HomeMy WebLinkAboutHORIZONS S12498Onsite File
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October 2, 2019
Municipality of Anchorage
Building Safety Division
On Site Water and Wastewater Program
4700 Elmore Street
Anchorage, AK 99507
Attention: Debbie Wockenfuss
Subject: Horizon Subdivision 512-99S
Septic System Feasibility Study
Dear Debbie:
The owner of the parcel identified as T15N R1 W Section 5, Lot 28 submitted a petition to
subdivide the property into two lots forming the new Horizon Subdivision. We have
completed a study of the proposed lots and have determined that each will support an onsite
septic system. The area is served by a community water system and each lot will be served
by the system. No wells in the area are in conflict with the locations of the proposed septic
systems.
The parcel is virtually flat and the areas proposed for septic systems slope slightly to the
west at grades of 0% to 10%. There are no areas within 50' of the proposed septic systems
which exceed slopes of 25%. Lot sizes are over 40,000 S.F. The attached site plan delineates
the areas specified for septic systems.
Test holes were placed on the proposed lots in April of 2019. The holes were placed in areas
deemed suitable for septic locations. Monitoring tubes were placed in the test holes and
groundwater checked periodically with the final reading on October 1, 2019. The test holes
were excavated from 14' to 14.5'. No groundwater was encountered in the test holes and
none has been noted since. We are confident no groundwater will accumulate when final
groundwater readings are taken in mid-October.
Soils were uniform in both test holes consisting of organic over burden from 2' to 3'
underlain by clean gravel frill depth of the holes. Percolation benches were constructed
between 2' and 3' below the ground surface in each test hole. The percolation cavity in each
bench was prepared and presoaked in accordance with municipal requirements. In both cases
water could not be contained in the percolation cavities and was fully absorbed into the
underlying strata in less than 10 seconds. The test results are included as attachments to
this study.
According to Table 7 of Municipal Code percolation rates between 1-5 minutes/inch require
10,000 SF of reserve area. This rate is appropriate for these lots even though the percolation
rates are less than 1 minute per inch. A reserve area of 10,000 square feet has been assigned
to each lot. In order to meet Municipal Code and adhere to design regulations a 2' M.O.A.
approved sand liner will be required for any septic system designed for the lots due to the
excessively fast percolation rate.
Our field studies, research, and water monitoring completed to date indicate that both lots of
the proposed subdivision are capable of supporting new onsite septic systems.
Sincerely,
L
Michael E. Anderson, P.E.
Attachments
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No. CE -4381
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Tl 5N R1 W SECTION 5 LOT 28
/
LOT 6 /
LOT 4
P R P (,) S E
10,000 9.F:
RESERVE'AREA
TH2
_ ENGINEERING
i
'113'
a
S il" 0 N
LOT 1
_ I
I
10,000 S.F.
RESERVE AREA
TH1
''•••i'tt
R/W PE ATENT/
J �
( ALDERLE�F COURT
O' TE:
PROPERTY IS SERVED BY A COMMUNITY WATER SYSTEM.
ALL WELLS ON SURROUNDING LOTS WITH IMPACTS TO THIS
PROPERTY ARE SHOWN. NO CONFLICTS WITH WELLS OR SEPTIC
SYSTEMS.
11 50 100
I= iim FEET
1
1
v
LEGEND
CO - CLEANOUT
2CO - DOUBLE CLEANOUT
FCO - FOUNDATION CLEANC
FS - FLOW SPLITTER VALVE
MH - MANHOLE
MT - MONITORING TUBE
SV - SEPTIC VENT
TH - TEST HOLE
SOILS LOG AND PERCOLATION TEST
ENG ! H E E R i N 6
LEGAL DESCRIPTION: T 15 N R I W SEC 5 L 2 8
PERFORMED FOR: LINDA FRANK
DATE: 4/18/19 PROJECT No.:
PARCEL ID#: 051-031-18 TECHNICIAN: J. MILLETTE
DEPTH TI I 1
(feet)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15-
16-
17-
18----1
5161718
19
20
COMMENTS:
SLOPE
GP (SANDY GRAVEL)
WAS GROUND WATER ENCOUNTERED? NO
IF YES '< WHAT DEPTH? -
DEPTH OF WATER AFTER N40NITORING: NONE
DATE OF MONITORING: 10/1/19—
LS
0/1/I9
L
P
E
DATE
READING
GROSS TIME
(MINUTES)
NET TIME
(MINUTES)
DEPTH To
WATER
(INCHES)
NET DROP
(INCHES)
4/18
TEST HOLE PRESOAKED PRIOR TO TESTING:
1
12:45
<10 sec
O 16 / 6 16
6 16
2
12:46
<10 sec
0 0/ 6 16
6 0
3
12:47
<10 sec
0-2-/6-1 / 6 16
6 0
4
12:48
<10 sec
0-9-/6-1 / 6 16
6 0
5
12:49
<10 sec
O 16/6 16
6 16
6
12:50
<10 sec
0 16 / 6 16
6 0
PERCOLATION RATE: <1 (MIN/INCH) PERC. HOLE DIA. 6 (INCHES)
TEST RUN BETWEEN: 3 FT. and 4 FT.
2' MOA APPROVED SAND LINER REQUIRED ON THIS LOT.
DEPTH
(feet)
1-
4
5
6
7
8
9
10-
11-
12-
13-
14-
15-
16-
17-
18-
19-
20 -
SOILS LOG AND PERCOLATION TEST
EN GiNEE&ING
LEGAL DESCRIPTION: T15N RIW SECS L28
PERFORMED FOR: LINDA FRANK
DATE: 4/18/19 PROJECT No.:
PARCEL ID#: 051-031-18 TECHNICIAN
TH 2
GP (SANDY GRAVEL)
J. MILLETTE
SLOPE
WAS GROUND WATER ENCOUNTERED? NO
IF YES qi WHAT DEPTH? -
DEPTH OF WATER AFTER MONITORING: NONE
DATE OF MONITORING: 10/l/19
DATE
READING
GROSS TIME
(MINUTES)
NET TIME
(MINUTES)
DEPTH To
WATER
(INCHES)
NET DROP
(INCHES)
4/18
TEST HOLE PRESOAKED PRIOR TO TESTING:
1
12:32
<10 sec
0-1/6 1 18
611
2
12:33
<10 sec
0- / 6 16
611
3
12:34
<10 sec
0-1/6 / 6 16
611
4
12:35
<10 sec
0 16 / 6 0
611
5
12:36
<10 sec
0-1/6 / 6 0
611
6
12:37
<10 sec
0 11 / 6 16
611
PERCOLATION RATE: <1 (MIN/INCH) PERC. HOLE DIA.-6—(INCHES)
TEST RUN BETWEEN: 2 FT. and 3 FT.
COMMENTS: 2' MGA APPROVED SAND LINER REQUIRED ON THIS LOT.