3/10/2011. Our Past. Burnsville Minnesota Paired Study

Transcription

1 Our Past Shirley E. Clark, Ph.D., P.E., D. WRE Associate Professor of Environmental Engineering Penn State Harrisburg WI DNR photo Strip off existing topsoil, grade it (compact it), add 6 new topsoil and plants Urbanization often shortens watershed response times and increases flow volumes and rates Burnsville Minnesota Paired Study Lincoln Creek, Milwaukee area, WI LA River 4 1

2 nfall_infiltration_rate2.gif 3/10/2011 Vegetation Introduction 5 Soil Compaction: Loss of Macropores in Soil Profile 3/10/2011 Vegetation Introduction 8 2

3 Infiltration Rates in Disturbed Urban Soils (AL tests) Sandy Soils Clayey Soils Recent research has shown that the infiltration rates of urban soils are strongly influenced by compacted, probably more than by moisture saturation. Impacts of Soil Compaction on Vegetation ils.cfm?problemid=1794 Symptoms of soil compaction vary with ih tree species and cause, but they can include: slow growth; small, distorted, sparse, chlorotic and nutrientdeficient leaves; scorch; premature autumn color; premature leaf drop; abnormally large "distress" crops of fruit; insufficient storage of food reserves for winter; and dieback of twigs or branches. Stormwater Volume Control through Infiltration Infiltration rate modeled as function of soil moisture. However, changes in infiltration rate occur over time as a function of compaction and of solids loading. Compaction during Construction requires long periods of time to recover From a stormwater quality standpoint, there is a balance between relationship between Infiltration Rate, required Drawdown Time and Chemical Removal Healthy, infiltrating soils provide volume removal (to meet requirements) and strongly support vegetation and the resultant ecosystem 3

4 Vegetation and Infiltration 31/images/ill4.gif Vegetation Introduction 3/10/2011 /34/1/0299f1.jpeg Vegetation Introduction /soil_compaction_effects.jpg 14 LID Based on Maintaining Natural Infiltration, but. Current Development Practices Greatly Affect Infiltration Prince George s County photo 4

5 How to Combine Infiltration, TMDLs and Water Quality Standards? NPDES permits (in the future and in some locations now) can be written as numeric permit limits based either on pollutant load (typically annual load) or effluent concentration (where ambient water quality and toxicity are a concern) Load = Volume x Concentration Bioretention can affect both. Question of how to quantify volume and concentration reductions? Not shown no difference in solids content before and after filtration for particles < 0.45 µm. Break point of solids removal approximately 1 3 µm. Limitation to physical straining below 2 3 µm. Engineered Media and Natural Soils as Pollutant Removal Media Flow as a Function of Solids Loading Infiltration rates typically decrease over a device s life due to solids capture on the surface of and in the media. Want higher initial infiltration rate knowing it will decrease over time. Need to meet draindown requirements just before maintenance. Most media typically fail when the total solids loading is about 10 to 25 kg/m 2 of media surface (flow rate < 1 m/d, generally). Media removal generally more effective maintenance technique, but must remove at least 4 6 because clogging solids are captured deep in the media (deeper than visible solids buildup). Minimal filtered metal removal when contact time <10 minutes (except peat). Optimal contact times removal ranged from 10 to 1,000 minutes, depending on metal and media type. Slowing Contact Time in Media Increases Pollutant Removal GAC Balance between draindown times (short) and contact time (moderate) Influent test water Rhyolite sand Surface modified zeolite Site zeolite Peat moss 20 5

6 Soil is Heterogeneous and Each Layer Has Specific BioGeoChemical Properties soil/geosoil.htm Soil Chemistry Effects on Design to Be Considered Remove pollutants in the upper layers of the media. The deeper into the soil profile that the pollutants penetrate, the greater the likelihood lih of groundwater contamination i or transport out of the device through an underdrain. Potential properties of interest in predicting removal: Soil and water ph Pollutant forms (relationship to solids loading and PSD) Cation Exchange Capacity (CEC) [and Anion Exchange Capacity (AEC)] Mineral matter Organic content Phosphorus content Oxidizing or reducing environment Salinity and Sodium Adsorption Ratio (SAR) Impact of Initial Soil P Content General Rule of Thumb: For nutrients, if soil is Low, it is more likely to remove nutrients from runoff. If soil is High, leaching more likely. Organic horizon has higher P content and minimal P removal. Mineral horizon has lower initial P content and thus P retention occurs. 6

