Chapter 16.103
CITY OF POWAY LOCAL SUSMP

Sections:

16.103.010    Compliance with City of Poway Local SUSMP.

16.103.020    General categories of water pollution.

16.103.030    Identifying pollutants from the project area.

16.103.040    Identifying pollutants of concern in receiving waters.

16.103.050    Identifying conditions of concern in receiving waters.

16.103.010 Compliance with City of Poway Local SUSMP.

All priority development projects, as defined by PMC 16.100.040, shall comply with the provisions of the City of Poway Local SUSMP, as adopted by the City Council by resolution, and incorporated by reference into this division. Compliance with the City of Poway Local SUSMP includes, but is not limited to:

A. Identifying pollutants and conditions of concern.

B. Establishing stormwater BMPs.

C. LID and site design BMPs including LID integrated management practices.

D. Source control BMPs.

E. Treatment control BMPs.

F. Hydromodification.

G. Operations and maintenance of stormwater facilities. (Ord. 702 § 7, 2010; Ord. 569 § 2, 2002)

16.103.020 General categories of water pollution.

Urban runoff from a developed site has the potential to contribute pollutants, including oil and grease, suspended solids, metals, gasoline, pesticides, and pathogens, to the stormwater conveyance system and receiving waters. For the purposes of identifying pollutants of concern and associated stormwater BMPs, pollutants are grouped in nine general categories as follows:

A. Sediments. Sediments are soils or other surficial materials eroded and then transported or deposited by the action of wind, water, ice, or gravity. Sediments can increase turbidity, clog fish gills, reduce spawning habitat, lower young aquatic organisms survival rates, smother bottom dwelling organisms, and suppress aquatic vegetation growth.

B. Nutrients. Nutrients are inorganic substances, such as nitrogen and phosphorus. They commonly exist in the form of mineral salts that are either dissolved or suspended in water. Primary sources of nutrients in urban runoff are fertilizers and eroded soils. Excessive discharge of nutrients to water bodies and streams can cause excessive aquatic algae and plant growth. Such excessive production, referred to as cultural eutrophication, may lead to excessive decay of organic matter in the water body, loss of oxygen in the water, release of toxins in sediment, and the eventual death of aquatic organisms.

C. Metals. Metals are raw material components in nonmetal products such as fuels, adhesives, paints, and other coatings. The primary sources of metal pollution in stormwater are typically commercially available metals and metal products. Metals of concern include cadmium, chromium, copper, lead, mercury, and zinc. Lead and chromium have been used as corrosion inhibitors in primer coatings and cooling tower systems. At low concentrations naturally occurring in soil, metals are not toxic. However, at higher concentrations, certain metals can be toxic to aquatic life. Humans can be impacted from contaminated groundwater resources and bioaccumulation of metals in fish and shellfish. Environmental concerns, regarding the potential for release of metals to the environment, have already led to restricted metal usage in certain applications.

D. Organic Compounds. Organic compounds are carbon-based. Commercially available or naturally occurring organic compounds are found in pesticides, solvents, and hydrocarbons. Organic compounds can, at certain concentrations, indirectly or directly constitute a hazard to life or health. When rinsing off objects, toxic levels of solvents and cleaning compounds can be discharged to storm drains. Dirt, grease, and grime retained in the cleaning fluid or rinse water may also adsorb levels of organic compounds that are harmful or hazardous to aquatic life.

E. Trash and Debris. Trash (such as paper, plastic, polystyrene packing foam, and aluminum materials) and biodegradable organic matter (such as leaves, grass cuttings, and food waste) are general waste products on the landscape. The presence of trash and debris may have a significant impact on the recreational value of a water body and aquatic habitat. Excess organic matter can create a high biochemical oxygen demand in a stream and thereby lower its water quality. Also, in areas where stagnant water exists, the presence of excess organic matter can promote septic conditions resulting in the growth of undesirable organisms and the release of odorous and hazardous compounds such as hydrogen sulfides.

F. Oxygen-Demanding Substances. This category includes biodegradable organic material as well as chemicals that react with dissolved oxygen in water to form other compounds. Proteins, carbohydrates, and fats are examples of biodegradable organic compounds. Compounds such as ammonia and hydrogen sulfide are examples of oxygen-demanding compounds. The oxygen demand of a substance can lead to depletion of dissolved oxygen in a water body and possibly the development of septic conditions.

G. Oil and Grease. Oil and grease are characterized as high-molecular-weight organic compounds. Primary sources of oil and grease are petroleum hydrocarbon products, motor products from leaking vehicles, esters, oils, fats, waxes, and high-molecular-weight fatty acids. Introduction of these pollutants to the water bodies is very possible due to the wide uses and applications of some of these products in municipal, residential, commercial, industrial, and construction areas. Elevated oil and grease content can decrease the aesthetic value of the water body, as well as the water quality.

H. Bacteria and Viruses. Bacteria and viruses are ubiquitous microorganisms that thrive under certain environmental conditions. Their proliferation is typically caused by the transport of animal or human fecal wastes from the watershed. Water containing excessive bacteria and viruses can alter the aquatic habitat and create a harmful environment for humans and aquatic life. Also, the decomposition of excess organic waste causes increased growth of undesirable organisms in the water.

