Item 5B 425 Arapahoe Ave Memo 10.09.24MEMORANDUM TO THE LANDMARKS BOARD
October 9, 2024
STAFF
Brad Mueller, Director of Planning and Development Service
Kristofer Johnson, Comprehensive Planning Senior Manager
Chris Reynolds, Deputy City Attorney, City Attorney’s Office
Marcy Gerwing, Principal Historic Preservation Planner
Clare Brandt, Historic Preservation Planner
Aubrey Noble, Historic Preservation Program Coordinator
Meron Shiferaw, Historic Preservation Intern
CONSIDERATION OF APPLICATION FOR NON-DESIGNATED BUILDINGS
Public hearing and consideration of an application to demolish the house constructed c.1908 at 425
Arapahoe Ave., a non-landmarked building older than 50 years old, pursuant to Section 9-11-23 of the
Boulder Revised Code, 1981, and under the procedures prescribed by chapter 1-3, “Quasi-Judicial
Hearings,” B.R.C. 1981.
Address: 425 Arapahoe Ave.
Legal Description: E 75 FT OF W 100 FT LOT 5 BLK A HIGHLAND LAWN & TR 1017-J & TR 416-A-
3 36-1N-71
Case Number: HIS2024-00177
Owner: Susan G. Ellis & Fred Raymond Ellis, Jr.
Applicant: Kari Whitman
Case Type: Non-Designated Demolition
Code Section: 9-11-23, B.R.C., 1981
EXECUTIVE SUMMARY
In August 2024, the owner submitted an application to demolish the c.1908 house located at 425
Arapahoe Ave. The Landmarks Design Review Committee referred the application to the full Landmarks
Board, finding “probable cause to believe the building may be eligible for landmark designation.” The
purpose of this hearing is to determine whether the building is eligible for designation and to consider
the cost, condition, and relationship to the surrounding area. After subsequent research and analysis,
staff considers that while the house dates from before 1908 and is associated with the Carpenter, Swan,
Teegarden, Clark–Taylor and Lewis–Cundiff families, staff considers the house does not have the integrity
needed to convey that significance and is therefore not eligible for landmark designation.
Item 5B - 425 Arapahoe Ave Memo
Staff recommends the Landmarks Board approve the application. If approved, the building would need
to be deconstructed as defined by Ordinance 8366. Recommended motion language and findings are
located at the end of the memo (link).
PUBLIC COMMENT
To date, staff has not received public comment regarding this application.
OPTIONS FOR THE BOARD’S DECISION
Pursuant to Section 9-11-23, B.R.C. 1981, if the Landmarks Board finds that the building proposed for
demolition may have significance under the criteria in subsection (f), the application shall be suspended
for a period not to exceed 180 days from the date it was accepted by the city manager as complete, in
order to provide the time necessary to consider alternatives to the building’s demolition. If imposed, a
180-day stay period would start when the completed application was accepted by the city manager
(Aug. 21, 2024, when the Landmarks Board fee was paid) and expire on Feb. 17, 2025.
If the Landmarks Board finds that the building proposed to be demolished does not have significance
under the criteria set forth in section 9-11-23(f), B.R.C. 1981, the city manager shall issue a demolition
approval.
BACKGROUND
• On Aug. 8, 2024, the Planning & Development Services Department accepted an application to
demolish the building.
• On, Aug. 21, 2024, the LDRC completed the initial review and referred the application to the
Landmarks Board for review in a public hearing, finding there was “probable cause to believe
that the building may be eligible for designation as an individual landmark.”
• On Aug. 21, 2024, the applicant paid the Landmarks Board hearing fee.
• The building has not been previously proposed for demolition.
PROPERTY DESCRIPTION
Date of Construction: c.1908 (Boulder County Records)
Zoning: RL-1 (Residential Low – 1)
Lot Size: 15,004 sq. ft. / 0.34 acre (Boulder County Assessor estimate)
Building Size - House: 1,320 sq. ft. (Assessor estimate of first floor above ground finished area)
The property is located on the north side of Arapahoe Avenue between 4th and 5th Streets. Boulder
Creek borders the property to the north. The front of the house faces south onto Arapahoe Avenue.
Item 5B - 425 Arapahoe Ave Memo
Figure 1. Left: Map of west Boulder showing location of 425 Arapahoe Ave. north of Arapahoe Avenue and south
of Boulder Creek. Left: Location of 425 Arapahoe Ave. between 4th and 5th Street on Arapahoe Avenue (property
outlined and flagged). eMapLink (link).
BUILDING DESCRIPTION
Figure 2. Left: 425 Arapahoe Ave., south elevation (façade) showing the frame hipped-roof house with front-
facing dormer and hipped porch. Applicant photograph. 4th Street Boulder Creek
Greenway 5th Street Arapahoe Ave.
Marine St.
Item 5B - 425 Arapahoe Ave Memo
Figure 3. Left: west elevation showing deep eaves of the hipped roof, roof dormer and shed roof over side
entrance to the rear. Right: shed roof over side entrance with knee backets and newer door.
The house is a one-and-one-half story frame vernacular building with a hipped roof and overhanging
eaves. The façade includes a gabled dormer with two vertically proportioned double-hung windows.
Below, there is a hipped roof porch with simple square porch supports. The dormer and porch are
centered within the original part of the building. On the west side, there is a shed roof with decorative
brackets over a side entry door. An side-gable roof addition, constructed in 1981 1, is located on the east
side.
Figure 4. Left: The east end of the south elevation (façade) showing the addition (c. 1980). Right: the east
elevation with gable roof form.
1 Planning and Development Services Permit Records. May 22, 1981.
Item 5B - 425 Arapahoe Ave Memo
Figure 5. Left: north elevation (interior lot) showing the hipped roof with wall dormer; newer addition on left side
of image (behind tree). Right: connection at rear between the newer addition (on the left) and the original house
with the wall dormer to the right.
The dormer on the east side was modified as part of the 1981 addition. At the rear, a new wall dormer
was added to the original part of the house. It appears the windows and doors were replaced in the
1980s at the time of the addition, and do not appear to be historic.
Analysis of Integrity
Historic integrity is the ability of a property to convey its historical associations or attributes. The
National Park Service defines seven aspects of integrity to evaluate properties (location, setting, design,
materials, workmanship, feeling, and association). 2
Figure 6. Left: Earliest Tax Assessor Card image of 425 Arapahoe Ave. c.1929 3 showing the southeast corner of
the house, the shed roof enclosed porch on the east side, dormer on the east side and brick chimney. Right: Tax
Assessor Card image c. 1962 showing the southwest corner of the house, hipped-roof form and wide eaves,
horizontal siding and turned porch posts.
According to County records, the house was constructed in 1908. Research indicates that there was a
house on the site much earlier (c. 1896 4) but staff was unable to confirm the construction date of the
2 U.S. Dept. of the Interior. “National Historic Landmarks Glossary of Terms.” National Park Service. Accessed November 2022. https://www.nps
.gov/subjects/nationalhistoriclandmarks/glossary.htm
3 Boulder County Tax Assessor. “425 Arapahoe Avenue real estate appraisal cards.” 1929-1949. Call number 880-Arapahoe-425. Carnegie
Library for Local History, Boulder.
4 Boulder City Directory. 1896.
Item 5B - 425 Arapahoe Ave Memo
existing house. In 1929, the building included a shed roof enclosed porch on the east side, matching
small dormers on the east and west sides, brick chimney, and decorative turned porch posts. The shed
roof porch has been removed, as has the brick chimney and decorative turned porch posts.
Permits on file with the Planning and Development Dept. include reroofing in 1948, 1962, and 1988; the
construction of the addition in 1981; and addition of fencing and a rear deck in 1988.
The building is in its original location. The original design of the building has been modified with the
addition on the east side and changes to the dormers on the east and south sides. The building retains
few of its historic materials; notably the narrow lap siding has been replaced with rough cedar siding
and most of the window have been replaced. The building does retain shingle at the dormers. The
building demonstrates workmanship typical of a c. 1980s remodel rather than the original construction,
although it does retain some of the original workmanship including the arched detailing in the gable
ends of the dormers. The building’s ability to convey a feeling of its time has been diminished.
The tree-lined setting of the building has not changed and the changes to neighboring properties has
not negatively impacted the context. However, in general, alterations have impacted the building’s
ability to convey its association with its early residents and architecture.
Figure 7. Left: Aerial image from Google Maps (link) showing the existing roof plan of the house. The solid blue
line indicates the approx. footprint of the original house; the dotted yellow line indicates the approx. extent of
the 1981 modifications. Right: The c. 1962 site plan 5 showing the original footprint of the house, front porch, and
enclosed porch at the northeast corner. The enclosed porch was removed in 1981 to construct the existing
addition.
AREA HISTORY
The area around 425 Arapahoe Ave. has seen significant transformations since the end of the 19th
century. This area is the ancestral homelands and unceded territory of Indigenous Peoples who have
traversed, lived in and stewarded lands in the Boulder Valley since time immemorial. When gold was
5 Boulder County Tax Assessor. “425 Arapahoe Avenue real estate appraisal cards.” 1929-1949. Call number 880-Arapahoe-425. Carnegie
Library for Local History, Boulder.
Item 5B - 425 Arapahoe Ave Memo
discovered in the mountains nearby, 60 original shareholders of Boulder City Town Company ignored
the 1851 Treaty of Fort Laramie, also known as the Horse Creek Treaty, and claimed 1,280 acres
alongside Boulder Creek on February 10th, 1859.6 In 1871, a town government was organized under
Boulder County regulations and included the original townsite and additions to the east, south and
west.7
In the early 1880s, Hannah Barker owned 73 acres to the southwest of Boulder, south of Boulder Creek.
