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Drilling services were provided by Independent Drilling, Inc., using a limited- access, track - mounted drilling rig. Each boring was completed in general accordance with ASTM D 1586 using the mud rotary drilling method. Soil samples were collected from each borehole using a 1.5 -inch ID split -spoon sampler driven with a 140 -pound slide hammer falling a distance of 30 inches. Soil samples from each boring were placed in sealed jars and returned to BCI's office for classification and laboratory testing. Upon completion, each borehole was plugged with cement - bentonite grout. Boring logs are included in Appendix C. 3.0 SUBSURFACE CONDITIONS 3.1 Geological Conditions The subsurface geology at the Barker residence is illustrated in the soil boring profiles shown on Figure 5. The profiles were developed using subsurface data from the SPT borings. Based on these data, three subsurface units, or strata, were identified at the site. These units are described below. Stratum 1 SAND and SAND with clay, light brownish gray, pale yellow, light brown, dark yellowish brown, and brown, fine- grained quartz, minor clay, local limestone fragment USCS classification = SP Stratum 2 CLAYEY SAND and SANDY CLAY, light brownish gray, orange, light brown, pale olive, mottled, variably clayey and sandy, local phosphorite and limestone fragments USCS classification = SP -SC, SC, CH Stratum 3 LIMESTONE, pale yellow and white, variably indurated, locally sandy, localized lenses of sand with clay (SAND with clay USCS classification = SP -SC) The surficial soil unit (Stratum 1) at the site consists of a layer of fine- grained quartz sand extending from the ground surface to a depth of 4 feet below grade in borings SPT -1 and SPT -2, and 8 feet below grade in boring SPT -3. Recorded SPT N- values in Stratum 1 ranged from 8 to 16 blows per foot, indicating a loose to medium dense relative density for the soil unit. Stratum 2 consists of variably clayey soils ranging in composition from clayey sand to sandy clay. The soil unit was encountered from 4 to 17 feet below grade in borings SPT -1 and SPT -2, and from 8 to 42 feet below grade in boring SPT -3. Recorded SPT N- values in Stratum 2 ranged from weight -of- hammer strength material to 27 blows per foot, indicating a very soft to very stiff consistency for the soil unit. In boring SPT -3, a strata transition was encountered from 33'/2 to 381/2 feet below grade. In this transition zone, silty and clayey soils were identified. The recorded N -value of the zone was weight -of- hammer, indicating a very soft consistency for the interval. Limestone bedrock (Stratum 3) was encountered in the lower portion of the borings. The limestone was • encountered at a depth of 17 feet below grade in borings SPT -1 and SPT -2, and 42 feet below grade in boring SPT -3. In borings SPT -1 and SPT -2, a lens of sand with clay was found interbedded within the limestone formation. The limestone was variably indurated with recorded SPT N- values ranging from weight -of- hammer strength material to greater than 50 blows per foot. An interval of very loose sand with clay soils was encountered from 331/2 to 37'/2 feet below grade in boring SPT -2, within an unconfined interbedded sand with clay lens. During drilling, losses of drilling fluid circulation were recorded at depths of 22 feet below grade in boring SPT -1, 20 feet below grade in boring SPT -2, and 34 feet below grade in boring SPT -3. The circulation losses in borings SPT -1 and SPT -2 occurred in the upper part of the limestone, near the soil/limestone contact. The circulation loss in boring SPT -3 occurred in the lower portion of Stratum 2, in association with the strata transition zone. Subsidence Investigation BCI Project No.: 19 -17094 Barker Residence March 2009 Claim No.: 3428 Page 5