I. Pesticides. Pesticides (including herbicides) are chemical compounds commonly used to control nuisance growth or prevalence of organisms. Excessive application of a pesticide may result in runoff containing toxic levels of its active component. (Ord. 671 §§ 39 – 42, 2008; Ord. 569 § 2, 2002)

16.103.030 Identifying pollutants from the project area.

Using Table 1, pollutants shall be identified that are anticipated to be generated from the proposed priority project categories. Pollutants associated with any hazardous material sites that have been remediated or are not threatened by the proposed project are not considered a pollutant of concern.

Table 1. Anticipated and Potential Pollutants Generated by Land Use Type
	General Pollutant Categories
Priority Project Categories	Sediments	Nutrients	Heavy Metals	Organic Compounds	Trash and Debris	Oxygen-Demanding Substances	Oil and Grease	Bacteria and Viruses	Pesticides
Detached Residential Development	X	X			X	X	X	X	X
Attached Residential Development	X	X			X	P(1)	P(2)	P	X
Commercial Development > One Acre	P(1)	P(1)		P(2)	X	P(5)	X	P(3)	P(5)
Industrial Development > One Acre	X		X	X	X	X	X
Automotive Repair Shops			X	X(4)(5)	X		X
Restaurants					X	X	X	X
Hillside Development >5,000 ft.2	X	X			X	X	X		X
Parking Lots	P(1)	P(1)	X		X	P(1)	X		P(1)
Retail Gasoline			X	X	X	X	X
Streets, Highways and Freeways	X	P(1)	X	X(4)	X	P(5)	X
X = anticipated P = potential (1) A potential pollutant if landscaping exists on site. (2) A potential pollutant if the project includes uncovered parking areas. (3) A potential pollutant if land use involves food or animal waste products. (4) Including petroleum hydrocarbons. (5) Including solvents.

(Ord. 671 § 43, 2008; Ord. 569 § 2, 2002)

16.103.040 Identifying pollutants of concern in receiving waters.

A. Pollutants generated by the proposed priority project that exhibit one or more of the following characteristics are considered primary pollutants of concern:

1. Current loadings or historical deposits of the pollutant are impairing the beneficial uses of a receiving water;

2. Elevated levels of the pollutant are found in water or sediments of a receiving water and/or have the potential to be toxic to or bioaccumulate in organisms therein; and

3. Inputs of the pollutant are at a level high enough to be considered potentially toxic.

B. To identify primary pollutants of concern in receiving waters, each priority project shall, at a minimum, do the following:

1. For each of the proposed project’s discharge points, identify the receiving water(s) that each discharge point proposes to discharge to, including hydrologic unit basin number(s), as identified in the most recent version of the Water Quality Control Plan for the San Diego Basin, prepared by the San Diego Regional Water Quality Control Board.

2. Identify any receiving waters, into which the developed area would discharge, listed on the most recent list of Clean Water Act Section 303(d) impaired water bodies. List any and all pollutants for which the receiving waters are impaired.

3. Compare the list of pollutants for which the receiving waters are impaired with the pollutants anticipated to be generated by the project (as identified in Table 1). Any pollutants identified by Table 1 which are also causing impairment of receiving waters shall be considered primary pollutants of concern.

C. For projects where no primary pollutants of concern exist, those pollutants identified through the use of Table 1 shall be considered secondary pollutants of concern. (Ord. 671 § 44, 2008; Ord. 569 § 2, 2002)

16.103.050 Identifying conditions of concern in receiving waters.

A. Common impacts to the hydrologic regime resulting from development typically include increased runoff volume and velocity; reduced infiltration; increased flow frequency, duration, and peaks; faster time to reach peak flow; and water quality degradation. These changes have the potential to permanently impact downstream channels and habitat integrity. A change to a priority project site’s hydrologic regime would be considered a condition of concern if the change would impact downstream channels and habitat integrity. Because of these potential impacts, the following steps shall be followed by each priority project:

1. Evaluate the project’s conditions of concern in a drainage study report prepared by a registered civil engineer in the State of California with experience in fluvial geomorphology and water resources management.

The report shall consider the project area’s location (from the larger watershed perspective), topography, soil and vegetation conditions, percent impervious area, natural and infrastructure drainage features, and any other relevant hydrologic and environmental factors to be protected specific to the project area’s watershed.

2. As part of the drainage study, a qualified, licensed professional shall provide a report on proposed infiltration techniques (trenches, basins, dry wells, permeable pavements with underground reservoir for infiltration) regarding any potential adverse geotechnical concerns. Geotechnical conditions such as slope stability, expansive soils, compressible soils, seepage, groundwater depth, and loss of foundation or pavement subgrade strength should be addressed, and mitigation measures provided.

3. As part of the drainage study, the civil engineer shall conduct a field reconnaissance to observe and report on downstream conditions, including undercutting erosion, slope stability, vegetative stress (due to flooding, erosion, water quality degradation, or loss of water supplies) and the area’s susceptibility to erosion or habitat alteration as a result of an altered flow regime.

