Post-Construction Ordinance Development Phase 1 Report
February 2005
3.2.4 Loading Rates for Untreated Land Uses
The following loading rates were calculated using the SET and the outlined assumptions (Table 3-4).
Table 3-4.
Base Loading Rates for Land Uses without BMP Treatment
TN
(lb/ac/yr)
TP
(lb/ac/yr)
TSS
(ton/ac/yr)
RR
3.59
0.58
0.30
LDR
4.10
0.66
0.28
MLDR
6.50
1.07
0.57
MDR
7.61
1.24
0.52
HDR
8.73
1.40
0.47
MFR
10.65
1.68
0.39
HMFR
11.67
1.83
0.34
9.03
1.45
0.46
COMM-L
12.44
1.88
0.69
COMM-H
19.44
2.85
0.73
OI-L
7.61
1.24
0.52
OI-H
11.87
1.86
0.34
IND
16.12
2.39
0.71
INS
8.63
1.39
0.48
MX
15.07
2.24
0.71
HMX
16.82
2.49
0.71
UHMX
20.31
2.97
0.73
PARK
4.18
0.68
0.30
GC
5.17
0.83
0.47
INTERSTATE
7.81
1.25
0.40
FRST
2.50
0.40
0.15
AG
5.06
0.32
0.33
MEADOW
2.39
0.38
0.13
Land Use
MHP
The SET-based loading rates for this study compare
favorably to rates reported elsewhere. Studies by
Beaulac and Reckhow (1982), Hartigan et. al (1983 –
Calibration of NPS model loading factors, Journal of
Environmental Engineering), the EPA Nationwide
Urban Runoff Program (1983), and CDM (1989)
show residential loading rates ranging from 0.6 to 1.8
lb/ac/yr TP and 5.7 to 13.3 lb/ac/yr TN.
Commercial and light industrial loading rates were
reported ranging from 1.6 to 3.4 lb/ac/yr TP and from
10.7 to 25 lb/ac/yr TN. Rates for forested land
ranged from 0.01 to 0.99 lb/ac/yr TP and from 0.6 to
2.8 lb/ac/yr TN. For sediment, Simmons (1993)
reported sediment yield from 152 North Carolina
watersheds ranging from 0.07 ton/ac/yr for pristine
forested watersheds to 0.98 ton/ac/yr for highly
disturbed urban watersheds. Crawford and Lenat
(1989) reported sediment yield in three NC Piedmont
watersheds ranging from 0.13 ton/ac/yr in a
predominantly forested watershed, to 0.31 ton/ac/yr
in a primarily agricultural watershed, to 0.59
ton/ac/yr in a mostly urban watershed.
3.2.5 Post-BMP Loading Rates
Under current regulations, certain model land uses in
specific areas are subject to treatment by stormwater
and water quality BMPs, which reduce overall
pollutant loads leaving a site. The ordinances,
locations, and affected land uses are discussed in
detail in Section 2.4.5.2, but are summarized here for
reference
(Table 3-5). Each treated land use was given a prefix
to indicate the type of treatment – DD for dry
detention, WD for water quality BMPs for water
supply watersheds, and HV for Huntersville
Ordinance BMPs.
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