Craig B. Lake

Effects of Hydraulic Loading Rate and Filter Length on the Performance of Lateral Flow Sand Filters for On-Site Wastewater Treatment

On-site treatment of residential wastewater is important for rural and remote regions where centralized wastewater treatment may not be feasible. Sand filtration is a proven method for secondary treatment of septic tank effluent (STE) and can be an economical option where soil conditions do not favor the installation of a typical disposal field. This study investigates the hydraulics and treatment performance of eight lateral flow sand filters (LFSFs) receiving domestic STE at the Bio-Environmental Engineering Centre (BEEC) in Truro, Nova Scotia, Canada. The main objectives of this study were to evaluate the long-term treatment performance associated with the LFSFs and to investigate the effects of filter length and wastewater loading on performance. Previous research conducted at the BEEC indicated that current technical guidelines used in Nova Scotia for the design of LFSFs may be conservative and that the design of these systems could be optimized. The hydraulics and treatment performance associated wi...

Examining Freeze/Thaw Cycling and Its Impact on the Hydraulic Performance of Cement-Treated Silty Sand

AbstractCement-based solidification/stabilization (s/s) is a remediation technology that has been widely used for treatment of a range of contaminants. Currently, there is limited published data on changes in hydraulic performance of cement-treated materials subjected to cycles of freezing/thawing (f/t). Fourteen sets of tests were performed to examine the influence of factors such as number of f/t cycles, freezing temperature, curing time, and mix design on changes in hydraulic conductivity and unconfined compressive strength (UCS) of cement-treated silty sand. Results showed an increase of up to three orders of magnitude in hydraulic conductivity as well as decreases in UCS values after exposure to 4 and 12  f/t cycles. Analysis of variance (ANOVA) performed on the results of a factorial experiment considering the effect of freezing temperature, curing time, and number of f/t cycles showed that all of these factors are significant in affecting the measured changes in the hydraulic conductivity and UCS v...

Modeling E.coli fate and transport in treatment wetlands using the water quality analysis and simulation program

Treatment wetlands can be a viable wastewater treatment option, especially in rural and remote regions where centralized wastewater treatment is not feasible. Bacteria fate and transport modeling within wetlands requires further development if they are to become a more reliable and predictable form of wastewater treatment. The goal of this paper was to calibrate and test an unsteady state numerical model for the simulation of E. coli fate and transport within full-scale surface flow (SF) wetlands treating domestic wastewater. The Water Quality Analysis and Simulation Program (WASP) was used to develop the model. Accurately predicting E. coli effluent concentrations using WASP was difficult due to the dynamic nature of the wetland environment including hydraulics, seasonal variability, and wetland maturity. WASP was successful in predicting average E. coli effluent concentrations but did not accurately forecast maximum and minimum values. The model produced better fits with observed E. coli effluent concentrations during the summer months, when observed effluent concentrations were less variable. Hydraulic tracer studies and model results suggest that preferential flow pathways may be affecting E. coli removal due to reduced retention times. Flow channelling or short circuiting may have been caused by high flow conditions and/or dense cattail growth. A more detailed understanding of treatment wetland hydraulics is required before we can accurately predict treatment performance.

Assessment of two thermally treated drill mud wastes for landfill containment applications.

Offshore oil and gas drilling operations generate significant amounts of drill mud waste, some of which is transported onshore for subsequent thermal treatment (i.e. via thermal remediation). This treatment process results in a mineral waste by-product (referred to as thermally treated drill mud waste; TTDMW). Bentonites are originally present in many of the drill mud products and it is hypothesized that TTDMW can be utilized in landfill containment applications (i.e. cover or base liner). The objective of this paper is to examine the feasibility of this application by performing various physical and chemical tests on two TTDMW samples. It is shown that the two TTDMW samples contained relatively small amounts of clay-sized minerals although hydraulic conductivity values are found to be less than 10—8 m/s. Organic carbon contents of the samples were approximately 2%. Mineralogy characterization of the samples confirmed varying amounts of smectite, however, peak friction angles for a TTDMW sample was greater than 36°. Chemical characterization of the TTDMW samples show potential leaching of barium and small amounts of other heavy metals. Discussion is provided in the paper on suggestions to assist in overcoming regulatory issues associated with utilization of TTDMW in landfill containment applications.

Hydraulic and strength properties of unexposed and freeze–thaw exposed cement-stabilized soils

A total of 108 specimens were prepared to examine the hydraulic performance and strength performance of nine different cement-stabilized soils under unexposed and freeze–thaw exposed conditions. Specimens from each mix design were evaluated under two levels of curing conditions (i.e., immature versus mature). Hydraulic conductivity and unconfined compressive strength (UCS) measurements were performed to assess changes in the performance of specimens after 12 cycles of freezing at −10 ± 1 °C and thawing at 22 ± 1 °C. Measured mass losses of the specimens from a standard brushing test were also monitored at different freeze–thaw cycles, and results were compared with the changes in the hydraulic performance for each mix design. Hydraulic conductivity measurements on unexposed mature specimens showed that the lowest values likely occurred at water contents slightly wet of optimum water content (OWC). The UCS values showed a general decreasing trend with the increase in the water content for both immature and...

