Geology topics

William R. Horwath

Publications and source records attributed to William R. Horwath.

10 recordsLinked to original sources

USGS2019

Chemically enhanced treatment wetland to improve water quality and mitigate land subsidence in the Sacramento-San Joaquin Delta: Cost and design considerations

Water quality impairment and land surface subsidence threaten the viability of the Sacramento-San Joaquin Delta (Delta), a critical component of California’s water conveyance system. Current day irrigation drainage through Delta island peat soils impacts drinking water treatment and is linked to mercury transport, potentially posing both ecological and public health concerns. Hybrid coagulation-treatment wetland systems, termed Chemically Enhanced Treatment Wetlands (CETWs), were studied as a means to cost-effectively treat agricultural drainage water from subsided Delta islands to reduce the export of drinking water quality constituents of concern and mitigate land subsidence through accretion. We provide cost estimates and design recommendations to aid broader implementation of this technology. Over a 20-year horizon using a Total Annualized Cost analysis, we estimate treatment costs of $602 – $747 per acre-foot (ac-ft) water treated and $36 – $70 per kg dissolved organic carbon (DOC) removed depending upon source water DOC concentrations for a small 3-acre CETW system. For larger CETW systems scaled for island sizes of 3,500 – 14,000 acres, costs decrease to $108 – $239 per ac-ft water treated and $11 – $14 per kg DOC removed. The footprints of CETW systems were estimated to be approximately 3% of the area being treated for 4-day hydraulic retention time systems but would decrease to less than 1% for 1-day hydraulic retention time systems. CETWs ultimately address several of the Delta’s key internal issues while keeping water treatment costs competitive with other currently available treatment technologies at similar scales on a per carbon removed basis. CETWs offer a reliable system to reduce out-going DOC and mercury loads and they provide the additional benefit of sediment accretion. System costs and treatment efficacy are highly dependent on inflow source water conditions, land availability and other practical matters. To keep costs low and removal efficacy high, wetland design features will need site-specific evaluation.

California↗

USGS2019

Aluminum- and iron-based coagulation for in-situ removal of dissolved organic carbon, disinfection byproducts, mercury and other constituents from agricultural drain water

Agricultural production on wetland soils can be significant sources of dissolved organic carbon (DOC), disinfection byproduct precursors, mercury and nutrients to downstream water bodies and accelerate land subsidence. Presented as a potential solution for in-situ water quality improvement and land subsidence mitigation, chemically enhanced treatment wetlands (CETWs) were used to leverage both coagulation and wetland processes. In this study, we evaluated the performance of coagulants ferric sulfate (Fe dosing) and polyaluminum chloride (Al dosing) to remove pollutants from agricultural drain water using the coagulation system designed for CETWs. Both coagulation treatments removed over 70% DOC from source waters, resulting in removal efficiencies (mg-DOC removed per mg-metal dosed) of 1 under Al dosing and 0.5 under Fe dosing. Coagulation by both treatments preferentially removed UV254 active compounds compared to the bulk DOC concentration, suggesting coagulation targeted aromatics more effectively. Phosphates and haloacetic acids were also removed more readily, whereas trihalomethanes, dissolved organic nitrogen and filtered mercury species were removed at similar or lower rates than DOC. Dissolved inorganic nitrogen was not amenable to coagulation and removal was not observed. Freundlich, Langmuir and Monod models explained 33% of the variance for Al dosing and 78 – 89% of the variance for Fe dosing. All three models indicated Al dosing had higher removal efficiency and affinity for DOC than Fe dosing under study conditions, but when used to predict maximum removal efficiency there was no cohesiveness between the three models due to different model assumptions. Consideration of fluorescence dissolved organic matter and UV254 as surrogates for DOC concentration showed both were equally suitable before coagulant application, but as surrogates after coagulant application, neither could be deemed more fit as a surrogate since both were shown suitable for different treatment scenarios.