She platted the area (working with F. O. Blake as an agent 8) in 1884 as Highland Lawn.9 Hannah Barker
was born in 1844 in Ireland. She married Ezra Barker, a prominent Boulder landowner, on Nov. 30, 1877.
Ezra died in 1883 and “left Hannah to manage their extensive landholdings and wealth, thus positioning
her to become a prominent Boulder businesswoman, civic leader and philanthropist.”10 She devoted her
time and money to an impressive number of causes in Boulder, including the Boulder Fortnightly Club,
the Women’s Christian Temperance Union, and the Woman’s Club of Boulder. She supported the free
reading rooms, and donated land for various parks and schools. She used her house, located at 800
Arapahoe Ave. (designated as the Hannah Barker House) for civic meetings and social events to support
her causes. In 1910, Barker donated the land for the Barker Reservoir above Boulder, securing Boulder’s
water supply.
The deed of a Highland Lawn lot included “a perpetual water right under the Anderson ditch, and also
contains a condition requiring the purchases to set out trees in front of his lot and build a fence around
it, trees not to be cottonwood and the fence not to be wire.”11 W. S. Carpenter is listed as one of the
original purchasers in 1884. While people were quick to purchase the land, very few constructed houses
until the 1890s and the area remained very rural through the early 1900s.
6 “Land Acknowledgement.” City of Boulder. https://bouldercolorado.gov/projects/land-acknowledgment
7 By 1882, the town was divided into wards, and the offices of mayor, treasurer, and aldermen were created to manage the now seventeen
additions to the original townsite and the increasing population. Although by 1900, Boulder’s population had grown to 6,150 with twenty-eight
additions added between 1890 and 1895, the residential subdivisions of North Boulder were not created until the 1940s, and the area was not
incorporated into the city until after 1954.
8 Gladden, Sanford. “Improvements of Boulder, Colorado through 1900.” Citing Boulder County Herald Sept. 17, 1884.
9 County Records. https://boulder.co.publicsearch.us/doc/181258508
10 Gibson, Campbell. “Era Barker (1838-1883), Husband of Hannah Connell Barker (1844-1918).” 2022. Carnegie Library for Local History,
Boulder
11 Gladden. Ibid. Boulder County Herald Sept. 17, 1884.
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Figure 8. Left: Hannah Barker’s plat of Highland Lawn from 1884.12 The location of 425 Arapahoe Ave. (the east
75 feet of lot 5 in Block A) is flagged. Right: Hannah Barker c. 1869.13
Figure 9. Block “A” and “C” of the Highland Lawn plat in 1901.14 The approx. location of 425 Arapahoe is flagged.
12 Boulder County Records. https://boulder.co.publicsearch.us/doc/181258508
13 “Ezra K. and Hannah Connell Barker.” 1860-1869. Call No. BHS 220-1-9. Boulder Historical Society/Museum of Boulder. Carnegie Library for
Local History. https://localhistory.boulderlibrary.org/islandora/object/islandora%3A21538
14 Sturtevant, Joseph. “Boulder City from Flag Staff Mountain. 1901. No. 123.” 1901. CU Museum of Natural History.
https://cudl.colorado.edu//luna/servlet/detail/CUB~26~26~355~294385
Item 5B - 425 Arapahoe Ave Memo
PROPERTY HISTORY
Arabella Burhans (Berham) Carpenter; Ella Belle Carpenter and Charles Winfield Carpenter
(1890-1903)
While W. S. (Winfield Scott) Carpenter is listed as purchasing the land in 1884 and “Carpenter” is marked
on a map from 1887,15 tax records show his widow, Arabella, purchased lots 5 and 6 from Hannah
Barker in 1890.16 She paid $150 for the land, which included one twenty-fourth of a share in the
Anderson Ditch Company. Arabella borrowed $300 from the Boulder Building and Loan Association the
same year.17
Arabella was born around 1843 in New York.18 She was married to Winfield Scott Carpenter. Winfield
was born around 1842 in Vermont. He enlisted as a Wisconsin Volunteer in the “War of the Rebellion” in
Sept. 1862 and was mustered out in April 1863 after he was injured.19 He received a war pension
beginning in 1881 and when he died on February 17, 1887,20 Arabella received the pension.21
Arabella lived on the property, at a house that was described as located “below Four Mile Creek and
Bummer Gulch.” She kept two horses and three cows on the property.22 Arabella died on March 9,
1895 23 and left the property to her children Ella and Charles.
Ella was born in 1868 in Wisconsin.24 She moved to Black Hawk before she was twelve years old, where
her father, Winfield worked as a carpenter. By 1885, the family moved to Boulder and Ella graduated
from the State University (now Colorado University) in Boulder in 1887.25 Ella worked as a teacher in
Boulder 26 until her mother died and after 1900 she moved to Denver to work.27
15 “Map of the City of Boulder.” 1887. Call No. MAP CITY 1887-1 (Map Case 4 #1). Carnegie Library for Local History, Boulder.
https://localhistory.boulderlibrary.org/islandora/object/islandora%3A76608
16 County Records. https://boulder.co.publicsearch.us/doc/181333531
17 County Records. https://boulder.co.publicsearch.us/doc/181251658
18 National Archives and Records Administration. Schedules of the Colorado State Census, 1885. Washington, D.C.: National Archives and
Records Administration. M158, 8 rolls. https://www.ancestry.com/discoveryui-content/view/31111:6837
19 American Civil War Research Database. https://www.ancestry.com/discoveryui-content/view/1063337%3A1555
20 Find a Grave. https://www.ancestry.com/discoveryui-content/view/3352515:60525
21 General Index to Pension Files, 1861-1934. Washington, D.C.: National Archives and Records Administration. T288, 546 rolls.
https://www.ancestry.com/discoveryui-content/view/2062827:4654
22 Boulder County Tax ledger. 1890.
23 Find a Grave. https://www.ancestry.com/discoveryui-content/view/3352505:60525
24 Tenth Census of the United States, 1880. (NARA microfilm publication T9, 1,454 rolls). Records of the Bureau of the Census, Record Group 29.
National Archives, Washington, D.C. https://www.ancestry.com/discoveryui-content/view/20080309:6742
25 The Rocky Mountain News (Daily), Volume 29, June 1, 1887. https://www.coloradohistoricnewspapers.org/?a=d&d=RMD18870601-01.2.120
26 Boulder Daily Camera, March 9, 1895. https://www.coloradohistoricnewspapers.org/?a=d&d=BDC18950309.2.25
27 City Directory 1896. https://www.ancestry.com/imageviewer/collections/2469/images/dvm_lochist011740-
00033_1?usePUB=true&_phsrc=XFQ47&_phstart=successSource&usePUBJs=true&pId=837385172
Item 5B - 425 Arapahoe Ave Memo
Charles was born in 1871. He married Jessie Irene Coon on October 2, 1895 28 and the couple worked as
fruit farmers. They had two children, Carl and Jack.29
Figure 10. The Carpenter family, including Arabella (top left), Ella Belle (top center) and Charles (top right) lived
at 425 Arapahoe Ave.30 Charles Carpenter with his son Carl c.1897.31
Siblings Ella and Charles rented the house to A. J. Piece in 1896 and Mary and Charles Dodd in 1898. The
property was vacant from 1900 until the siblings sold it in 1903.
Squire J. Swan and Nancy Antoinette “Nettie” Swan; Martha “Mattie” Maxson; Lela Belle
Green and Frank L Green (1903-1921)
Squire Swan purchased the house and the easternmost 150 feet of lot 5 (which became 425 Arapahoe
Ave.) from Ella and Charles and the estate of Arabelle Carpenter in 1903 for $450.32 Married couple
28 Marriage Records. Colorado Marriages. State Archives, Denver, Colorado. https://www.ancestry.com/discoveryui-content/view/61674:61366
29 Fourteenth Census of the United States, 1920. (NARA microfilm publication T625, 2076 rolls). Records of the Bureau of the Census, Record
Group 29. National Archives, Washington, D.C. https://www.ancestry.com/discoveryui-content/view/62265491:6061
30 Find a Grave. https://www.findagrave.com/memorial/50002469/arabella_burhans_carpenter
31 Find a Grave. https://www.findagrave.com/memorial/248016356/carl_arthur-carpenter/photo
32 County Records. https://boulder.co.publicsearch.us/doc/181729530
Item 5B - 425 Arapahoe Ave Memo
Squire and Nancy “Nettie” Swan came to Boulder in 1900 with Nettie’s sister Martha “Mattie”
Maxson.33 Nettie was disabled and relied on Mattie, a schoolteacher, to care for her.34
Squire was born in Watson, New York on July 31, 1847. He served in the United States Army as a
member of the One Hundred Eighty-ninth Regiment, New York Infantry. He was a deacon of the Seventh
Day Baptist church of Boulder in addition to working as a miner.35
Squire deeded the property to Nancy Swan for “One Dollar, Love and Affection”36 and recorded the
document shortly after he suffered a “mental collapse.” Although it wasn’t known at the time, the
neurological disorder was likely caused by poisoning from exposure to mercury and other dangerous
chemicals associated with mining. Squire died two months later on September 28, 1913.37
Figure 11. Left: Newspaper article from July 1913 announcing Squire Swan’s “mental collapse”. The article reads
in part that “Mr. Swan has been resident of Boulder for eighteen years, during most of which time he has been
engaged in mining.”38 Right: Funeral announcement for Mr. Swan from September 1913.39
33 Thirteenth Census of the United States, 1910 (NARA microfilm publication T624, 1,178 rolls). Records of the Bureau of the Census, Record
Group 29. National Archives, Washington, D.C. https://www.ancestry.com/discoveryui-content/view/1964966:7884
34 Find a Grave. https://www.findagrave.com/memorial/91933737/martha_maxson
35 Find a Grave. https://www.findagrave.com/memorial/74226335/squire-j.-swan
36 County Records. https://boulder.co.publicsearch.us/doc/181673512
37 Find a Grave. https://www.findagrave.com/memorial/74226335/squire-j.-swan
38 “Veteran of Civil War Suffers Mental Collapse.” Boulder Daily Camera, Volume 23, Number 93, July 2, 1913.
