Pollutant loading from low-density residential neighborhoods in California

Abstract

This paper presents a comparison of pollutant load estimations for runoff from two geographically distinct residential suburban neighborhoods in northern and southern California. The two neighborhoods represent a single urban land use type: low-density residential in small catchments (<0.3 km) under differing regional climates and irrigation practices. Pollutant loads of pesticides, nutrients, and drinking water constituents of concern are estimated for both storm and non-storm runoff. From continuous flow monitoring, it was found that a daily cycle of persistent runoff that peaks mid-morning occurs at both sites. These load estimations indicate that many residential neighborhoods in California produce significant non-storm pollutant loads year-round. Results suggest that non-storm flow accounted for 47-69% of total annual runoff and significantly contributed to annual loading rates of most nutrients and pesticides at both sites. At the Southern California site, annual non-storm loads are 1.2-10 times higher than storm loads of all conventional constituents and nutrients with one exception (total suspended solids). At the Northern California site, annual storm loads range from 51 to 76% of total loads for all conventional constituents and nutrients with one exception (total dissolved solids). Non-storm yields of pesticides at the Southern California site range from 1.3-65 times higher than those at the Northern California site. The disparity in estimated pollutant loads between the two sites indicates large potential variation from site-to-site within the state and suggests neighborhoods in drier and milder climates may produce significantly larger non-storm loads due to persistent dry season runoff and year-round pest control.

Role of Sediments in Insecticide Runoff from Urban Surfaces: Analysis and Modeling

“…The two catchments have been continuously monitored for selected stormwater quality parameters, flows, and rainfall quantities using automatic monitoring stations established at the outlets. In particular, a bubble level meter and an auto-sampler were installed to measure flow rate and to collect samples for total suspended solids (TSS) and insecticide concentration analyses [ 17 ]. The flow meter sensor directly provides the water depth in the runoff channel with an accuracy of +/−0.033 m and the average velocity of the flow stream by using an acoustic Doppler velocimeter; it calculates flow based on the current level and the definition of discharge (Wetted Area × Velocity = Flow).…”

Urban Stormwater Characterization, Control and Treatment

“…Three studies sought to better characterize herbicides and pesticides present in urban runoff. As may be expected, pesticides may be transported in irrigation runoff, which, in dry climates, may deliver the bulk of annual pesticide loads (Bale et al, 2017). Pesticides were found to occur ubiquitously in streams throughout eastern Australia in two different studies; however, concentrations were typically below limits set for public health and ecological protection (Allinson et al, 2017;Rippy et al, 2017).…”

“…Several studies published in 2017 provided valuable information to better understand sources of nutrients to stormwater runoff, and, hence, to improve efforts to manage N and P export from urban watersheds. Irrigation return flows from urban areas with distinct dry seasons (such as experienced in Mediterranean climates) were identified as major nutrient sources, contributing 1.5 to 10 times more N and P than generated by storm-driven runoff from study sites in Southern California (Bale et al, 2017;Toor et al, 2017).…”

Urban Drool Water Quality in Denver, Colorado: Pollutant Occurrences and Sources in Dry-Weather Flows

“…Notably, the majority of recent research on urban water impairment focuses on urban stormwater [4]. While stormwater runoff has a significant impact on urban pollutant loads, dry-weather urban flows in streams, channels, and storm sewers, termed "urban drool", has also been identified as an important source of contamination to urban waterways [4][5][6][7][8][9]. Dry-weather pollutant loads are especially relevant to consider in arid and semi-arid climates because less annual rainfall and longer dry periods result in more concentrated dry-weather contaminant loads being added to urban streams [4,5,7].…”