Ecological Engineering↗

USGS2019

Effects of ferric sulfate and polyaluminum chloride coagulation enhanced treatment wetlands on Typha growth, soil and water chemistry

Land surface subsidence is a concern in many deltas worldwide as it contributes to water quality degradation, loss of fertile land and increased potential for levee failure. As a possible solution to these concerns, on-site coagulation enhanced treatment wetlands(CETWs), coagulation water treatment followed by wetland passage serving as a settling basin, were implemented in a field-scale study located on a subsided island of the Sacramento-San Joaquin Delta in northern California under three treatments; coagulation with polyaluminum chloride (PAC), coagulation with ferric sulfate and an untreated control. Because CETWs offer a relatively novel solution for water quality improvement and subsidence reversal due to its low-infrastructure requirements and in-situ nature, effects from these systems remain uncharted and they may have adverse effects on plant biomass production that also contribute to sediment accretion. This study focuses on the effect CETWs had on the growth of Typha spp .; the dominant vegetation in the wetlands. Plant growth parameters and nutrient content were measured in conjunction with soil, pore waterand surface water chemistry. Soil analysis indicated there was no intermixing of newly formed flocs and original soil material. Where there was significant deposition of floc, PAC treatment reduced phosphate concentrations and ferric sulfate treatment increased total Fe concentrations in surrounding water compared to the control. Results indicated coagulation treatments had no negative effects on Typha leaf nutrient content, Typha growth or allometric parameters. Additionally, no signs of plant toxicity such as necrosis, wilting or chlorosis were observed in any of the treatments. Overall, this study suggests that CETWs are viable treatment option for water quality improvement and sediment accretion while having no negative impact on the growth of Typha plants.

Science of the Total Environment↗

USGS2019

Sequestration and transformation in chemically enhanced treatment wetlands: DOC, DBPPs and Nutrients

We examined the effectiveness of chemically enhanced treatment wetlands (CETWs), wetlands that received water treated with coagulants, to remove dissolved organic carbon (DOC), disinfection byproduct precursors (DBPPs), nutrients and metals from agricultural drain water. Wetlands consisted of controls with no coagulant addition, ferric sulfate dosed and polyaluminum chloride dosed treatments. CETWs were more effective in removal of DOC, DBPPs, phosphate, dissolved organic nitrogen and metals than control wetlands. Coagulation treated wetlands removed 245 – 349 g/m2yr DOC, whereas control wetlands produced 51 g/m2yr. Wetland passage released DOC in the controls and treatments; this release was directly correlated to temperature and suggested thermally dependent mechanism(s) were partly responsible. A first-order plug flow reactor kinetic model that considered hydraulic retention time (HRT), temperature and concentration was tested for wetland DOC processing. Models indicate that operating CETWs at high coagulant dosing and low temperature can result in lowest DOC release with additional release suppression. Operating at the lowest HRT to meet discharge targets help overcome wetland processes that increase DOC release and provide the smallest footprint needed for treatment.

Journal of Environmental Engineering↗

USGS2018

Sediment accretion and carbon storage in constructed wetlands receiving water treated with metal-based coagulants

In many regions of the world, subsidence of organic rich soils threatens levee stability and freshwater supply, and continued oxidative loss of organic matter contributes to greenhouse gas production. To counter subsidence in the Sacramento-San Joaquin Delta of northern California, we examined the feasibility of using constructed wetlands receiving drainage water treated with metal-based coagulants to accrete mineral material along with wetland biomass, while also sequestering carbon in wetland sediment. Nine field-scale wetlands were constructed which received local drainage water that was either untreated (control), or treated with polyaluminum chloride (PAC) or iron sulfate (FeSO4) coagulants. After 23 months of flooding and coagulant treatment, sediment samples were collected near the inlet, middle, and outlet of each wetland to determine vertical accretion rates, bulk density, sediment composition, and carbon sequestration rates. Wetlands treated with PAC had the highest and most spatially consistent vertical accretion rates (~6 cm year-1), while the FeSO4 wetlands had similarly high accretion rates near the inlet but rates similar to the untreated wetland (~1.5 cm year-1) at the middle and outlet sites. The composition of the newly accreted sediment in the PAC and FeSO4 treatments was high in the added metal (aluminum and iron, respectively), but the percent metal by weight was similar to native soils of California. As has been observed in other constructed wetlands, the newly accreted sediment material had lower bulk densities than the native soil material (0.04-0.10 g cm-3 versus 0.2-0.3 g cm-3), suggesting these materials will consolidate over time. Finally, this technology accelerated carbon burial, with rates in PAC treated wetland (0.63 kg C m-2 yr-1) over 2-fold greater than the untreated control (0.28 kg C m-2 yr-1). This study demonstrates the feasibility of using constructed wetlands treated with coagulants to reverse subsidence by accreting the resulting organo-metal flocculent and storing carbon at rates exceeding untreated wetlands. Management and design questions remain for how to best integrate this technology into heavily subsided land to lower the risks and consequences associated with levee failure, improve water quality, and ultimately restore these lands to tidal wetlands.

