140R4026B0002_-__Attachment_3_1_00_00_02A_Test_Pit_Log_TPTB-25-2_20261008_0002.pdf
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About this file
This is a geotechnical test pit log documenting subsurface soil conditions at the Sonostee Turnout location for the Navajo Gallup Water Supply Project.
The test pit (TPTB-25-2) was excavated to a depth of 9.0 feet using a Deere 310G backhoe on July 31, 2025, at coordinates N 1,976,721.2 E 2,462,194.7 with a ground elevation of 5,564.8 feet. The exploration revealed three primary soil layers: (1) 0.0 to 3.3 feet of lean clay with sand (CL)s composed of approximately 75% fines with medium plasticity and 25% fine sand, classified as Quaternary Alluvium backfill; (2) 3.3 to 6.0 feet of poorly graded sand with silt (SP-SM) consisting of approximately 90% fine sand and 10% nonplastic fines, with in-place unit weight of 86.3 lb/ft³ at 3.7% moisture (73.8% compaction), maximum dry density of 116.9 lb/ft³, and optimum water content of 13.3%; and (3) 6.0 to 9.0 feet of lean clay with sand (CL)s similar to the upper layer. All materials exhibited strong reactions with hydrochloric acid and were gray in color, homogeneous, and dry. A corrosivity sample and in-place density test were collected at 4.0 feet. Excavation was discontinued at 9.0 feet due to difficult excavation conditions in very stiff dry clay. The surface was sparsely vegetated with weeds, and no groundwater was encountered.
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Text version
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7-1336-A (1-86) Bureau of Reclamation LOG OF TEST PIT NO. TPTB-25-2 SHEET 1 OF 1
FEATURE: San Juan lateral Turnout Buildings PROJECT: Navajo Gallup Water Supply Project LOCATION: Sonostee Turnout GROUND ELEVATION: 5564.8 ft
COORDINATES: N 1,976,721.2 E 2,462,194.7 METHOD OF EXPLORATION: Deere 310G Backhoe APPROXIMATE DIMENSIONS: 12'X10'X9' LOGGED BY: C. Beyer
DEPTH TO WATER: NE DATE: 7/31/2025 DATE EXCAVATED: 7/31/2025
ASSIFICATION
GROUP
SYMBOL
CLASSIFICATION AND DESCRIPTION OF MATERIAL
(SEE USBR 5000, 5005)
% PLUS 3 in
(BY VOLUME)
3 -in
5 -in
PLUS
in
(CL)s
3.3 ft ()
0.0 to 3.3 ft LEAN CLAY WITH SAND: About 75% fines with medium plasticity, medium dry strength, and medium toughness; about 25% fine sand; maximum size, fine sand; strong reaction with HCl.
IN-PLACE CONDITION: Gray in color, homogeneous, dry.
GEOLOGIC INTERPRETATION: Quaternary Alluvium (Qal) /BACKFILL.
SP-SM 3.3 to 6.0 ft POORLY GRADED SAND WITH SILT: About 90% fine sand;
about 10% nonplastic fines; maximum size, fine sand; Strong reaction with HCl.
IN-PLACE CONDITION: Gray in color, homogeneous, dry.
IN-PLACE UNIT WEIGHT AND MOISTURE FROM 4.0 ft.
Total: 86.3 lb/ft³, 3.7 % (73.8 % compaction) LAB TEST DATA: 60.0% sand, 40.0 % fines, 0 % gravel, LL=NP PI = NP, SPG=2.63
Maximum dry density: 116.9 lb/ft³, optimum water content = 13.3 % Laboratory classification is SILTY SAND.
GEOLOGIC INTERPRETATION: Quaternary Alluvium (Qal) / BACKFILL.
6.0 to 9.0 ft LEAN CLAY WITH SAND: About 75% fines; with medium plasticity, medium dry strength, and medium toughness; about 25% fine sand; maximum size, fine sand; strong reaction with HCl.
IN-PLACE CONDITION: Gray in color, homogeneous, dry.
GEOLOGIC INTERPRETATION: Quaternary Alluvium (Qal) /BACKFILL.
Corrosivity sample and in-place density test at
4.0 ft.
6.0 ft ()
(CL)s
9.0 ft ()
COMMENTS: Surface scarcely vegetated with weeds. Discontinued excavation due to difficult excavation in very stiff dry clay.
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