250 R.I. Code R. 250-RICR-150-10-8.36

Current through November 21, 2024

Section 250-RICR-150-10-8.36 - Pollutant Loading Analyses - Overview

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.

250 R.I. Code R. 250-RICR-150-10-8.36

Amended effective 11/13/2018