California↗

USGS2018

Wetlands receiving water treated with coagulants improve water quality by removing dissolved organic carbon and disinfection byproduct precursors

Constructed wetlands are used worldwide to improve water quality while also providing critical wetland habitat. However, wetlands have the potential to negatively impact drinking water quality by exporting dissolved organic carbon (DOC) that upon disinfection can form disinfection byproducts (DBPs) like trihalomethanes (THMs) and haloacetic acids (HAAs). We used a replicated field-scale study located on organic rich soils in California's Sacramento-San Joaquin Delta to test whether constructed flow-through wetlands which receive water high in DOC that is treated with either iron- or aluminum-based coagulants can improve water quality with respect to DBP formation. Coagulation alone removed DOC (66–77%) and THM (67–70%) precursors, and was even more effective at removing HAA precursors (77–90%). Passage of water through the wetlands increased DOC concentrations (1.5–7.5 mg L − 1 ), particularly during the warmer summer months, thereby reversing some of the benefits from coagulant addition. Despite this addition, water exiting the wetlands treated with coagulants had lower DOC and DBP precursor concentrations relative to untreated source water. Benefits of the coagulation-wetland systems were greatest during the winter months (approx. 50–70% reduction in DOC and DBP precursor concentrations) when inflow water DOC concentrations were higher and wetland DOC production was lower. Optical properties suggest DOC in this system is predominantly comprised of high molecular weight, aromatic compounds, likely derived from degraded peat soils.

Science of the Total Environment↗

USGS2015

Investigating the temporal effects of metal-based coagulants to remove mercury from solution in the presence of dissolved organic matter

The presence of mercury (Hg), particularly methylmercury (MeHg), is a concern for both human and ecological health as MeHg is a neurotoxin and can bioaccumulate to lethal levels in upper trophic level organisms. Recent research has demonstrated that coagulation with metal-based salts can effectively remove both inorganic mercury (IHg) and MeHg from solution through association with dissolved organic matter (DOM) and subsequent flocculation and precipitation. In this study, we sought to further examine interactions between Hg and DOM and the resulting organo-metallic precipitate (floc) to assess if (1) newly added IHg could be removed to the same extent as ambient IHg or whether the association between IHg and DOM requires time, and (2) once formed, if the floc has the capacity to remove additional Hg from solution. Agricultural drainage water samples containing ambient concentrations of both DOM and IHg were spiked with a traceable amount of isotopically enriched IHg and dosed with ferric sulfate after 0, 1, 5, and 30 days. Both ambient and newly added IHg were removed within hours, with 69–79 % removed. To a separate sample set, isotopically enriched IHg was added to solution after floc had formed. Under those conditions, 81–95 % of newly added Hg was removed even at Hg concentrations 1000-fold higher than ambient levels. Results of this study indicate coagulation with ferric sulfate effectively removes both ambient and newly added IHg entering a system and suggests rapid association between IHg and DOM. This work also provides new information regarding the ability of floc to remove additional Hg from solution even after it has formed.

Environmental Management↗

USGS2015

Mercury, monomethyl mercury, and dissolved organic carbon concentrations in surface water entering and exiting constructed wetlands treated with metal-based coagulants, Twitchell Island, California