The Effects of Dosed versus Gravity-Fed Loading Methods on the Performance and Reliability of Contour Trench Disposal Fields Used for Onsite Wastewater Treatment.

In Nova Scotia, Canada, contour trench disposal fields are the most common type of onsite wastewater system. In this study, two identical contour trench disposal fields were monitored for 3 yr to compare performance under gravity-fed versus periodically dosed loading conditions. Influent and effluent from both systems were analyzed for a suite of water quality parameters, and the hydraulics of the systems were assessed using tracer studies and measurements of ponded water depth in the distribution trenches. Ponded water depths in the distribution trench of the gravity-fed disposal field were observed to increase steadily during the monitoring period, indicating progressive clogging. This was not observed in the periodically dosed field. Regarding treatment, both systems performed well, consistently producing effluent with 5-d biochemical oxygen demand and total suspended solids (TSS) concentrations <10 mg L and achieving >5 log reductions in . However, the gravity-fed system produced statistically lower average effluent concentrations for total P and TSS. It is speculated that the slightly better treatment performance achieved by the gravity-fed system is due to enhanced biomat formation. This study demonstrated adequate treatment of residential wastewater by contour trench disposal fields regardless of loading method. However, because the hydraulic performance of these systems is heavily dependent on pretreatment and loading methods, it is recommended that a dosing system be used to distribute wastewater to contour trench disposal fields to help prevent hydraulic failure.

Bacterial Pathogen Indicator Transport from Livestock Mortality Biopiles.

Biopiles can be used to dispose of slaughterhouse residuals (SLRs); however, the fate of pathogenic bacteria (e.g., pathogenic strains of , ) in these systems is not well understood. The transport of these bacteria in water leaching from the biopile could represent a significant contamination source. This research examined the transport of Enterobacteriaceae and Enterococcaceae indicator bacteria from SLR biopiles. Three biopiles (2.6 m wide by 4.6 m long by 1.8 m high) were formed on soil layers in concrete cells that allowed for real-time monitoring of environmental parameters, hydrologic flux, and indicator bacteria levels in effluent leaching from the piles. In biopile effluent, indicator bacteria populations decreased exponentially following biopile formation. Indicator bacteria loads in effluent constituted <0.01% of the initial indicator bacteria levels in the biopiles, which was attributed to retention, inactivation, and death. Nearly 90% of the total indicator bacteria loads coincided with large precipitation events (>15 mm d). Movement of the indicator bacteria through the biopiles and underlying soil appeared to be consistent with preferential flow phenomena. The populations of the Enterobacteriaceae indicators remained low in conditions of higher soil water content and lower biopile temperatures, whereas the Enterococcaceae indicator appeared to regrow in these conditions. This indicated that bacterial pathogen transport from a biopile could be a concern after the disappearance of conventional bacterial indicators, such as . Management considerations should attempt to divert excess water from entering a biopile, such as locating a biopile under a roof. Unsaturated biopile and soil conditions should be maintained to impede water flow through preferential pathways in the soil underneath a biopile.

A method to assess risk reduction when utilizing geosynthetic clay liners (GCLs) with compacted soil liners

This paper presents an analytical solution developed to estimate probabilities of “failure” or advective flux “exceedance” for the case of a spatially variable geosynthetic clay liner (GCL) situate...

Evaluating Impact Resonance Testing As a Tool for Predicting Hydraulic Conductivity and Strength Changes in Cement-Stabilized Soils

In this paper the impact resonance (IR) test method is used as a nondestructive tool to examine the curing progression, freeze/thaw (f/t) resistance, and healing potential of cement-stabilized soils. Resonant frequency (RF) measurements on specimens moist cured for up to 241 days indicate that the main portion of the hydration process is completed after about 60 days. Results of RF measurements on immature (i.e., cured for 16 days) and mature (i.e., cured for over 110 days) specimens exposed to 12 cycles of f/t indicate that the initial f/t exposure had a significant effect on the degradation of the structure. After the initial f/t cycle, some specimens exhibited continued reductions in RF values to as low as 10% of the initial measurements, while several specimens showed signs of recovery leading to minor increases in the RF values. Changes in RF values are compared with the hydraulic conductivity changes measured on the same specimens reported in a previous publication by the authors. Based on the results, a prescreening scheme is proposed that can significantly reduce the time required for f/t studies of cement-stabilized soils. Also, RF measurements after 120 days of a post-exposure healing period show a significant potential for recovery in RF values for f/t exposed specimens. However, the recoveries in RF values are not proportional to the hydraulic conductivity recovery of the specimens.

Diffusion and Sorption of VOCs Through Soil-Cement Materials

Portland Cement Association, Cement Association of Canada, Natural Sciences and Engineering Research Council of Canada, Killam Trusts, and the Canadian Foundation for Innovation.