EAST BENCH SLIDE AREA
The slide area on the east bench of Riverdale City is active and extremely dangerous. The area has been fenced off and identified and marked as "No Trespass", as such stay out of the area for your safety!! Three homes have been evacuated. The City is working with multiple state, county, and other agencies regarding the slide itself and it's ongoing impacts to the neighborhood and the lands below.
A Geologist from the Utah Geological Survey sent the following information:
I was able to visit the landslide yesterday (5/29/18) and there has been further movement. Since my last visit on May 17, the scarp is now 6.5 feet from the 4839 South garage and lost 13 feet on the south flank, now impacting the 4887 South fence line. We are in the process of reworking our well database so the the portal has yet to be updated. My pictures from yesterday are available at our archive https://geodata.geology.utah.gov/pages/search.php?search=!collection315 and the measurements are available here: https://docs.google.com/document/d/1XKU4cb8xDPsktBcygpgoiVXkvOAF2IUjtTCLO6Sqxgw/edit?usp=sharing
The UGS (Utah Geological Survey) website published a reference page for the slide. The page is available under Hazards and Landslides & Rockfall, part of the Recent Landslide Events section named Spring Creek Road Landslide. Here is the direct link https://geology.utah.gov/hazards/landslides-rockfalls/spring-creek-road-landslide/
The UGS went to the site yesterday and gathered groundwater elevation levels, GPS measurements, and scarp distance from houses. They will maintain frequent site visits based on slide activity and continue to measure distances from scarp to houses.
Here are the current and past measurements, closest to scarp:
North house (4839 S.)
March 7 - 28.8 ft
March 14 - 27.8 ft
March 20 - 26.5 ft
March 27 - 16.6 ft
April 3 - 16.5 ft
Middle house (4851 S.)
March 7 - 53.45 ft
March 14 - 50.5 ft
March 20 - 50.0 ft
March 27 - 46.8 ft
April 3 - 43.3 ft
South house (4865 S.)
March 7 - 41.33 ft
March 13 - 41.6 ft
March 20 - 41.5 ft
March 27 - 37.0 ft
April 3 - 32.0 ft
Volunteer house (4887 S.)
(*adding estimated 20 ft from fence to house corner, due to dogs in yard)
March 7 - 75 ft*
March 13 - 74 ft*
March 20 - 71 ft*
March 27 - 60 ft*
April 3 - 59 ft*
These measurements demonstrate that this area is very dangerous and continues to be a threat to safety.
Landslide boundary maps:
Landslide boundary with redeposited area
Landslide boundaries with borehole locations
Click on an image to view in a larger PDF format.
The images below were taken from a drone on April 3, 2018.
To view a larger image click on a picture.
The images below were taken from a drone on March 6, 2018.
To view a larger image click on a picture.
Attached herewith is the boring log information and summary letter from the forthcoming geotechnical study being performed by GSH. This study is the core analysis or if you will “summary of soil boring logs” on the three core drill holes completed on 600 West street. This summary is a portion of the GSH geotechnical study and is a written record of information about the soil removed from a hole(s) drilled in the earth, it also lists the depth of the underground aquifer that is in the area. These core wells now house the inclinometer (with base measurements) and the piezometers which will be used to gather data on earth movement and water table levels. This gathering of data will be overseen with GSH and UGS geologists and will be useful in water table behavior and potential diagnoses of rotational earth movement or lateral movement of earth.
To view the boring letter click here
January 12, 2018 - WATER TEST RESULTS
This is in response to questions regarding sources of water being "man-induced" in the area of the recent land slide. Shortly after the slide event, Riverdale City and other water purveyors completed several different test activities to rule-out man induced water sources. These inspections and tests have included the following: visual pipeline inspections, pipe line water-pressure tests, residual chlorine testing, pipe resonance inspections, visually inspecting all water meters and valves in the vicinity, sensitive acoustical testing of water lines, and lastly, a STIFF ion test of water. The STIFF ion test was performed upon water delivered by Weber Basin Water Conservancy District to the communities of South Ogden, Washington Terrace, & Riverdale in contrast to water obtained from the land slide toe. This latest test (STIFF ion test) was to compare the ion analysis with water extruding from the slide area to culinary water delivered to all communities, the compared waters are very different in ion makeup and not from the same source...as such, all of the performed tests have again confirmed water emanating from the toe of the slide is not man induced water.
As mentioned above, the most recent water sample test performed was a STIFF ion test. The diagram or ion panel results of this test is shown below; a STIFF ion test is used to show graphical representation of water chemical ion analysis. Essentially, the "finger-print" of water; in this particular case the compared samples have completely different ion or chemical make up. Geo-chemists use these STIFF plots for analysis and presentation of geochemistry data that are particularly useful in hydro-geologic investigations.
The City continues to monitor the slide and working with geologists will be performing a geotechnical investigation of the soil composition. The geo-investigation work will be within the 600 West street itself beginning Jan. 18th. This work will involve drilling rigs performing work directly east (within the street) of the slide impact zone. The resulting geotechnical study will take some time to complete with on-going monitoring of the slide and associated soils through installed piezometers and inclinometers. The slide area continues to be very active and dangerous with additional sluffing of soil highly probable as was noted yesterday; as such the City and other agencies continue to monitor the situation. For your safety please stay out of this area.
Email statement for Weber Basin Water (March 5, 2018):
This email is just to restate what we have stated before regarding the water testing of the different water sources. The District employees collected samples from the drinking water pipeline in the area and at the water treatment plant. They also collected two samples from the springs near the slide ares in Riverdale. an ion analysis was done on all samples, comparing the cations and anions of each source. From the results, shown below, as well as the plotted numbers and the shape of the STIFF diagrams, we are confident that the water from the drinking water system is different from the water from the spring sources near the slide area.
To view the USG landslide location map click here.
To view the geologic emergency report for the State of Utah click here.
To view the Weber County landslide projection image (Jan. 23, 2018) click here.
To view an historical 1937 aerial image of the area click here.
Past pictures of the landslide in Riverdale City along the terrace.