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No description available.

No description available.

Vacant lots in cities and surrounding urban areas can potentially be used for stormwater management because they are pervious. However, the extent to which vacant lots provide pervious cover to increase infiltration and reduce stormflow is poorly understood. The goal of this study was to develop faster methods for monitoring stormwater infiltration to improve characterization of heterogeneous urban systems. Geophysical techniques are capable of mapping and characterizing subsurface materials, but are often limited by time and sensitivity constraints. In this study, the infiltration characteristics of a vacant lot created by the demolition of a house was characterized using a series of modeling, field and lab experiments. Site characterization under background conditions with an EM Profiler was used to map zones of different fill materials. Three zones were identified in the study site: grass area, driveway area, and a former house area. Transient soil moisture conditions were monitored during irrigation tests using two geophysical methods (electrical resistivity tomography [ERT] and electromagnetic induction [EM]) to evaluate method sensitivity and differences between the three zones. ERT proved more sensitive than EM profiling at detecting changes in the three zones. Soil moisture changes in the driveway area were particularly difficult to detect using EM. The EM Profiler showed a reduction rather than increase in conductivity at the start of irrigation and storms, which was attributed to flushing of high conductivity pore fluids by dilute irrigation or rain water. This explanation was supported using Archie’s Law to model the response of apparent conductivity under highly conductive pore fluid conditions. The EM Profiler was also used under natural precipitation conditions to quickly monitor areas too large for the ERT to reasonably survey. The results suggested that EM instrument drift needs to be corrected to make the method more sensitive. It was difficult to detect differences in hydrologic characterization between areas of the vacant lot using traditional soil point measurements because of the inherent spatial variability. The most useful point measurement was soil moisture loggers. Data from soil moisture loggers was used to parameterize the model; in addition, the soil moisture loggers showed a slow drying period. By combining the EM Profiler method with soil moisture data and applying corrections for drift, some improvement in sensitivity might be achieved. Quantitative characterization of fill material was shown by ERT, which detected more heterogeneous infiltration in the area of the former house than in the grass area. / Geology

Suburban Philadelphia is a densely populated region with a history of urbanization and waterway channelization. Situated within the Delaware River watershed, 70% of the region’s stream segments are impaired, primarily due to excess sediment and nutrients. To improve water quality, the Upstream Suburban Philadelphia Cluster of the Delaware River Watershed Initiative (DRWI) established focus areas within the region for targeted implementation of stormwater control measures and community outreach about stormwater management. The focus areas consisted of upstream headwaters to four streams flowing into the Delaware River. The objective of this study was to determine sediment and nutrient concentrations in first flush overland flow (OLF) in three of the DRWI focus areas. Seven sites were selected for collection of OLF, stream, and rain samples. A total of 228 samples from 24 sample locations across 17 storms were collected from the Pennypack Creek, Jenkintown Creek, and Sandy Run watersheds. Samples were analyzed for nitrate (N), total dissolved phosphorous (TDP), total phosphorous (TP), suspended sediment concentration (SSC), and chloride (Cl), and results were compared to catchment metrics including area and land cover. OLF samples showed a wider variability of sediment, chloride, and nutrient concentrations than stream samples, and the stormwater quality varied between catchments with different land cover composition. Higher N correlated with increased road coverage and landscaping applications in vegetated areas. Lower TDP was linked to increased tree canopy, while higher TP was linked to smaller lot sizes. In the stream samples, higher SSC was linked to increased road coverage and smaller building sizes, and higher Cl was linked to nearby impervious surfaces. SSC was often reduced in the OLF samples after flowing downhill or through vegetated patches. Two bioretention basins were sampled at the inlet and outlet. Both basins experienced a decrease in SSC and N at the outlets, showed marginal to poor efficiency for TDP and TP removal, and provided an increase in Cl in outlet. A review of all collected data suggests that land cover and human activity in these watersheds are greater drivers of stormwater quality than rainfall and weather patterns. The data presented in this report has implications for stormwater control. First, this study provides an understanding of local heterogeneities in the distribution of nutrients, sediment, and chloride in stormwater runoff from seemingly similar watersheds in terms of land use. Second, the presented data can be used in projects and models at the headwater scale and the micro-catchment scale to improve planning and monitoring. / Geology