https://www.coloradohistoricnewspapers.org/?a=d&d=BDC19130702-01.2.7
39 “Attention Comrades.” Boulder Daily Camera, Volume 23, Number 169, September 30, 1913.
https://www.coloradohistoricnewspapers.org/?a=d&d=BDC19130930-01.2.29
Item 5B - 425 Arapahoe Ave Memo
Nettie was born in Truxton, New York on June 26, 1849.40 She had two daughters with her first husband
Luther G. Potter, who died in 1888. Their older daughter, Melissa, died in 1892.41 Nettie’s younger
daughter, Lela Belle Potter was born on March 14, 1875 and married Frank Green in 1891. The Greens
lived in North Loup, Nebraska.42 In 1919, Nettie deeded Lela the house for $1 and Nettie and Mattie
moved back to North Loup where they lived the remainder of their lives. Nettie died on June 16, 1928
(aged 78) and Mattie died on November 13 1934 (aged 86).
The Greens rented the house to C. W. Bent in 1918 43 and to Myron Teegarden before 1920.44
Myron Murphy Teegarden and Ramona Civonia Teegarden (c. 1920-1921)
After renting the house from the Greens for at least a year, married couple Myron and Ramona
Teegarden purchased the property in 1921.45
Myron was born on March 19, 1899 in Indiana and his family moved to Boulder when he was a child.
Myron’s father was a book-keeper for a plumbing company and both of his sons worked as plumbers at
the same company.46 He became a police officer in 1934, police captain in 1947, and chief in 1949. After
his retirement, Myron became a photographer and donated many of his images to the Carnegie Library
for Local History archive.
Ramona Demmon was born in Gold Hill on May 10, 1900.47 Myron and Ramona married on June 8,
1918 48 and their first child, Dorse “Doc”, was born in September 1919. The Teegarden family moved
from 425 Arapahoe Ave. shortly before their second child, Donald “Don” was born in 1922.
Myron died on July, 16 1984 (age 85); Ramona died on December 29, 1987 (age 87).
40 Find a Grave. https://www.findagrave.com/memorial/91933795/nancy-antoinette-swan
41 Find a Grave. https://www.findagrave.com/memorial/64654865/melissa_a_loofboro
42 Find a Grave. https://www.findagrave.com/memorial/53380047/lela-belle-green
43 Boulder City Directory. 1918.
https://www.ancestry.com/imageviewer/collections/2469/images/13964747?usePUB=true&_phsrc=XFQ22&_phstart=successSource&usePUBJ
s=true&pId=930245881
44 Fourteenth Census of the United States, 1920. (NARA microfilm publication T625, 2076 rolls). Records of the Bureau of the Census, Record
Group 29. National Archives, Washington, D.C. https://www.ancestry.com/discoveryui-content/view/62273714:6061
45 County Records. https://boulder.co.publicsearch.us/doc/181383058
46 Thirteenth Census of the United States, 1910 (NARA microfilm publication T624, 1,178 rolls). Records of the Bureau of the Census, Record
Group 29. National Archives, Washington, D.C. https://www.ancestry.com/discoveryui-content/view/1966102:7884
47 United States of America, Bureau of the Census. Twelfth Census of the United States, 1900. Washington, D.C.
https://www.ancestry.com/discoveryui-content/view/6712784:7602
48 Marriage Records. Colorado Marriages. State Archives, Denver, Colorado. https://www.ancestry.com/discoveryui-
content/view/401978:61366
Item 5B - 425 Arapahoe Ave Memo
Figure 12. Left: Ramona and Myron Teegarden, 1968.49 Middle: Mrs. Ramona Teegarden at her kitchen table in
1964.50 Right: Myron Teegarden, 1967.51
Ray Richard Clark and Anna Gertrude Clark; Lulu “Marguerite” (Clark) Taylor; Jean G. (Taylor)
Degener; Adrian Harold Taylor and Faye Elsie Taylor (1921-1975)
Ray Clark borrowed money from his sister and brother-in-law (Walter and Lulu Snair) to purchase the
property from the Teegardens on October 28, 1921.52
Ray was born around 1878 in Nebraska.53 He married Anna “Gertrude” Pease on January 8, 1899 in
Boulder.54 Gertrude was born around 1880 in South Dakota.55 The married couple lived at 400 Marine
St. with nine children in 1920.56 Ray worked for the U. S. Forest Service and he and Gertrude may never
have lived in the house as in April 1922, Ray was promoted to deputy supervisor for the Gunnison
National Forest and relocated the family to Gunnison, Colorado.57 They rented the house to J.B. White in
1923 58 and H. R. Trask in 1928.59
One of Ray and Gertrude’s daughters, Lulu “Marguerite” was born in Boulder on Oct. 22, 1901 and
married Adrian Taylor on November 10, 1921.60 By 1930, Adrian and Marguerite had moved to the
49 “Anniversary Reception Set for the Myron Teegardens.” June 2, 1968. Boulder Daily Camera.
50 O’Brien, Sadie. “Police Chief’s Wife Collects China.” April 13, 1964. Boulder Daily Camera.
51 March 31, 1967. Boulder Daily Camera.
52 County Records. https://boulder.co.publicsearch.us/doc/181381680
53 United States of America, Bureau of the Census. Twelfth Census of the United States, 1900. Washington, D.C.
https://www.ancestry.com/discoveryui-content/view/74429462:7602
54 Marriage Records. Colorado Marriages. State Archives, Denver, Colorado. https://www.ancestry.com/discoveryui-
content/view/900071447:61366
55 Fourteenth Census of the United States, 1920. (NARA microfilm publication T625, 2076 rolls). Records of the Bureau of the Census, Record
Group 29. National Archives, Washington, D.C. https://www.ancestry.com/discoveryui-content/view/62267376:6061
56 Fourteenth Census of the United States, 1920. (NARA microfilm publication T625, 2076 rolls). Records of the Bureau of the Census, Record
Group 29. National Archives, Washington, D.C. https://www.ancestry.com/discoveryui-content/view/62267376:6061
57 “Ranger Ray Clark Sent to Gunnison.” Fort Collins Courier, April 20, 1922.
https://www.coloradohistoricnewspapers.org/?a=d&d=FCC19220420.2.145
58 City Directory. 1923. https://www.ancestry.com/imageviewer/collections/2469/images/14515434
59 City Directory. 1928. https://www.ancestry.com/imageviewer/collections/2469/images/14777342
60 Marriage Records. Colorado Marriages. State Archives, Denver, Colorado. https://www.ancestry.com/discoveryui-
content/view/900400649:61366
Item 5B - 425 Arapahoe Ave Memo
house at 425 Arapahoe Ave. with their seven-year-old daughter Jean.61 In 1950, Adrian worked as a
powerhouse engineer for the public utility company.62 Adrian and Marguerite purchased the property
from Marguerite’s father in 1942 for $100.63
Daughter Jean married Charles Melvin Degener on October 22, 1949 and the couple moved to Denver.64
Marguerite died on July 19, 1957 and officially deeded the property to her daughter Jean, although
Adrian continued to live there.65 He remarried on June 20, 1959 to Faye Elsie Arbuthnot.66 Adrian and
Faye officially purchased the property from Jean Degener in 1961.67 They lived there until 1975.
Alan Stark and Barbara Arata Stark (1975-1977)
Married couple Alan and Barbara Stark purchased the property in 1975 from the Taylors.68
Philip Dustin “Dusty” DeLario and Terry Kim Danko (1977-1981)
Philip Dustin “Dusty” DeLario and Terry Kim Danko purchased the property in 1977 from the Starks.69
Dusty DeLario was coach of the women’s tennis team at CU Boulder.70 Terry Danko graduated from CU
in 1968. Following graduation, he spent four years in the Air Force and attained the rank of Captain. He
was assistant swim coach at CU from 1972 to 1974 and was the named the coach of the swim team at
CU in 1974. He directed both the men’s and women’s swim teams in 1978.71
Michael S. Burney and Rita M. Burney (1981-1984)
Married couple Michael and Rite Burney purchased the property in 1981 from Philip Dustin DeLario and
Terry Kim Danko.72
Clayton H. Lewis and Alcinda A. Cundiff (1984 - 2024)
Clayton Lewis and Alcinda Cundiff purchased the property in 1984 from the Burneys.73
61 United States of America, Bureau of the Census. Fifteenth Census of the United States, 1930. Washington, D.C.
https://www.ancestry.com/discoveryui-content/view/101343139:6224
62 Department of Commerce. Bureau of the Census. 1913-1/1/1972. Population Schedules for the 1950 Census, 1950 - 1950. Washington, D.C.
https://www.ancestry.com/discoveryui-content/view/19999691:62308
63 County Records. https://boulder.co.publicsearch.us/doc/186006882
64 Find a Grave. https://www.findagrave.com/memorial/78318647/jean-t.-degener
65 City Directory. 1958. https://www.ancestry.com/imageviewer/collections/2469/images/13468276
66 Geneanet Community Trees Index. Paris, France: Geneanet. https://www.ancestry.com/discoveryui-content/view/6442458959:62476
67 County Records. https://boulder.co.publicsearch.us/doc/181980263 and County Records. https://boulder.co.publicsearch.us/doc/181976890
68 County Records. https://boulder.co.publicsearch.us/doc/182694913
69 County Records. https://boulder.co.publicsearch.us/doc/182740496
70 “Women’s Tennis Team Prepares for Opener.” Colorado Daily - University of Colorado Boulder, Volume 21, Number 11, September 15, 1972.
https://www.coloradohistoricnewspapers.org/?a=d&d=CDY19720915-01.2.53
71 “CU fills Women’s Athletic Posts.” Aug 10, 1978. Boulder Daily Camera.
