The Ground Water Recharge and Pollution Potential of Dry Wells in Pima County, Arizona

Abstract

This paper summarizes a study to estimate the potential for dry‐well drainage of urban runoff to recharge and pollute ground water in Tucson, Arizona. We selected three candidate dry wells for study. At each site we collected samples of runoff, dry‐well sediment, vadose‐zone sediment, perched ground water, and ground water. Water content data from vadose‐zone samples suggest that dry‐well drainage has created a transmission zone for water movement at each site. Volatile organic compounds, while undetected in runoff samples, were present in dry‐well sediment, perched ground water at one site, and ground water at two sites. The concentrations of volatile organics (toluene and ethylbenzene) in the water samples were less than the corresponding EPA human health criteria. Pesticides were detected only in runoff and dry‐well sediment. Lead and chromium occurred in runoff samples at concentrations above drinking water standards. Nickel, chromium, and zinc concentrations were elevated in vadose‐zone samples at the commercial site. Of the metals, only manganese, detected at the residential site, exceeded Secondary Drinking Water Standards in ground water. It is concluded that the three dry wells examined during this study are currently not a major source of ground water pollution.

Assessing the effectiveness of drywells as tools for stormwater management and aquifer recharge and their groundwater contamination potential

“…Contaminant attenuation in the vadose zone was indicated in many studies, and contaminant fate and transport modeling performed as part of some studies further supports this conclusion (Bandeen, 1987;BrodyHeine et al, 2011;City of Portland, 2008;Izuka, 2011;Olson, 1987;Wilson et al, 1990;Wogsland, 1988). Four out of the 13 drywell studies performed predictive contaminant fate and transport modeling as part of their determination of groundwater protectiveness (Bandeen, 1984(Bandeen, , 1987Brody-Heine et al, 2011;City of Portland, 2008;Izuka, 2011).…”

“…Although some contaminants were detected in stormwater samples above regulatory levels, these contaminants were rarely detected in groundwater at similar levels (Jurgens et al, 2008;Olson, 1987;Wilson et al, 1990). Even in Modesto, California, where drywells have been used for more than half a century, no contaminants detected in downgradient groundwater monitoring wells exceeded regulatory values (Jurgens et al, 2008).…”

“…The complexity of monitoring implementation varied from four drywells sampled one time each as was the case for the study conducted in Pima County, Arizona, to a single drywell sampled for 17 storm events over the course of five years as was the case for the study done in Pierce County, Washington, to 30 drywells sampled for five storm events each year for ten years as was the case for the study conducted in Portland, Oregon (Adolfson, 1995;City of Portland, 2008;Wilson et al, 1990). During the Pierce County study, stormwater quality monitoring samples were taken at the point where the water entered the drywell, and also beneath the drywell, after the water had infiltrated.…”

“…Sedimentation can be a major problem for drywells, and so sedimentation traps, manholes, filters, or settling chambers are often constructed to receive influent stormwater before it reaches the drywell (Adolfson and Clark, 1991;Adolfson, 1995;Bandeen, 1987;City of Portland, 2008;Dallman and Spongberg, 2012;Olson, 1987;Wilson et al, 1990). See Fig.…”

“…In this paper, soakaway will be used as a broad term, and the specification will be made whether or not a described soakaway is also a drywell. A typical drywell design consists of a perforated precast casing, usually made of concrete but in some cases PVC, with an average diameter of approximately 1.2 meters (m), and a depth of anywhere from 0.6 to 26 m, usually backfilled with gravel and/ or sand (Adolfson and Clark, 1991;Adolfson, 1995;Bandeen, 1984Bandeen, , 1987Barraud et al, 1999;Chen et al, 2007;City of Portland, 2008;Clark and Pitt, 2007;Dallman and Spongberg, 2012;Izuka, 2011;Jurgens et al, 2008;Lindemann, 1999;Pitt et al, 2012;Wilson et al, 1990;Wogsland, 1988). Fig.…”