Time-lapse electrical resistivity tomography (TL-ERT) enables an accurate characterization of the heterogeneity of flow through the unsaturated zone especially when compared to point measurements taken within the same survey area. The most powerful tool for understanding the unsaturated zone is a combination of several techniques. Many models of unsaturated zone flow assume a uniform wetting front even though the existence of preferential flow paths is well-documented in the literature. TL-ERT surveys were collected perpendicular to a stream at the Stroud Water Research Center in Chester County, PA to provide continuous measurement of unsaturated flow during two natural infiltration events. Dielectric sensors were installed along this transect to collect soil moisture data during these events. Additionally, slug tests and infiltrometer tests were collected along the transect to characterize the subsurface at the study site. TL-ERT successfully located sections with preferential flow, and these results were reproducible three months later. Other methods of measuring soil moisture content or infiltration rates were less successful at identifying preferential flow. The rates determined from point measurements often did not match where the TL-ERT identified zones of preferential flow. This comparison reveals that slow-infiltration points can exist within preferential pathways and exemplifies the importance of large-scale measurements in the unsaturated zone. Any scientific study looking at infiltration should consider utilizing TL-ERT to map where preferential flow may be occurring. / Geology

Karst aquifers are dynamic hydrologic systems which are sensitive to short-term recharge events (storms) and heterogeneous recharge characteristics (point recharge at sinks, irregular soil thicknesses). These aquifers are highly productive yet also vulnerable to contamination, in large part because the conduit network is a significant unknown for predicting karst flow paths. To address these uncertainties, two adjacent karst springs, Tippery Spring and Near Tippery Spring, were monitored to better understand flow and source mixing characteristics. The two springs in central Pennsylvania’s Nittany Valley have similar discharges and are only 65 meters apart, yet they show unique behaviors in terms of water chemistry and discharge response to storms. First examined for flow characterization in 1971 by Shuster and White, the springs were analyzed in this study using high-resolution logging and new tracers such as rare earth element (REEs) and Ca/Zr ratios. This research contributes to the field of karst hydrology through innovative water sampling and monitoring techniques to investigate karst recharge and flow behavior along with conduit flow models incorporating multiple calibration target datasets such as water temperature and dye tracing. Stable isotope signatures (δD & δ18O) of storm water samples at the two springs varied based on storm intensity, but also due to their unique recharge behaviors. Increased spring discharge preceded the arrival of storm water as conduits were purged of pre-storm water, indicated by no change in isotopic composition on the rising limb. The isotopic signature then became progressively more enriched at both springs, indicating storm water recharge. At Tippery, this enrichment began around peak flow, sooner than at Near Tippery where enrichment began during the descending limb. Thus, isotopes indicated a stronger surface connection at Tippery Spring. Storm intensity also affected the relative contribution of recharging water reaching both springs, with a larger storm producing a larger recharge signature compared to a smaller storm. At Tippery Spring, for a short time the majority of emerging water was storm water, which may indicate a reversal in water exchange between the conduits and the surrounding matrix, an important consideration in karst contaminant transport. Two natural tracers were applied in new ways for this study: Ca/Zr ratios and REE patterns. Both tracers provided additional information about flow paths and recharge sources as they varied during the storm hydrograph. Ca/Zr ratios changed in timing and intensity with storm intensity, and both springs exhibited a decline in Ca/Zr ratios as calcium-rich carbonate matrix water was displaced by zirconium-rich storm recharge water from sinking streams off the clastic upland ridges. Being a storm water arrival indicator in clastic-ridge-fed Valley and Ridge springs, this relationship made Ca/Zr ratios a useful substitute for stable water isotopes while also providing information on source area. In response to storm water recharge, REE concentrations increased with the arrival of storm water. The timing and magnitude of concentration increases were influenced both by the degree of surface connectivity intrinsic to each spring and the intensity of the recharge event. Elevated REE concentrations persisted after other parameters recovered to pre-storm levels, suggesting water which has interacted with either the local carbonate matrix or the upland siliciclastics. These slower flow paths recharging the two springs were not apparent from other geochemical parameters. This study illustrated the relationships among multiple tracers to understand source waters in different periods of storm hydrographs. A flow and transport model using the Finite Element Subsurface Flow Model (FEFLOW) was calibrated using quantitative dye trace and high resolution temperature data to simulate the connection between a sinking stream and Tippery Spring. Dye was injected at the sink and monitored at the spring while temperature data was collected using loggers at both the sink and the spring. FEFLOW was used to simulate the connection between sink and spring through varying conduit geometries, sink and spring discharges, conduit conductivity, conduit cross-sectional area, matrix transmissivity, matrix porosity, and dispersivity. Single conduit models reproduced larger peak and recession concentrations than observed. A forked conduit model diverted flow from the main conduit, reducing the concentration of dye reaching the spring, provided a better match. Latin Hypercube sensitivity analysis indicated that dye concentration breakthrough curves were most sensitive to conduit conductivity and less sensitive to other model parameters. Temperature data from high-resolution loggers at the sink and spring were then incorporated into the model scenarios to reproduce seasonal spring temperature using the conduit configuration fit to the dye trace. Simulated temperature signals at the spring were sensitive to parameters in addition to conduit conductivity, most notably matrix transmissivity and inflow rates at the sink. The dual approach to karst model calibration using a temperature model set up from an initial dye trace results in greater model confidence due to a limited possible range in conduit conductivity. This study improved conceptual and numerical models for karst by examining how data from storm events and tracers can be used to better understand recharge and flow paths. / Geoscience