72 County Records. https://boulder.co.publicsearch.us/doc/182922924
73 County Records. https://boulder.co.publicsearch.us/doc/183118655
Item 5B - 425 Arapahoe Ave Memo
Susan Ellis and Fred Raymond Ellis, Jr. (2024 – )
Married couple Susan and Fred Raymond Ellis purchased the property in July and are the current
owners.
PURPOSE AND CRITERIA FOR THE BOARD’S DECISION
Buildings proposed for demolition (as defined in Section 9-16-1, B.R.C. 1981) that are not located in a
historic district or designated as a landmark but are older than 50 years old are reviewed pursuant to
Section 9-11-23, B.R.C. 1981, using criteria defined by Section 9-11-1, Purpose and Legislative Intent,
and Section 9-11-2, City Council May Designate or Amend Landmarks and Historic Districts. The
Significance Criteria for Individual Landmarks (link) was adopted by the Landmarks Board on Sept. 17,
1975.
STAFF ANALYSIS
CRITERION 1: INDIVIDUAL LANDMARK ELIGIBILITY
The following is a result of staff’s research of the property relative to the Significance Criteria for
Individual Landmarks (link).
HISTORIC SIGNIFICANCE:
Summary: While the building at 425 Arapahoe Ave. dates from before 1908 and is associated with the
Carpenter, Swan, Teegarden, Clark–Taylor and Lewis–Cundiff families, staff considers the house does not have
the integrity needed to convey that significance. The changes to the building diminish the connection between
the property and the community’s cultural, political, economic or social heritage or the development of the
community.
1. Date of Construction: Pre-1908
Elaboration: According to County records, the house was constructed in 1908. Research indicates
that there was a house on the site much earlier (c. 1896) but staff was unable to confirm the exact
date of construction of the existing house.
2. Association with Persons or Events: Carpenter, Swan, Teegarden, Clark–Taylor and Lewis–Cundiff
families.
Elaboration: Arabella Burhans Carpenter purchased the land from Hannah Barker. The Carpenter
family likely constructed the house. After Arabella’s death, her heirs sold the house to Squire Swan
and Nettie Swan. Nettie was disabled and relied on her sister Mattie Maxson. After Squire’s death,
the sisters moved back to their childhood home in Nebraska. Myron and Ramona Teegarden were
the most notable residents, although lived in the house for a short time. Myron was Boulder’s Police
Captain. The Clark–Taylor family owned the house for 54 years and the Lewis–Cundiff family owned it
for 40 years.
3. Distinction in the Development of the Community: Highland Lawn
Elaboration: The area was platted by Hannah Barker in 1894. Due to her conditions that the
properties include shade trees and “a neat fence” the area remained generally rural with single-
family homes and mature trees.
Item 5B - 425 Arapahoe Ave Memo
4. Recognition by Authorities: Front Range Research Associates (1989)
Elaboration: The house was surveyed and the significance noted: “Although this house has been
altered, elements of its late nineteenth century style are still apparent, including the front gabled,
shingled dormer, the hipped roof, and the tall, narrow windows.”74 See Historic Building Inventory
Form (link).
ARCHITECTURAL SIGNIFICANCE:
Summary: The house located at 425 Arapahoe Ave. is representative of vernacular residential construction
of the period. However, the changes to the building diminish the architectural/aesthetic interest or value. It is
not a significant example of architectural styles of the past and does not include innovative use of material or
exemplary craftsmanship to be considered significant.
1. Recognized Period or Style: Vernacular frame with hipped roof
2. Architect or Builder of Prominence: Unknown.
3. Artistic Merit: None noted
4. Example of the Uncommon: None noted
5. Indigenous Qualities: None noted
ENVIRONMENTAL SIGNIFICANCE:
Summary: The house does not represent a unique natural or man-made environment and the property
is not located within the boundaries of a potential historic district.
1. Site Characteristics: Mature trees dominate the site.
2. Compatibility with Site: None observed
3. Geographic Importance: None observed
4. Environmental Appropriateness: None observed
5. Area Integrity: Potential Expanded Highland Lawn Historic District.
Elaboration: Within the context of Hannah Barker’s original 1894 plat, the area has remained
residential with mature trees lining the street and within the properties. The area was identified as a
potential historic district in 1989.75
CRITERION 2: RELATIONSHIP TO THE CHARACTER OF THE NEIGHBORHOOD
The surrounding area retains a rural and residential feel. Although some of the surrounding buildings
have been modified, the area retains much of its historic character as the Highland Lawn neighborhood,
platted by Hannah Barker in 1884. Buildings in the area reflect the prevailing architectural tastes of turn-
of -the twentieth century, including Queen Anne, Classic Cottage, Edwardian Vernacular, and hipped-
roof brick buildings. While this vernacular hipped-roof buildings adds to the character of the area, it
does not retain its architectural integrity.
74 Front Range Research Associates. “425 Arapahoe Avenue historic building inventory record.” 1898. Call No. 780 Arapahoe 425. Carnegie
Library for Local History, Boulder. https://localhistory.boulderlibrary.org/islandora/object/islandora%3A22137
75 Simmons, R. Laurie and Christine Whitacre. Front Range Research Associates. “1989 Boulder Survey of Historic
Places.” Aug. 1989.
Item 5B - 425 Arapahoe Ave Memo
CRITERION 3: CONDITION OF THE BUILDING
The owner has submitted information related to the condition of the building in a letter from GFE
Structural, structural engineering consultants (see Attachment B – Structural Engineering Letter). The
conclusion of this report includes details regarding the following:
• Recommendations for “re-framing a significant portion of the existing roof framing for size
appropriate roof members and required insulation”;
• Recommendations to “to strengthen the [existing upper floor structure] for compliance with the
current adopted IRC code”;
• Recommendations for “additional beams, posts and foundation support to properly support the
floor and structure above” on the first floor;
• Recommendations that a “new foundation (retaining walls) is recommended for the proper
support of the soil in the crawl space and prevent future settlement and movement” and
general foundation repair.
The owner also submitted a geotechnical subsurface exploration report from Substrata Consulting
Engineers regarding construction of a new building (see Attachment C - Geotechnical Subsurface
Exploration Report).
CRITERION 4: PROJECTED COST OF RESTORATION OR REPAIR:
The owner has not submitted information related to the projected cost of restoration/repair of the
building. However, the letter from GFE Structural, structural engineering consultants (Attachment B –
Structural Engineering Letter) includes the statement that:
“It is our overall conclusion that the building is in poor to satisfactory condition. If any remodeling is to
occur, significant structural revisions will be likely at all levels of the building. Structural repairs and
revisions of this type are expensive and often more expensive than demolishing and replacing the
structure with a new building built to code with modern building materials. In addition, repair of homes
of this type of construction are time consuming and requires a skilled contractor.”
RECOMMENDED MOTION
Issue Historic Preservation Approval
If the Landmarks Board finds the building not eligible for individual landmark designation based upon its
historic, architectural, and environmental significance, staff recommends the following motion
language:
I move the Landmarks Board adopt the findings of the staff memorandum dated Oct. 9, 2024 and
approve the application to demolish the building at 425 Arapahoe Ave., finding that the building does
not have significance under the criteria set forth in section 9-11-23(f), B.R.C. 1981.
ALTERNATE MOTION
Issue a Stay-of-Demolition
Item 5B - 425 Arapahoe Ave Memo
If the Landmarks Board finds the building may be eligible for individual landmark designation based
upon historic, architectural, and environmental significance, staff recommends the following motion
language:
I move that the Landmarks Board issue a stay-of-demolition for the building located at 425 Arapahoe
Ave. for a period not to exceed 180 days from the day the application was accepted by the city manager
in order to explore alternatives to demolishing the building.
A 180-day stay period would expire on February 10, 2025 (180 days from Aug. 21, 2024, when the
Landmarks Board review fee was paid).
FINDINGS
Staff recommends that the Landmarks Board adopt the following findings:
Approval of the historic preservation demolition application for the house at 425 Arapahoe Ave. is
appropriate under the criteria set forth in Section 9-11-23(f), B.R.C. 1981, as the property does not meet
the significance criteria for individual landmark designation:
1. While the building at 425 Arapahoe Ave. dates from before 1908 and is associated with the
Carpenter, Swan, Teegarden, Clark–Taylor and Lewis–Cundiff families, the house does not have the
integrity needed to convey that significance;
2. The additions to the building diminish the architectural interest or value, it is not a significant example
of architectural styles of the past and does not include innovative use of material or exemplary
craftsmanship to be considered significant; and
3. The house does not represent a unique natural or man-made environment and the loss of the
building would not constitute a significant impact on Boulder’s historic resources.
