a field study assessing the impact of on site valerie mc-carthy_slideshare

www.valeriemccarthy.me

A field study assessing the impact of on-site wastewater treatment systems on surface

water quality in a Co. Monaghan catchment

Valerie McCarthy, DkIT

International Symposium On Domestic Wastewater Treatment & Disposal Systems

Trinity College, Dublin, September 2012

Study Site Location Milltown Lake is an abstraction point for the Churchill and Oram Group water Scheme Services 1,922 people Approximately 735 m3 of water being abstracted daily

Background Collected Data Study Aims Site Summary Results Conclusions

Milltown Lake catchment Monitoring has taken place within Milltown Lake catchment for point & diffuse sources of contamination Identifying the various locations, land uses & activities, which are likely sources of contamination Actively engaging community support, commitment & participation through inclusion at all stages of the process


Milltown Lake catchment Pressures to water quality identified within the catchment include:

Poor farmyard practices Direct access of cattle to water courses Run-off from slurry & fertiliser spreading


Geological Survey of Ireland (GSI) subsoil permeability map records the subsoil in the general area as of ‘low’ permeability, suggesting that runoff usually dominates over infiltration.

Soil type: Grain size Chemical composition

Depth to bedrock Proximity to surface water Potential presence of preferential flow path Capacity of the system in relation to the number of people using it Chemical composition of the effluent received by the system Frequency at which the tank is de-sludged Correct functioning of components of the system itself Depth of unsaturated subsoil layer

Ability of OSWTS at effectively treating effluent is dependent on:


OSWTS were also identified as a potential source of contamination within the catchment Consequently they were characterised through a combination of:

Household questionnaires Non-intrusive site inspections Intrusive monitoring programme

Collected data


Household Questionnaire

Total of 154 households surveyed Average number of occupants per house = 3.1 91 % of the systems were septic tanks 27 % of the respondents never de-sludged their tank

Over half of the systems > 16 yrs old


Non-intrusive survey A subset of 42 systems were visually inspected 83 % of which were septic tanks 45 % had percolation areas 38 % of systems relied on soakways (pits filled with stones)


Non-intrusive survey

17 % of systems which direct discharges into drains (two of which had no settlement tanks at all)


Intrusive Study Five sites were selected for intrusive investigation Varying numbers of piezometers were installed down-gradient of each system depending on proximity to water courses & one control located outside predicted area of plume Samples collected once every two weeks between Aug 08 – Aug 09 from each piezometers and from nearest water course – up & down-stream from the OSWTS

Analysed for a range of biological & chemical indicator parameters


Aims & Objectives

This project focused on systems currently in use, regardless of age, type or level of maintenance & aimed to:

Investigate the fate of contaminants arising from OSWTS To provide quantifiable data on the contribution of OSWTS to nutrient loading within the catchment Possible effects of factors such as poor maintenance, incorrect installation & operation & location in areas with unsuitable site characteristics were taken into account


Site summary

System Dispersal

method

Distance to

watercourse

(m)

No. of

Residents

Age

(yrs)

De-sludging

Site D Secondary Percolation ~ 102 2 - 4 ~ 5 Every 2 yrs

Site F Septic Tank Soakaway ~ 44 2 - 3 ~ 35 Every 1 yr

Site K Septic Tank Soakaway ~ 12 1 - 3 ~ 30 intermittently

Site J Septic Tank Soakaway ~ 15 2 ~ 35 intermittently

Site S Septic Tank Percolation >200 2 ~ 30 intermittently


Site characterisation Site characterisation carried in Nov 2008 (EPA, 2000) Incorporated a percolation test to ascertain the assimilation capacity of the subsoil

T value

min/25 mm

P value

min/25 mm

Site D 38 23

Site F 98 25

Site S > 100 63

Site K > 82 60

Site J > 90 65

Site S >100 63

None of the sites were deemed suitable for a conventional septic tank system Two were considered suitable for the installation of an advanced wastewater sewage treatment system by the assessor, both with recommendations for a soil polishing filter

EPA (2000) Wastewater Treatment Manuals: Treatment Systems for Single Houses. Environmental Protection Agency


Water Table Levels Depth to Water Table The water table was relatively stable

throughout the monitoring period The combined effects of a shallow water table and a thick capillary fringe at these sites indicate a reduced unsaturated zone

Depth to Water Table

(m.b.g.l.)