Urbanization affects in-stream biogeochemical processes that control nutrient export. Attempts to restore urban streams will not be successful unless the biological and physical controls on water quality are thoroughly understood. The objective of this study was to identify the relative influences of tributary dilution, groundwater discharge, and biological processing on nitrate concentrations in an urban stream during high and low flow periods. A wastewater treatment plant (WTP) on Pennypack Creek, an urban stream near Philadelphia, PA, increases nitrate concentrations to a mean of 8.5 mg-l-1 (as N). Concentrations decrease to 5.5 mg-l-1 about 7.5 km downstream. Reaches along this distance were sampled for nitrate concentration and delta-15N at fine spatial intervals to determine the reasons for this decrease. To quantify the effects of dilution, samples were collected from tributaries, groundwater springs, and upstream and downstream of tributaries or groundwater discharge zones identified through terrain analysis and continuous temperature modeling. These methods were also used to identify and sample reaches along which hyporheic flow occurred, where nitrate biological processing is often concentrated. In addition, loggers were installed at closely spaced sites to monitor daily fluctuations in nitrate, dissolved oxygen, and related parameters, which provided further indications of biological processing. Longitudinal sampling revealed decreases in nitrate concentration of 2 and 6.5 mg-l-1 during high and low flow, respectively. During high flow, delta-15N varied from 9.5 to 10.5 per mille downstream of the WTP, while delta-15N varied from 10.14 to 11.06 per mille throughout this reach during low flow. Mixing analysis indicated that groundwater discharge and biological processing both control nitrate concentration during both flow periods. Larger declines in nitrate concentration were observed during low flow than during high flow, and delta-15N fell between biological and groundwater signatures, indicating that both processes were enhanced. Continuous nitrate concentrations displayed distinct diurnal cycles often out-of-phase with dissolved oxygen cycles, indicating autotrophic processing. However, shifts occurred in nitrate cycle timing at a weekly scale wherein daily maximum concentrations were observed as many as 6 hours closer to noon than previously. These shifts were comparable to shifts observed across seasons in other studies, and by the end of the summer, nitrate and dissolved oxygen cycles were in-phase. Furthermore, shifts in nitrate cycles could not be linked to shifts in daily fluctuations of WTP discharge. Longitudinal sampling and continuous monitoring suggest that biological processing is an important control on nitrate concentrations in urban systems, though documenting its signature may be complicated by groundwater discharge and anthropogenic inputs. / Geology