ATTACHMENTS
A: Application Materials
B: Structural Engineering Letter
C: Geotechnical Subsurface Exploration Report
Item 5B - 425 Arapahoe Ave Memo
Attachment A - Application Materials
Item 5B - 425 Arapahoe Ave Memo
Attachment A - Application MaterialsItem 5B - 425 Arapahoe Ave Memo
425 ARAPAHOE - PHOTOS FOR DEMO APP - ZP - 8/7/2024
WEST VIEW
Attachment A - Application Materials
Item 5B - 425 Arapahoe Ave Memo
425 ARAPAHOE - PHOTOS FOR DEMO APP - ZP - 8/7/2024
NORTH VIEW
Attachment A - Application Materials
Item 5B - 425 Arapahoe Ave Memo
425 ARAPAHOE - PHOTOS FOR DEMO APP - ZP - 8/7/2024
EAST VIEW
Attachment A - Application Materials
Item 5B - 425 Arapahoe Ave Memo
425 ARAPAHOE - PHOTOS FOR DEMO APP - ZP - 8/7/2024
SOUTH VIEW
Attachment A - Application Materials
Item 5B - 425 Arapahoe Ave Memo
425 ARAPAHOE - PHOTOS FOR DEMO APP - ZP - 8/7/2024
STREET VIEW
Attachment A - Application Materials
Item 5B - 425 Arapahoe Ave Memo
425 ARAPAHOE - PHOTOS FOR DEMO APP - ZP - 8/7/2024
STREET VIEW (2)
Attachment A - Application Materials
Item 5B - 425 Arapahoe Ave Memo
August 19, 2024
Re: Residential Evaluation
425 Arapahoe Avenue
Boulder, CO
Whitman Interiors:
Earlier this summer we visited the residence at the address above to discuss the state of the existing
structure and the possibility for a remodel and/or addition. While on site, we walked the building
and spent much of our time in the basement/crawl space. Below is a summary of our observation
and conclusions:
Observations:
1.The roof structure was not exposed, but based on the vault and flat coffer, we are under the
impression that the roof is framed with 2x4 or 2x6 rafters and higher collar ties. In addition,
dormers have been cut into the roof framing to allow for a higher ceiling and usable space.
2.The upper floor structure was not exposed but is likely 2x joists at a regular spacing supported
by main level bearing walls.
3.The main floor structure was visible below in the basement and crawl space.
a.At the crawl space we noted 2x floor joists and supporting beams and posts. Most posts
and beams were supported in the dirt, on rocks or blocks.
b.In the basement, 2x floor joists were supported by beams and posts. Most posts extend to
the slab or dirt below. It appears that additional posts and beams have been added
throughout the life of the building due to poor floor performance.
4.The foundation structure consisted of stack stone in most areas and a concrete foundation at the
east 1-story addition. Excavation had occurred to create a basement section of the building. No
retaining structure was observed to support the excavation.
Conclusions:
1.The existing roof structure does not meet current IRC code specifications for a prescriptive
roof. Any revisions to the existing roof structure with a remodel would result in bringing the
roof structure to the current adopted IRC code. This is typically difficult to complete within
the existing space and often results in bent steel beams and re-framing a significant portion
of the existing roof framing for size appropriate roof members and required insulation.
2.We were unable to determine the size and spacing of the existing upper floor structure.
From our experience with other buildings of this age and type, the upper floor joists are
likely small 2x members that do not meet current IRC code specifications for f loor joist size
and span. When remodeling a building of this type, often interior walls are removed or
reconfigured. It is our experience that this would result in the need to strengthen the floor
for compliance with the current adopted IRC code. This can also be difficult to complete
within the depth of the existing floor structure.
Attachment B – Structural Engineering Letter
Item 5B - 425 Arapahoe Ave Memo
3. Based on our observation, the main floor needs additional beams, posts and foundation
support to properly support the floor and structure above. This would require work in both
crawl spaces and the basement. We also find that additional joists may be needed to level
floors of this age and type of construction. Work in the crawl space can be difficult due to
limited access and often the flooring and floor sheathing must be removed for proper access.
4. Further observation of the foundation is needed for proper evaluation. Much of the
foundation could not be accessed due to a small crawl space. But the following is a
recommendation based on what was observed:
a. Existing crawl space foundations appear to be shallow and likely do not have frost
protection. Based on the age of this home, often the stacked stone requires re-tuck
pointing and repair. Access is limited, which results in the need to deconstruct some
of the home and remove finish materials to access the existing foundation for
evaluation and repair.
b. The stacked stone is not suitable for any additional loading and new foundation will
likely be required for any remodeling of the existing space.
c. New foundation is also required within the crawl space to properly support the
existing structure above and for any revisions to the main and upper-level structure.
Often removal of flooring, sheathing and finish materials is required to install these
foundation elements.
d. There is no existing foundation retaining the crawl space grade between the
foundation and crawl space. New foundation (retaining walls) is recommended for
the proper support of the soil in the crawl space and prevent future settlement and
movement.
e. The basement posts likely bear on dirt of the basement slab and should be properly
supported by interior footing pads.
It is our overall conclusion that the building is in poor to satisfactory condition. If any remodeling is
to occur, significant structural revisions will be likely at all levels of the building. Structural repairs
and revisions of this type are expensive and often more expensive than demolishing and replacing
the structure with a new building built to code with modern building materials. In addition, repair of
homes of this type of construction are time consuming and requires a skilled contractor.
The owner should also keep in mind that repair of buildings of this type will likely not result in the
same performance of a new structure. The owner must accept that the repairs will help future
performance built will not guarantee future performance or eliminate damage to finish materials in
the future. It is for this reason that we recommend considering demolishing and replacing the
structure prior to continuing with a remodel and addition.
At the owner’s request, please contact us for further evaluation of the building and preliminary
design of any repairs, revisions or new structure. In addition, please feel free to contact us with any
further questions or concerns.
The goal of this report is to educate the owner on the possible extent of structural repairs required if
a remodel and addition to the building are desired. Please also refer to the structural report provided
prior to purchase.
Attachment B – Structural Engineering Letter
Item 5B - 425 Arapahoe Ave Memo
The information contained in this report is the author’s professional opinion based on visual
evidence readily available at the site, without the removal of finishing materials, as indicated above.
Of course, this means there could be hidden defects which are not discoverable at this time, without
demolition of finish materials. That is true for most buildings, and an inherent limitation for this
kind of report. Should additional information become available or additional movement is
perceived, we recommend that our firm be contacted for further review.
Our observation was conducted only to review structural items and did not include evaluation of
mechanical (heating, cooling, plumbing) and electrical systems, subsoil conditions, nor architectural
features. In addition, we have not completed a full structural evaluation of the building only a
preliminary review at the time of our observation.
The issuance of this report does not provide the building’s current or future owners with a guarantee,
certification or warranty of future performance. Acceptance and use of this report does not transfer
financial liability for the building or the property to its author, (Jesse Sholinsky), or any other
owners or employees of GFE Structural.
Written by:
Jesse Sholinsky, P.E
`
Attachment B – Structural Engineering Letter
Item 5B - 425 Arapahoe Ave Memo
Substrata LLC
3522 Draft Horse Court • Loveland, CO 80538 • (970) 535-6144
September 13, 2024
Susan Ellis
431 Arapahoe Avenue
Boulder, Colorado 80302
Re: Geotechnical Subsurface Exploration Report
Redevelopment of Part of Lot 5, Block A, Highland Lawn
425 Arapahoe Avenue
Boulder, Colorado
Substrata Project # 24-1174
Ms. Ellis:
Substrata LLC (Substrata) personnel have completed the geotechnical subsurface
exploration you requested for the proposed single-family residence to be constructed at 425
Arapahoe Avenue in Boulder, Colorado. The results of our subsurface exploration and
pertinent geotechnical engineering recommendations are included with this report.
We understand an existing single-family residence and associated site improvements will
be demolished and removed from the property prior to construction of a new single-family
residence. The existing residence is a single to two-story wood frame structure constructed
over a crawl space and includes a small below-grade mechanical storage area and is
reported to be supported by a combination of stacked stone and mortar and conventional
spread footing foundations. We understand the proposed new residence will be a two-story
wood frame structure constructed over a basement and may also include a crawl space area.
Foundation loads for the residence are expected to be relatively light, with continuous wall
loads less than 3.5 kips per lineal foot and individual column loads less than 75 kips. Small
grade changes are anticipated to develop finish site grades in the residence area.
The purpose of our exploration was to describe the subsurface conditions encountered in
the completed site boring and develop the test data necessary to provide recommendations
concerning design and construction of the residence foundations and support of floor slabs.
The conclusions and recommendations outlined in this report are based on results of the
completed field and laboratory testing and our experience with subsurface conditions in
this area.
Attachment C - Geotechnical Subsurface Exploration Report
Item 5B - 425 Arapahoe Ave Memo
Geotechnical Subsurface Exploration Report
Redevelopment of Part of Lot 5, Block A, Highland Lawn
425 Arapahoe Avenue, Boulder, Colorado
Substrata Project # 24-1174
2
SITE DESCRIPTION
The proposed residence will be constructed in the same general location as the existing
residence situated on the south-central part of Lot 5 of Block A in the Highland Lawn
residential development, located at 425 Arapahoe Avenue in Boulder, Colorado. At the
time of our site exploration, an existing shed, studio, and associated exterior flatwork and
various landscape improvements were noted on the property in the vicinity of the existing
residence. Numerous mature deciduous and coniferous trees, shrubs and bushes were also
noted in the area surrounding the existing residence and proposed construction area. The
maximum difference in ground surface elevation across the existing residence footprint
was estimated to be on the order of two (2) feet or less.
EXPLORATION AND TESTING PROCEDURES
To develop subsurface information for the proposed new residence, one (1) soil boring was
extended to a depth of approximately 15 feet below present site grade as close to the
existing and approximate new residence footprint as site access would allow. The boring
location was established in the field by Substrata personnel based on discussion with a
representative of the client, the accessibility of the site and by pacing and estimating angles
and distances from identifiable site references. A diagram indicating the approximate
boring locations is included with this report. The boring location should be considered
accurate only to the degree implied by the methods used to make the field measurements.