Site D 0.15 - 2.65

Site F 0.18 – 2.9

Site K 0.37 – 2.77

Site J 0.77 – 1.37

Site F 0.12 – 0.93

Number of issues relating to installation of systems were observed following site assessment



Example of Site Layout (Site D)

Example of Site Layout (Site F) Background Collected Data Study Aims Site Summary Results Conclusions

Subsurface Water Quality

Distribution of chloride (Cl-) concentrations, Site F, Aug 08 – Aug 09


Subsurface Water Quality Distribution of ammonia (NH3

+-N) and nitrate (NO3--N) conc, Site F, Aug

08 – Aug 09


Site F Site D Up-

gradient Down-gradient Up- gradient Down-gradient

Distance from Tank BHF2 (6.4 m)

BHF8 (48 m)

BHD4 (22 m)

BHD9 (102 m)

DIN (mg L-1-N)

46.7

9.57

128.2

8.11

DOC (mg L-1)

16.5

2.4

29.1

2.6

SRP (PO4

3--P mg L-1) 0.02 0.03 27.6 0.02 TC (MPN/100 ml)

96 - 397,260

0 - >2,420

18. - 241,960

0 - >2,420

E. coli (MPN/100 ml)

1 - 310,620

0 - >2,420

0 - 11,190

0 - 365

Subsurface Water Quality Mean values of indicator parameters up- and down-gradient along the effluent plume path, Site F and D, Aug 08 – Aug 09


Direct Discharges

Site K

Site J

Direct Discharges

Direct Discharges

Accordingly, the principal pathway of potential contaminant delivery to nearby watercourses is unlikely to have been via subsurface flow


Direct Discharges Preliminary investigation of direct discharge points:

Sampling carried out at 4 discharge pipes Two pipes were of unknown origin Monitored for the presence of caffeine & other indicator parameters


Caffeine was detected at two of the sites: Site K and one unknown (Site TH5) A linear relationship was observed between E. coli and caffeine at these sites r2=0.95

Direct Discharges Caffeine was detected at two of the sites:

Site K and one unknown (Site TH5) A linear relationship was observed between E. coli and caffeine at these sites r2=0.95


TC (MPN/100 ml)

Site K 261.3 - > 2419.6 >2419.6

TH5 64.4 – 1,553 >2419.6

Min

MPN day-1

Max

MPN day-1

1,960 4.8 x 105

Faecal bacteria, Site K & TH5, Feb 12


E. coli, Site K, Feb 12

Surface Water Quality Summary of surface water quality adjacent to sites


NH3+ (mg L-1

- N) 0.08 ± 0.01

NO2-(mg L-1

- N) 0.04 ± 0.009

NO3-- (mg L-1

- N) 1.13 ± 0.1

SRP (PO43-- mg L-1-P) 0.01 ± 0.001

TP (PO43-- mg L-1-P) 0.02 ± 0.002

Total Coliforms (MPN/100 ml)

10 – 24,196


0 – 17,329

Conclusions Parameters such as P were largely removed during the soil treatment process Some, such as indicator bacteria also experienced large reductions, nevertheless, max total coliform >2,420 MPN/100 ml within 1 m of a nearby water course (102 m from the tank) Nitrate experienced a low rate of reduction and was found at relatively high concentrations within 1 m of adjacent water course at one site (max 12.3 mg L-1 NO3-N) Problem of OSWTS, which may have their subsoil treatment systems either fully or partially by passed - This warrants further investigation -Correct identification of the source of contamination is vital An appropriate inspection system, which is capable of detecting pollution arising from OSWTS is needed


Conclusions Of the sites intrusively investigated:

Site D and Site S had inappropriately designed percolation systems Site F had a suspected broken inflow pipe, concern that a portion of greywater maybe piped separately Sites J and K had pipes discharging directly to a watercourse. The system at Site D had never been switched on (Homeowner, pers. comm.)

Therefore, there were issues relating to installation and maintenance even before the permeability and characteristics of the subsoil and soil were taken into account. Effective education of homeowners regarding the correct care and maintenance of their OSWTS is crucial.


Acknowledgements Patrick Rafferty1, Eddy Minet1, Suzanne Linnane1, Alison Orr2 & Raymond Flynn2

1 Centre for Environment & Freshwater Studies, DkIT 2 Queens University Belfast

This work was funded by the Western River Basin District, ESB International and the Department of the Environment, Heritage and Local Government

www.valeriemccarthy.me [email protected]

McCarthy, V., Flynn, R., Orr, A., Minet, E., Rafferty, P., Meehan, R. and Linnane S. (2010) A field study assessing the impact of onsite wastewater treatment systems (OSWTS) on surface water in the Milltown Lake catchment, Co. Monaghan .

Acknowledgements The National Federation of Group Water Schemes and the Churchill and Oram Group Water Scheme The homeowners for allowing us access their land and OSWTS Eddy Minet, Michelle Reilly and other staff and students at the Centre for Freshwater and Environmental Studies, DkIT Jim O’ Donohue and Tom McGoldrick questionnaires and site investigation Robbie Meehan and Nevin Traynor for carrying out site assessments and percolation tests

www.valeriemccarthy.me [email protected]

a field study assessing the impact of on site valerie mc-carthy_slideshare

Education