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SEC. 91.7109.  ADDITIONAL REMEDIAL MEASURES.
 
91.7109.1.  General Remedial Measures.  In the event the concentration of methane gas in any building located in a Methane Zone or Methane Buffer Zone reaches or exceeds 25 percent of the minimum concentration of gas that will form an ignitable mixture with air at ambient temperature and pressure, the owner shall hire an engineer to investigate, recommend and implement mitigating measures.  These measures shall be subject to approval of this Department and the Fire Department.
 
91.7109.2.  Abandoned Oil Well.  (Amended by Ord. No. 185,587, Eff. 7/16/18.)  Any abandoned oil well encountered during construction shall be evaluated by the Fire Department and may be required to be re-abandoned in accordance with applicable rules and regulations of the Division of Oil, Gas and Geothermal Resources of the State of California.  Buildings shall comply with these provisions and the requirements of LAMC Section 91.6105, whichever is more restrictive.
 
TABLE 71.  MINIMUM METHANE MITIGATION REQUIREMENTS
(Amended by Ord. No. 185,587, Eff. 7/16/18.)
 
 
Site Design Level
LEVEL I
LEVEL II
LEVEL III
LEVEL IV
LEVEL V
Design Methane Concentration (ppmv)
0-100
101-1,000
1,001-5,000
5,001-12,500
>12,500
Design Methane Pressure
(inches of water pressure)
2
>2
2
>2
2
>2
2
>2
All
Pressures
P
A
S
S
I
V
E

S
Y
S
T
E
M
De-watering System 1
X
X
X
X
X
X
X
X
X
Sub-Slab Vent System
Perforated Horizontal Pipes
X
X
X
X
X
X
X
X
X
Gravel Blanket Thickness Under Impervious Membrane
2"
2"
2"
3"
2"
3"
2"
4"
4"
Gravel Thickness Surrounding Perforated Horizontal Pipes
2"
2"
2"
3"
2"
3"
2"
4"
4"
Vent Risers
X
X
X
X
X
X
X
X
X
Impervious Membrane
X
X
X
X
X
X
X
X
X
A
C
T
I
V
E

S
Y
S
T
E
M
Sub-Slab System
Mechanical Extraction System 2
X
X
Lowest Occupied Space System
Gas Detection System 3
X
X
X
X
X
X
X
Mechanical Ventilation 3, 4, 5
X
X
X
X
X
X
X
Alarm System
X
X
X
X
X
X
X
Control Panel
X
X
X
X
X
X
X
M
I
S
C.

S
Y
S
T
E
M
Trench Dam
X
X
X
X
X
X
X
X
X
Conduit or Cable Seal Fitting
X
X
X
X
X
X
X
X
X
Additional Vent Risers 5
X
 
For SI: 1 inch = 25.4 mm.
X = Indicates a Required Mitigation Component
 
1.   See LAMC Subdivision 91.7104.3.7 for exception.
2.   The Mechanical Extraction System shall be capable of providing an equivalent of a complete change of air every 20 minutes of the total volume of the Gravel Blanket. 
3.   The mechanical ventilation systems shall be capable of providing an equivalent of one complete change of the lowest occupied space air every 15 minutes.
4.   Vent opening complying with LAMC Subdivision 91.7104.3.4 may be used in lieu of mechanical ventilation.
5.   The total quantity of installed vent risers shall be increased to double the rate for passive system.