Coagulation with metal-based salts is a practice commonly employed by drinking-water utilities to decrease particle and dissolved organic carbon concentrations in water. In addition to decreasing dissolved organic carbon concentrations, the effectiveness of iron- and aluminum-based coagulants for decreasing dissolved concentrations both of inorganic and monomethyl mercury in water was demonstrated in laboratory studies that used agricultural drainage water from the Sacramento–San Joaquin Delta of California. To test the effectiveness of this approach at the field scale, nine 15-by-40 ‑ meter wetland cells were constructed on Twitchell Island that received untreated water from island drainage canals (control) or drainage water treated with polyaluminum chloride or ferric sulfate coagulants. Surface-water samples were collected approximately monthly during November 2012–September 2013 from the inlets and outlets of the wetland cells and then analyzed by the U.S. Geological Survey for total concentrations of mercury and monomethyl mercury in filtered (less than 0.3 micrometers) and suspended-particulate fractions and for concentrations of dissolved organic carbon. In the control wetland cells, total mercury concentrations in filtered water samples ranged from 0.94 to 2.47 nanograms per liter (ng/L) at the control inlets and from 0.84 to 2.63 ng/L at the control outlets, and particulate total mercury concentrations in water ranged from 0.27 to 1.49 ng/L at the control inlets and from 0.17 to 1.11 ng/L at the control outlets. Monomethyl mercury concentrations in filtered water ranged from 0.16 to 0.88 ng/L at the control inlets and from 0.13 to 1.30 ng/L at the control outlets; particulate monomethyl mercury concentrations in water ranged from 0.03 to 0.24 ng/L at the control inlets and from 0.03 to 0.23 ng/L at the control outlets. Dissolved organic carbon concentrations in water ranged from 7.9 to 26.7 milligrams per liter at the control inlets and from 8.5 to 28.0 milligrams per liter at the control outlets. Following coagulation, but prior to passage through the wetland cells, coagulation treatments transferred dissolved mercury and carbon to the particulate fraction relative to untreated source water: at the wetland cell inlets, the coagulation treatments decreased concentrations of filtered total mercury by 59–76 percent, filtered monomethyl mercury by 40–70 percent, and dissolved organic carbon by 65–86 percent. Passage through the wetland cells decreased the particulate fraction of mercury in wetland cells that received coagulant-treated water. Changes in total mercury, monomethyl mercury, and dissolved organic carbon concentrations resulting from wetland passage varied both by treatment and season. Despite increased monomethyl mercury in the filtered fraction during wetland passage between March and August, the coagulation-wetland systems generally decreased total mercury (filtered plus particulate) and monomethyl mercury (filtered plus particulate) concentrations relative to source water. Coagulation—either alone or in association with constructed wetlands—could be an effective way to decrease concentrations of mercury and dissolved organic carbon in surface water as well as the bioavailability of mercury in the Sacramento–San Joaquin Delta.

California↗

USGS2013

The role of irrigation runoff and winter rainfall on dissolved organic carbon loads in an agricultural watershed

We investigated the role of land use/land cover and agriculture practices on stream dissolved organic carbon (DOC) dynamics in the Willow Slough watershed (WSW) from 2006 to 2008. The 415 km 2 watershed in the northern Central Valley, California is covered by 31% of native vegetation and the remaining 69% of agricultural fields (primarily alfalfa, tomatoes, and rice). Stream discharge and weekly DOC concentrations were measured at eight nested subwatersheds to estimate the DOC loads and yields (loads/area) using the USGS developed stream load estimation model, LOADEST. Stream DOC concentrations peaked at 18.9 mg L −1 during summer irrigation in the subwatershed with the highest percentage of agricultural land use, demonstrating the strong influence of agricultural activities on summer DOC dynamics. These high concentrations contributed to DOC yields increasing up to 1.29 g m −2 during the 6 month period of intensive agricultural activity. The high DOC yields from the most agricultural subwatershed during the summer irrigation period was similar throughout the study, suggesting that summer DOC loads from irrigation runoff would not change significantly in the absence of major changes in crops or irrigation practices. In contrast, annual DOC yields varied from 0.89 to 1.68 g m −2 yr −1 for the most agricultural watershed due to differences in winter precipitation. This suggests that variability in the annual DOC yields will be largely determined by the winter precipitation, which can vary significantly from year to year. Changes in precipitation patterns and intensities as well as agricultural practices have potential to considerably alter the DOC dynamics.

California↗

USGS2012

Structural stability of coprecipitated natural organic matter and ferric iron under reducing conditions

The objective was to assess the interaction of Fe coprecipitated with dissolved organic matter (DOM) and its effect on Fe (hydr)oxide crystallinity and DOM retention under abiotic reducing conditions. A Fe-based coagulant was reacted with DOM from an agricultural drain and the resulting precipitate (floc) was exposed to S(-II) and Fe(II). Solution concentrations of Fe(II/III) and DOM were monitored, floc crystallinity was determined using X-ray diffraction, and the composition and distribution of functional groups were assessed using scanning transmission X-ray microscopy (STXM) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Results indicate coprecipitation of Fe(III) with DOM forms a non-crystalline floc that withstands crystallization regardless of change in pH, Fe:DOM ratio and type of reductant added. There was no evidence that exposure to reducing conditions led to release of DOM from the floc, indicating that coprecipitation with complex natural DOM in aquatic environments may stabilize Fe (hydr)oxides against crystallization upon reaction with reduced species and lead to long term sequestration of the DOM. STXM analysis identified spatially distinct regions with remarkable functional group purity, contrary to the model of DOM as a relatively uniform complex polymer lacking identifiable organic compounds. Polysaccharide-like OM was strongly and directly correlated with the presence of Fe but showed different Fe binding strength depending on the presence of carboxylic acid functional groups, whereas amide and aromatic functional groups were inversely correlated with Fe content.

Organic Geochemistry↗