Rhode Island Code of Regulations › Title 250 - Department of Environmental Management › Chapter 150 - Water Resources › Subchapter 10 - Wastewater And Storm Water › Part 8 - Stormwater Management, Design and Installation Rules › Section 250-RICR-150-10-8.36 - Pollutant Loading Analyses - Overview

Current through June 14, 2024
A. The permitting
				  agency may require applicants to document that a particular project does not
				  unduly contribute to, or cause, water resource degradation (generally for
				  sensitive resource areas or where an elevated concern for water quality exists)
				  or to document a reduction in pollutant load (generally, as a consequence of a
				  TMDL requirement). In these cases, applicants may be required to calculate
				  potential stormwater pollutant loadings for projects for pre-development and
				  post-development conditions.
B.
				  When such an analysis is required of the applicant, the Simple Method
				  (Schueler, T.R. 1987. Controlling Urban Runoff: A Practical Manual for Planning
				  and Designing Urban BMPs, Department of Environmental Programs, Metropolitan
				  Washington Council of Governments, Washington, DC) can be used to demonstrate
				  urban stormwater pollutant loadings. The Simple Method requires estimates of
				  annual rainfall, site percent impervious cover, land use type, and pollutant
				  loading coefficients based on land use.
C. The table below in §
										8.36(D) of
				  this Part provides event mean concentrations in milligrams per liter (mg/L) for
				  typical pollutants of concern associated with stormwater runoff (# col/100ml
				  for bacteria). There may be an interest in calculating the loading rates of
				  other pollutants not listed in this table. If this is necessary, an applicant
				  shall use event mean concentration data from a reliable source, as approved by
				  the approving agency, based on the land use category. These event mean
				  concentration values must be documented by scientific studies and referenced by
				  the applicant.
D. Median Event Mean
				  Concentration Values for Differing Land Use Categories
Pollutant (mg/l)
Land Use Category
Residential
Commercial
Industrial
Highways
Undeveloped/
								  Rural3
TSS
1001
751
1201
1501
51
TP
0.32
0.22
0.252
0.25
0.11
TN
2.12
2.12
2.12
2.32
1.74
Cu
.0052
.0962
.0022
.0012
-
Pb
.0122
.0182
.0262
.0352
-
Zn
.0732
.0592
.1122
.0512
-
BOD
9.02
11.02
9.02
8.02
3.0
COD
54.52
58.02
58.62
100.02
27.0
Bacteria
(#col/100
ml)
70002
46002
24002
17002
300
1 Caraco, D. 2001. The Watershed Treatment Model. Center
					 for Watershed Projection. Ellicott City, Maryland.
2 Pitt, R. E., Maestre, A., and Center for Watershed
					 Protection. 2005. The National Stormwater Quality Database (NSQD), version 1.1.
					 USEPA Office of Water, Washington, D.C.
3 CDM. 2004. Merrimack River Watershed Assessment Study,
					 Screening Level Model.
E.
				  The method outlined in §
										8.37 of this Part is most
				  often applied to calculating loadings to surface water bodies. Other pollutant
				  loading methods may be acceptable, provided the applicant submits the
				  methodology and data used along with the reasoning for the chosen method. All
				  information supplied by the applicant will be reviewed by the approving agency
				  to determine the relevance of the model to the situation.