A graphic log of the auger boring is also included.
The test hole was advanced using 4-inch diameter continuous-flight auger, powered by a
truck-mounted CME-45 drill rig. Samples of the subsurface materials were obtained at
regular intervals using California barrel sampling procedures in general accordance with
ASTM specification D-1586. Penetration resistance measurements were obtained by
driving the standard sampling barrel into the substrata using a 140-pound hammer falling
30 inches. The number of blows required to advance the sampler 12 inches is recorded and
helpful in estimating the consistency or relative density of the soils encountered. In the
California barrel sampling procedure, less disturbed samples are obtained in removable
brass liners. Samples of the subsurface materials obtained in the field were sealed and
returned to the laboratory for further evaluation, classification and testing.
Attachment C - Geotechnical Subsurface Exploration Report
Item 5B - 425 Arapahoe Ave Memo
Geotechnical Subsurface Exploration Report
Redevelopment of Part of Lot 5, Block A, Highland Lawn
425 Arapahoe Avenue, Boulder, Colorado
Substrata Project # 24-1174
3
The samples collected were tested in the laboratory to measure natural moisture content
and were visually and/or manually classified in accordance with the Unified Soil
Classification System (USCS). The USCS group symbols are indicated on the attached
boring log. An outline of the USCS classification system is included with this report.
As part of the laboratory testing, a calibrated hand penetrometer (CHP) was used to
estimate the unconfined compressive strength of essentially cohesive specimens. The CHP
also provides a more reliable estimate of soil consistency than tactual observation alone.
Dry density, Atterberg limits, -200 wash and swell/consolidation tests were completed on
selected samples to help establish specific soil characteristics. Atterberg limits tests are
used to determine soil plasticity. The percent passing the #200 size sieve (-200 wash) test
is used to determine the percentage of fine-grained materials (clay and silt) in a sample.
Swell/consolidation tests are performed to evaluate soil volume change potential with
variation in moisture content. The results of the completed laboratory tests are outlined on
the attached boring log and swell/consolidation test summary.
SUBSURFACE CONDITIONS
The materials encountered in the completed site boring can be summarized as follows.
Approximately 3 to 4 inches of driveway concrete was encountered at the surface at the
boring location underlain by brown/beige/rust sandy lean clay which varied to clayey sand
and contained varying amounts of gravel. The lean clay/clayey sand was hard in terms of
consistency or medium dense in terms of relative density, exhibited borderline low/
moderate swell potential at current moisture and density conditions, and extended to a
depth of about 3½ feet below ground surface, where it was underlain by brown/beige/gray/
rust clayey to silty sand with varying amounts of gravel. The clayey/silty sand varied from
dense to very dense in terms of relative density, would be expected to be non-expansive or
possess low swell potential based upon the physical properties and engineering
characteristics of the material and extended to the bottom of the boring at a depth of about
15 feet below ground surface.
The stratigraphy indicated on the included boring log represents the approximate location
of changes in soil types. Actual changes may be more gradual than those indicated.
Attachment C - Geotechnical Subsurface Exploration Report
Item 5B - 425 Arapahoe Ave Memo
Geotechnical Subsurface Exploration Report
Redevelopment of Part of Lot 5, Block A, Highland Lawn
425 Arapahoe Avenue, Boulder, Colorado
Substrata Project # 24-1174
4
Groundwater was not encountered in the bore hole to the depth explored (about 15 feet
below ground surface) when checked immediately after completion of drilling. When
checked about three (3) days after drilling, the boring remained dry to the depth explored
at that time. Groundwater levels will vary seasonally and over time based on weather
conditions, site development, irrigation practices and other hydrologic conditions. Perched
and/or trapped groundwater conditions may also be encountered at times throughout the
year. Perched water is commonly encountered in soils overlying less permeable soil layers
and/or bedrock. Trapped water is typically encountered within more permeable zones of
layered soil and bedrock systems. The location and amount of perched/trapped water can
also vary over time.
ANALYSIS AND RECOMMENDATIONS
General
As previously outlined, the near-surface lean clay/clayey sand soils identified in the boring
drilled at this site were relatively dry and hard at the time of drilling and exhibited
borderline low/moderate swell potential at current moisture and density conditions.
Heaving of site improvements placed directly on or immediately above the expansive lean
clay/clayey sand soils would be expected as the moisture content of those materials
increases subsequent to construction.
Careful observation of the exposed foundation bearing materials should be completed at
the time of construction by Substrata personnel or another qualified geotechnical engineer
to ensure all footing foundations will be supported on like, natural materials with suitable
strength and low volume change potential. In order to develop consistent low-volume-
change (LVC) foundation bearing across the residence footprint, we recommend extending
all foundations through any moderately expansive near-surface lean clay/clayey sand to
bear on clayey/silty sand with no to low swell potential at slightly greater depth than is
typical (anticipated to be encountered at a depth of about 3 to 4 feet below ground surface).
Based on results of the completed field and laboratory testing, it is our opinion
overexcavation/backfill procedures could be completed beneath at-grade floor slabs (if
any) to reduce the potential for movement of those supported elements subsequent to
Attachment C - Geotechnical Subsurface Exploration Report
Item 5B - 425 Arapahoe Ave Memo
Geotechnical Subsurface Exploration Report
Redevelopment of Part of Lot 5, Block A, Highland Lawn
425 Arapahoe Avenue, Boulder, Colorado
Substrata Project # 24-1174
5
construction. Recommendations concerning overexcavation/backfill procedures to
redevelop LVC potential at-grade floor slab support are outlined below.
Demolition and Site Development
We understand the existing residence will be razed and removed from the site prior to
construction of the new residence. Within the new residence and any proposed fill areas,
any remaining foundations, floor slabs and other site improvements should be completely
removed. Care will be needed to ensure all expansive near-surface lean clay/clayey sand
soils and any existing fill/backfill materials associated with the demolished residence are
also completely removed from within the new structure footprint at this time. In addition,
all trees, tree root systems, and dry and desiccated soils associated with the tree root
systems should be completely removed from within the proposed residence and any
proposed fill areas. The depth and extent of required removal can best be established at the
time of excavation through openhole observation. If/where required, the excavated/
removed materials should be replaced as controlled and compacted fill as outlined below.
After stripping and completing all cuts and removal procedures and prior to placement of
any new fill/backfill or flatwork concrete, we recommend the exposed subgrade soils be
scarified to a depth of 9 inches, adjusted in moisture content and compacted to at least 95%
of the materials standard Proctor maximum dry density. The moisture content of the
scarified soils should be adjusted to be within the range of ±2% of standard Proctor
optimum moisture content at the time of compaction. If some backfilling of the demolished
structure removal excavations is required, we recommend the excavation be continuously
and horizontally benched during backfilling in order to reduce the potential for
development of a shear plane between the natural site soils and controlled backfill.
Fill and removal area backfill soils required to develop the site should consist of approved
LVC soils free from organic matter, debris and other objectionable materials. Based on
results of the completed laboratory testing, it is our opinion the natural site lean clay and
clayey/silty sand could be used as fill in these areas provided cobble/boulder-sized
materials (greater than 3 inches in any dimension) are screened and removed prior to use,
and the proper moisture content can be developed in these materials at the time of
placement and compaction. We recommend the site lean clay, clayey/silty sand and/or
Attachment C - Geotechnical Subsurface Exploration Report
Item 5B - 425 Arapahoe Ave Memo
Geotechnical Subsurface Exploration Report
Redevelopment of Part of Lot 5, Block A, Highland Lawn
425 Arapahoe Avenue, Boulder, Colorado
Substrata Project # 24-1174
6
similar soils be placed in loose lifts not to exceed 9 inches thick, adjusted in moisture
content and compacted as recommended for the scarified materials above.
Care should be taken to avoid disturbing all subgrade soils prior to placement of any
overlying improvements. Soils which are allowed to dry out or become wet and softened
or disturbed by the construction activities should be removed and replaced or reworked in
place prior to concrete placement.
Foundations
Based on the materials encountered in the completed site boring and results of laboratory
testing, it is our opinion the proposed lightly loaded residence could be supported by
continuous spread footing and isolated pad foundations bearing on natural, undisturbed
clayey/silty sand with no to low swell potential. For design of footing foundations bearing
on natural, undisturbed, medium dense to very dense clayey/silty sand, we recommend
using a maximum net allowable soil bearing pressure of 2,500 psf.
Exterior footings should bear a minimum of 32 inches below finished adjacent exterior
grade to provide frost protection. We recommend formed strip footings have a minimum
width of 12 inches and isolated pad foundations have a minimum width of 24 inches in
order to facilitate construction and reduce the potential for development of eccentrically
loaded footings. Actual footing widths should be designed by a structural engineer.
For design of footing foundations and foundation walls to resist lateral movement, a
passive equivalent fluid pressure value of 275 pcf could be used. The top 32 inches of
subgrade could be considered a surcharge load but should not be used in the passive
resistance calculations. A coefficient of friction of 0.45 could be used between foundation
and floor slab concrete and the bearing soils to resist sliding. The recommended passive
equivalent fluid pressure value and coefficient of friction do not include a factor of safety.
We estimate settlement of footing foundations designed and constructed as outlined above
and resulting from the assumed structural loads would be on the order of 1 inch or less.
Differential settlement could approach the amount of total settlement estimated above. If
Attachment C - Geotechnical Subsurface Exploration Report
Item 5B - 425 Arapahoe Ave Memo
Geotechnical Subsurface Exploration Report
Redevelopment of Part of Lot 5, Block A, Highland Lawn
425 Arapahoe Avenue, Boulder, Colorado
Substrata Project # 24-1174
7
water from any source is allowed to infiltrate the foundation bearing soils, additional
movement of foundations could occur.