Pump and treat remediation is the most commonly used method to remediate contaminated aquifers, but the effectiveness decreases when heterogeneities are introduced. Fractures within the matrix cause large differences in hydraulic conductivity. The low hydraulic conductivity of the matrix acts as an area of storage for contaminant, allowing for attenuation of the plume. The attenuation of the plume causes the effectiveness of the system to decrease and cost of remediation to increase. In order to understand what parameters enhance contaminant storage in the matrix, rapid transport in fractures, and both of their influences on the efficiency of the pumping system, a hypothetical model was developed to simulate the release and remediation of a plume using pumping. The code used was HydroGeoSphere, which allowed for the interpretation of parameters influencing contaminant storage during the withdrawal phase of the pump and treat remediation by allowing transport of contaminant within both the matrix and the fractures. Matrix parameters of porosity and hydraulic conductivity influenced the effectiveness of the withdrawal system most. For instance, the difference in percent mass extracted between porosity values of 0.01 and 0.4 was 23.75%, while the difference between fracture lengths of 200 and 400 m was 5.59%. Fracture pattern influenced where the stored contaminant was located within the matrix. Downgradient of the source, six different fracture patterns resulted in a difference in relative concentration of 0.4 at the start of the withdrawal phase. Evaluation of remediation included both percent extraction of contaminant and finer scale remediation of the contaminant specifically within the matrix. Multiple length-scale observations helped determine how fracture and matrix parameters influence remediation in dual permeability media. / Geology

Managing stormwater volume and quality has become an important issue in urban hydrology. Impervious cover associated with urbanization increases surface runoff volumes and degrades the water quality of urban streams and rivers. Cities with combined stormwater and sewer lines such as Philadelphia, have been tasked with decreasing runoff volumes to help reduce combined sewer overflows and improve the water quality of local waterways. The Philadelphia Water Department uses the Environmental Protection Agency’s Storm Water Management Model (SWMM) to predict runoff and evaluate if proposed stormwater infrastructure will reduce overflows. This study focused on the hydrogeological properties of grassy areas on and near Temple University’s main campus in north Philadelphia. The dataset includes terrestrial LiDAR, ground penetrating radar, soil moisture sensor, surface compaction, and double ring and mini disk infiltrometer measurements. These data were used to establish what controls infiltration rates in the area and also provide input parameters for a SWMM model. A terrestrial LiDAR scan of the Berks St. site, a grassy vacant lot located just east of Temple’s campus was used to generate a high-resolution digital elevation model. This elevation model was used to calculate the depression storage parameter, partition subcatchments in the SWMM model, and calculate a topographic wetness index (TWI). The TWI is a microtopography-based predictor of where runoff will collect and infiltrate. The TWI assumes a homogeneous infiltration rate and that runoff is routed by topography. This TWI was compared with soil moisture sensor measurements to determine if the microtopographic index could predict the majority of change in soil moisture at the field site. To determine if accounting for buried debris helped strengthen the TWI, GPR was used to map the extent and depth of subsurface objects. The results indicate that the TWI and GPR data could not predict where runoff would accumulate and then infiltrate because the TWI’s assumptions were not met. Measurements made with a double ring infiltrometer indicate that infiltration rates at the site were both high and heterogeneous (40 to 1060 mm/hr), allowing precipitation to infiltrate into the subsurface rather than become runoff, minimizing the influence of microtopography. Co-located surface compaction and double ring infiltrometer measurements at sites on and nearby Temple’s campus showed a negative correlation between surface compaction and infiltration rate (R2 = 0.67). Compacted areas on campus had lower infiltration rates and exhibited depression storage and runoff during rain events. Less compacted areas off campus had higher infiltration rates and exhibited no depression storage or runoff. The results of this study showed variance in surface compaction caused grassy areas around Temple’s campus respond differently to rain events. The results not only provided field-based parameter values for a SWMM model, but shows that compaction’s influence on infiltration should be considered when constructing a SWMM model. Runoff volumes in SWMM may be underestimated if compacted grassy areas are modeled with high infiltration rates. / Geology