4. The drainage study shall compute rainfall runoff characteristics from the project area including, at a minimum, peak flow rate, flow velocity, runoff volume, time of concentration, and retention volume. These characteristics shall be developed for the two-year and 10-year frequency, Type I storm, of six-hour or 24-hour duration (whichever is the closer approximation of the site’s time of concentration), during critical hydrologic conditions for soil and vegetative cover. The drainage study shall report the project’s conditions of concern based on the hydrologic and downstream conditions discussed above. Where downstream conditions of concern have been identified, the drainage study shall establish that pre-project hydrologic conditions affecting downstream conditions of concern would be maintained by the proposed project, satisfactory to the Director of Development Services, by incorporating the site design, source control, and treatment control requirements identified in this division.

B. Priority development projects are subject to the City’s Hydromodification Management Plan (HMP) as incorporated in the Poway Local SUSMP. The HMP shall demonstrate how priority projects will manage increases in runoff discharge rates and durations where such increased rates and durations are likely to cause increased erosion of channel beds and banks, sediment pollutant generation, or other impacts to beneficial uses and stream habitat due to increased erosive force. Projects will be required to utilize a continuous hydrological simulation and the results of a hydromodification management analysis must adhere to the following criteria:

1. For flow rates between the pre-project lower flow threshold and the pre-project 10-year runoff event, the post-project discharge rates and durations may not deviate above the pre-project discharge rates and durations by more than 10 percent over more than 10 percent of the length of the flow duration curve.

2. Lower flow thresholds may be determined using the tools provided in the local SUSMP along with a critical flow calculator and channel screening tools developed by the Southern California Coastal Water Research Project (SCCWRP). These methods identify lower flow thresholds for a range of channel conditions. The critical flow calculator recommends a lower flow value of 0.1Q2, 0.3Q2 or 0.5Q2 dependent on the receiving channel material and dimensions, where Q2 is defined as the two-year runoff event. This value will be compared to channel susceptibility rating (High, Medium or Low) as determined from the most recent SCCWRP screening tools to determine the final lower flow threshold.

3. The lower flow threshold may alternately be determined as 10 percent of the pre-project two-year runoff event or 0.1Q2. This approach is available if the project applicant chooses not to complete the channel screening analysis.

C. Priority Development Projects are required to implement hydromodification mitigation measures so that post-project runoff flow rates and durations do not exceed pre-project flow rates and durations. Hydromodification mitigation can be provided as follows:

1. Demonstrate no post-project increase in impervious area and resultant peak flow rates as compared to pre-project conditions.

2. Installation of LID BMPs such as bioretention facilities to control runoff flows and durations from new impervious areas.

3. Mitigation of flow and durations through implementation of extended detention flow duration control basins.

4. Preparation of continuous simulation hydrologic models and comparison of the pre-project and mitigated post-project runoff peaks and durations (with hydromodification flow controls) until compliance is achieved.

5. Implementation of in-stream rehabilitation controls to demonstrate that projected increases in runoff peaks and/or durations would not accelerate erosion to the rehabilitated receiving stream reach.

D. Priority development projects shall be exempt from the HMP criteria under the following conditions.

1. If the proposed project does not increase the impervious area or peak flows to any discharge location.

2. If the proposed project discharges runoff directly to an exempt receiving water such as the Pacific Ocean, an exempt river reach, an exempt reservoir, or a tidally influenced area.

3. If the proposed project discharges to a stabilized conveyance system that extends to the Pacific Ocean, a tidally influenced area, an exempt river reach or reservoir.

4. If the contributing watershed area to which the project discharges has an impervious area percentage greater than 70 percent.

5. If an urban infill project discharges to an existing hardened or rehabilitated conveyance system that extends beyond the domain of analysis, the potential for cumulative impacts in the watershed is low, and the ultimate receiving channel has a low susceptibility to erosion as defined in the SCCWRP channel assessment tool.

E. LID facilities must be designed to be practically built and maintained within the urban environment. Projects are encouraged to use LID design approaches to provide both treatment for the 85th percentile water quality event as well as flow control to meet hydromodification criteria. To assure compliance with hydromodification flow control requirements, design criteria, specifications, and long-term operations and maintenance requirements have been provided in the local SUSMP for a variety of LID-based flow control methods including bioretention basins, flow-through planter boxes, and bioretention systems in combination with cisterns and vaults. Sizing factor development shall include the use of continuous simulation of runoff from the long-term rainfall record.

F. Proof of a long-term maintenance responsibility and mechanism will be required for all post-construction BMP and flow control facilities. If not properly designed or maintained, hydromodification flow control devices may create a habitat for vectors such as mosquitoes or rodents. Maintenance activities for flow control and LID devices shall be specified in the proposed Project Submittal.

G. The local SUSMP outlines the monitoring program to assess the effectiveness of hydromodification management facilities. Monitoring activities will include inflow and outflow monitoring from BMPs, baseline cross section monitoring, and flow-based sediment monitoring. (Ord. 712 § 2, 2010; Ord. 671 § 45, 2008; Ord. 569 § 2, 2002)