Thread: A sign I haven't seen yet

Here's a new one...

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Holy Cow, Batman!

I've seen several with very similar wording. All were on or inside of buildings located on or near former landfill sites. Garbage gives off methane as it decomposes.

The landfill I drive past almost every day burns the stuff off to produce electricity, and every now and then burns off excess in the air, as waste--guess the turbines/generators can't keep up with it.

IIRC the requirements in your area (Marc M) became more stringent and the areas requiring testing & mitigation sometime early last decade after some detailed and more complete testing, studies, and specific special zoning districts requiring impervious membraning not just clay or other capping in addition to test wells, and the recharging of fields with the water & gas waste to the sites providing flow in prev vertical "tapped" fields (such as near "the pits"; and other requirements were more fully developed after some catastrophic explosions (mid 80s & late 80s)and developments in the late 90s were experiencing problems and organized efforts at the turn of the century led to the state, the city & county of LA and surrounding areas to more fully study and address the issues (having been forced to acknowledge same). Prior to that smaller areas (mostly near fairfax...) had some mid-80s and early 90s requirements after some explosions & fires earlier in the prior decade and the affects of activites since the 50s, 60s & 80s were being realized.

Some history (attached also below) direct link:

http://www.saveballona.org/gasoilfie...han-RossGC.pdf

Common when pinning encountering "pockets", clay liner cracks, recent "movement" or slow perking, etc. It is not limited to prior landfill locations, but is likewise common where oil and gas wells are or were common, also where underground coal mining. Becoming more recent problem in areas not previously considered as resources for "regular drilling" with the advent of "fracking", (example a return of activites in NE Ohio region). There was a time when oil & gas wells even dotted the center of streets throughout many areas in LA, the county, and the greater area in So.Cal., and many more locations where drilling occurred and long since improperly abandonded "tapped out" or prior capping having failed. "Wild catting" was common in So. Calif. IIRC issues known/common near "the pits" too.

Naturally occuring methane is found in soil and can be formed by thermal decomposition of buried organic material often associated with the formation of coal and oil (thermogenic), or by the microbial decomposition of organic material in the absence of oxygen (biogenic). Therefore, the presence of methane gas in the subsurface is common where organic material - such as grass, leaves, wood, manure, hydrocarbons, etc. are present in the soil. Methane may also be present in the shallow subsurface as a result of its migrtion from deeper oil and gas bearing zones.

Methane is not considered to be "toxic", (can smother - anoxic), however it is combustible and potentially explosive at concentrations between approx. 50,000 ppm and 150,000 ppm (parts per million) in the presence of oxygen. The lower concentration is referred to as its Lower Explosive Level (LEL) and the higher concentrtion is referred to as its Upper Explosive Level (UEL). Methane is lighter than air and therefore has a natural tendency to rise to the ground surface where it typiclly dissipates into the atmosphere. As methane migrates to the ground surface, the potential exists for its accumulation beneath slab-on-grade and sub-grade foundation systems or in structures.

There are special zoning "methane zones" and "methane buffer zones" in LA City and other surrounding jurisdictions. Membranes are usually only a part of the mitigation.

The City of Los Angeles conducted a detailed study of methane levels all over Los Angeles and created two special zoning areas regarding methane: Methane Buffer Zone(s) and Methane Zone(s). (IIRC est. approx '04).

All developments within the Methane Buffer Zone are first subjected to a methane level assessment. Any property within the Methane Buffer Zone that is found to be free of methane may proceed without any additional methane mitigation plans. However, if the assessment testing proves methane is present than a Methane level is determined, and a mitigation plan is designed to keep the methane from entering the building

Developments within the Methane Zone itself are more stringent. All developments within the Methane Zone require the same assessment testing as the Buffer Zone, but require a minimum Mitigation Plan regardless of the methane levels discovered. The minimum plan required consists of a below grade passive venting network, complete with risers and an impervious membrane just below the slab, and behind any below grade walls.

You can find more information at (for example) the Los Angeles Department of Building and Safety (LADBS) website, or (another example) the Department of Public Works at the LA County (unincorporated areas)website (or whichever jurisdiction the home is located in), and also the "wild cat" maps found at the state's department of conservation (here's a link to those: Oil, Gas & Geothermal - District 1 Maps )

HTH.

P.S. here's a link (unofficial hosting at one of the many enivorn. firms that specialize locally in the issue) to a map of zones in LA, just found it a quicker-to-load and easier to link to (directly) location than the city site: http://rayconenvironmental.com/image...e_Zone_Map.jpg

..or at new housing at former military bases.
This one at Hamilton in Novato - a former air force base. Lots of soil contamination from fuel...but the plastic will save them.

How Big is the Sign , or how small is the sheet rock ?

Is the house by any chance in Sun Valley or Pacoima?

The sign is at eye level on the side wall of the garage. about 12" x 16". This is a former military base - Hamilton - in Novato, Ca. I dont know what kind of material is used to form the barrier - I would guess a heavy duty plastic sheet placed prior to the placement of the concrete slab... which by the way is a post-tensioned slab. So, for two reasons, dont cut or core the slab. And I know most buyers are baffled as to why would they not cut or core the slab -- I tell them, for instance, if they wanted to install a floor safe. "DON'T! Cutting the cables or damaging the methane barrier will cause a problem."

Originally Posted by Chris Weekly

..or at new housing at former military bases.
This one at Hamilton in Novato - a former air force base. Lots of soil contamination from fuel...but the plastic will save them.

Chris,

Yes, I have inspected a few of those. In the attic, I have also seen stickers on the vent piping that extends to under the slab. I believe the property owners are prohibited from installing in-ground pools as well. Certainly of concern.

Earlier this year, I inspected a very expensive home in one our very exclusive (expensive) neighborhoods. There was a notice posted on a ventilation system that that the system was a methane mitigation system. I had never seen that before. But subsequent inquiry revealed that many homes in that area had a methane mitigation system installed. No one could tell me if the home had been tested for methane intrusion or the system had been installed as a good idea because the neighbors had them. The home was on the shore of a man made pond and someone suggested that organic material breaking down in the pond can generate methane that can seep into the homes on the shore.