Floor Slabs
In the basement area of the residence, the floor slab could be supported directly above
natural, undisturbed silty/clayey sand with no to low swell potential. At this time, we do
not expect any at-grade floor slabs will be constructed as part of the proposed construction.
At-grade floor slabs (if any) could be supported on reconditioned natural site soils and/or
properly placed and compacted fill/backfill developed as outlined in the “Demolition and
Site Development” section of this report.
Floor slabs should be designed and constructed as floating slabs, separated from foundation
walls, columns and plumbing and mechanical penetrations using block-outs or appropriate
isolation material. Additionally, we recommend all partition walls supported above slabs-
on-grade be constructed as floating walls to help reduce the potential for differential slab-
to-foundation movement causing distress in upper sections of the structure. A minimum
one and one-half (1½) inch void space is recommended beneath all floating walls. Special
attention to door and stair framing, drywall installation, garage door tracks and trim
carpentry should be taken to isolate those elements from the floor slabs, allowing for some
differential floor slab-to-foundation movement to occur without transmitting stresses to the
overlying structure.
Depending on the type of floor covering and floor covering adhesive used in finished slab-
on-grade areas, a vapor barrier may be required immediately beneath the floor slabs in
order to maintain flooring product manufacturer warranties. A vapor barrier would help
reduce the transmission of moisture through the floor slab. However, the unilateral
moisture release caused by placing concrete on an impermeable surface can increase slab
curl. The amount of slab curl can be reduced by careful selection of an appropriate concrete
mix; however, slab curl cannot be eliminated. We recommend the owner, architect and
flooring contractor consider the performance of the slab, in conjunction with the proposed
flooring products to help determine if a vapor barrier will be required and where best to
position the vapor barrier in relation to the floor slab. Additional guidance and
Attachment C - Geotechnical Subsurface Exploration Report
Item 5B - 425 Arapahoe Ave Memo
Geotechnical Subsurface Exploration Report
Redevelopment of Part of Lot 5, Block A, Highland Lawn
425 Arapahoe Avenue, Boulder, Colorado
Substrata Project # 24-1174
8
recommendations concerning slab-on-grade design can be found in American Concrete
Institute (ACI) section 302.
Below-Grade Construction
As a precaution, we recommend a perimeter drain system be constructed around the
basement and any crawl space areas to reduce the potential for water infiltration into the
below-grade areas of the residence and/or the development of hydrostatic pressures behind
the foundation walls. The perimeter drain system should consist of a 4-inch diameter
perforated drain pipe surrounded by a minimum of six (6) inches of free-draining gravel.
A filter fabric should be considered around the free-draining gravel or perforated pipe to
reduce the potential for an influx of fine-grained soils into the system. The invert of the
drain pipe, at its high point, should be placed at approximate foundation bearing levels, run
around the interior or exterior perimeter of crawl space areas (if any) and exterior perimeter
of the basement area with a minimum slope of ⅛-inch per foot to facilitate efficient water
removal and should discharge to a sump pump and pit system. Care should be taken at the
time of perimeter drain installation to avoid disturbing those soils providing support to the
residence footing foundations (extending down at a 1:1 slope from the bottom edges of the
footings).
As an additional precaution, we recommend a vapor barrier be installed in crawl space
areas (if any) in order to help maintain in-situ soil moisture conditions and reduce the
potential for migration of soil moisture into the crawl space area. Subgrades in the crawl
space areas should be sloped to drain to the perimeter drain system. The owner/client
should consider consulting with a mold prevention specialist for additional precautions that
could be implemented to reduce the potential for development of moist air conditions in
the crawl space areas of the residence.
Backfill placed adjacent to the below-grade walls should consist of approved LVC soils
free from organic matter, debris and other objectionable materials. The site lean clay and
clayey/silty sand could be used as backfill in this area. The site lean clay, clayey/silty sand
and/or similar soils should be placed in loose lifts not to exceed 9 inches thick, adjusted in
moisture and compacted as previously outlined in the “Demolition and Site Development”
section of this report.
Attachment C - Geotechnical Subsurface Exploration Report
Item 5B - 425 Arapahoe Ave Memo
Geotechnical Subsurface Exploration Report
Redevelopment of Part of Lot 5, Block A, Highland Lawn
425 Arapahoe Avenue, Boulder, Colorado
Substrata Project # 24-1174
9
Excessive lateral stresses can be imposed on below-grade walls when using heavier
mechanical compaction equipment. We recommend compaction of unbalanced foundation
wall backfill soils be completed using light mechanical or hand compaction equipment.
Lateral Earth Pressures
For design of below-grade foundation walls where preventative measures have been taken
to reduce the potential for development of hydrostatic loads on the walls, we recommend
using an at-rest equivalent fluid pressure value of 65 pounds per cubic foot. A modified
active equivalent fluid pressure of 55 pounds per cubic foot could be used for partially
restrained conditions where some rotation of the below-grade walls must occur to develop
the active earth pressure state. That rotation can result in cracking of the below-grade walls
typically in between corners and other restrained points. The amount of deflection of the
top of the wall can be estimated at 0.5% times the height of the wall.
Variables that affect lateral earth pressures include but are not limited to the shrink/swell
potential of the backfill soils, backfill compaction and geometry, wetting of the backfill
soils, surcharge loads and point loads developed in the backfill materials. The
recommended equivalent fluid pressure values do not include a factor of safety or an
allowance for hydrostatic loads. Use of expansive soil backfill, excessive compaction of
the wall backfill or surcharge loads placed adjacent to the below-grade walls can add to the
lateral earth pressures causing the equivalent fluid pressure values used in design to be
exceeded.
Drainage
Positive drainage is imperative for satisfactory long-term performance of the proposed
residence and associated site improvements. We recommend positive drainage be
developed away from the structure during construction and maintained throughout the life
of the site improvements, with twelve (12) inches of fall in the first 10 feet away from the
residence. Shallower slopes could be considered in hardscape areas. In the event that poor
or negative drainage develops adjacent to the residence over time, the original grade and
associated positive drainage outlined above should be immediately restored.
Attachment C - Geotechnical Subsurface Exploration Report
Item 5B - 425 Arapahoe Ave Memo
Geotechnical Subsurface Exploration Report
Redevelopment of Part of Lot 5, Block A, Highland Lawn
425 Arapahoe Avenue, Boulder, Colorado
Substrata Project # 24-1174
10
Care should be taken in the planning of landscaping to avoid features which could result in
the fluctuation of the moisture content of the foundation bearing and/or flatwork subgrade
soils. We recommend watering systems be placed a minimum of 5 feet away from the
perimeter of the site structures and be designed to discharge away from all site
improvements. Gutter systems should be considered to help reduce the potential for water
ponding adjacent to the building, with the gutter downspouts, roof drains or scuppers
extended to discharge a minimum of 5 feet away from structural, flatwork and pavement
elements. Water which is allowed to pond adjacent to site improvements can result in
unsatisfactory performance of those improvements over time.
GENERAL COMMENTS
This report was prepared based upon the data obtained from the completed site exploration,
laboratory testing, engineering analysis and any other information discussed. The
completed boring provides an indication of subsurface conditions at the boring location
only. Variations in subsurface conditions can occur in relatively short distances away from
the boring. This report does not reflect any variations which may occur across the site or
away from the boring. If variations in the subsurface conditions anticipated become
evident, the geotechnical engineer should be notified immediately so that further evaluation
can be completed and when warranted, alternative recommendations provided.
The scope of services for this project does not include either specifically or by implication
any biological or environmental assessment of the site or identification or prevention of
pollutants or hazardous materials or conditions. Other studies should be completed if
concerns over the potential of such contamination or pollution exist.
The geotechnical engineer should be retained to review the plans and specifications so that
comments can be made regarding the interpretation and implementation of our
geotechnical recommendations in the design and specifications. The geotechnical engineer
should also be retained to provide testing and observation services during construction to
help determine that the design requirements are fulfilled.
This report has been prepared for the exclusive use of our client for specific application to
the project discussed and has been prepared in accordance with the generally accepted
Attachment C - Geotechnical Subsurface Exploration Report
Item 5B - 425 Arapahoe Ave Memo
Geotechnical Subsurface Exploration Report
Redevelopment of Part of Lot 5, Block A, Highland Lawn
425 Arapahoe Avenue, Boulder, Colorado
Substrata Project # 24-1174
11
standard of care for the profession. No warranties express or implied, are made. The
conclusions and recommendations contained in this report should not be considered valid
in the event that any changes in the nature, design or location of the project as outlined in
this report are planned, unless those changes are reviewed and the conclusions of this report
modified and verified in writing by the geotechnical engineer.
We appreciate the opportunity to be of service to you on this project. If you have any
questions concerning the enclosed information or if we can be of further service to you in
any way, please do not hesitate to contact us.
Respectfully,
Substrata LLC Reviewed by:
09/13/2024 09/13/2024
Darrel DiCarlo, P.E. Alec Kaljian, P.E.