7 Treatability of Organics (example: Pesticides, PAHs) Compounds with high Log Kow (preferentially partition to organic phase) typically better removed by organic based media(gac, peat moss, compost). Limited removal by sand filters and ion exchange resin. Compounds with high solubility (Log S) variable removal by media; likely tied to whether they are negatively or positively charged in solution. Limited removal in ion exchange resins such as zeolite because of molecular size. Zeolites are called molecular sieves because the lattice openings will screen out larger molecules. These molecules are removed in organic based media because of variety of removal sites. Plus media that support microbial growth (organic content) encourage degradation. Cations and Anions (NH 4+, NO 3, PO 4 3, Cl, Metals) Nitrogen removal: Ammonia (NH3) uncharged Ammonium (NH4 + ) positively charged (+1) Ammonia pka = 9.3; at runoff ph, ammonia typically charged ion if an ion and not complexed with metals. Charged positive ion able to be removed by ion exchange resin, although not bound as tightly as ions with higher valence charge (+2 or greater). Ammonia/ammonium is small molecule and can be removed by ionexchange resins acting as molecular sieves Nitrate (NO3 ) negatively charged ( 1) Need media with higher anion exchange capacity or uptake with vegetation Because of small valence charge, not strongly held and can leach out from organic media Cations and Anions (NH 4+, NO 3, PO 4 3, Na +, K +, Cl, Metals) Phosphorus Removal: If in root zone of media, uptake by plants possible Higher valence charge than nitrogen anion; more likely to be attracted to cations on surface of media Reacts and forms stable compounds with iron and aluminum oxides. Can form precipitates with some metals. (measure using Ksp). Chloride Removal: Similar problems for removal as nitrate, but limited uptake by plants. For non salt tolerant plants, can cause plant stress. Cations and Anions (NH 4+, NO 3, PO 4 3, Na +, K +, Cl, Metals) +1 Valence Cations: Sodium and potassium difficult to remove because comparatively weakly charged. Easily leached from soils if stronger cation enters soil. If limited competition by +2 cations, ion exchange resins/zeolites could provide treatment. Sodium at high concentrations destabilizes clays and causes dispersion of clays in soil structure. Metals: Challenge because of complexation with other components in runoff. Removal based on valence state and size of molecule. 7

8 Observed Correlations Between Soil Parameters and Chemical Capacity (Batch Testing of 16 Media) Al Ca Cd Cu Fe Ni Mg Soil CEC Soil OM Soil C Soil N Soil P Soil ph Soil K + Soil Mg Soil Cu Soil S Soil Zn Soil Ca Significance level of p = Mn Zn K Cr Tl Sb NH3 TP Inverse removal behavior of nitrate and phosphate. Reducing GAC content reduces nitrate removal life, but decreases amount of phosphate released. Selecting Media Mix Components Copper Column testing breakthrough capacity = ~ 15 mg/kg Bench scale batch capacity testing = ~ 45 mg/kg g Difference potentially due to inability of/insufficient time for metal ions to migrate to inner pore spaces during flow through operation and therefore, total removal ability of media not used. Transfer of batch testing data to field analysis of capacity problematic. Breakthrough Copper Accumulation in Upper Layers of Soil with Subsequent Downward Migration Limited Release of CEC Cations or Decrease in CECe (sum of K, Ca, Mg) May be also complexation/chelation / exchange with organic compounds, which is not measured in CECe calculations CECe = sum (K, Ca, Mg) Organic (0 3 layer) Maintenance: A Criteria for Investigating (Bio)Filtration Systems University i of Minnesota Guidance for Inspecting and Documenting Water Quantity/Flowrates in Rain Gardens/Filtration Facilities Level 1 Visual Inspection Level 2 Infiltration Testing Level 3 Synthetic Runoff Testing Level 4 Monitoring NOTE: Caveats on next pages. 8

9 Effect of Temperature on Viscosity of Infiltrating Water Recession Rate [in/hr] BioInfiltration Traffic Island Tem mp. [C] Restoration of Soil Infiltration Capacity Prevention of soil compaction in (bio)(in)filtration systems best. Do not compact base of infiltration systems. Age eventually will restore some soil structure and infiltration capacity BTI (4.25 years of data) seven point moving average best fit periodic function Y = *Sin(X(days)/55) EMERSON and TRAVER Prince Georges Cty, MD photo Need soil ripping to similar depths as compaction effects. Shallow depth restoration techniques generally not effective. From Website of Stu Schwartz, UMBC. Compaction effects extend to depths of 1 2 feet. 9

10 Snow Piles on Bioretention Facilities Snowmelt contains high concentrations of a cation and chloride (Cl ). Sodium regenerates ion exchange resins (washing off previously captured pollutants). t Sodium destabilizes clays (measured in sodium adsorption ratio). On a larger scale, Cluster and/or Mixed Use Land Development? Conservation Development? Low Impact Development? 10