 - (225 sq. ft. per bedroom) I -20 I ....... Seepage area required based upon a 12' pit with a 2' cover ts 180 square feet per bedroom 0 COMPLETION DEPTH: 20. 0' DEPTH TO WATER: No water ,DATE: June 10, 1971 DATE: NATIONAL SOIL SERVICES ALASKA GEOLOGICAL CONSULTANTS CONSULTING ENGINEERS CONSUl.TING GEOLOGIST8 LOG OF BORING NO. 5 CONIFER HEIGHTS SUBDIVISION TYPE BORING: Auger LOCATION: See Plat I-.2 _j L~J n-u.i u.. m° " o ' ~ ~§ o ~-~ . ~ >° __.~. F-~ ~,~ :~c° ;Eh SOil DESCRIPTION ~ / SU ~ ' I ELEV.: 845' mm ,,, Organics (topsoil) SP Gravelly sand with minor amounts of slits $- to (200 sqo ft., per bedroom) SM -10- . . GP Sandy gravel wtth cobbles (125 sq, fl:, per bedroorr ) .: -15 .... - 20- ' ' Seepage area required based upon a 12' deep pit with 2' of cover ts 189 square feel: per bedroom · ~. .. © COMPLETION DEPTH: 15. 0' DEPTH TO WATER: No water DATE: June 10, 1971 DATE NATIONAL SOIL SERVICES ~I..ASKA GEOLOGICAL CONSULTANTS CONSULTING ENGINEERS ~',ONSUL.TING GEOLOGISTS LOG OF BORING NO. 6 CONIFER HEIGHTS SUBDIVISION TYPE 8ORING: Auger LOCATION: See Plat I-J -J uJ r,'tU "O ~ _x.,Organics (topsoil) .... GP Sand gravel with slits (125 sq. ft. per bedroom) SP Medium grain sand with occasional gravels (150 sq. fro per bedroom) -20 - GW Gravelly sand to sandy gravel (I00' ~q. ft, per to bedroom) SW -N , Seepage area required based upon a 12' deep pit with 2' of cover is i46 square feel: per bedroom. © COMPLETION DEPTH: 23.'5' DEPTH TO' WATER:' No water .... DATE: June 10, 1971 , DATE,: NATIONAL SOIL SERVICES AI. ASKA GEOLOGICAL CONSULTANTS CONSULTING ENGINEERS CONSULTING GEOLOGIST8