Senior Project Engineer Senior Project Engineer
Attachment C - Geotechnical Subsurface Exploration Report
Item 5B - 425 Arapahoe Ave Memo
Attachment C - Geotechnical Subsurface Exploration Report
Item 5B - 425 Arapahoe Ave Memo
LOG OF BORING B-1
1/1 CME 45
4" CFA
Automatic
JJ / CB
Estimated Swell % Passing
SOIL DESCRIPTION Depth "N"MC DD qu % Swell @ Pressure # 200 Sieve
(ft)(%)(pcf)(psf)500 psf (psf)LL PI (%)
3 - 4" DRIVEWAY CONCRETE -
1
CL-SC SANDY LEAN CLAY to CLAYEY SAND -
brown, beige, rust 2
hard / medium dense -
varying amounts of GRAVEL 3 CS 38 13.3 118.4 9000+2.9%9300 33 18 43.7%
-
4
-
5 CS 50/8 1.4 -------
-
6
-
7
-
8
SP-SM SAND with varying amounts of -
CLAY, SILT and GRAVEL / COBBLES 9
brown, beige, gray, rust -
dense to very dense 10 CS 50/4 2.0 ------13.4%
-
11
-
12
-
13
-
14
-
15 CS 50/2 2.9 -------
BOTTOM OF BORING @ 15.0'-
16
-
17
-
18
-
19
-
20
-
21
-
22
-
23
-
24
-
25
REDEVELOPMENT OF PART OF LOT 5, BLOCK A, HIGHLAND LAWN
425 ARAPAHOE AVENUE, BOULDER, COLORADO
Project # 24-1174
September 2024
Sheet Drilling Rig:Water Depth Information
Start Date 8/27/2024 Auger Type:During Drilling None
Finish Date 8/27/2024 Hammer Type:After Drilling None
USCSSamplerAtterberg Limits
Surface Elev.-Field Personnel:3 Days After Drilling None
Attachment C - Geotechnical Subsurface Exploration Report
Item 5B - 425 Arapahoe Ave Memo
Liquid Limit 33
Plasticity Index 18
% Passing #200 43.7%
Dry Density (pcf)118.4
REDEVELOPMENT OF PART OF LOT 5, BLOCK A, HIGHLAND LAWN
425 ARAPAHOE AVENUE, BOULDER, COLORADO
Project # 24-1174
September 2024
SWELL/CONSOLIDATION TEST SUMMARY
Sample ID: B-1 @ 2
Initial Moisture 13.3%
Sample Description: Brown Sandy Lean Clay (CL)
500
Final Moisture 9.3%
% Swell @ 500 psf 2.9%
Swell Pressure (psf)9,300
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
10 100 1000 10000 100000
---------
Applied Load (psf)
Attachment C - Geotechnical Subsurface Exploration Report
Item 5B - 425 Arapahoe Ave Memo
UNIFIED SOIL CLASSIFICATION SYSTEM
Criteria for Assigning Group Symbols and Group Names Using Laboratory TestsA Soil Classification
Group
Symbol Group NameB
Cu ! 4 and 1 " Cc " 3E GW Well graded gravelF Clean Gravels
Less than 5% finesC Cu < 4 and/or 1 > Cc > 3E GP Poorly graded gravelF
Fines classify as ML or MH GM Silty gravelF,G, H
Coarse Grained Soils
More than 50% retained
on No. 200 sieve
Gravels
More than 50% of coarse
fraction retained on
No. 4 sieve Gravels with Fines More
than 12% finesC Fines classify as CL or CH GC Clayey gravelF,G,H
Cu ! 6 and 1 " Cc " 3E SW Well graded sandI Clean Sands
Less than 5% finesD Cu < 6 and/or 1 > Cc > 3E SP Poorly graded sandI
Fines classify as ML or MH SM Silty sandG,H,I
Sands
50% or more of coarse
fraction passes
No. 4 sieve Sands with Fines
More than 12% finesD Fines classify as CL or CH SC Clayey sandG,H,I
PI > 7 and plots on or above “A” lineJ CL Lean clayK,L,M Silts and Clays
Liquid limit less than 50
Inorganic
PI < 4 or plots below “A” lineJ ML SiltK,L,M
Liquid limit - oven
dried
Organic clayK,L,M,N
Fine-Grained Soils
50% or more passes the
No. 200 sieve
Organic
Liquid limit - not
dried
<0.75 OL
Organic siltK,L,M,O
Inorganic PI plots on or above “A” line CH Fat clayK,L,M Silts and Clays
Liquid limit 50 or more PI plots below “A” line MH Elastic siltK,L,M
Liquid limit - oven dried Organic clayK,L,M,P Organic
Liquid limit - not dried
<0.75 OH
Organic siltK,L,M,Q
Highly organic soils Primarily organic matter, dark in color, and organic odor PT Peat
A Based on the material passing the 3-in. (75-mm) sieve
B If field sample contained cobbles or boulders, or both, add “with cobbles
or boulders, or both” to group name.
C Gravels with 5 to 12% fines require dual symbols: GW-GM well graded
gravel with silt, GW-GC well graded gravel with clay, GP-GM poorly
graded gravel with silt, GP-GC poorly graded gravel with clay.
D Sands with 5 to 12% fines require dual symbols: SW-SM well graded
sand with silt, SW-SC well graded sand with clay, SP-SM poorly graded
sand with silt, SP-SC poorly graded sand with clay
E Cu = D60/D10 Cc =
F If soil contains ! 15% sand, add “with sand” to group name.
G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM.
HIf fines are organic, add “with organic fines” to group name.
I If soil contains ! 15% gravel, add “with gravel” to group name.
J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay.
K If soil contains 15 to 29% plus No. 200, add “with sand” or “with
gravel,” whichever is predominant.
L If soil contains ! 30% plus No. 200 predominantly sand, add
“sandy” to group name.
M If soil contains ! 30% plus No. 200, predominantly gravel, add
“gravelly” to group name.
N PI ! 4 and plots on or above “A” line.
O PI < 4 or plots below “A” line.
P PI plots on or above “A” line.
Q PI plots below “A” line.
Attachment C - Geotechnical Subsurface Exploration Report
Item 5B - 425 Arapahoe Ave Memo
GENERAL NOTES
DRILLING & SAMPLING SYMBOLS:
SS: Split Spoon - 1⅜" I.D., 2" O.D., unless otherwise noted HS:
ST: Thin-W alled Tube – 2.5" O.D., unless otherwise noted PA:
RS: Ring Sampler - 2.42" I.D., 3" O.D., unless otherwise noted HA:
CS: California Barrel - 1.92" I.D., 2.5" O.D., unless otherwise noted RB:
BS: Bulk Sample or Auger Sample WB:
Hand Sample
Power Auger
Hand Auger
Rock Bit
Wash Boring or Mud Rotary
The number of blows required to advance a standard 2-inch O.D. split-spoon sampler (SS) the last 12 inches of the total 18-inch
penetration with a 140-pound hammer falling 30 inches is considered the “Standard Penetration” or “N-value”. For 2.5” O.D.
California Barrel samplers (CB) the penetration value is reported as the number of blows required to advance the sampler 12
inches using a 140-pound hammer falling 30 inches, reported as “blows per inch,” and is not considered equivalent to the
“Standard Penetration” or “N-value”.
WATER LEVEL MEASUREMENT SYMBOLS:
W L: Water Level WS: W hile Sampling
W CI: Wet Cave in WD: W hile Drilling
DCI: Dry Cave in BCR: Before Casing Removal
AB: After Boring ACR: After Casing Removal
W ater levels indicated on the boring logs are the levels measured in the borings at the times indicated. Groundwater levels at other
times and other locations across the site could vary. In pervious soils, the indicated levels may reflect the location of groundwater.
In low permeability soils, the accurate determination of groundwater levels may not be possible with only short-term observations.
DESCRIPTIVE SOIL CLASSIFICATION: Soil classification is based on the Unified Classification System. Coarse Grained Soils
have more than 50% of their dry weight retained on a #200 sieve; their principal descriptors are: boulders, cobbles, gravel or sand.
Fine Grained Soils have less than 50% of their dry weight retained on a #200 sieve; they are principally described as clays if they
are plastic, and silts if they are slightly plastic or non-plastic. Major constituents may be added as modifiers and minor constituents
may be added according to the relative proportions based on grain size. In addition to gradation, coarse-grained soils are defined
on the basis of their in-place relative density and fine-grained soils on the basis of their consistency.
FINE-GRAINED SOILS COARSE-GRAINED SOILS BEDROCK
(CB)
Blows/Ft.
(SS)
Blows/Ft. Consistency
(CB)
Blows/Ft.
(SS)
Blows/Ft.
Relative
Density
(CB)
Blows/Ft.
(SS)
Blows/Ft.Consistency
< 3 0-2 Very Soft 0-5 < 3 Very Loose < 24 < 20 Weathered
3-5 3-4 Soft 6-14 4-9 Loose 24-35 20-29 Firm
6-10 5-8 Medium Stiff 15-46 10-29 Medium Dense 36-60 30-49 Medium Hard
11-18 9-15 Stiff 47-79 30-50 Dense 61-96 50-79 Hard
19-36 16-30 Very Stiff >79 >50 Very Dense >96 >79 Very Hard
>36 >30 Hard
RELATIVE PROPORTIONS OF SAND AND
GRAVEL
GRAIN SIZE TERMINOLOGY
Descriptive Terms of
Other Constituents
Percent of
Dry Weight
Major Component
of Sample Particle Size
Trace < 15 Boulders Over 12 in. (300mm)
W ith 15 – 29 Cobbles 12 in. to 3 in. (300mm to 75 mm)
Modifier >30 Gravel 3 in. to #4 sieve (75mm to 4.75 mm)
Sand
Silt or Clay
#4 to #200 sieve (4.75mm to 0.075mm)
Passing #200 Sieve (0.075mm)
RELATIVE PROPORTIONS OF FINES PLASTICITY DESCRIPTION
Descriptive Terms of
Other Constituents
Percent of
Dry Weight Term Plasticity Index
Trace
W ith
Modifiers
< 5
5 – 12
>12
Non-plastic
Low
Medium
High
0
1-10
11-30
30+
Attachment C - Geotechnical Subsurface Exploration Report
Item 5B - 425 Arapahoe Ave Memo