Page 483 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

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12.6 Combined Sewer Overflow Control Practices 441

Table 12.6 Maximum Development Intensity in Austin, Texas

Waterways Development Limits Acceptable
Structural
Watershed Water Quality Uplands Pollution
Category Minor Intermediate Major Buffer Zone Area Type Zone 1 Transfer Controls

Suburban
% Impervious Cover
Drainage area: 320 ac 640 ac 1,280 ac 30% Residential: 50 60 Sedimentation
Critical WQ zone: 100 ft 200 ft 400 ft impervious cover Duplex: 55 60 Sedimentation
WQ buffer zone: None 100 ft 150 ft Multifamily: 60 70 Filtration
Commercial: 80 90 Filtration
Water Supply Suburban—Class I
% Impervious Cover
Drainage area: 128 ac 320 ac 640 ac 18% Residential: 30 40 Filtration
Critical WQ zone: 100 ft 200 ft 400 ft impervious Multifamily: 40 55 Filtration
WQ buffer zone: 100 ft 200 ft 300 ft cover; no Commercial: 40 55 Filtration
development
over recharge zone
Water Supply Suburban—Class II
% Impervious Cover
Drainage area: 128 ac 320 ac 640 ac 30% Residential: 40 55 Filtration
Critical WQ zone: 100 ft 200 ft 400 ft impervious Multifamily: 60 65 Filtration
WQ buffer zone: 100 ft 200 ft 300 ft cover; no Commercial: 60 70 Filtration
development
over recharge zone
Water Supply Suburban—Class III
% Impervious Cover
Drainage area: 320 ac 640 ac 1,280 ac 30% Residential: 45 50 Filtration
Critical WQ zone: 100 ft 200 ft 400 ft impervious cover Duplex: 55 60 Filtration
WQ buffer zone: 100 ft 200 ft 300 ft Multifamily: 60 65 Filtration
Commercial: 65 70 Filtration
Water Supply Rural
Units/ac
Drainage area: 64 ac 20 ac 640 ac One unit per 3 Single-family: 0.5 1.0 —
Critical WQ zone: 100 ft 200 ft 400 ft acres; no Cluster: 1.0 2.0 40% buffer 2
WQ buffer zone: 100 ft 200 ft 300 ft development
over recharge zone
% Impervious Cover
Multifamily: 20 25 40% buffer
Commercial: 20 25 40% buffer
Planned: 50 50 40% buffer
Retail: 50–60 3 60–70 Filtration
1
Net site area.
2
Except in Lake Austin/Lake Travis, where filtration is required.
3
Only at major intersections.
Conversion factors: ac acre; 1 acre 0.4046 ha; 1 ft 0.3048 m.
Source: U.S. Environmental Protection Agency, Stormwater Best Management Practice Design Guide—Volume 1—General Considerations (2004).