Economic and ecological costs and benefits of streamflow augmentation using recycled water in a California coastal stream

http://pubs.acs.org/doi/abs/10.1021/es305011z

Abstract: 

Streamflow augmentation has the potential to become an important application of recycled water in water scarce areas. We assessed the economic and ecological merits of a recycled water project that opted for an inland release of tertiary-treated recycled water in a small stream and wetland compared to an ocean outfall discharge. Costs for the status-quo scenario of discharging secondary-treated effluent to the ocean were compared to those of the implemented scenario of inland streamflow augmentation using recycled water. The benefits of the inland-discharge scenario were greater than the increase in associated costs by US$1.8M, with recreational value and scenic amenity generating the greatest value. We also compared physical habitat quality, water quality, and benthic macroinvertebrate community upstream and downstream of the recycled water discharge to estimate the effect of streamflow augmentation on the ecosystem. The physical-habitat quality was higher downstream of the discharge, although streamflow came in unnatural diurnal pulses. Water quality remained relatively unchanged with respect to dissolved oxygen, pH, and ammonia-nitrogen, although temperatures were elevated. Benthic macroinvertebrates were present in higher abundances, although the diversity was relatively low. A federally-listed species, the California red-legged frog (Rana draytonii), was present. Our results may support decision-making for wastewater treatment alternatives and recycled water applications in Mediterranean climates.

Calera Creek Water Recycling Plant

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[In "Is Urban Stream Restoration Worth It?" which appeared in the Journal of the American Water Resources Association (2012) Kenney, Wilcock, Hobbs, Flores, and Martínez valued urban streams in Baltimore, depending on vegetation type] at US$1,800 - US$3,600 per linear meter of restored riparian habitat based on recreation and aesthetic benefits alone.

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Total habitat value for the Calera Creek Water Recycling Plant (CCWRP) in Pacifica, California urban park and aquatic habitat was estimated using the results from a meta-analysis of 39 wetland valuation studies, broken down by ecosystem service, which reported wetland habitat values of $996 per hectare per year, with a 90% confidence interval of $309/hectare-yr to $3,192/hectare-yr (29). We multiplied the lower-limit, base-case, and upper-limit values by 6.5 hectares, the area of the rehabilitated CCWRP aquatic habitat.

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Under the lower-limit and base-case, capital and O&M costs of the ocean-outfall scenario were less than for the CCWRP scenario. The cost of the CCWRP scenario was calculated to be greater than the cost of the ocean outfall scenario by $32.7M for the lower-limit, and $16.4M for the base-case. However, in the upper-limit scenario, the CCWRP scenario costs were calculated to be less than the ocean outfall scenario by $10.4M.
Ecosystem service benefits were evaluated for the implemented, CCWRP scenario (assuming no such benefits for the ocean discharge alternative). The average number of weekday visitors to the CCWRP urban park was estimated to be 420 per day and weekend visitors to be 635 per day. The upper-limit of the number of visitors per year was estimated at 175,000, with a base-case total recreational value of the CCWRP scenario estimated at $11.1M using the recreational values [in previous studies].

Percent increases in property value [in prior studies] ranged from 0% to 13%. The radius of influence for a measurable property value increase ranged from 0 to 750 meters. The most commonly reported property value increase was 5%, and the most commonly reported radius of influence was 500 meters. These base-case values gave a total aesthetic value of $6.3M. When these ecosystem services are accounted for (i.e., the above visitor recreation and property values), the NPV of the CCWRP scenario exceeded the NPV of the ocean outfall scenario for both the base-case and upper-limit. In the lower-limit, the ocean outfall scenario still has the greater NPV. With respect to ecosystem services for the CCWRP scenario, recreational benefits had the largest NPV, ranging $4.4M to $85.5M. The second largest estimated benefit was aesthetics, ranging $0 to $33M. Habitat value was comparatively insignificant, with a NPV ranging $21K to $500K.

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As a result of the inherent uncertainties in the benefit transfer model, we erred on the side of conservatism when applying values from other studies to Calera Creek. First, recreational value, which was the highest valued ecosystem service in our study, was estimated at $10.20 (SD=$5.80) per visitor per recreation day for the 320 base-case. In comparison, average values reported in other studies for a recreation day of bird watching and hiking were $29.60 and $30.84, respectively .

by Brian James Halaburka , Justin E Lawrence , Heather Nicole Bischel , Janet Hsiao , Megan H Plumlee , Vincent H Resh , and Richard G Luthy
Environmental Science and Technology American Chemical Society http://pubs.acs.org/journal/esthag

Just Accepted Manuscript; Publication Date (Web): May 20, 2013