Geology – The Foundation Upon Which We Build, and Why This Matters for Ascente
I thought it might be useful to address the geologic issues that dog this project, using general language so that we understand WHY this project is way more complex, expensive and risky than the current owners and the real estate agents want us all to believe.
Almost all of the Washoe Valley area is geothermically active, with parts holding molten lava below the water line. Steamboat Hills was named for the geothermally active area in South Washoe County, and the Ormat Geothermal Plant is perched on the east side of these hills. Ascente is on the west side, less than two miles away.
Metro Washoe County land is sitting on well over 30 fault lines, most of which have been active within the last 11,000 years which classifies them, according to seismic geologists as seismically threatening. These two geologic phenomena – geothermal and seismic activity can be very threatening to the human environment. For this reason, federal, state and county jurisdictions have compliance codes that include provisions for pre-construction geologic investigations to identify and mitigate geologic hazards.
Other aspects of geologic science that can impact construction included geomorphology, the physical features of the landscape (topography) and the very rocks and soils that comprise a landscape. Building on the side of a cliff requires additional attention to foundation and support which costs money, and designing that support requires a geologic report robust enough to ensure that design is safe and sound. Likewise, a building constructed on rock that is less than stable, or is subject to geothermal or seismic activity must be designed in such a way that potential effects are mitigated.
Let’s look at these four geologic considerations, and why it’s necessary to have a technically robust Geologic Investigation, prior to design, building and infrastructure construction, and final permits:
Geothermal Activity: The heat of the earth can be dangerous when it’s up close. Geothermal activity usually produces steam and mineral-laden gas which will affect the quality of the surface rock. This is why we have mercury, arsenic, cadmium, lead, and other toxic elements and minerals in some surface rock and soils in Washoe County. Homes built on areas affected by geothermal activity can suffer a variety of ill effects including poor soils, foundation instability and exposure to toxic elements. Geothermal activity goes hand in hand with seismic instability, thus buildings in these areas may be subject to earthquakes. Soils and rock studies are required prior to construction to ensure that the surface material is both structurally and chemically sound and toxic exposure is minimized.
Faulting and Earthquakes: Simply put, a fault is a break in the earth’s surface, or a fracture along which “blocks” of rocks have been displaced by stress and movement below the earth’s surface. Faults can be active or inactive, based on determination of last movement of rock on each side of the fault. Faults 11,000 years of age or less are considered active and we have many, many of those in Western Nevada due to our proximity to the San Andreas Fault system along the West Coast. Earthquakes are caused by movement along a fault. Federal and State regulations require that construction be offset from an active fault line to minimize impact of earthquake movement.
The Steamboat Hills were most likely created as part of the “Basin and Range” system comprising most of Nevada. These are created by uplifted and down-dropped blocks along a series of North-South trending faults. The USGS Report on the Little Valley Fault System (not included in this report by the way) suggests that the Callahan Ranch area rests on the downdropped portion of a block and that a fault may exist along the western edge of the Steamboat Hills. The whole southwest Washoe County area is littered with faults and undoubtedly, some older home construction has taken place on or right next to these faults, and roads and other infrastructure are built over them as well. What happens when these faults move again? What happens when Tentative Maps do not include a complete and accurate assessment of active faulting in a construction area? For instance, the 2013 Geologic Map of Washoe County identifies a concealed potentially-active fault that runs along the west side of the Steamboat hills. During our 2016-17 appeal of the original Ascente Tentative Map, we highlighted the need for this fault to be further investigated by Symbio. A brief and probably inadequate field study was done by Lumos Associates later in 2017, the results of which have not been published. Again, based on our professional assessment of the field work, we do NOT think this fault, or other geologic features of the project were evaluated completely enough to address the County’s Conditions.
Geomorphology: The topography of the Steamboat Hills area, and most of the Ascente site, is steep with a few cliff faces. Plenty of grading will be required to flatten the home foundation areas and even more for the access roads. The cost of this grading has not been published, but the Tentative Map has maximized building sites using grading as a mitigation for extreme topography for the obvious reason of creating more lots, thus more profit. But what is the actual cost of this grading?
The topography of this area also contributes to flooding, as precipitation runs directly off the hills and into the Callahan Ranch area. The residents conducted their own stormwater studies during the 2016-17 winter season and determined that the current Plan will contribute to flooding and subject Callahan and Fawn Lane residents to increased traffic without improvements to road widths or structure, increase fire risk and decrease dramatically the ability of current and future residents to evacuate. At what stage does residents’ safety take priority?
Lastly, extreme grading will alter the topography of this area thus marring the landscape and visual beauty of this area.
Rock Quality and Mineral Composition:
Rock hardness and cohesiveness are two important characteristics for design and construction of building foundations. Too soft (such as sand and beach deposits) and a foundation will crumble with time. Too hard (such as the andesite/rhyolite rocks of the Steamboat Hills) and so much blasting is required that a construction project might well be deemed too expensive and risky from a health and safety perspective.
Rocks are made up of minerals and minerals are made up of elements. These elements, as discussed above, may be toxic to human and environmental health. Lead compounds have been found throughout the surface of the Steamboat Hills area. Mercury compounds are found to the east and south of Steamboat area. Lead toxicity is well-studied. If these compounds become airborne, or somehow ingested in sufficient quantities, they can become toxic. Ascente conducted a brief soil surface survey of their project area. This study was hotly contested by technical experts as not being statistically robust. The old Galena Mine at the top of Steamboat Hills is most likely the source for much of this surface lead and the relict mine workings and mine waste piles have yet to be remediated.
From an aesthetics perspective, the Ascente site has little to no topsoil. Any vegetative and landscaping amenities will require thousands of tons of topsoil, at a huge cost.
No wonder the sale price of the Ascente Site keeps dropping! Mother Nature has provided so many costly barriers in the name of geology:
- Geothermal and local faulting must be thoroughly evaluated prior to final approvals and there’s no evidence to suggest that the 2018 Lumos field work achieved that goal. If they did, why a Geological Report not published for the public to view? Could it be because the Steamboat Fault mapping will necessitate removal of many lots, thus significantly lowering potential profits?
- The geomorphology and topography of the Steamboat Area is such that robust attention must be paid to lot size and grading as well as infrastructure design, roads and stormwater management, including drains and infiltration basins. The Tentative Map glosses over these issues, but the Callahan Ranch neighbors have already proven that stormwater issues can develop with high stormwater events and that a more robust stormwater model is needed. And what if a more robust model indicates that the topography does indeed prove that additional stormwater management controls are needed to adhere to regulation. These cost money, thus reducing profits.
- The Tentative Map correctly states that excavation into the rock particularly for confined excavations for utilities will require blasting. Blasting could be in locations directly above existing residents and protection of existing residents located downhill of blast areas must be managed, thus an additional cost.
- Blasting and excavation in hard rock will generate a large quantity of angular rock boulders because of the hardness of the andesite rock. These blast rocks, because of the size cannot be used in engineered fill and the County has stated that all blast rock must be removed from the Project site – another cost. Additionally, large quantities of soil may need to be imported in order to create proposed building pads and landscaping. The import of these material would add greatly to construction traffic. Importing soil for fill could also contribute to rendering this project financially unfeasible.